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It is known that rare-earth-based pyrochlore oxide may accommodate the well-defined two-in-two-out spin ice state with its tetrahedral unit. Low-energy excitation is argued to favor the highly concerned monopole state which attracts essential attention. However, such an excitation cannot be directly tracked and imaged using advanced characterizations, raising challenges to our understanding of the physics of monopoles. In this work, we propose an improved two-dimensional artificial spin ice structure on the Shastry–Sutherland lattice to restore the degeneracy of realistic pyrochlore systems. Such a structure avoids the deficiency of inequivalent nearest and next-nearest exchanges in the planar quadrate unit, which, however, is equivalent to the tetrahedral unit of realistic pyrochlore oxides. Therefore, this spin ice model restores state degeneracy that is lost in conventional planar artificial spin ice structures, representing an improved simulator of real spin ice systems. Our careful investigations of such improved structures reveal the rich physics of spin ice excitations, including the phase diagram, which allows different ordered phases and interesting critical phase transitions between spin ice phase I and phase II. Energy spectrum analysis suggests that restoration of state degeneracy substantially reduces monopole excitation energy, resulting in a striking monopole emergency at the critical point. Furthermore, the emergent spin dimer phase in this improved model allows high-density monopole excitations and exhibits high-correlated monopole fluid states. [ABSTRACT FROM AUTHOR]

Achieving the formation of target open crystalline lattices from colloidal particles is of paramount importance for their potential application in photonics. Examples of such desired structures are the diamond, tetrastack, and pyrochlore lattices. Here, we demonstrate that the self-assembly of tetravalent patchy particles results in the selective formation of cubic tetrastack crystals, both in the bulk and in the systems subjected to external fields exerted by the solid substrate. It is demonstrated that the presence of an external field allows for the formation of well-defined single crystals with a low density of defects. Moreover, depending on the strength of the applied external field, the mechanism of epitaxial growth changes. For weakly attractive external fields, the crystallization occurs in a similar manner as in the bulk, since the fluid does not wet the substrate. Nonetheless, the formed crystal is considerably better ordered than the crystals formed in bulk, since the surface induces the ordering in the first layer. On the other hand, it is demonstrated that the formation of well-ordered cubic tetrastack crystals is considerably enhanced by the increase in external field strength, and the formation of the thick crystalline film occurs via a series of layering transitions. [ABSTRACT FROM AUTHOR]

Rare-earth titanate oxides are believed to be prospective functional materials for photocatalytic and photoluminescent applications because of their excellent optical properties and thermal stability of their physical properties. However, the relationships between optical properties and photoelectron trapping mechanisms are unclear. Herein, the structure, electronic, and optical properties of pyrochlore-structure Re2Ti2O7 (Re = Sm and Eu) were investigated using the first-principles approach with the Hubbard parameter U (GGA + U). The calculated bandgap is 2.5 eV for Sm2Ti2O7 and 2.4 eV for Eu2Ti2O7, which is in good agreement with the experimental observation. The results indicate that the strongly localized f states at the top of valence band are charge-trapping sites for photoexcitation of Re2Ti2O7, where electrons can absorb photon energy and transfer from the valence band to the conduction band, resulting in the photocatalytic and/or fluorescent effects in the visible and early UV regions. The important optical parameters, dielectric function ε (ω) , refractive index n (ω) , extinction coefficient k (ω) , reflectivity R (ω) , absorption coefficient I (ω) , optical conductivity σ (ω) , and electron energy-loss L (ω) were studied in detail, indicating that these optical parameters of Sm2Ti2O7 and Eu2Ti2O7 are insensitive to the ultra-violet (UV) radiation, but both Sm2Ti2O7 and Eu2Ti2O7 exhibit excellent optical properties in the visible and early UV regions. This work provides a clear understanding on the photoelectron trapping mechanism of pyrochlore-structure Re2Ti2O7, which will help to improve the photocatalytic and photoluminescent performance of Re2Ti2O7 and broaden their applications. [ABSTRACT FROM AUTHOR]

Magnetic refrigeration technology is regarded as one of the ideal solutions for cryogenic refrigeration, while magnetocaloric materials are the crucial ones. A series of polycrystalline RE2Ti2O7 (RE = Gd, Tb, and Ho) compounds were prepared by a simple one-step solid-phase reaction method in the atmosphere. The crystal structure, magnetic properties, and magnetocaloric effect (MCE) of these compounds were systematically investigated. Crystallographic research indicates that these compounds crystallized in a pyrochlore structure. Meanwhile, magnetic measurements illustrate that this class of pyrochlore oxides is highly frustrated magnetic materials and exhibits complex magnetic behavior. In addition, under the field change of 0–1 T, the values of the maximum magnetic entropy change (− Δ S M max ) and the refrigeration capacity are calculated to be 0.9 and 5.8 J/kg for Gd2Ti2O7, 9.0 and 32.9 J/kg for Tb2Ti2O7, 9.9 and 29.9 J/kg for Ho2Ti2O7, respectively. Therefore, RE2Ti2O7 (RE = Tb and Ho) pyrochlores exhibit excellent MCEs under low magnetic fields, providing candidate materials for the application of cryogenic magnetic refrigeration technology. [ABSTRACT FROM AUTHOR]

In this study, La 2 (TiZrSnHfGe) 2 O 7 high entropy oxides were firstly prepared by solid state reaction method. The effects of different sintering temperatures on the structure, morphology and dielectric properties were studied. When the pre-calcination temperature is 1300 °C, the powder exhibits a single pyrochlore phase instead of defective fluorite phase. The existence of high entropy affects the changes in the crystal structure of A 2 B 2 O 7 type oxides, resulting in lattice distortion. The dielectric results showed that the ceramics have certain frequency dispersion, and the dielectric properties are affected by temperature and frequency. Due to the high entropy effect, the La 2 (TiZrSnHfGe) 2 O 7 ceramic exhibits good dielectric stability at both high and low frequencies. The formation of defect dipole clusters in the system results in the increase of dielectric constant. It is feasible to change the dielectric properties of ceramics by designing high entropy oxides, which showed the potential value in microelectronics field. [ABSTRACT FROM AUTHOR]

A new series of 20-component fluorite-based compositionally complex oxides (20CCFBO x Nb/Ta) with the general chemical formula (15RE 1/15) 2 x +1 (Ce 1/3 Zr 1/3 Hf 1/3) 3–3 x (Nb 1/2 Ta 1/2) x O 8- δ (0 ≤ x ≤ 1, where 15RE 1/15 = La 1/15 Pr 1/15 Nd 1/15 Sm 1/15 Eu 1/15 Gd 1/15 Tb 1/15 Dy 1/15 Y 1/15 Ho 1/15 Er 1/15 Tm 1/15 Yb 1/15 Lu 1/15 Sc 1/15) are synthesized. Despite that the Gibbs phase rule allows for the existence of up to 20 phases at the thermodynamic equilibrium, 17 of the 20CCFBO x Nb/Ta compositions synthesized in this study all possess single ultrahigh-entropy phases in fluorite, pyrochlore, or weberite structure, as shown by X-ray diffraction (XRD). Only < 1 vol% of secondary phases are observed in two compositions near the phase-transition points. With changing compositional variable x , this series of 20CCFBO x Nb/Ta undergoes an abrupt fluorite-pyrochlore transition at x = ∼0.27 and an abrupt pyrochlore-weberite transition at x = ∼0.87. Careful characterization reveals abrupt changes of order parameters at both phase transitions. In addition, weberite short-range ordering can persist into the long-range pyrochlore phase, which leads to the lowest thermal conductivities. [ABSTRACT FROM AUTHOR]

