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The sodium tungsten bronzes are nonstoichiometric metal oxides which have recently attracted interest for their applications as plasmonic materials. Although several synthesis routes have been repo...

Tetragonal CuMnAs was the first antiferromagnet where reorientation of the N\'eel vector was reported to occur by an inverse spin galvanic effect. A complicating factor in the formation of phase-pure tetragonal CuMnAs is the formation of an orthorhombic phase with nearly the same stoichiometry. Pure-phase tetragonal CuMnAs has been reported to require an excess of Cu to maintain a single phase in traditional solid state synthesis reactions. Here we show that subtle differences in diffraction patterns signal pervasive inhomogeneity and phase separation, even in Cu-rich Cu$_{1.18}$Mn$_{0.82}$As. From calorimetry and magnetometry measurements, we identify two transitions corresponding to the N\'eel temperature (T$_N$) and an antiferromagnet to weak ferromagnet transition in Cu$_{1.18}$Mn$_{0.82}$As and CuMn$_{0.964}$As$_{1.036}$. These transitions have clear crystallographic signatures, directly observable in the lattice parameters upon in-situ heating and cooling. The immiscibility and phase separation could arise from a spinoidal decomposition that occurs at high temperatures, and the presence of a ferromagnetic transition near room temperature warrants further investigation of its effect on the electrical switching behavior., Comment: 11 pages, 9 figures, added author middle initial, additional text and figures in supplementary, and resizing the figures

Metastable austenite strongly influences the mechanical properties of many advanced high strength steels (AHSS) and its formation kinetics during intercritical annealing strongly depend on the initial microstructure. In this contribution, we have performed detailed kinetic studies of austenite formation from cementite-ferrite aggregate in a range of Fe-C-Mn and Fe-C-Mn-Si/Al alloys via in situ neutron powder diffraction. Depending on the relative contribution of cementite dissolution in respect to migrating interface of austenite/ferrite, the incomplete dissolution of enveloped cementite limited by slow diffusion in austenite could result in austenite plateauing below equilibrium, while fast dissolution of matrix cementite could result in austenite plateau above equilibrium. Both contributions need to be considered and modelled to describe the austenite formation kinetics.

In this work, we report the first observation of a structure-driven ferroelectric (FE) wake-up effect in polycrystalline AgNbO3-based antiferroelectric (AFE) materials, by which polarization gradua...

Symmetry-mode analysis has been used to construct the direct linkage between structure and properties for (anti)ferroelectric materials., Functional materials are of critical importance to electronic and smart devices. A deep understanding of the structure–property relationship is essential for designing new materials. In this work, instead of utilizing conventional atomic coordinates, a symmetry-mode approach is successfully used to conduct structure refinement of the neutron powder diffraction data of (1−x)AgNbO3–xLiTaO3 (0 ≤ x ≤ 0.09) ceramics. This provides rich structural information that not only clarifies the controversial symmetry assigned to pure AgNbO3 but also explains well the detailed structural evolution of (1−x)AgNbO3–xLiTaO3 (0 ≤ x ≤ 0.09) ceramics, and builds a comprehensive and straightforward relationship between structural distortion and electrical properties. It is concluded that there are four relatively large-amplitude major modes that dominate the distorted Pmc21 structure of pure AgNbO3, namely a Λ3 antiferroelectric mode, a T4+ a − a − c 0 octahedral tilting mode, an H2 a 0 a 0 c +/a 0 a 0 c − octahedral tilting mode and a Γ4− ferroelectric mode. The H2 and Λ3 modes become progressively inactive with increasing x and their destabilization is the driving force behind the composition-driven phase transition between the Pmc21 and R3c phases. This structural variation is consistent with the trend observed in the measured temperature-dependent dielectric properties and polarization–electric field (P-E) hysteresis loops. The mode crystallography applied in this study provides a strategy for optimizing related properties by tuning the amplitudes of the corresponding modes in these novel AgNbO3-based (anti)ferroelectric materials.

Compounds that exhibit the unique behavior of negative thermal expansion (NTE)-the physical property of contraction of the lattice parameters on warming-can be applied widely in modern technologies. Consequently, the search for and design of an NTE material with operational and controllable qualities at room temperature are important topics in both physics and materials science. In this work, we demonstrate a new route to achieve magnetic manipulation of a giant NTE in (Mn0.95Ni0.05)CoGe via strong magnetostructural (MS) coupling around room temperature (∼275 to ∼345 K). The MS coupling is realized through the weak bonding between the nonmagnetic CoGe-network and the magnetic Mn-sublattice. Application of a magnetic field changes the NTE in (Mn0.95Ni0.05)CoGe significantly: in particular, a change of Δ L/ L along the a axis of absolute value 15290(60) × 10-6-equivalent to a -31% reduction in NTE-is obtained at 295 K in response to a magnetic field of 8 T.

La-doped AgNbO3 lead-free ceramics were fabricated by conventional solid-state reaction, and the phase stability and energy storage properties were investigated. The temperature- and electric field-dependent dielectric constants show that the antiferroelectric (AFE) phase stability is enhanced via the La doping. Neutron diffraction was performed to obtain insights into the structural evolution with composition and temperature, where the local structural variation is found to involve subtle ion displacement as well as oxygen octahedral tilting, leading to the disruption of the long-range interactions, which is responsible for the enhanced AFE phase stability. As expected, the enhanced AFE phase stability, together with the improved breakdown strength, gives rise to a high energy density of 4.4 J cm−3 and an improved efficiency of 70%, which are achieved in 2 mol% La-doped AgNbO3 ceramics. Our research opens a new way to tailor the macroscopic properties by tuning the microstructure of AgNbO3-based materials.

