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We report the first observation of bulk superconductivity of a η-carbide-type oxide Zr4Pd2O. The crystal structure and the superconducting properties were studied through synchrotron X-ray diffraction, magnetization, electrical resistivity, and specific heat measurement. The superconducting transition was observed at Tc = 2.73 K. Our measurement revealed that the η-carbide-type oxide superconductor Zr4Pd2O shows an enhanced upper critical field μ0Hc2(0) = 6.72 T, which violates the Pauli-Clogston limit μ0HP = 5.29 T. On the other hand, we found that the enhanced upper critical field is absent in a Rh analogue Zr4Rh2O. The large μ0Hc2(0) of Zr4Pd2O would be raised from strong spin–orbit coupling with Pd-4d electrons. The discovery of new superconducting properties for Zr4Pd2O would shed light on the further development of η-carbide-type oxide superconductors. [ABSTRACT FROM AUTHOR]

A highly dispersed carbonate‐intercalated Cu2+‐Al3+ layered double hydroxide (CuAl LDH) was created on an unreactive α‐Al2O3 surface (CuAl LDH@α‐Al2O3) via a simple coprecipitation method of Cu2+ and Al3+ under alkaline conditions in the presence of α‐Al2O3. A highly reducible CuO nanoparticles was generated, accompanied by the formation of CuAl2O4 on the surface of α‐Al2O3 (CuAlO@α‐Al2O3) after calcination at 1073 K in air, as confirmed by powder X‐ray diffraction (XRD) and Cu K‐edge X‐ray absorption near edge structure (XANES). The structural changes during the progressive heating process were monitored by using in‐situ temperature‐programmed synchrotron XRD (tp‐SXRD). The layered structure of CuAl LDH@α‐Al2O3 completely disappeared at 473 K, and CuO or CuAl2O4 phases began to appear at 823 K or 1023 K, respectively. Our synthesised CuAlO@α‐Al2O3 catalyst was highly active for the acceptorless dehydrogenation of benzylic, aliphatic, or cyclic aliphatic alcohols; the TON based on the amount of Cu increased to 163 from 3.3 of unsupported CuAlO catalyst in 1‐phenylethanol dehydrogenation. The results suggested that Cu0 was obtained from the reduction of CuO in the catalyst matrix during the reaction without separate reduction procedure and acted as a catalytically active species. [ABSTRACT FROM AUTHOR]

Temperature-dependent structural variations of ceramic coatings of lead titanate PbTiO3 (PT) formed at room temperature (RT) via aerosol deposition (AD) have been investigated to evaluate the stability of the ferroelectric phase. Synchrotron radiation x-ray diffraction experiments in the as-deposited state showed a polycrystalline film oriented preferentially along the c-axis of the perovskite-type ferroelectric tetragonal structure on the quartz glass substrate. The c-axis orientation may be attributed to the anisotropic structural characteristics of the crystal with a layered structure composed of a two-dimensional (2D) covalent bonding network in the ferroelectric phase at RT. The 2D interfaces of the ceramic particles in the aerosol, which are chemically activated by collision with the substrate, are most likely to recombine during the AD process and form a dense and hard coating at RT. When the PT film was heated to the paraelectric phase with a cubic structure at 1000 K, the c-axis orientation observed in the as-deposited state disappeared upon cooling owing to the degree of freedom in selecting the polar axis associated with the cubic-tetragonal phase transition. The spontaneous lattice distortion of the AD film at RT was smaller than that of the bulk ceramic. However, the phase transition temperature (TC) was approximately 100 K higher only during the first heating process from the c-oriented as-deposited state. The AD method stabilizes the ferroelectric phase up to a higher temperature, although the spontaneous polarization is suppressed. The ferroelectric ceramic materials synthesized mainly via particle collisions are assumed to have low ferroelectricity but high TC. [ABSTRACT FROM AUTHOR]

Recently, uniaxial negative thermal expansion has been revealed in transition-metal zirconide TrZr2 superconductors (Tr: transition metal). In this study, to expand structural variation of Tr-Zr superconductors with anomalous thermal expansion, we investigated the temperature evolution of crystal structure of orthorhombic CoZr3, which is a superconductor with a transition temperature of 4.3 K, by synchrotron and laboratory (CuKα) X-ray diffraction. Uniaxial negative thermal expansion along the c-axis, which is similar to that observed in tetragonal CoZr2, has been observed at a wide temperature range of T = 90–800 K in CoZr3, while a- and b-axis exhibit positive thermal expansion. [ABSTRACT FROM AUTHOR]

