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In this work, we presented investigations on the microstructural, magnetic, dielectric and conductive properties of (1-x)Na0.5Bi0.5TiO3-xCoFe2O4 (NBT-CFO) composite ceramics (x = 0.1, 0.2, 0.3 and 0.5). The composites were synthesized using the in-situ sol-gel method, and the resulting CFO/NBT embedded structure was observed in the 0.9NBT–0.1CFO sample. Rietveld refinement confirmed that the embedded structure had remarkable effects on the c/a ratios of NBT-CFO composites. Increasing normalization saturation magnetizations were observed with increasing of CFO contents, thus revealing the influence of phase interfaces on magnetism. Dielectric relaxation anomalies were observed on both temperature dependent permittivity and loss spectra. Two sets of anomalies in these spectra were caused by space charges on the phase interfaces of embedded CFO grains and the NBT matrix. The conduction behavior of ceramics with and without the embedded structure obeyed the double power law and Jonscher's fraction power law, respectively, which inferred a transformation from the AC to the DC conduction mechanism with the disappearance of the embedded structure.

Water evaporation and steam production have been recognized to be considerably crucial due to the vast applications, ranging from waste water treatment, water purification, to alternative green energy solutions by water splitting, catalysis, and in-door heating. Albeit the big variety of photothermal conversion materials (PCMs) developed for this purpose, certain drawbacks, e.g. high cost, complicated synthesis, weak/narrow absorbance, bulkiness, and low evaporation rate, have hindered the application potential. Herein, we report the dual-phase molybdenum nitride nanorambutans, synthesized by a facile method, for solar steam generation. Not only the inherent properties, including strong full-spectrum absorbance, high-efficiency photothermal conversion, and super-hydrophilicity, benefit their water evaporation performance, the interconnected open mesopores of the nanorambutans further boost their capability of light harvesting and water/vapor transportation. Solar energy conversion efficiency of ∼97% under one sun together with excellent cycling stability has been demonstrated. In the desalination systems, integrating with the high salt rejection rate, the nanorambutans film can produce a water evaporation rate as high as ∼1.70 kg m −2 h −1 with an efficiency of ∼98%. Besides its compact size, the record-breaking water evaporation performance of these nanorambutans has exceeded the previous best inorganic PCM. This work introduces molybdenum nitride as a new PCM for efficient solar steam generation and all applications that can benefit from highly localized heating from nano to macro scale.

Morphotropic phase boundaries (MPB) consisting of rhombohedral and orthorhombic phases formed within the range of 0.1 ≤ x ≤ 0.15 in Bi1-xErxFe0.97Ti0.03O3 ceramics. Orthorhombic phase transition was verified by the appearance of a new mode at 310 cm−1 in Raman spectra. Bridging phases as intermedia phases of MPB were rare in Bi1-xErxFe0.97Ti0.03O3. Polarization and permittivity improved at MPB. Moreover, impedance spectroscopy revealed additional arcs with a distinct small polaron conduction mechanism. Er3+ ions enhanced magnetic properties and induced a permittivity change at Neel temperature. The magnetodielectric effect resulted in a permittivity change rate of ~1% at 10000 Oe.

We present extensive investigations of the crystallographic phase diagram and electronic properties of the Fe-based superconductor FeSe under extreme conditions (high pressure (HP) and low temperature (LT)) by synchrotron X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). An isostructural phase transition (Tetragonal (T) →high-pressure Tetragonal (Tʹ)) is discovered in FeSe at ∼2.8 GPa based on the axial ratio c/a with finer pressure step as observed in Fe-As-based superconductor such as EuFe2As2. We also find a pressure-induced Tʹ → MnP-type phase transition at 7.6 GPa in FeSe, which is consistent with the documented pressure-induced high-spin → low-spin transition (∼6–7 GPa). These results reveal the pressure-induced structural phase transition sequence in FeSe at room temperature to be T → Tʹ → Tʹ+MnP-type at pressures of 0–10.6 GPa, enriching the crystallographic phase diagram. The HPLT XRD data also indicate that a sluggish structural phase transition (Cmma → Pnma) begins at 7.5 GPa, and these two phases coexist up to 26.5 GPa. The HP X-ray absorption near-edge spectroscopy (XANES) measurement shows that Eo of Se experiences a pressure-induced shift to high energy, evidencing strongly charge transfer between Fe and Se under high pressure. Our results shed lights on the correlation between crystallographic/electronic structure and superconductivity in this material.