Explosive energy conversion materials with extremely rapid response times have broad and growing applications in energy, medical, defense, and mining areas. Research into the underlying mechanisms and the search for new candidate materials in this field are so limited that environment-unfriendly Pb(Zr,Ti)O3 still dominates after half a century. Here, we report the discovery of a previously undiscovered, lead-free (Ag0.935K0.065)NbO3 material, which possesses a record-high energy storage density of 5.401 J/g, enabling a pulse current ~ 22 A within 1.8 microseconds. It also exhibits excellent temperature stability up to 150°C. Various in situ experimental and theoretical investigations reveal the mechanism underlying this explosive energy conversion can be attributed to a pressure-induced octahedral tilt change from a−a−c+ to a−a−c−/a−a−c+, in accordance with an irreversible pressure-driven ferroelectric-antiferroelectric phase transition. This work provides a high performance alternative to Pb(Zr,Ti)O3 and also guidance for the further development of new materials and devices for explosive energy conversion.

Due to growing concern for the environment and human health, searching for high-performance lead-free piezoceramics has been a hot topic of scientific and industrial research. Despite the significant progress achieved toward enhancing piezoelectricity, further efforts should be devoted to the synergistic improvement of piezoelectricity and its thermal stability. This study provides new insight into these topics. A new KNN-based lead-free ceramic material is presented, which features a large piezoelectric coefficient (d33) exceeding 500 pC/N and a high Curie temperature (Tc) of ∼200°C. The superior piezoelectric response strongly relies on the increased composition-induced structural flexibility due to lattice softening and decreased unit cell distortion. In contrast to piezoelectricity anomalies induced via polymorphic transition, this piezoelectricity enhancement is effective within a broad temperature range rather than a specific small range. In particular, a hierarchical domain architecture composed of nano-sized domains along the submicron domains was detected in this material system, which further contributes to the high piezoelectricity.

The structural and magnetic properties of magnetocaloric Mn(Co1–xNix)Ge compounds have been studied. Two responses to the increase of valence electron concentration on substitution of Ni (3d84s2) for Co (3d74s2) in the orthorhombic phase (Pnma) are proposed: expansion of unit-cell volume and redistribution of valence electrons. We present experimental evidence for electronic redistribution associated with the competition between magnetism and bonding. This competition in turn leads to complex dependences of the reverse martensitic transformation temperature TM (orthorhombic to hexagonal (P63/mmc)) and the magnetic structures on the Ni concentration. Magnetic transitions from ferromagnetic structures below x = 0.50 to noncollinear spiral antiferromagnetic structures above x = 0.55 at low temperature (e.g., 5 K) are induced by modification of the density of states at the Fermi surface due to the redistribution of valence electrons. TM is found to decrease initially with increasing Ni content and then increa...

The influence of molecular confinement on the melting transition of oriented Na-DNA fibers submerged in poly(ethylene glycol) (PEG) solutions has been studied. The PEG solution exerts an osmotic pressure on the fibers which, in turn, is related to the DNA intermolecular distance. Calorimetry measurements show that the melting temperature increases and the width of the transition decreases with decreasing intermolecular distance. Neutron scattering was used to monitor the integrated intensity and width of a Bragg peak from the B-form of DNA as a function of temperature. The data were quantitatively analyzed using the Peyrard-Bishop-Dauxois model. The experiments and analysis showed that long segments of double-stranded DNA persist until the last stages of melting and that there appears to be a substantial increase of the DNA dynamics as the melting temperature of the DNA is approached.

The reduction of New Zealand titanomagnetite ironsand in a dilute hydrogen–nitrogen gas mixture was studied in situ using neutron diffraction. Neutron diffraction allowed in situ observation of lar...

Through the detailed studies utilizing x-ray and neutron powder diffraction and magnetometry measurements, we report the magnetic phase transitions in the B-site disorder perovskite oxide PrFe0.5Cr0.5O3. The Fe3+/Cr3+ sublattice was observed to form a long-range magnetic order with the GxFz configuration below TN = 270 K from neutron powder diffraction. It then undergoes the second-order phase transition to FxGz spin configuration below 210 K and the transition ends at ~170 K. On the other hand, long range magnetic ordering with FxCy configuration at Pr3+ sublattice can be identified at base temperature. The magnetic phase diagram is derived with spontaneous spin ordering and reorientation at A- and B-sublattices.

We detected a crossover from negative to positive thermal expansion with increasing Mn in HoCo2Mnx below the Curie temperature through high quality neutron diffraction measurements from 5 K to 400 K. Almost isotropic zero thermal expansion with coefficient of thermal expansion αl = −4.894 × 10−7/K was achieved over a large range of temperature from 5 K to TC = 225 K in the compound HoCo2Mn0.5. While the addition of manganese was shown to change the temperature dependence of the lattice, it was also noted that the Curie temperature rose significantly from 88 K in HoCo2 to 253 K in HoCo2Mn providing a hope for a room temperature transition in similar doping series materials.