The superconducting properties and structural parameters, including the Grüneisen parameter (γG), of the BiCh2-based (Ch: S, Se) layered superconductor LaO0.5F0.5BiS2−xSex were investigated. The superconducting transition temperature (Tc) increased with increasing Se concentration (x), and bulk superconductivity was induced by Se substitution. γG exhibited a larger value when x ≥ 0.4, where the superconducting properties were improved. These results suggest that the increase of lattice anharmonicity is preferable for superconductivity in LaO0.5F0.5BiS2−xSex. The discussion includes data for related superconductors REO0.5F0.5BiS2 (RE = Pr, Nd), where a positive correlation between γG and Tc is revealed for Se-poor samples. In addition, specific heat analyses suggest the presence of a low-energy optical phonon mode for LaO0.5F0.5BiS2−xSex. [ABSTRACT FROM AUTHOR]

In functional materials such as thermoelectric materials and superconductors, the interplay between functionality, electronic structure, and phonon characteristics is one of the key factors to improve functionality and to understand the underlying mechanisms. In the first part of this article, we briefly review investigations on lattice anharmonicity in functional materials on the basis of the Grüneisen parameter (γG). We show that γG can be a good index for large lattice anharmonicity and for detecting a change in anharmonicity amplitude in functional materials. Then, we show original results on the estimation of γG for recently developed high-entropy alloy-type (HEA-type) functional materials with a layered structure and a NaCl-type structure. As a common trend for those two systems with two- and three-dimensional structures, we found that γG increased with a slight increase in the configurational entropy of mixing (ΔSmix) and then decreased with increasing ΔSmix in the high-entropy region. [ABSTRACT FROM AUTHOR]

Recently, high-entropy alloys (HEAs) and HEA-type compounds have been extensively studied in the fields of material science and engineering. In this article, we report on the synthesis of a layered system MBi2Te4 where the M site possesses low-, middle-, and high-entropy states. The samples with M = Pb, Ag1/3Pb1/3Bi1/3, and Ag1/5In1/5Sn1/5Pb1/5Bi1/5 were newly synthesized and the crystal structure was examined by synchrotron X-ray diffraction and Rietveld refinement. We found that the M-Te2 distance was systematically compressed with decreasing lattice constants, where the configurational entropy of mixing at the M site is also systematically increased. The details of structural refinements and the electrical transport property are presented. [ABSTRACT FROM AUTHOR]

The origin of material softening in BiFeO3–BaTiO3 ceramics was assessed by studying the crystal structure and structural parameters. The crystal structure was investigated at 950 K by synchrotron radiation X-ray diffraction using structure refinement; structural parameters were calculated from the final structure refinement results. The crystal structure was cubic, with Bi3+ ions off-centering into six equivalent neighboring sites along the 〈100〉 direction. We suggested that the stability of the Bi off-centering position and Bi off-centering displacement affects the material softening. The maximum material softening occurred in 0.70BiFeO3–0.30BaTiO3 ceramics with the largest Bi ion off-centering displacement and smallest Bi–O bond length, which provided the stable Bi ion off-centering position. Therefore, the material softening is attributed to the stability of the Bi ion off-centering position and the Bi ion off-centering displacement. The suggested model of material softening can provide essential information for the design and development of next-generation lead-free piezoelectric materials. [ABSTRACT FROM AUTHOR]

The validity of the mechanochemical solid-state reaction by dry ball milling for synthesizing Pb(Zr, Ti)O3 (PZT) fine ceramic powder at room temperature (RT) was evaluated using synchrotron radiation X-ray diffraction (SXRD). A mixture of PbZrO3 (PZ) and PbTiO3 (PT) powders with a molar ratio of 1:1 was prepared as the starting powder. To confirm the synthesis of PZT, the structural characteristics of the ball-milled samples with different milling times were investigated by analyzing the SXRD data using the Rietveld method. The solid-state reaction was nearly complete in a short milling time of 4 h at RT. After ball milling for approximately 8 h, only a single phase of PZT was detected. The Rietveld refinement for the crystal structure analysis demonstrated that slightly Ti-rich PZT, Pb(Zr0.485(1)Ti0.515(1))O3, with a tetragonal crystal system, is synthesized in the 8 h sample. The tetragonality is sufficiently suppressed to resemble a cubic system even at RT, whereas the phase transition temperature (TC) is significantly high. We quantitatively demonstrate that PZT with a higher TC can be synthesized at RT by dry ball milling, despite the smaller spontaneous lattice distortion. [ABSTRACT FROM AUTHOR]