A comprehensive study of the structural properties of the heavily investigated rare-earth A 2 Ir 2 O 7 iridate series under extreme conditions is presented. From Pr 2 Ir 2 O 7 to Lu 2 Ir 2 O 7 , the series is sufficiently covered by iridates with A = Pr, Sm, Dy, Ho, Er, Tm, Yb, and Lu; general trends and systematics within the series, including the understudied heavy-rare-earth members, are dependably followed. Temperature- and pressure-dependent synchrotron X-ray powder diffraction experiments reveal robustness of the pyrochlore structure throughout the series, down to 4 K and up to 20 GPa. The thermal expansivity of the pyrochlore lattice is determined, all falling in the Debye temperature range of θ D = 360–420 K. The pressure compressibility shows a systematic increase of the bulk modulus with the rare-earth atomic number from K = 180–210 GPa. Combining the results of thermal measurements (Debye temperature) and pressure measurements (bulk modulus) enables us to determine the Grüneisen parameter of selected members and compare it to previous studies. Temperature and pressure evolution of the fractional coordinate of oxygen at 48 f Wyckoff position, the sole free fractional coordinate in the crystal structure, is investigated and discussed regarding the antiferromagnetic ordering of the Ir magnetic moments. In addition to results on A 2 Ir 2 O 7 iridates, the temperature and pressure evolution of the crystal structure of an IrO 2 minority phase is followed. The tetragonal rutile-type structure is stable down to the lowest temperature. However, an application of pressure of approximately 15 GPa induces a structural transition: The tetragonal structure is orthorhombically distorted. The orthorhombic structure is still not fully stabilised at 20 GPa, and further distortion of the lattice (or subsequent structural transformations) is expected with increasing external pressure. [ABSTRACT FROM AUTHOR]

In this present work, photocatalysts based on a new pyrochlore-type solid solution were prepared using the ceramic method at 1000°C. X-ray diffraction (XRD) analysis shows the existence of a solid solution with pyrochlore structure Bi1.5Sb1.5Zn1–xCuxO7 (0 ≤ x ≤ 1). Scanning Electron Microscope (SEM) images exhibited a slight difference in the external morphology of the samples. The UV-diffuse measurement revealed a change in the absorbance from the UV part for the zinc-rich compound to the visible part for the copper-rich compound. The Energy band gap values were between 3.15 and 1.84 eV. The photocatalytic activity of these prepared mixed oxides was studied for the photo-degradation of the dye Orange II (ORII) as an organic pollutant, in the presence of hydrogen peroxide (H2O2) as an oxidising agent, under sunlight irradiation, by varying different parameters such as the catalysts mass, the oxidant volume, the concentration of the pollutant and the pH. The experimental results obtained by UV-visible spectroscopy revealed that the removal efficiency of ORII increased with increasing the irradiation time for all tested photocatalysts. The pseudo-first-order kinetic model gave the best fit, with the highest correlation coefficients (R2 = 0.99). The results of this study revealed the potential and various advantages of these new efficient photocatalysts. [ABSTRACT FROM AUTHOR]

In addition to complex spin-ice and spin-liquid states of rare-earth pyrochlore oxides, A2Ir2O7 iridates have been recently proposed to host a cooling-field-controllable antiferromagnetic domain structure of iridium moments. Reliable and profound studies of the magnetic domain structure, including domains’ interfaces, have been frequently limited by insufficient sample quality or lack of single crystals. We report the magnetic properties of the for-the-first-time synthesised Lu2Ir2O7 and Er2Ir2O7 single crystals; focussing on the robust ferromagnetic component of magnetisation present in the material with the antiferromagnetically ordered state of the all-in-all-out (AIAO) type. Anisotropy of the system, as well as the effects of magnetic (Er3+) or nonmagnetic (Lu3+) local environments on Ir4+ moments, is studied. The size of the domains is calculated based on a simplified domain wall model. Results are discussed in the framework of AIAO and AOAI domains and interfaces on the geometrically frustrated lattice. [ABSTRACT FROM AUTHOR]

Helium (He) exerts significant influence on the physicochemical, structural, and electronic properties of pyrochlores. This paper reviews recent advancements in computer simulations aimed at stabilizing nuclear waste, focusing on disordered structures of pyrochlores, zirconate pyrochlores, and high‐entropy pyrochlores. Using Pu‐La2Zr2O7 as a case study, we demonstrate how a first‐principles approach facilitates the understanding of how He modifies the structural and electronic properties of this system. The incorporation of He interstitials in Pu‐La2Zr2O7 typically leads to an expansion in lattice constant and volume swelling. Analysis of the formation energies in this system reveals that octahedral interstitial sites or zirconium (Zr) vacancy sites are favored for He occupation, resulting in the formation of substitutional He atoms. The low concentration of He atoms in Pu‐La2Zr2O7 reduces the formation energy of cation antisite defects. Bader charge analysis indicates that the < Zr‐O > bond exerts a greater influence on the irradiation resistance of the He‐Pu‐La2Zr2O7 system compared to the < La‐O > bond. Moreover, the capacity for He interstitials increases with higher Pu concentration in the octahedrons. [ABSTRACT FROM AUTHOR]

This study presents the successful synthesis of Sr2Ta2O7 with a pyrochlore crystal structure, which was previously unreported. Traditionally, Sr2Ta2O7 is synthesized in an orthorhombic layered perovskite‐type structure using traditional solid‐state reaction and batch‐type subcritical hydrothermal methods. Here, we utilize a continuous‐flow supercritical hydrothermal method, a technique primarily applied for nanoparticle synthesis and minimally explored for the synthesis of metastable crystals. Through detailed evaluations employing X‐ray diffraction and scanning electron microscopy, we confirmed the synthesis of the pyrochlore phase, characterized by particles with a diameter of less than 100 nm, synthesized at 633 K. Notably, the synthesized pyrochlore structure demonstrated remarkable stability, even after thermal treatment at 773 K for 1 h. Pyrochlore Sr2Ta2O7 stands out as a rare exception to the traditional tolerance factor approach among 278 known A2B2O7 compositions. Systematic evaluation of formation energies through first‐principles calculations revealed that the pyrochlore Sr2Ta2O7 synthesized in this study is located 0.06 eV/atom above the convex hull. This achievement underscores the potential of the continuous‐flow supercritical hydrothermal method in automating the exploration and discovery of novel crystal structures, suggesting a systematic pathway for advancing the field of material synthesis. [ABSTRACT FROM AUTHOR]