The magnetic properties and magnetic structure of an as-prepared Mn(Co0.96Fe0.04)Ge sample has been investigated by powder neutron diffraction as well as X-ray diffraction and magnetisation measurements. The sample has a ferromagnetic structure in the low-temperature orthorhombic phase and a magneto-structural transition at 299 (1) K to the high-temperature paramagnetic hexagonal phase. This transition occurs at a higher temperature than for as-prepared (Mn0.96Fe0.04)CoGe (TM = 239 (1) K). Increased occupancy by Fe of the Co (4c) site rather than the Mn (4c) site results in this smaller suppression of the structural transition temperature away from that of undoped MnCoGe. It was found that chemical pressure increased the Curie temperature T C orth in the orthorhombic phase from 355 (5) K in Mn(Co0.96Fe0.04)Ge to 379 (6) K in MnCoGe. Mn(Co0.96Fe0.04)Ge exhibits a large magnetocaloric effect around the magneto-structural transition, − Δ S m peak = 11 (2) J kg−1 K−1 and RC = 187 (30) J kg−1 with μ0ΔH = 5 T. The magneto-structural transition is a first order transition as demonstrated by master curve analysis.

Duplex stainless steels are designed to solidify with ferrite as the parent phase, with subsequent austenite formation occurring in the solid state, implying that, thermodynamically, a fully ferrit ...

Hexaferrites with noncollinear conical magnetic structures are among the most interesting and promising single-phase multiferroics. One puzzle remaining unsolved is why the spin-induced electric polarization can be either reversible or nonreversible by applying magnetic fields. We have unraveled a solution to this puzzle by a systematic study in the multiferroic hexaferrite ${\mathrm{Ba}}_{0.3}{\mathrm{Sr}}_{1.7}{\mathrm{Co}}_{2}{\mathrm{Fe}}_{11}{\mathrm{AlO}}_{22}$ where the electric polarization is reversible at low temperatures but nonreversible at high temperatures. Neutron diffraction results reveal that the rotation of spin cones with applied $ab$-plane magnetic field takes distinct paths at 150 and 305 K: in-plane and out-of-plane rotation, respectively. A theoretical analysis based on the spin current model confirms that the reversal of electric polarization is caused by the in-plane rotation. Our study clarifies the mechanism underlying the reversibility of spin-induced electric polarization in multiferroic hexaferrites.

Skyrmions with multiple helicity or topology in centrosymmetric crystals are intriguing magnetic-domain objects due to their diverse dynamics under external stimuli. Here we illustrate how the two key gradients of magnetocrystalline anisotropy (MCA) and spin reorientation transition (SRT) affect the skyrmion formation and topology by Cu substitution in the biskyrmion-host MnNiGa alloy. The MCA and SRT are simultaneously tuned in a large scope, while the original high Curie temperature (${T}_{C}$) is retained. Detailed neutron-scattering studies revealed the construction of a noncollinear canted magnetic structure below the SRT temperature (${T}_{\mathrm{SR}}$), which effectively correlates the SRT with the evolution of the MCA, as well as the exchange interaction. The Cu substitution raises the ${T}_{\mathrm{SR}}$ to merge with the ${T}_{\mathrm{C}}$, and meanwhile, reduces the $c$-axis anisotropy. Lorentz transmission electron microscopy revealed the formation of stacked biskyrmions from above room temperature to lower temperatures in $\mathrm{MnN}{\mathrm{i}}_{1\ensuremath{-}x}\mathrm{C}{\mathrm{u}}_{x}\mathrm{Ga}\phantom{\rule{0.28em}{0ex}}(x=0--0.3)$ in the presence of proper MCA. Micromagnetic simulations further confirmed the great effect of uniaxial anisotropy on the stabilization of biskyrmions. Our work has helped clarify the evolution of magnetic structures and their correlation to the SRT, providing an account of the effect of MCA and exchange interaction on the biskyrmion formation.

Neutron powder diffraction was used in operando to determine the macroscopic strain and piezoelectric coefficient as a function of applied electric field in a technically relevant actuator material. We were able to individually investigate the two coexisting phases in the material and reveal the origin of maximized strain at phase boundaries. Insight into the strain mechanisms gives evidence that, on average, the classic inverse piezoelectric effect does not apply for polycrystalline materials.

We report on a detailed neutron diffraction and $^{1}\mathrm{H}$-NMR study on the frustrated spin-1/2 chain material linarite, ${\mathrm{PbCuSO}}_{4}{(\mathrm{OH})}_{2}$, where competing ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor interactions lead to frustration. From the magnetic Bragg peak intensity studied down to 60 mK, the magnetic moment per Cu atom is obtained within the whole magnetic phase diagram for $H\ensuremath{\parallel}b$ axis. Further, we establish the detailed configurations of the shift of the SDW propagation vector in phase V with field and temperature. Finally, combining our neutron diffraction results with those from a low-temperature/high-field NMR study, we find an even more complex phase diagram close to the quasisaturation field suggesting that bound two-magnon excitations are the lowest energy excitations close to and in the quasisaturation regime. Qualitatively and semiquantitatively, we relate such behavior to $XYZ$ exchange anisotropy and contributions from the Dzyaloshinsky-Moriya interaction to affect the magnetic properties of linarite.

Neutron powder diffraction experiments were carried out on the magnetoelectric compound series (Co

TbRu 2 Al 10 is found to undergo two magnetic phase transitions as a function of temperature and three as a function of applied field at low temperature. The Tb 3+ magnetic moments order antiferromagnetically along the c -axis at 15.0(3) K, with an incommensurate sinusoidally modulated structure with a propagation vector of k = (0, 0.759(1), 0). At 6.5(3) K the structure switches to square wave order. Analysis of single crystal TbRu 2 Al 10 has revealed that this square wave structure is altered to a ‘pulse wave’ on application of a 1.30 T magnetic field along the c -axis, with two in fifty of the magnetic moments across the structure changing direction to be aligned parallel with the direction of the field. At 1.85 T a further three moments flip, leading to a duty cycle of 60% and resulting in a total change of one in ten moments from the starting square wave structure.

