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Crystallographic order-disorder phenomena in solid state compounds are of fundamental interest due to intimate relationship between the structure and properties. Here, by using high-pressure and high-temperature synthesis, we obtained vanadium perovskite oxyhydrides Sr1-xNaxVO3-yHy (x = 0, 0.05, 0.1, 0.2) with an anion-disordered structure, which is different from anion-ordered SrVO2H synthesized by topochemical reduction. High-pressure and high-temperature synthesis from nominal composition SrVO2H yielded the anion-disordered perovskite SrVO3-yHy (y ∼ 0.4) with a significant amount of byproducts, while Na substitution resulted in the almost pure anion-disordered perovskite Sr1-xNaxVO3-yHy with an increased amount of hydride anion (y ∼ 0.7 for x = 0.2). The obtained disordered phases for x = 0.1 and 0.2 are paramagnetic with almost temperature-independent electronic conductivity, whereas anion-ordered SrVO2H is an antiferromagnetic insulator. Although we obtained the anion-disordered perovskite under high pressure, a first-principles calculation revealed that the application of pressure stabilizes the ordered phase due to a reduced volume in the ordered structure, suggesting that a further increase of the pressure or reduction of the reaction temperature leads to the anion ordering. This study shows that anion ordering in oxyhydrides can be controlled by changing synthetic pressure and temperature.

The layered perovskite (MA)2PbI2(SCN)2 (MA = CH3NH3+) is a member of an emerging series of compounds derived from hybrid organic-inorganic perovskites. Here, we successfully synthesized (MA)2PbI2-xBrx(SCN)2 (0 ≤ x < 1.6) by using a solid-state reaction. Despite smaller bromide substitution for iodine, 1% linear expansion along the a axis was observed at x ∼ 0.4 due to a change of the orientation of the SCN- anions. Diffuse reflectance spectra reveal that the optical band gap increases by the bromide substitution, which is supported by the DFT calculations. Curiously, bromine-rich compounds where x ≥ 0.8 are light sensitive, leading to partial decomposition after ∼24 h. This study demonstrates that the layered perovskite (MA)2PbI2(SCN)2 tolerates a wide range of bromide substitution toward tuning the band gap energy.

A morphotropic phase boundary (MPB) with coexisting tetragonal and monoclinic phases was observed in perovskite-type (ABO3) (1 – x)PbVO3–xBiFeO3 solid solutions that were synthesized with a high-pr...

BiCoO3 is a PbTiO3 type of perovskite oxide with a giant tetragonal distortion (c/a = 1.27) that shows a pressure-induced transition from tetragonal to orthorhombic phases accompanied by a large volume shrinkage at 3 GPa. In this study, we carried out electron doping of BiCoO3 by substituting Ti4+ for Co3+ in order to destabilize the tetragonal phase and observe a giant negative thermal expansion (NTE) at ambient pressure. BiCo1-xTixO3 (x = 0, 0.1, 0.2, and 0.25) was successfully obtained by using high-pressure synthesis. However, the c/a ratio of the tetragonal phase was almost constant against x (≤0.2), and NTE was not observed at any x, suggesting that the tetragonal distortion coupled with high-spin Co3+ is robust against electron doping. In x = 0.25, a metastable orthorhombic phase was obtained by the high-pressure synthetic process, while it partially transformed into a tetragonal phase after annealing at 600 K. The stability of the giant tetragonal phase is strongly connected with the spin state of Co3+.