Ionizing events having a wide variety of radiation‐induced effects can radically affect the kinetics of defect production or structural transformation in the pyrochlore structured oxides (A2B2O7). Therefore, a thorough understanding of the kinetics associated with cation ordering and disordering is required for various technological applications. The structural responses of Gd2Ti2‐yZryO7 (y = 0.4, 1.2, 1.6) pyrochlore series irradiated by 120 MeV Au9+ ions were investigated using in situ synchrotron x‐ray diffraction (SR‐XRD), micro‐Raman spectroscopy, and scanning electron microscopy (SEM). Each pyrochlore composition irradiated at the highest fluence, where structural modifications occur, was subsequently isochronally annealed from room temperature to 1000°C. The SR‐XRD results indicate that Ti‐rich composition (y = 0.4) retains its pre‐irradiated pyrochlore structure (Fd3¯$\bar{3}$m) at 1000°C. In contrast, Zr‐rich compositions exhibit recrystallization to an intermediate defect‐fluorite phase (Fm3¯$\bar{3}$m) above 500°C, and the pre‐irradiated pyrochlore superstructure does not recover even on annealing at 1000°C. These results reveal that recrystallization temperature strongly depends on the accumulated radiation damage, generally described with the cationic radius ratio (rA/rB). Thus, investigation of the thermal annealing behavior of irradiated pyrochlores helps better understanding the general mechanisms of radiation damage and recovery of pyrochlores, which is important for their use in nuclear applications. [ABSTRACT FROM AUTHOR]

Nine glazed porcelain artifacts bearing the coat of arms of France, from King Louis XV tableware orders, were analysed at the laboratory or in their conservation secure room. Based on the experience acquired in the study of 18th century European and Chinese porcelain using mobile XRF (pXRF) and Raman microspectroscopy, a comparison of the impurities in the paste (Y, Rb, and Sr), the elements associated with cobalt in the blue overglaze (Bi, Mn, Zn, and As) and those present in the tin yellow and Naples yellow pigments (Sn, Sb, and Zn) highlights the use of different raw materials for some of these objects. Differences regarding the Ag content in the gold decorations also provide information. Raman identification of the different types of yellow pigment confirms the categorization. The results obtained on the Louis XV tableware are compared to those of "Chine de commande", attributed to the same places and periods of production or recognized copies. The clustering of the quantitative comparison pXRF signals of the abovementioned elements and a consideration of the Raman parameters of the yellow pigments appear to be effective tools for object categorization to confirm or refute questions about the authenticity of objects. [ABSTRACT FROM AUTHOR]

The challenge of producing dense fine-grained high-entropy ceramics is hereby addressed by a combined cold and conventional pressureless sintering method for the first time. It provides nearly fully dense high-entropy pyrochlores with better microstructural homogeneity, and only half the grain size of conventional pressurelessly sintered samples with identical density. Both the finer and more homogeneous microstructures benefit better mechanical properties in hardness and reduced Young's modulus. The kinetics and activation energies of both densification and grain growth were quantified and discussed to understand how cold sintering affects the microstructural evolution during the following pressureless sintering. More importantly, cathodoluminescence analysis suggested that cold sintering could cause more defects on the surface of the original particles, which could promote the grain boundary diffusion and have drag effects on grain boundary motion. The lessons learned here offer scientific understanding and technological guidance towards pressureless sintering of dense bulk high-entropy ceramics. [ABSTRACT FROM AUTHOR]

When exposed to severe environments, the short-range order in pyrochlores significantly influences their physicochemical properties. Using the DFT + U method, this study investigates the effect of short-range order on the solubility of actinides (An = Th, U, Np, Pu, Am, and Cm) in Gd 2 Zr 2 O 7 with distinct coordinated Gd and Zr sites. Our findings indicate that all the actinides under consideration are susceptible to being incorporated into the 7-fold Zr-site of quasi -weberite Gd 2 Zr 2 O 7. The weberite-like short-range order also favors immobilization of these actinides in the 6-fold Zr-site. The effect of the weberite-like motif on the solubility of actinides in the Gd-site of quasi -WB Gd 2 Zr 2 O 7 depends on the chemistry of the actinides. Furthermore, the short-range order results in a lower solution energy for An incorporation into the Gd and Zr sites of the quasi -weberite Gd 2 Zr 2 O 7 with cation antisites, thereby favoring An immobilization in a disordered environment. These results strongly demonstrate the importance of the short-range order on the solubility of actinides in disordered pyrochlores. [ABSTRACT FROM AUTHOR]

The temperature dependence of the heat capacity of Y2Ti2O7 and Eu2Ti2O7 with a pyrochlore structure in the temperature range of 7–1800 K has been studied. The existence of a small shallow anomaly of the heat capacity of europium titanate in the range of 10–60 K was confirmed. The thermodynamic properties (entropy, enthalpy change, and reduced Gibbs energy) were calculated. Based on the results of calculation of the Gibbs energy of formation of the titanates from oxides it was concluded that both titanates are thermodynamically stable in the high temperature region. [ABSTRACT FROM AUTHOR]

Matrix based on pyrochlore Y2Ti2O7 for immobilization of high-level radioactive waste was prepared via SHS process. The phase composition and structure of the synthesized matrices were characterized. The influence of aluminum additive and composition/amount of gases emitted during combustion on the porosity of the matrices was studied. [ABSTRACT FROM AUTHOR]

The effective solubilities (maximum contents) of Ta and Nb in model felsic lithium-fluoride melts of variable alkalinity and alumina content were experimentally determined at the dissolution of Ta–Nb and Nb minerals: pyrochlore, microlite, ilmenorutile, and ferrotapiolite at T = 650–850°C and P = 100 and 400 MPa. The Ta and Nb partitioning in the mineral-melt systems was also studied. When pyrochlore is dissolved in granitoid melts at P = 100 MPa and T = 650–850°C, the highest effective solubilities of Nb (0.7–1.8 wt %) are obtained in alkaline melt, and they significantly decrease (to 0.03–0.5 wt %) in subaluminous and peraluminous melts. A temperature increase increases the solubility (content) of Nb in the melt. Similar dependences were obtained for Ta solubility by dissolving microlite. In peraluminous granitoid melt, microlite remains stable, while pyrochlore becomes unstable. A pressure decrease from 400 to 100 MPa in alkaline and subaluminous melts was found out to not significantly affect on the dissolution of microlite and pyrochlore, whereas Ta and Nb contents in the peraluminous melt noticeably decrease. The dependences of Nb solubility and its partitioning between granitoid melts and ilmenorutile on the alkalinity–alumina content of the melt are similar to those for the dissolution of columbite and tantalite. The dependences obtained by dissolving ferrotapiolite, pyrochlore, and microlite differ from them. [ABSTRACT FROM AUTHOR]

The new generation of T/EBCs requires their top layer materials with good resistance to severe corrosion by CMAS. Rare-earth zirconates/hafnates with pyrochlore structure are regarded as promising candidates for T/EBC. In this work, the corrosion behaviours and mechanisms of plasma-sprayed Gd 2 M 2 O 7 (M = Zr, Hf) coatings at 1300 and 1500 °C for 4–25 h were investigated. The Gd 2 M 2 O 7 coating showed good corrosion resistance under long-term corrosion at 1300 °C. The Gd 2 M 2 O 7 coatings reacted with CMAS and precipitated apatite and fluorite, forming a dense layer that can prevent further penetration of CMAS. However, the CMAS penetrated into the Gd 2 M 2 O 7 coatings because of the sharply decreased viscosity of the CMAS as the temperature raised to 1500°C, forming another infiltration layer. The results also suggested that the Gd 2 Hf 2 O 7 possessed better resistance to CMAS corrosion than Gd 2 Zr 2 O 7. [ABSTRACT FROM AUTHOR]