The mechanical flexibility of coordination frameworks can lead to a range of highly anomalous structural behaviours. Here, we demonstrate the extreme compressibility of the LnFe(CN)6 frameworks (Ln = Ho, Lu or Y), which reversibly compress by 20% in volume under the relatively low pressure of 1 GPa, one of the largest known pressure responses for any crystalline material. We delineate in detail the mechanism for this high compressibility, where the LnN6 units act like torsion springs synchronized by rigid Fe(CN)6 units performing the role of gears. The materials also show significant negative linear compressibility via a cam-like effect. The torsional mechanism is fundamentally distinct from the deformation mechanisms prevalent in other flexible solids and relies on competition between locally unstable metal coordination geometries and the constraints of the framework connectivity, a discovery that has implications for the strategic design of new materials with exceptional mechanical properties.

Rare earth orthoferrites demonstrate great application potentials in spintronics and optical devices due to their multiferroic and magnetooptical properties. In RFeO3, magnetic R3+ undergo a spontaneous spin reorientation in a temperature range determined by R (rare earth), where the magnetic structure changes from Γ2 to Γ4. The b-axis component of their magnetic moment, Mb, is reported in numerous neutron diffraction studies to remain zero at all temperatures. More sensitive magnetometer measurements reveal a small non-zero Mb, which is minute above ∼200 K. Mb increases with cooling and reaches values of ∼10–3 μB/f.u. at temperatures within or below the spin reorientation temperatures. Our results can be explained by assuming the Fe3+ spins as the origin of non-zero Mb, while R3+ spins suppress Mb. The representation analysis of point groups shows that non-zero Mb is associated with a small admixture of the Γ3 phase to Γ2 or Γ4. Such a mixing of the three magnetic phases requires at least a fourth order of the spin Hamiltonian for RFeO3 to describe the non-zero Mb.

Neutron powder diffraction experiments reveal that $\mathrm{C}{\mathrm{o}}_{4}\mathrm{N}{\mathrm{b}}_{2}{\mathrm{O}}_{9}$ forms a noncollinear in-plane magnetic structure with $\mathrm{C}{\mathrm{o}}^{2+}$ moments lying in the $ab$ plane. The spin-wave excitations of this magnet were measured by using inelastic neutron scattering and soundly simulated by a dynamic model involving nearest- and next-nearest-neighbor exchange interactions, in-plane anisotropy, and the Dzyaloshinskii-Moriya interaction. The in-plane magnetic structure of $\mathrm{C}{\mathrm{o}}_{4}\mathrm{N}{\mathrm{b}}_{2}{\mathrm{O}}_{9}$ is attributed to the large in-plane anisotropy, while the noncollinearity of the spin configuration is attributed to the Dzyaloshinskii-Moriya interaction. The high magnetoelectric coupling effect of $\mathrm{C}{\mathrm{o}}_{4}\mathrm{N}{\mathrm{b}}_{2}{\mathrm{O}}_{9}$ in fields can be explained by its special in-plane magnetic structure.

This in situ neutron-diffraction study on antiferroelectric (AFE) $\mathrm{P}{\mathrm{b}}_{0.99}(\mathrm{N}{\mathrm{b}}_{0.02}\mathrm{Z}{\mathrm{r}}_{0.65}\mathrm{S}{\mathrm{n}}_{0.28}\mathrm{T}{\mathrm{i}}_{0.05}){\mathrm{O}}_{3}$ polycrystalline materials describes systematic structural and associated preferred orientation changes as a function of applied electric field and temperature. It is found that the pristine AFE phase can be poled into the metastable ferroelectric (FE) phase at room temperature. At this stage, both AFE and FE phases consist of modes associated with octahedral rotation and $A$-site ionic displacements. The temperature-induced phase transition indicates that the octahedral rotation and ionic displacements are weakly coupled in the room-temperature FE phase and decoupled in the high-temperature FE phase. However, both temperature and $E$-field-induced phase transitions between the AFE and high-temperature FE phase demonstrate the critical role of coupling between octahedral rotation and $A$-site ionic displacements in stabilizing the AFE structure, which provides not only experimental evidence to support previous theoretical calculations, but also an insight into the design and development of AFE materials. Moreover, the associated preferred orientation evolution in both AFE and FE phases is studied during the phase transitions. It is found that the formation of the preferred orientation can be controlled to tune the samples' FE and AFE properties.

The MPS3 family of layered magnetic materials (M = Fe2+, Ni2+, Mn2+, etc) shows many unusual properties. We have recently observed time-dependent magnetisation and two magnetic phase transitions in Fe0.5Ni0.5PS3, and here we use neutron diffraction and Mossbauer spectroscopy to explore the magnetic and structural ordering. Neutron diffraction shows that the staggered magnetisation lies closest to the Brillouin curve for J = 1, which is the spin for quenched Ni2+. In agreement with neutron diffraction, Mossbauer spectroscopy shows a magnetic ordering temperature of ∼120K. It does not show any evidence of a second, low temperature (re)ordering, suggesting that the low temperature transition seen previously is a result of the time dependence of the magnetisation and is not apparent when the sample is given time to relax between measurements. The presence of three magnetic Fe-site environments when four chemical environments (Fe3, Fe2Ni, FeNi2 and Ni3) are possible may indicate that the mixture is not random, but shows some local ordering; the neutron results show evidence for a similar conclusion.

