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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]

Mechanical damage and stress caused by polishing and cutting of ferroelectric materials could deteriorate their dielectric, ferroelectric, and piezoelectric properties. BaTiO3 piezoelectric ceramics were polished and cut, and thermally annealed at 600, 800, 1000, and 1200 °C for recovery. The electrical measurements revealed a reduction in the coercive field, elimination of imprint behavior, and an increase in saturation polarization in the thermally annealed ceramics. Furthermore, the electromechanical properties measured by the resonance method, prior to thermal annealing were d33 = 184 pC/N, k33 = 0.36, and s33E = 10.9 × 10−12 m2/N, while the values after 1200 °C-4 h thermal annealing were d33 = 287 pC/N, k33 = 0.54, and s33E = 12.1 × 10−12 m2/N. The in situ crystal structure evaluation and Williamson-Hall analysis suggested the decrement of microstrain from 6.38 × 10−4 to 5.20 × 10−4, indicating the retrieval of the residual stress imposed. The enhancement of piezoelectricity by 56% was ascribed to the effective annealing out of the surface mechanical damaged layers. [ABSTRACT FROM AUTHOR]

We report here the relaxor ferroelectric (RFE) behaviour in a multiferroic solid solution system, (Bi1-xBax)(Fe1-xTix)O3, at a critical disorder level of xC ∼ 0.35 in BiFeO3 and 0.65 (i.e., 1-xC = 0.35) in BaTiO3 similar to the 1:2 ratio of Mg2+ and Nb5+ in the canonical RFE Pb(Mg1/3Nb2/3)O3. This Pb-free system, like canonical Pb-based RFEs, does not exhibit macroscopic symmetry breaking and shows only the signatures of ergodicity breaking at Vogel-Fulcher freezing temperature (TVF). The atomic displacement parameters (ADPs) of Fe3+/Ti4+ and O2−, obtained using high wave vector (Q) and high-resolution synchrotron x-ray diffraction data as a function of temperature, show anomalous diffuse peaks in the Curie range. It is shown that the diffuse peak in ADPs is due to softening of the vibrational frequencies of the B-O chain (B = Fe3+/Ti4+ and O = O2−) below the Burns temperature (TB) followed by hardening below the characteristic temperature (T′m), which corresponds to a peak in the dielectric permittivity (ε′). [ABSTRACT FROM AUTHOR]