Gd 2 Zr 2 O 7 is considered a promising host material for immobilizing high-level radioactive waste. However, its interplay between grain sizes, radiation resistance and chemical stability is not well understood yet. Herein, Gd 1.7 Nd 0.3 Zr 0.5 Ce 1.5 O 7 ceramics with defect-fluorite phase and three different grain sizes (96, 390 and 1959 nm) were successfully fabricated and irradiated by 140 keV He ion beam up to a fluence of 8 × 1017 ions/cm2. Phase evolutions, microstructure changes and chemical stabilities were investigated. The nano-grained ceramic exhibits the lowest degree of amorphization and a delayed irradiation-induced lattice expansion and damage evolution process, demonstrating an enhanced ability in suppressing the coalescence of He bubbles inside the grain. Grain boundaries parallel to the surface were found to be more favorable sinks for irradiation-induced defects. Chemical stability tests showed that the 42 days leaching rates of all elements were between 10−7∼10−5 g/m2·d. All samples have maintained this superior chemical stability even after irradiation. Interestingly, the leaching test results also suggested that grain size may be not the primary factor influencing the long-term leaching rate. [ABSTRACT FROM AUTHOR]

This study investigated the viability of Hf and/or W doping in Li7La3Zr2O12 (LLZO) through an alkoxide derived sol-gel process aimed at stabilizing the ion-conductive cubic garnet phase. Results revealed that Hf doping tends to favor the tetragonal garnet phase, while co-doping with Hf and W effectively stabilizes the cubic garnet structure. This stabilization is attributed to the similar ionic radii of Hf4+ (0.71 Å) and the slightly smaller W6+ (0.62 Å) compared to Zr4+ (0.72 Å), considering charge neutrality. In both doping scenarios, a coexisting Li-deficient pyrochlore phase is observed, likely due to the use of HfCl4 and WCl6 as starting reagents in the alkoxide process, which results in reduced Li-coordinated carboxyl sites attached to chelated Zr alkoxide. However, increasing the Li excess content above 30% effectively eliminates the pyrochlore phase, thus stabilizing the cubic garnet phase. Impedance measurements conducted on Hf-doped LLZO and Hf,W co-doped LLZO (with 40% excess Li) sintered ceramics reveal a significant enhancement in bulk ion conductivity, with the Hf,W co-doped LLZO pellet exhibiting two orders of magnitude higher conductivity (1.09 × 10−4 S cm−1). This finding confirms the stability of the cubic phase even with partial substitution of W and with 40% excess Li. [ABSTRACT FROM AUTHOR]

Pyrochlore oxides, specifically G d 2 Z r 2 O 7 , have been a subject of interest due to their unique structural, physical, and magnetic properties. These properties make pyrochlore oxides potential candidates for various technological applications, including magnetocaloric refrigeration. Magnetocaloric refrigeration is a promising alternative to conventional refrigeration methods, as it is more energy-efficient and environmentally friendly. By studying the magnetocaloric effect of pyrochlore oxides like G d 2 Z r 2 O 7 , researchers can gain a deeper understanding of the underlying mechanisms and potential applications of these materials in magnetocaloric refrigeration systems. By employing advanced computational methods such as Monte Carlo simulations and first-principles calculations based on the full-potential linearized augmented plane wave (FP-LAPW) a technique is employed to examine the magnetic structure, researchers can investigate the magnetocaloric effect of pyrochlore oxides with high accuracy and precision. This information has the potential to aid in the advancement of more effective magnetocaloric systems materials and ultimately lead to the design and optimization of advanced magnetocaloric refrigeration systems. [ABSTRACT FROM AUTHOR]

Zirconate pyrochlores have been extensively studied as candidate waste forms for the immobilization of actinide wastes due to their flexible crystal chemistry, excellent structural stability, and exceptional radiation tolerance. Herein, we report the synthesis of a series of compounds Eu2Zr2–xO7–2x (x = 0–1, step = 0.125) using a co‐precipitation route to form solid solutions between the two end members, Eu2Zr2O7 pyrochlore and Eu2ZrO5 defect fluorite. It is important to understand the pyrochlore to defect fluorite transformation as a function of Zr/Ln molar ratio. The structural investigation by x‐ray diffraction has shown the increasing cation disorder and corresponding structural transitions from the ordered pyrochlore to disordered pyrochlore, then to defect fluorite. While diffuse reflectance spectroscopy provides similar optical absorption features reflecting the presence of Eu(III) ion, Raman spectroscopy has revealed more details on the phase transition and short‐range structures. This work highlights the structural flexibility in zirconate materials as potential nuclear waste forms for the immobilization of actinide‐rich waste streams, especially suitable for the separated minor actinides. [ABSTRACT FROM AUTHOR]

We present a combined Brillouin light scattering (BLS) and micromagnetic simulation investigation of the magnetic-field-dependent spin-wave spectra in a hybrid structure made of permalloy (NiFe) artificial spin-ice (ASI) systems, composed of stadium-shaped nanoislands, deposited on the top of an unpatterned permalloy film with a nonmagnetic spacer layer. The thermal spin-wave spectra were recorded by BLS as a function of the magnetic field applied along the symmetry direction of the ASI sample. Magneto-optic Kerr effect magnetometry was used to measure the hysteresis loops in the same orientation as the BLS measurements. The frequency and the intensity of several spin-wave modes detected by BLS were measured as a function of the applied magnetic field. Micromagnetic simulations enabled us to identify the modes in terms of their frequency and spatial symmetry and to extract information about the existence and strength of the dynamic coupling, relevant only to a few modes of a given hybrid system. Using this approach, we suggest a way to understand if the dynamic coupling between ASI and film modes is present or not, with interesting implications for the development of future three-dimensional magnonic applications and devices. [ABSTRACT FROM AUTHOR]

We report interfacial transport properties in in situ grown orthorhombic perovskite oxide heterostructures consisting of an antiferromagnetic insulator DyFeO3 and a paramagnetic conductor CaRuO3. We observe Hall effect with a step-like increase amounting to an effective magnetic field of 30 T at 20 K. We provide a plausible explanation in the context of topological Hall effect originating from a non-coplanar spin texture and resultant emergent field in DyFeO3 associated with the scalar spin chirality. Our results demonstrate that the proximity effect of the emergent field at heterointerfaces is a universal physical phenomenon, while it has been reported originally in a heterointerface composed of pyrochlore oxides. This will greatly expand the choice of materials to the heterointerfaces for the research in emergent transport phenomena, which has been limited to single compounds with both metallic properties and special spin textures. Additionally, this will pave the way for possible device application of the emergent field by designing and combining perovskite oxides with versatile functionalities such as multiferroicity. [ABSTRACT FROM AUTHOR]