Neutron powder diffraction data of TbNiAl4 has been re-examined using a representational analysis, allowing a new model of the magnetic structure to be deduced. The basis vectors obtained describe an ‘elliptical helix’ type structure in which the moments rotate in the ab-plane as one moves along the c-axis. This new model has been used to simulate the expected result of a Low Temperature Nuclear Orientation (LTNO) experiment involving 299 keV gamma-ray emission from the 160Dy daughter of aligned 160Tb nuclei. Results of the simulation along the a-axis appear to partly match currently existing experimental data, with good agreement in the magnitude of lost anisotropy.

The formation and decomposition of silico-ferrite of calcium and aluminium (SFCA) and SFCA-I iron ore sinter bonding phases have been investigated usingin situsynchrotron and laboratory X-ray diffraction (XRD) and neutron diffraction (ND). An external standard approach for determining absolute phase concentrations via Rietveld refinement-based quantitative phase analysis is discussed. The complementarity ofin situXRD and ND in characterising sinter phase formation and decomposition is also shown, with the volume diffraction afforded by the neutron technique reducing errors in the quantification of magnetite above ~1200 °C. Finally, by collecting 6 s laboratory XRD datasets and using a heating rate of 175 °C min−1, phase formation and decomposition have been monitored under heating rates more closely approximating those encountered in industrial iron ore sintering.

The wide ranging magnetic behavior in intermetallic compounds continues to attract broad interest. Effective control of their magnetic properties is of great importance for fundamental research and potential applications. In this work the structural and magnetic properties of $\mathrm{TbC}{\mathrm{o}}_{2}\mathrm{M}{\mathrm{n}}_{x}$ compounds are studied by a combination of temperature dependent synchrotron x-ray diffraction, neutron powder diffraction, specific heat, and magnetic measurements. Magnetization measurements show that the addition of Mn can modify the magnetic behavior significantly: first, the magnetic transition temperatures increase from \ensuremath{\sim}227 K to 332 K with $x=0.0\phantom{\rule{0.28em}{0ex}}\mathrm{to}\phantom{\rule{0.28em}{0ex}}0.3$; secondly, the nature of the magnetic transitions change from the first order to second order, as identified by three methods (Banerjee criterion, master curves of magnetic entropy changes, and detailed crystal structure analysis through neutron diffraction). Both synchrotron x-ray diffraction and neutron diffraction confirm that a structural transition, from cubic $Fd\overline{3}m$ to rhombohedral $R\overline{3}m$ on cooling, occurred accompanying the magnetic transition. To further clarify the nature of the second order magnetic phase transitions, we have carried out a detailed critical exponent analysis. The derived critical exponents are close to the theoretical prediction from the mean-field model, indicating the magnetic interactions are long range. This work benefits our general understanding of magnetic interactions in intermetallic compounds and provides guidance to design a functional magnetic material for room temperature magnetic devices.

A novel mechanism of spin-induced ferroelectricity is unraveled in the alternating longitudinal conical (ALC) magnetic structure. Because the noncollinear ALC structure possesses a $c$-axis component with collinear \ensuremath{\uparrow}--\ensuremath{\uparrow}--\ensuremath{\downarrow}--\ensuremath{\downarrow} spin order, spin-driven ferroelectricity along the $c$ axis due to the exchange striction mechanism is predicted. Our experiments verify this prediction in the Y-type hexaferrite $\mathrm{B}{\mathrm{a}}_{0.3}\mathrm{S}{\mathrm{r}}_{1.7}\mathrm{C}{\mathrm{o}}_{2}\mathrm{F}{\mathrm{e}}_{11}\mathrm{Al}{\mathrm{O}}_{22}$, where ferroelectricity along the $c$ axis is observed up to room temperature. Neutron diffraction data clearly reveal the ALC phase and its evolution with magnetic fields. The $c$-axis electric polarization can be well modulated by applying either $ab$-plane or $c$-axis magnetic fields, even at 305 K. This kind of spin-induced ferroelectricity associated with the ALC magnetic structure provides a new resource of type II multiferroics.

Peculiar L-shaped diffuse streaks along pc were observed in (Na 0.5 Bi 0.5 )TiO 3 (NBT) below the Burns temperature, revealing the existence of polar nanoregions (PNRs). The displacement of Bi 3+ cations is ∼0.26 A along pc in the PNRs, with a size of ∼13 A in NBT. The BaTiO 3 doping drives the diffuse scattering patterns to evolve from the L-shape into an ellipsoidal along pc in (Na 0.5 Bi 0.5 )TiO 3 –x BaTiO 3 . An abnormally large correlation length was observed in the morphotropic phase boundary composition with x = 0.05.

Effects of basicity, B (CaO:SiO2 ratio) on the thermal range, concentration, and formation mechanisms of silico-ferrite of calcium and aluminum (SFCA) and SFCA-I iron ore sinter bonding phases have been investigated using an in situ synchrotron X-ray diffraction-based methodology with subsequent Rietveld refinement-based quantitative phase analysis. SFCA and SFCA-I phases are the key bonding materials in iron ore sinter, and improved understanding of the effects of processing parameters such as basicity on their formation and decomposition may assist in improving efficiency of industrial iron ore sintering operations. Increasing basicity significantly increased the thermal range of SFCA-I, from 1363 K to 1533 K (1090 °C to 1260 °C) for a mixture with B = 2.48, to ~1339 K to 1535 K (1066 °C to 1262 °C) for a mixture with B = 3.96, and to ~1323 K to 1593 K (1050 °C to 1320 °C) at B = 4.94. Increasing basicity also increased the amount of SFCA-I formed, from 18 wt pct for the mixture with B = 2.48 to 25 wt pct for the B = 4.94 mixture. Higher basicity of the starting sinter mixture will, therefore, increase the amount of SFCA-I, considered to be more desirable of the two phases. Basicity did not appear to significantly influence the formation mechanism of SFCA-I. It did, however, affect the formation mechanism of SFCA, with the decomposition of SFCA-I coinciding with the formation of a significant amount of additional SFCA in the B = 2.48 and 3.96 mixtures but only a minor amount in the highest basicity mixture. In situ neutron diffraction enabled characterization of the behavior of magnetite after melting of SFCA produced a magnetite plus melt phase assemblage.