Perovskite oxyhydrides may find diverse applications, ranging from catalysis, topochemical synthesis to solid state ionics, but the understanding of their hydride transport behavior has remained limited. Here, gaseous hydrogen exchange and release experiments were analyzed using the Kissinger method to estimate the activation energy (Ea) for H/D exchange and H2 release in BaTiO3–xHx (x = 0.35–0.60) and LaSrCoO3H0.70. It is revealed that, for each BaTiO3–xHx at a given hydride concentration (x), both H/D exchange and H2 release experiments provide similar Ea values. For BaTiO3–xHx with different x, the obtained Ea values significantly decrease with increasing x until around 0.4; beyond 0.4, it becomes nearly constant (200–220 kJ mol–1). This observation suggests that the diffusion process in the low hydride concentration (x < 0.4) includes oxide as well as hydride diffusion, whereas, for 0.4 < x (

We successfully synthesized the ternary bismuthides La3MBi5 (M = Ti, Zr, Hf). These compounds crystallize in the hexagonal Hf5Sn3Cu-anti type structure (space group: P63/mcm) consisting of face-sharing MBi6 octahedral chains and hypervalent Bi linear chains, both separated by La atoms. Magnetic susceptibility and electrical resistivity measurements revealed that all of the compounds, including the solid solution La3Ti(Bi1–xSbx)5, exhibit a Pauli paramagnetic behavior without any trace of superconductivity down to 1.85 K, as opposed to a recently reported 4 K superconductivity in La3TiSb5. The absence of superconductivity is supported by first-principles band calculations of La3TiBi5 and La3TiSb5 that demonstrate similar electronic structures with three-dimensional Fermi surfaces.

We have studied electronic properties of perovskite oxyhydrides ATiO3–xHx (A = Ba, Sr). Epitaxial thin films of ATiO3–xHx with various hydride compositions, up to x = 0.58 for Ba and x = 0.45 for Sr, are prepared by the low-temperature CaH2 reduction of the corresponding oxide films deposited on (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 (LSAT) substrates by pulsed laser deposition. Resistivity measurements for A = Sr show a metallic phase over a wide range of H– composition, implying a substantial stabilization of H 1s orbitals that should be distributed over O 2p orbitals. On the other hand, for A = Ba, a semiconducting behavior is seen up to ∼5–8% of H– substitution. Interestingly, a similar contrasting behavior is observed in a Nb-substituted BaTiO3 and SrTiO3, which suggests that a local cation–off centering in lightly doped Ba films creates in-gap states in the band structure (as opposed to the Sr films), hindering the electron transport.

We have prepared the oxyhydride perovskite EuTiO(3-x)H(x) (x ≤ 0.3) by a low temperature CaH2 reduction of pyrochlore Eu2Ti2O7 and perovskite EuTiO3. The reduced EuTiO(3-x)H(x) crystallizes in the ideal cubic perovskite (Pm3̅m), where O/H anions are randomly distributed. As a result of electron doping by the aliovalent anion exchange, the resistivity of EuTiO(3-x)H(x) shows metallic temperature dependence. Moreover, an antiferromagnetic-to-ferromagnetic transition is observed even when a small amount of hydride (x ∼ 0.07) is introduced. The Curie temperature TC of 12 K is higher than those of any other EuTiO3-derived ferromagnets. The ferromagnetism can be explained by the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between the Eu(2+) spins mediated by the itinerant Ti 3d electrons. The present study shows that controlling the oxide/hydride ratio is a versatile method to tune magnetic and transport properties.

Skeletal siloxane bonding structure of nanocrystalline MEL pure silica zeolite film was investigated. Nanocrystalline zeolite (nc-zeolite) suspension was prepared by the two-stage hydrothermal treatment, and thin film was obtained by spin-coating. After a quantitative analysis of Fourier-transform infrared spectra with the variable incidence angles of light probe, skeletal complex dielectric function concerning the siloxane bond vibration was derived in the 1400–400 cm–1 range. Then, the widening of the AS1-(LO-TO) frequency splitting width and the enhancement of the normalized integrated oscillator strength of AS vibration mode were observed in the nc-zeolite film in comparison with those of sol–gel derived amorphous silica film. Those improvements must be attributed to the increased siloxane network connectivity and the crystal structure of zeolite. The effect of the UV assist anneal was also discussed.