A multi-crystalline specimen of gadolinium zirconate (Gd 2 Zr 2 O 7) has been synthesized by solid-state reaction method (un-milled sample). The sample underwent high-energy ball-milling for 6 h, 12 h, 18 h, and 24 h durations (milled samples). An investigation has been conducted to examine the effects of mechanical attrition on structural, microstructural, vibrational, and dielectric properties. Notably, the elemental analysis of the samples reveals a substantial increase in the atomic percentage of oxygen. This indicates the partial development of an oxygen-enriched phase during the milling process. The Rietveld refinement of X-ray diffraction profiles indicates that all the samples have a disordered fluorite structure however, in the 18 h and 24 h milling samples in addition to this main phase, a minor ordered phrochlore-phase has been formed. The nano-phasic character of all the milled samples has been confirmed by the SEM, TEM, and BET surface area analysis. The BET isotherms displayed a type –II hysteresis loop, indicating that all the samples are macro-porous with a pore diameter exceeding 50 nm. The FTIR and Raman spectrum studies indicate the presence of both defect fluorite and pyrochlore phases in the samples. An in-depth investigation has been conducted on the impact of mechanical milling-induced reduction in particle size and micro-strain on conduction mechanism, dielectric relaxation, and variation of various dielectric properties with frequency. [ABSTRACT FROM AUTHOR]

The pyrochlore oxide La 2 Hf 2 O 7 (LHO) has attracted extensive attention in thermal management applications. Accurate determination and comprehensive understanding of thermal conductivity (κ) stand as imperative prerequisites for the effective utilization and manipulation of LHO in various applications. In this study, with the assistance of machine learning interatomic potential, we investigate the microscopic mechanisms of phonon thermal transport in LHO crystals. Our findings show that the thermal transport in LHO defies a precise explication through the conventional framework of the Boltzmann transport equation (BTE) due to the emergence of diffusive phonon modes, engendered by strong anharmonicity. Using the state-of-the-art dual-phonon model incorporating both propagating and diffusive modes, we successfully reproduce the experimentally measured results in both magnitude and temperature dependence. It is also shown that the thermal conduction in LHO crystals is dominated by the propagating modes at low temperatures while by the diffusive modes at high temperatures, which synergistically lead to a low κ for LHO crystals. The novel insights into phonon thermal transport provide a stepping stone for regulating the thermal transport properties of LHO crystals. [ABSTRACT FROM AUTHOR]

Many factors impact the formability of single phase high-entropy pyrochlore ceramics (HEPCs) which become a research hotspot owing to their excellent properties. To investigate the effect of size disorder, two combinations with same mixing entropy and different size disorder were designed, thermodynamic analysis of first-principles calculations and experimental research were conducted in this paper. The calculation results reveal that the enthalpy change decreases significantly with the decrease of size disorder, promoting the synthesis of single-phase high-entropy pyrochlore. The experimental results prove that the combination with lower size disorder leads to single-phase HEPCs, and the prepared material exhibits low thermal conductivity (1.68 W/(m·K)) and low theoretical density (5.73 g/cm3). [ABSTRACT FROM AUTHOR]

In this work, the irradiation response of A 2 Ti 2 O 7 (A represents rare earth elements of Gd, Dy, Ho, Er, Yb and Nd) series ceramics were systematically studied under 3 MeV Au2+ ions. The structural changes pre- and post-irradiation were characterized using X-ray diffraction (XRD), grazing incidence X-ray diffraction (GIXRD) and Raman spectroscopy. After heavy ion irradiation, all the samples undergo structural transformations from ordered pyrochlore to disordered fluorite and then to amorphous phase. The sample surface became fully amorphous when exposed to the maximum irradiation dose. The 5RETO high-entropy pyrochlore exhibits the lowest rate of amorphization during the process of structural transformation. The cation radius ratio and mixed entropy are the primary factors influencing amorphization rate. The cation radius ratio shows a strong positive correlation with the amorphization rate, while the mixed entropy demonstrates a weak negative correlation with the amorphization rate. The cation radius ratio can thus serve as a reliable indicator for predicting the radiation resistance of high-entropy pyrochlore ceramics. [ABSTRACT FROM AUTHOR]

The study investigated the formation of inhomophase ceramics through Zn doping in Bi 2 СrTa 2 O 9.5–Δ. It was found that all Bi 2 Zn x Cr 1– x Ta 2 O 9.5–Δ (0.3 ≤ x ≤ 0.7) investigated samples crystallized in the pyrochlore structural type (sp. Gr. Fd-3m) and contained an admixture of triclinic β-BiTaO 4 (up to 24 wt %, sp. gr. P-1), with the admixture concentration proportional to the degree of zinc doping. It was shown that impurities in the samples could be eliminated by creating a defective bismuth sublattice proportional to the impurity content, resulting in single-phase Bi 2– y Zn x Cr 1– x Ta 2 O 9.5–Δ (y ≤ 0.5, 0.3 ≤ x ≤ 0.7) samples with the pyrochlore structure. The unit cell parameter of pyrochlore increased with an increase in zinc ion content in the samples from 10.4493 Å (x = 0.3) to 10.4976 Å (x = 0.7). The microstructure of ceramics was represented by individual slightly melted grains 0.5–2 μm in size, which increased in size and fuse with each other with an increase in zinc content. The near edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS) data showed that zinc doping did not change the oxidation degree of bismuth and tantalum in pyrochlore, with the ions in charge states Bi(+3), Zn(+2) and Ta(+5). The study also observed an energy shift of the absorption band in the Ta 4f spectrum toward lower energies (Δ E = 0.55 eV) characteristic of tantalum ions with an effective charge (+5–δ) and a shift of the Bi 4f 7/2 and Bi 4f 5/2 bands shift to lower energies with increase in x (Zn), due to the distribution of some Zn(II) ions in the bismuth position. The oxidation degree of chromium ions in the samples was mainly (+3), with some chromium ions oxidized and having an oxidation degree close to (+6) according to NEXAFS data. The studied ceramics showed promise as dielectrics for multilayer ceramic capacitors and devices for microwave applications due to their low sintering temperature and high porosity. [ABSTRACT FROM AUTHOR]

The increasing anthropogenic emissions of greenhouse gases (GHG) is encouraging extensive research in CO 2 utilisation. Dry reforming of methane (DRM) depicts a viable strategy to convert both CO 2 and CH 4 into syngas, a worthwhile chemical intermediate. Among the different active phases for DRM, the use of nickel as catalyst is economically favourable, but typically deactivates due to sintering and carbon deposition. The stabilisation of Ni at different loadings in cerium zirconate inorganic complex structures is investigated in this work as strategy to develop robust Ni-based DRM catalysts. XRD and TPR-H 2 analyses confirmed the existence of different phases according to the Ni loading in these materials. Besides, superficial Ni is observed as well as the existence of a CeNiO 3 perovskite structure. The catalytic activity was tested, proving that 10 wt.% Ni loading is the optimum which maximises conversion. This catalyst was also tested in long-term stability experiments at 600 and 800°C in order to study the potential deactivation issues at two different temperatures. At 600°C, carbon formation is the main cause of catalytic deactivation, whereas a robust stability is shown at 800°C, observing no sintering of the active phase evidencing the success of this strategy rendering a new family of economically appealing CO 2 and biogas mixtures upgrading catalysts. [Display omitted] [ABSTRACT FROM AUTHOR]