This paper outlines measurement and analysis methodologies created for determining the structural responses of electroceramics to an electric field. A sample stage is developed to apply electric fields to ceramic materials at elevated temperatures during neutron diffraction experiments. The tested voltages and temperatures range from −20 kV to +20 kV and room temperature to 200 °C, respectively. The use of the sample environment for measuring the response of ferroelectric ceramics to an electrical stimulus is demonstrated on the instrument Wombat, a monochromatic neutron diffractometer employing a curved positive sensitive detector. Methodologies are proposed to account for the geometrical effects when vector fields are applied to textured materials with angularly dispersive detector geometries. Representative results are presented for the ferroelectric (Bi1/2Na1/2)TiO3-6%BaTiO3 (BNT-6BT) which show both phase transformation and ferroelectric domain texturing under the application of an electric field. This experimental and analysis approach is well suited for time-resolved measurements such as stroboscopic and in situ studies on a variety of electro-active materials.

This work presents a detailed microstructure and texture study of various hydrided Zircaloy-4 materials by neutron diffraction and microscopy. The results show that the precipitated δ-ZrH1.66 generally follows the δ (111) //α (0001) and δ[]//α[] orientation relationship with the α-Zr matrix. The δ-hydride displays a weak texture that is determined by the texture of the α-Zr matrix, and this dependence essentially originates from the observed orientation correlation between α-Zr and δ-hydride. Neutron diffraction line profile analysis and high-resolution transmission electron microscopy observations reveal a significant number of dislocations present in the δ-hydride, with an estimated average density one order of magnitude higher than that in the α-Zr matrix, which contributes to the accommodation of the substantial misfit strains associated with hydride precipitation in the α-Zr matrix. The present observations provide an insight into the behaviour of δ-hydride precipitation in zirconium alloys and may help with understanding the induced embrittling effect of hydrides. Fil: Wang, Zhiyang. University of Wollongong; Australia. Australian Nuclear Science and Technology Organisation; Australia Fil: Garbe, Ulf. Australian Nuclear Science and Technology Organisation; Australia Fil: Li, Huijun. University of Wollongong; Australia Fil: Wang, Yanbo. University of Sydney; Australia Fil: Studer, Andrew J.. Australian Nuclear Science and Technology Organisation; Australia Fil: Sun, Guangai. Institute of Nuclear Physics and Chemistry, CAEP; China Fil: Harrison, Robert P.. Australian Nuclear Science and Technology Organisation, Institute of Materials Engineering; Australia Fil: Liao, Xiaozhou. University of Sydney; Australia Fil: Vicente Alvarez, Miguel Angel. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Santisteban, Javier Roberto. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Kong, Charlie. University of New South Wales; Australia

We report a wide-range reciprocal space observation with neutron diffraction in an iron vacancy controlled YbFe2O4 crystal, which is proposed as a prototype of electronic ferroelectrics arising fro...

The poling of hard Lead Zirconate Titanate (PZT) materials is a complex process requiring optimisation of the poling parameters time, temperature, and electric field magnitude. A unique method is presented to monitor the poling process in operando on the unit cell level with neutron diffraction through the analysis of changes in reflection patterns. Diffraction analysis after poling reveals the lattice and domain contributions using poling strain as a measure. This allows for the evaluation of induced dipole alignment and process efficiency. It gives insight into the role of domain wall motions in hard PZT ceramics and how they are affected by poling parameters. Additionally, a poled sample is cycled bipolar and analyzed. It shows a strongly asymmetric strain hysteresis with major contributions from domain wall motions in the tetragonal phase. Macroscopically measured hysteresis loops verify the findings from diffraction. The present work contributes to improving poling results, efficiency and saving energy. The diffraction analysis allows a novel investigation method of the poling mechanisms and provides extensive results that give new insights into the material behavior. With a fundamental research method, this work reveals unprecedented details that can be directly applied to the specific application field of poling technology.

Neutron powder diffraction experiments were carried out on the magnetoelectric compound series (Co4-x Mn x )Nb2O9 (x = 0, 1, 2, 3, 3.5, 3.9, 3.95 and 4) from base temperature to above their Neel temperatures. Their magnetic structures were analysed by using the irreducible representation analysis and Rietveld refinement method. Similar to Co4Nb2O9, the compounds with x ⩽ 3.9 have noncollinear in-plane magnetic structures (Γ6) with magnetic moments lying purely in the ab plane with certain canting angles. Mn4Nb2O9 has a collinear antiferromagnetic structure (Γ2) with magnetic moments aligning along the c axis. The compound of x = 3.95 shows two magnetic phases in the magnetization, which was confirmed to have the Γ2 magnetic structure above 60 K and develop a second Γ6 local phase in addition to the main Γ2 phase due to doping. This study indicates 2.5 at% Co2+ doping is sufficient to alter the collinear easy-axis magnetic structure of Mn4Nb2O9 into the noncollinear easy-plane magnetic structure, which is attributed to the large easy-plane anisotropy of Co2+ and relative small Ising-like anisotropy of Mn2+. The doping effects on the Neel temperature and occupancy are also discussed.