In this study, a series of Bi2Te2-xS1+x compounds were prepared by traditional melting-quenching-annealing process. In the range of 0.03 ≤ x ≤ 0.25, Bi2Te2-xS1+x compounds possess the Bi2Te3 structure. S atoms preferentially fully occupy the Te(2) sites, while any extra S atoms randomly occupy the Te(1) sites. Experimental results and phonon dispersion calculations demonstrate that the strong coupling of the phonon density of state contributed by Bi and Te(1) atoms results in the low avoided-crossing frequencies, sound velocities, Debye temperature and therefore the low lattice thermal conductivities. Moreover, substitutions of extra S atoms on the Te(1) site intensifies alloy phonon scattering that further suppresses the lattice thermal conductivity. An ultra-low lattice thermal conductivity of 0.49 W m−1 K−1 is achieved at 523 K. Doping with Cl increases the room temperature carrier concentration, resulting in a significantly enhanced power factor from 1.5 mW m−1 K−2 for the Bi2Te1.93S1.07 sample to 1.7 mW m−1 K−2 for the Cl-doped sample at 323 K. Furthermore, doping with Cl enhances phonon point defect scattering that leads to a suppression of the thermal conductivity to 0.41 W m−1 K−1 at 573 K. As a result of the optimization of the electronic transport properties and the reduction in the lattice thermal conductivity, Bi2Te1.93S1.065Cl0.005 sample achieved the highest ZT of 0.67 at 623 K which is superior to intrinsic Bi2Te3 in the whole temperature range.

In this paper, a novel composite La0.9Ca0.1Fe0.9Nb0.1O3-δ/Sc0.2Zr0.8O2−δ (LCFNb/ScSZ) is developed and investigated as a fuel electrode candidate for direct electrolyzing carbon dioxide (CO2) in solid oxide electrolysis cells (SOECs). XRD patterns of LCFNb powder sintered in CO2 at 850 °C for 10 h indicate that no secondary phases are found during the heat treatment and linear thermal expansion results prove that the LCFNb is compatible with ScSZ electrolyte used in this work. The electrolyser with porous LCFNb membrane cathode fabricated by infiltration method shows impressive electrochemical performance. The current density of 1.97 A/cm2 at 2.0 V at 800 °C is obtained. The polarization resistance Rp of the SOEC decreases with the increase of the applied voltage between the electrodes. The obtained lowest Rp is as low as 0.113 Ω cm2 at 2.0 V and this value is much lower than its many other perovskite and nickle-based counterparts. Besides, the LCFNb/ScSZ cathode shows excellent stability in pure CO2 at different applied voltage, especially at 2.0 V. Furthermore, the LCFNb/ScSZ electrode exhibits the current efficiencies close to theoretical ones for CO2 electrolysis, indicating that the LCFNb/ScSZ composite ceramic is an excellent cathode for zirconia-based high temperature electrolyser.

(Gadolinium) Gd-doped antiperovskite compounds Mn 3 Cu 1−x Gd x N were synthesized by the conventional solid-state reaction. With increasing Gd concentration, two magnetic transitions appeared at a high Curie temperature (T C1 ) corresponding to paramagnetic (PM)-ferromagnetic (FM) transition and a low temperature (T C2 ) ascribed to the FM-antiferromagnetic (AFM) transition. The magnetic relaxation results show the formation of a magnetic metastable state after the FM-AFM transition at low temperature (lower than T C2 ), forming a novel magnetic-step feature in the process from AFM to FM under a certain magnetic field.

The high-pressure effect on valence fluctuation of the ThCr2Si2-type intermetallic compound EuNi2P2 has been investigated using in situ synchrotron Mossbauer spectroscopy (SMS). The isomer shift of 151Eu in EuNi2P2 increases monotonically with increasing pressure up to 50 GPa, suggesting a valence transition of the Eu from mixed toward trivalent. The synchrotron angle-dispersive X-ray diffraction (AD-XRD) experiment shows that EuNi2P2 remains in the tetragonal structure up to 32.5 GPa at room temperature. We propose that the evolutions of bonding distance with pressure have an obvious effect on the valence fluctuation.

The layered Cr2Ge2Te6 (CrGT) has captured vast attentions because it is capable of retaining the long-range ferromagnetic order even in its monolayer form, thus offering potential applications in spintronic devices. We report herein the Raman spectra of CrGT under pressure up to 35.1 GPa at room temperature. We observed a structural phase transition at ∼14 GPa as was revealed by a change in pressure derivate frequencies of the E g 3 and A g 1 modes. Both of the two peaks became broad and the A g 1 mode eventually disappeared with further increasing the pressure. Raman modes above 26.4 GPa could not be experimentally observed, suggesting that the CrGT was pressed into the amorphous phase. Interestingly, a pressure-induced soft phonon mode is identified in CrGT at ∼23 GPa by dynamical property calculation. The phonon instability at the Brillouin zone boundary T point is suggested as the driving force for the experimentally observed crystalline-to-crystalline phase transition at ∼ 18 GPa. The appearance of soft phonon might indicate the possibility of superconductivity induced by much higher pressure.