High-performance photovoltaic devices require active photoanodes with superior optoelectric properties. In this study, we synthesized neodymium ruthenate, Nd2Ru2O7 (NRO), and gadolinium ruthenate pyrochlore oxides, Gd2Ru2O7 (GRO), via the solid-state reaction technique, showcasing their potential as promising candidates for photoanode absorbers to enhance the efficiency of dye-sensitized solar cells. A structural analysis revealed predominantly cubic symmetry phases for both materials within the Fd-3m space group, along with residual orthorhombic symmetry phases (Nd3RuO7 and Gd3RuO7, respectively) refined in the Pnma space group. Raman spectroscopy further confirmed these phases, identifying distinct active modes of vibration in the predominant pyrochlore oxides. Additionally, a scanning electron microscopy (SEM) analysis coupled with energy-dispersive X-ray spectroscopy (EDX) elucidated the morphology and chemical composition of the compounds. The average grain size was determined to be approximately 0.5 µm for GRO and 1 µm for NRO. Electrical characterization via I-V measurements revealed that these pyrochlore oxides exhibit n-type semiconductor behavior, with conductivity estimated at 1.5 (Ohm·cm)−1 for GRO and 4.5 (Ohm·cm)−1 for NRO. Collectively, these findings position these metallic oxides as promising absorber materials for solar panels. [ABSTRACT FROM AUTHOR]

Introduction of Th into synthetic disordered fluorite-type Gd2Zr2O7 induces a transition to an ordered pyrochlore-type phase at a Th concentration of 10 % at the Gd site (Gd1.8Th0.2Zr2O7 composition). The degree of order of the fluorite-type phase reaches 50 % for a Th concentration of 25 % (Gd1.5Th0.5Zr2O7 composition). Upon application of high pressure, the Gd2Zr2O7 phase retains the fluorite-type structure until 33 GPa (K0 = 167(1) GPa), where it undergoes reversible amorphization. The Gd1.7Th0.3Zr2O7 phase was found to be stable up to at least a pressure of 25 GPa (K0 = 169(3) GPa). Upon heating to Tmax of 1135 K, the Gd2Zr2O7 phase retains its disordered fluorite-type structural arrangement (α = 3.03 × 10−5 K−1). The excellent stability of the Gd2−xThxZr2O7 phases under extreme conditions of temperature and pressure makes Gd2Zr2O7 a promising candidate as a host matrix for radioactive elements for safe long-term underground storage of nuclear waste. [ABSTRACT FROM AUTHOR]

High-throughput methods are extremely important in today's materials science, especially in the case of thin film characterization. The micro-combinatorial method enables the deposition and characterization of entire multicomponent thin film systems within a single sample. In this paper, we report the application of this method for the comprehensive TEM characterization of the Y-Ti-O layer system. Variable composition samples (YxTi1−xOy) were prepared by dual DC magnetron sputtering, covering the entire (0 ≤ x ≤ 1) concentration range. The structure and morphology of phases formed in both as-deposited and annealed samples at 600, 700, and 800 °C were revealed as a function of Y-Ti composition (x). A comprehensive map showing the appropriate amorphous and crystalline phases, and their occurrence regions of the whole Y-Ti-O layer system, was revealed. Thanks to the applied method, it was shown with ease that at the given experimental conditions, the Y2Ti2O7 phase with a pyrochlore structure forms already at 700 °C without the TiO2 and Y2O3 by-phases, which is remarkably lower than the required temperature for most physical preparation methods, demonstrating the importance and benefits of creating phase maps in materials science and technology. [ABSTRACT FROM AUTHOR]

This contribution provides a thorough examination of the structural characteristics of pyrochlore-type lanthanide titanates and zirconates Ln2Ti2O7 and Ln2Zr2O7, across various length scales. This paper also examines their processing, interesting physical properties (electrical, magnetic, and thermal characteristics), and responses to high pressure and ion irradiation. Brief sections on the elemental oxides' crystal chemistry, pertinent phase diagrams, and energetics of defect formation are also provided. Pyrochlore-type Ln2Ti2O7 and Ln2Zr2O7 stand out as truly multifunctional materials. Moreover, they have emerged as fascinating materials due to magnetic geometrical frustration, arising from the ordering of magnetic Ln3+ and non-magnetic Ti4+ (or Zr4+) cations into separate, interpenetrating lattices of corner-sharing tetrahedra. This results in a diverse array of exotic magnetic ground states, such as spin-ice (e.g., Dy2Ti2O7 or Ho2Ti2O7) or quantum spin ice (e.g., Tb2Ti2O7), observed at both low and room temperatures. They also exhibit varied electrical and electrochemical characteristics. Some members such as Gd2Zr2O7, function as fast ion conductors with a conductivity (σ) of ≈10−2 S·cm−1 at 800 °C and activation energy (Ea) ranging from 0.85 to 1.52 eV, depending on the degree of structural disorder. Others, such as Gd2TiMoO7, are mixed ionic-electronic conductors with σ ≈ 25 S·cm−1 at 1000 °C, making them promising candidate materials for applications in energy conversion and storage devices and oxygen separation membranes. Their exceptionally low thermal conductivity (e.g., κ ∼ 1.1–1.7 W·m−1·K−1 between 700 and 1200 °C for Ln2Zr2O7), close to the glass-like lower limit of highly disordered solids, positions them as valuable materials for thermal barrier coatings. They can also effectively accommodate actinides (e.g., Pu, Np, Cm, Am) in solid solutions and sustain prolonged exposure to radiation due to alpha-decay events, while preserving the integrity of the periodic atomic structure. Proposed as major components in actinide-bearing ceramics, they contribute to the long-term immobilization and disposal of long-lived waste radionuclides from nuclear programs. Some of these properties are displayed simultaneously, opening avenues for new applications. Despite the wealth of data available in the literature, this review highlights the need for a better understanding of order/disorder processes in pyrochlore-type materials and the influence of the structural length scale on their physical and chemical properties. Recent experimental evidence has revealed that pyrochlore short-range structure is far more complex than originally thought. Moreover, pyrochlore local structure is now believed to include short-range, lower symmetry, ordered domains, such as the orthorhombic weberite-type of structure. Notably, short- and long-range structures appear decoupled across different length scales and temperature regimes, and these differences persist even in well-ordered samples. We believe that the pyrochlore structure offers a unique opportunity for examining the interplay between chemical composition, defect chemistry, and properties. [ABSTRACT FROM AUTHOR]

Pyrochlore structures with composition Pr 2−x Sm x Zr 2 O 7 (x = 0, 1, and 2) were synthetized and studied. Spark Plasma Sintering (SPS) was employed to produce ceramics with over 95% of relative density. The reoxidation behavior and the influence of the sintering process on the electrical properties were studied by Electrochemical Impedance Spectroscopy. The overall conductivity of the materials is higher for the samples with Pr, while the introduction of Sm induced an additional electrical contribution. The reoxidation of the samples presented fast kinetics and increased conductivity, particularly in the PrSmZr 2 O 7 (PSZO) sample. PSZO also exhibits a total conductivity comparable to that of the reference materials used as ionically conductive solid electrolytes. The prepared ceramics, especially the PSZO sample, demonstrate excellent relative density, good conductivity, and fast oxidation, holding promise for applications such as Solid Oxide Fuel Cells, gas sensors, and clean energy technologies that require thermal and physical stability, as well as rapid oxidation-reduction processes. [ABSTRACT FROM AUTHOR]