The hydride formation and its influence on the mechanical performance of hydrided Zircaloy-4 plates containing different hydrogen contents were studied at room temperature. For the unnotched plate samples with the hydrogen contents ranging from 25 to 850 wt. ppm, the hydrides exerted an insignificant effect on the tensile strength, while the ductility was severely degraded with increasing hydrogen content. The fracture mode and degree of embrittlement were strongly related to the hydrogen content. When the hydrogen content reached a level of 850 wt. ppm, the plate exhibited negligible ductility, resulting in almost completely brittle behavior. For the hydrided notched plate, the tensile stress concentration associated with the notch tip facilitated the hydride accumulation at the region near the notch tip and the premature crack propagation through the hydride fracture during hydriding. The final brittle through-thickness failure for this notched sample was mainly attributed to the formation of a continuous hydride network on the thickness section and the obtained very high hydrogen concentration (estimated to be 1965 wt. ppm).

Using neutron single crystal and powder diffraction, the first thorough investigation of the structure of fully deuterated triglycine sulphate, (ND2CD2COOD)3.D2SO4 is presented, including its evolution with T, through its structural phase transition. This includes new precise structural parameters determined at several key temperatures above and below TC using single crystal diffraction, and for the first time a parametric study has been undertaken over a wide temperature range — from 4 to 500 K in 2 K steps. It was found that fully deuterated TGS shows a structure consistent with hydrogenous TGS and partially deuterated TGS. The evolution of several key hydrogen bond lengths suggests that weakening of the H-bond network with T is crucial in decoupling the polarising glycine molecules from the other glycines and allowing the long-range ferroelectric order to break down. A new parameterisation of the phase transition is demonstrated. Contrary to results of physical properties measurements, there is no evidence of a second low temperature phase transition in TGS – no low temperature anomalies were observed in the crystal structure.

In situneutron powder diffraction patterns and dielectric spectra of 0.93Bi0.5Na0.5TiO3-0.07BaTiO3ceramic were investigated under different electrical fields and temperatures. An electric-field-induced phase transition from metrically cubic to metrically tetragonal, associated with strong domain wall motion, occurs. Such induced phase and domain wall motion are unchanged until the high-temperature phase transition occurs from metrically tetragonal to metrically cubic. All these changes are irrelevant to the observed depolarization temperature (75°C). The depolarization behaviour is thus suggested to be associated with the local structure caused by the octahedral tilt twinning disorder.

We characterized the temperature dependent (~25–200°C) electromechanical properties and crystal structure of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3single crystals usingin situelectrical measurement and neutron diffraction techniques. The results show that the poled crystal experiences an addition phase transition around 120°C whereas such a transition is absent in the unpoled crystal. It is also found that the polar order persists above the maximum dielectric permittivity temperature at which the crystal shows a well-defined antiferroelectric behavior. The changes in the electrical properties and underlying crystal structure are discussed in the paper.

The gaseous hydriding-induced evolutions of the microstructure, texture and mechanical properties of Zircaloy-4 processed by high-pressure torsion (HPT) were assessed. Much δ-ZrH1.66 precipitation at 15 atm (21%) incurred significant hardening of vacuum-annealed HPT samples, and pure e-ZrH2 obtained at 20 atm showed a superior microhardness of 470 HV0.3 and a low fracture toughness of 0.63 MPa m1/2. The δ-hydrides presented strong (1 1 1) texture and followed the (0 0 0 1)α-Zr//{1 1 1}δ-ZrH1.66 orientation relationship with the α-Zr matrix. During hydriding, α-Zr recrystallization texture was developed from the initial deformation texture.

Electric-field-induced, antiferroelectric-ferroelectric (AFE-FE) phase transitions are common for AFE materials. To date, the strain and preferred orientation evolution as well as the role of the intermediate FE state during the successive AFE-FE-AFE phase transitions has not been clear. To this end, we have herein studied a typical AFE Pb0.97La0.02(Zr0.56Sn0.33Ti0.11)O3 (PLZST) material using in-situ neutron diffraction. It is striking that the AFE-FE phase transition is not fully reversible: in the electric-field-induced FE state, the induced strain exhibits an elliptical distribution, which in turn leads to significant preferred orientation in the final AFE state after withdrawal of the applied electric-field. The ω-dependent neutron diffraction patterns show clear evidence of the induced strain distribution and associated preferred orientation arising from the AFE-FE phase transition. The current work also provides an explanation for several temperature and electric-field dependent dielectric anomalies as well as unrecovered strain change which appear in AFE materials after exposure to sufficiently high electric fields.

Low-temperature neutron diffraction and NMR studies of field-induced phases in linarite are presented for magnetic fields H∥b axis. A two-step spin-flop transition is observed, as well as a transition transforming a helical magnetic ground state into an unusual magnetic phase with sine-wave-modulated moments ∥H. An effective J[over ˜]_{1}-J[over ˜]_{2} single-chain model with a magnetization-dependent frustration ratio α_{eff}=-J[over ˜]_{2}/J[over ˜]_{1} is proposed. The latter is governed by skew interchain couplings and shifted to the vicinity of the ferromagnetic critical point. It explains qualitatively the observation of a rich variety of exotic longitudinal collinear spin-density wave, SDW_{p}, states (9≥p≥2).