The 6H and 6M Ba 1− x Sr x RuO 3 at x ⩽0.6 with the normal and distorted hexagonal BaTiO 3 structures were synthesized by using high-pressure and high-temperature method. It is found that the unit cell volume deviates from Vegard's law between 0.3 and 0.4 for the solid solutions due to the increasing distortion degree of crystal structure. With the increasing x , the electrical resistivity at the same temperature is increasing. With the substitution of Sr for Ba ion, the 6H BaRuO 3 transforms to a Fermi-liquid metal at x =0.25 from the primal non-Fermi-liquid metal, and then becomes a semiconductor at low temperature when x is larger than 0.4.

Activated carbon was treated at 5 GPa up to 1600 °C, and the structural evolution in the graphitization process was investigated. The graphitization temperature is equal to 1200 °C at 5 GPa, reflected by X-ray diffraction (XRD) patterns. Honeycomb-like structures in micron scale come into being in the high-pressure sintering temperature range of 1000−1100 °C and slice-like structures appear after graphitization. The existence of D and D’ lines in the Raman spectra for the graphitized-activated carbon indicates that there are still some disordered structures. The continuous occurrence of variable-range hopping, the approximately linear ρ–T relationship, and semimetal conduction mechanism accords with the graphitization process.

The high-pressure phase of iridium-based compound Ba3CaIr2O9 was synthesized using high-pressure sintering. Being different from the distorted hexagonal BaTiO3 structure of the ambient Ba3CaIr2O9, the high-pressure phase crystals into the 1:2 B-site-ordered perovskite structure with the space group P-3m1 (Z=1). Through fitting the X-ray powder diffraction (XRD) data with Rietveld analysis, in which the obtained Rp, Rwp, and Rexp factors are 7.49%, 11.4%, and 4.82%, respectively, the lattice parameters are a=5.8296(1) A and c=7.1659(2) A. The atomic coordinates and the main interatomic distances and bond angles were also obtained. The relationship of electrical resistivity versus temperature shows that the high-pressure phase of Ba3CaIr2O9 is a semiconductor in the temperature range of 5–300 K. The measurement of temperature dependence of magnetic susceptibility indicates that it is paramagnetic.

The 6H BaRu{sub 1-x}Mn{sub x}O{sub 3} with the hexagonal BaTiO{sub 3} structure was synthesized using high-pressure sintering method. It is found that the lattice parameter deviates from Vegard's law at x=0.3 for the solid solutions due to the charge transfer effects at B-site. The substitution of Mn for Ru cations gives rise to the short-range magnetic ordering, due to the disordered arrangement of Ru and Mn cations. The compounds are weak ferromagnetic in the x range 0.05-0.40, with the maximal Curie temperature T{sub c} 175.2 K at x=0.10. They are of spin-glass-like magnetism at lower temperature at x{>=}0.1. With Mn doping, the 6H BaRuO{sub 3} transforms to a semiconductor from the primal metal at x=0.30. The resistance as a function of temperature below about 70 K follows the two-dimensional variable-range hopping conduction mechanism in BaRu{sub 0.50}Mn{sub 0.50}O{sub 3}. - Graphical abstract: The 6H BaRu{sub 1-x}Mn{sub x}O{sub 3} was synthesized using high-pressure sintering. The substitution of Mn for Ru cations gives rise to the short-range magnetic ordering, with the maximal Curie temperature T{sub c} 175.2 K at x=0.10. The compounds are of spin-class magnetism at lower temperature at x{>=}0.05. Mn doping results in the transition from the primal metal to semiconductormore » at x=0.30.« less

The single-phase 6H BaRuO{sub 3} with the hexagonal BaTiO{sub 3} structure was synthesized at 5 GPa and 1000 deg. C. Rietveld refinement of the powder X-ray data for the 6H phase resulted in the lattice parameters to be a=5.7127(1) A and c=14.0499(2) A; the average Ru-O distance and direct Ru-Ru distance in the Ru{sub 2}O{sub 9} dioctahedron being 1.992(6) and 2.5658(14) A, respectively. The electrical resistivity of the 6H BaRuO{sub 3} follows a relationship of {rho} versus T{sup 3/2} below 60.0 K, a signature deviation from the Fermi-liquid behavior. Both magnetic susceptibility and specific heat data indicate that the 6H BaRuO{sub 3} is an exchange-enhanced Pauli paramagnet due to the electron correlation effect with large Wilson ratio R{sub W} and Stoner enhancement factor. The comprehensive evolution of transport and magnetic properties from 9R across 4H to 6H BaRuO{sub 3} was discussed. - Graphical abstract: The single-phase 6H BaRuO{sub 3} was synthesized under high pressure high temperature. The electrical resistivity of 6H BaRuO{sub 3} follows a T{sup 3/2} relation below 60.0 K. Both magnetic susceptibility and specific heat data indicate that 6H BaRuO{sub 3} is an exchange-enhanced Pauli paramagnet with the large Wilson ratio and Stoner enhancement factor.