The order-disorder transition (ODT) of RE zirconate (RE 2 Zr 2 O 7) has received much attention due to its potential applications in the design of thermal barrier coatings (TBCs). A series of high entropy RE zirconates (RE = La, Sm, Gd, Er and Lu) were designed and synthesized in order to regulate the fluorite-pyrochlore phases, and to investigate the effect of phase composition on the microstructures and performances. The results showed that the sintering temperature, as well as equivalent ion radius, played an important role in regulating the phase transformation of fluorite-pyrochlore. The coexistence of pyrochlore-fluorite phases not only can result in the decrease in grain size but also increased the lattice strain of each phase, thereby enhancing the phonon scattering and contributing to the reduction in the thermal conductivity. The CMAS corrosion resistance was mainly related to phase compositions, and the thicknesses of reaction layer decreased gradually with the increasing fluorite phase content. The results will provide theoretical guidance for the microstructural design of high entropy RE zirconates as next generation TBC materials in future. [ABSTRACT FROM AUTHOR]

The (Sm 1-x Yb x) 3 TaO 7 compounds were prepared using high-temperature calcining technology to evaluate the impact of Yb 2 O 3 on the crystal-type and thermal-physical performances for Sm 3 TaO 7. Final analytical conclusions show that the synthesised compounds have a sole pyrochlore or fluorite crystal structure, and the lattice variation from pyrochlore to fluorite is found with an increase in Yb 2 O 3 fraction. Owing to the phonon scattering caused by substituting cation and disorder atomic arrangement, the heat insulation ability of (Sm 1-x Yb x) 3 TaO 7 oxides is improved, which meets the requirements for thermal barrier coatings. The synthesised (Sm 1-x Yb x) 3 TaO 7 oxides also present relatively high linear thermal expansion coefficients owing to the combined influence of ionic radius and crystal lattice energy. The addition of Yb 2 O 3 also improves the crystal constancy until 1200 °C. [ABSTRACT FROM AUTHOR]

Inspired in pyrochlore materials presenting residual entropy and featuring collective excitation behaving like emergent monopoles, geometrically frustrated arrays of nanomagnets, denominated artificial spin ices (ASIs), were proposed as an interesting platform to investigate such excitation at room temperature. However, in such artificial systems, emergent magnetic monopoles lack the same freedom present their natural counterpart, once energetic strings connecting opposite magnetic charges arise. In this work, we aim to experimentally investigate the proposed degeneracy obtained in connected square arrays of ASIs, a characteristic that allows a reduction in the string connecting monopole–antimonopole pairs in regular non-connected ASIs and could represent an important development for technological applications of connected nanomagnets. As in general those systems are developed by nanofabrication processes involving expensive and time-consuming physical vapour deposition techniques, we also present a new nanofabrication route using an electrodeposition technique for permalloy growth in different lattice geometries as an alternative for fast and low-cost ASI system production. [ABSTRACT FROM AUTHOR]

Sophisticated statistical mechanics approaches and human intuition have demonstrated the possibility of self-assembling complex lattices or finite-size constructs. However, attempts so far have mostly only been successful in silico and often fail in experiment because of unpredicted traps associated with kinetic slowing down (gelation, glass transition) and competing ordered structures. Theoretical predictions also face the difficulty of encoding the desired interparticle interaction potential with the experimentally available nano- and micrometer-sized particles. To overcome these issues, we combine SAT assembly (a patchy-particle interaction design algorithm based on constrained optimization) with coarse-grained simulations of DNA nanotechnology to experimentally realize trap-free self-assembly pathways. We use this approach to assemble a pyrochlore three-dimensional lattice, coveted for its promise in the construction of optical metamaterials, and characterize it with small-angle x-ray scattering and scanning electron microscopy visualization. [ABSTRACT FROM AUTHOR]

The document is a contents list for the journal CrystEngComm. It highlights various papers and communications published in the journal, including topics such as hydrogen storage, coordination polymers, luminescent sensors, and chemical solution deposition. The cover image features the Tembleque Aqueduct World Heritage Site in Mexico. The journal is published by the Royal Society of Chemistry, a leading chemistry community that connects the world with the chemical sciences. [Extracted from the article]

Herein, we used a hydrothermal method and calcination at different temperatures to synthesize Ca2Nb2O7 composite oxides with two different sub-crystalline phases, namely perovskite and pyrochlore. From the photocatalytic degradation of tetracycline, the catalytic activity of the pyrochlore crystalline phase is higher than that of the perovskite crystalline phase. This is because the pyrochlore phase structure is more disordered, which has abundant oxygen vacancies and can generate more ·O2−, h+, and ·OH under visible light irradiation. Additionally, it has a smaller bandgap and a lower valence band energy. The combination of these factors enables the higher reaction activity of the pyrochlore phase structure compared with the perovskite crystalline phase. [ABSTRACT FROM AUTHOR]

Ideally, a solid electrolyte which is a central component of SOFC should exhibit high anionic or cationic ionic conductivity at the proposed operating temperatures. In most cases, the performance is compromised when operating above 1000 °C due to poor mechanical, thermal and chemical stability of selected functional and non-functional materials. In this context, pyrochlores are one of the potential candidates due to their high conductivity, flexibility to accommodate large cations, and high mechanical, thermal and chemical stability. In this study, we report the synthesis of nano-powders of Ho 2 Hf 2 O 7 (HH) and Ho 2 Zr 2 O 7 (HZ) pyrochlore ceramics by eco-friendly alginate mediated ion-exchange process also known as Leeds Alginate Process (LAP) and provide further insight into the structure - conductivity relationship of HH and HZ compounds by EXAFS studies. Both the compositions were sintered at temperatures, ranging from 1100 °C-1500 °C at 2 h dwell time to achieve the desired high-density ceramic with stable pyrochlore structure. X-ray diffraction and Extended X-ray absorption fine structural (EXAFS) analysis showed superlattice reflections and complex coordination geometry of these oxides. The coordination number and disorder factor in the case of HZ were found to be more stable than the HH sample, as evident from the EXAFS. Impedance spectroscopy and dc-conductivity analysis showed a better charge transport behavior in HZ ceramics than in HH making HZ as a preferred solid electrolyte for SOFC. The conductivity of Ho 2 Zr 2 O 7 is comparable with the best-known fluorite oxide-ion conductor such as Sc 2 O 3 -stabilized ZrO 2 at 500 °C. [ABSTRACT FROM AUTHOR]