International audience; Great effort has been devoted to developing single-phase magnetoelectric multiferroics, but room-temperature coexistence of large electric polarization and magnetic ordering still remains elusive. Our recent finding shows that such polar magnets can be synthesized in small-tolerance-factor perovskites AFeO3 with unusually small cations at the A-sites, which are regarded as having a LiNbO3-type structure (space group R3c). Herein, we experimentally reinforce this finding by preparing a novel room-temperature polar magnet, LiNbO3-type InFeO3. This compound is obtained as a metastable quench product from an orthorhombic perovskite phase stabilized at 15 GPa and an elevated temperature. The structure analyses reveal that the polar structure is characterized by displacements of In3+ (d10) and Fe3+ (d5) ions along the hexagonal c-axis (pseudocubic [111] axis) from their centrosymmetric positions, in contrast to well-known perovskite ferroelectrics (e.g., BaTiO3, PbTiO3, and BiFeO3) where d0 transition-metal ions and/or 6s2 lone-pair cations undergo polar displacements through the so-called second-order Jahn-Teller (SOJT) distortions. Using density functional theory calculations, the electric polarization of LiNbO3-type InFeO3 is estimated to be 96 μC/cm2 along the c-axis, comparable to that of an isostructural and SOJT-active perovskite ferroelectric, BiFeO3 (90-100 μC/cm2). Magnetic studies demonstrate weak ferromagnetic behavior at room temperature, as a result of the canted G-type antiferromagnetic ordering of Fe3+ moments below TN ∼ 545 K. The present work shows the functional versatility of small-tolerance-factor perovskites and provides a useful guide for the synthesis and design of room-temperature polar magnets. © 2016 American Chemical Society.

Coupling of order parameters provides a means to tune functionality in advanced materials including multiferroics, superconductors, and ionic conductors. We demonstrate that the response of a frustrated ferroelectric state leads to coupling between order parameters under electric field depending on grain orientation. The strain of grains oriented along a specific crystallographic direction, ⟨h00⟩, is caused by converse piezoelectricity originating from a ferrodistortive tetragonal phase. For ⟨hhh⟩ oriented grains, the strain results from converse piezoelectricity and rotostriction, as indicated by an antiferrodistortive instability that promotes octahedral tilting in a rhombohedral phase. Both strain mechanisms combined lead to a colossal local strain of (2.4 ± 0.1) % and indicate coupling between oxygen octahedral tilting and polarization, here termed “rotopolarization”. These findings were confirmed with electromechanical experiments, in situ neutron diffraction, and in situ transmission electron microscopy in 0.75Bi1/2Na1/2TiO3-0.25SrTiO3. This work demonstrates that polar and non-polar instabilities can cooperate to provide colossal functional responses This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0

We report the first growth of a large (cm-scale) single crystal of the brownmillerite-type oxide ionic conductor Sr 2 Fe 2 O 5 , by the floating-zone method. Although the crystal is twinned on a microscopic scale with respect to the unit cell of the disordered oxygen-deficient perovskite from which it forms, this twinning is not complete or equivalent in all directions, and so it presents the possibility of direction-dependent measurements of conductivity and other properties. Single crystal neutron diffraction revealed a supercell with a doubled a axis, compared to the conventional Icmm model containing disordered left- and right-handed tetrahedral chains. It corresponds to the β = 0, γ = 1/2 case of the I 2/ m (0 βγ )0 s chain-ordering modulation proposed by D'Hondt et al. on the basis of electron microscopy and electron diffraction evidence. Its observation by neutron diffraction for the first time proves that the tetrahedral chains are long-range ordered at room temperature, and in a more complex manner than the Ibm 2 model, which has previously been assumed to describe local chain order.

The phase evolution during the sintering of metal injection moulded stainless steel, 316Land 17-4PH, has been observed using in situ neutron diffraction and Rietveld analysis. The formationof the ferrite phase in the final product is associated with the production of -ferrite at high temperatures.Coexistence of phases at high temperature is thought to allow the segregation of alloyingelements, stabilising the ferrite to lower temperature. To prevent ferrite in the final products the sinteringmust occur at a lower temperature than that at which -ferrite is formed. An alternative regimeis proposed in which the temperature would be cycled around the formation temperature of -ferrite.

Using sol–gel synthesis, single phase perovskite-related compounds in the family La 1 − x Ca x FeO 3 − δ have been formed for x=0.2 and x=0.33, but not for x=0.5. The x=0.2 and x=0.33 compounds are isostructural with LaFeO 3 (Pnma). The magnetic structure of La 0.8 Ca 0.2 FeO 3 − δ has been studied through Mossbauer spectroscopy and neutron powder diffraction. La 0.8 Ca 0.2 FeO 3 − δ is a G-type antiferromagnet with a magnetic moment magnitude of 3.0 ± 0.2 μ B at room temperature. The reduction in the magnitude of the antiferromagnetic moment compared to that published for LaFeO 3 is explained by the measurement being taken at room temperature rather than 4 K and by the presence of Fe 4 + ions which have weaker exchange interactions than Fe 3 + , causing a strong reduction in TN. Room temperature Mossbauer shows a broad magnetic hyperfine field distribution on the Fe sites in both La 0.8 Ca 0.2 FeO 3 − δ and La 0.67 Ca 0.33 FeO 3 − δ . On cooling, disproportionation of Fe 4 + into Fe 3 + and Fe5+ is apparent, and the resulting Fe5+ sextet measured at low temperature gives a reliable measure of the Fe 4 + fraction. This in turn shows that creation of high-oxidation-state Fe is the dominant charge balance mechanism on doping Ca 2 + into the Ln 3 + site indicating a disordered distribution of Fe 3 + and Fe 4 + . The lack of broadening of the Fe5+ sextet suggests that there may be ordering in the distribution of Fe5+.