In this study, a series of pyrochlore-type compounds (Y 2-x Zn x)Ti 2 O 7- δ with x = 0.0, 0.1, and 0.2 were synthesized using the molten salt method. The samples were studied by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and UV–visible spectroscopy. Rietveld refinement of the XRD patterns shows that Zn2+ ions occupy Y3+ sites. Consequently, a lattice parameter and ionic radius ratio r A /r B decrease; consequently, the crystal structure is less ordered. Raman spectroscopy shows that the disorder manifests by broadening of FWHM Raman modes and increasing the A 1g Raman mode frequency as the Zn content (x) rises. Another repercussion arising from the disorder observed in the pyrochlore is the occurrence of oxygen vacancies, which are associated with ionic conductivity and are localized at 531 eV in the high-resolution O1s XPS spectra. First-principles studies using LDA + U show that Y 2 Ti 2 O 7 has a 3.07 eV electronic band gap, slightly lower than the 3.12 eV experimentally reported. The valence band (VB) is a contribution of O 2p hybridized states with Ti-3d and Y-4d, while the conduction band (CB) has Ti-3d states hybridized with O-2p states. The VB XPS spectrum and calculated DOS for Y 2 Ti 2 O 7 are well correlated. As the Zn content (x) increases, the VB XPS spectra shift to low energies, with an increment in partial states at zero eV, which induces an increase in the carrier charge. UV–visible absorption measurements using the Tauc plot approximation show a decrease in the optical band gap due to an increased concentration of Zn content. [ABSTRACT FROM AUTHOR]

In response to the low separation efficiency of actinide nuclide (An) and fission product (FP) in the separation process of high‐level radioactive waste, as well as the large amount of secondary waste. A novel Ln(1‐x)SrxZrO(3.5‐0.5x) (0 ≤ x ≤1) multiphase ceramic waste form (Nd3+ simulating An3+), which can cure both An and Sr simultaneously, was in‐situ synthesized by sol‐gel spray pyrolysis method. The series of multiphase ceramics are composed of cubic pyrochlore phase Nd2Zr2O7 (NZO) and orthorhombic perovskite phase SrZrO3 (SZO), without any accompanying impurities. The two phases exhibit excellent compatibility, and their content can change regularly with the change of x. Nd and Sr occupy their most stable crystal lattice positions, with low transposition doping levels. The density of the composite ceramics is high, and the measured density is as high as 88 % of the theoretical density. The above experimental results confirm that the new multiphase ceramics can cure An and Sr simultaneously and separately, showing strong adaptability to waste components and high chemical stability. [ABSTRACT FROM AUTHOR]

A2B2O7 oxides comprise four subcrystalline phase structures, which include the layered perovskite, pyrochlore, disordered defect fluorite, and rare‐earth C‐type structures. Herein, a series of A2B2O7 oxides have been synthesized using simple methods, and the X‐ray diffraction (XRD) and Raman spectroscopic characteristics of their subcrystalline phase structures are systematically summarized. It was found that the rA/rB ratio can be used to correctly determine the subcrystalline phase structure of the A2B2O7 oxides when the A‐site ions are rare‐earth ions. Although the A‐site ions are the main‐group metal ions, the rA/rB ratio cannot be used to accurately determine probably due to f electrons. Raman spectroscopy proves to be the most effective method for determining the subcrystalline phase structure, which is followed by XRD. The characteristic Raman spectral bands of disordered defect fluorites are closely related to their B‐site ion oxides with fluorite phase structures. For these A2B2O7 oxides with rA/rB ratios located at the edge value possessing the same elemental composition, different subcrystalline phase structures have been prepared by adopting different synthesis methods and calcination temperatures. The crystal phase of A2B2O7 oxides comprising two types of subcrystalline structures with a lower disorder degree is more stable at high temperatures. [ABSTRACT FROM AUTHOR]

This study presents the successful synthesis of a cesium–nickel–vanadium fluoride (CsNiVF6) pyrochlore nano-sheet catalyst via solid-phase synthesis and its electrochemical performance in green hydrogen production through urea electrolysis in alkaline media. The physicochemical characterizations revealed that the CsNiVF6 exhibits a pyrochlore-type structure consisting of a disordered cubic corner-shared (Ni, V)F6 octahedra structure and nano-sheet morphology with a thickness ranging from 10 to 20 nm. Using the CsNiVF6 catalyst, the electrochemical analysis, conducted through cyclic voltammetry, demonstrates a current mass activity of ~1500 mA mg−1, recorded at 1.8 V vs. RHE, along with low-resistance (3.25 ohm) charge transfer and good long-term stability for 0.33 M urea oxidation in an alkaline solution. Moreover, the volumetric hydrogen production rate at the cathode (bare nickel foam) is increased from 12.25 to 39.15 µmol/min upon the addition of 0.33 M urea to a 1.0 KOH solution and at a bias potential of 2.0 V. The addition of urea to the electrolyte solution enhances hydrogen production at the cathode, especially at lower voltages, surpassing the volumes produced in pure 1.0 M KOH solution. This utilization of a CsNiVF6 pyrochlore nano-sheet catalyst and renewable urea as a feedstock contributes to the development of a green and sustainable hydrogen economy. Overall, this research underscores the potential use of CsNiVF6 as a cost-effective nickel-based pyrochlore electrocatalyst for advancing renewable and sustainable urea electrolysis processes toward green hydrogen production. [ABSTRACT FROM AUTHOR]

Demand of energy storage materials has been drastically increased in the past few decades since they play a vital role in the fabrication of storage devices, supercapacitors etc. In this work, cerium-doped CexBi2−xSn2O7/(β-Bi2O3)-SnO2 nanocomposites with concentration (x = 0.0–1.0) were prepared via sol-gel route. XRD analysis confirmed the formation of mixed-phase nanocomposites and the crystalline structure of the material. The crystallite size was calculated to be between 5 and 18 nm using the Debye Scherrer formula. Fourier-transform infrared-spectroscopy (FTIR) confirmed the presence of functional groups. The particle size, calculated using a transmission electron microscope, ranged from 13 to 20 nm. Electrical properties like dielectric constant (ε′), complex impedance (Z), alternating current (AC) conductivity and other parameters of prepared nanocomposites were studied via impedance analyzer (1 MHz–3 GHz). Dielectric constant increased with the increasing doping concentration. Relaxation phenomenon and polarization stages were discussed in detail. Dielectric studies show that the prepared CexBi2−xSn2O7/(β-Bi2O3)-SnO2 nanocomposites are found to be a good candidate for energy storage devices, Dye sensitized solar cell, super capacitors and are also suitable for high frequency devices. [ABSTRACT FROM AUTHOR]

A set of medium-/high-entropy pyrochlore oxides (M-HEPOs) with different compositions were designed and synthesized. The phase compositions of the prepared materials were determined through X-ray diffraction and Raman spectroscopy. Among the 24 designed samples, two high-entropy and six medium-entropy samples formed single-phase pyrochlore materials, two medium-entropy samples formed dual-phase pyrochlore materials, and the others formed multiphase materials dominated by the pyrochlore phase. The factors affecting the formation of single-phase pyrochlore structure were studied. The results revealed that size disorder is a major element determining the formation of single-phase pyrochlore, whereas mixing entropy has minimal effect. It is anticipated that this study will provide significant insights into the effects of size disorder and mixing entropy on the formation of M-HEPOs. [ABSTRACT FROM AUTHOR]