BiInO₃: A Polar Oxide with GdFeO₃-Type Perovskite Structure

A new oxide, BiInO3, was prepared using a high-pressure high-temperature technique at 6 GPa and 1273 K. BiInO3 has the GdFeO3-type perovskite structure, but crystallizes in the polar space group Pna21. Structure parameters of BiInO3 were refined from laboratory X-ray powder diffraction data (Z = 4; a = 5.95463(7) Å, b = 5.60182(7) Å, and c = 8.38631(11) Å). BiInO3 shows a second-harmonic generation signal of about 120−140 times that of quartz. BiInO3 decomposes at ambient pressure on heating above 873 K to give In2O3 and Bi25InO39. No phase transitions were found between 140 and 873 K using differential scanning calorimetry and differential thermal analysis. Vibrational properties of BiInO3 were studied by Raman spectroscopy

New Noncentrosymmetric Vanadates Sr₉R(VO₄)₇ (R = Tm, Yb, and Lu): Synthesis, Structure Analysis, and Characterization

New vanadates Sr9R(VO4)7 (R = Tm, Yb, and Lu) were synthesized using a standard solid-state method at 1373 K and found to be isotypic with Ca3(VO4)2 at room temperature (RT). Their structure parameters were refined using the Rietveld method from synchrotron X-ray diffraction (XRD) data measured at RT (space group R3c and Z = 6). Sr9R(VO4)7 (R = Y and La−Er) do not form a phase isotypic with Ca3(VO4)2. Sr9R(VO4)7 (R = Tm, Yb, and Lu) were characterized through the magnetic susceptibility (2−400 K), the specific heat (0.45−31 K), thermal analysis (300−1573 K), and high-temperature XRD, second-harmonic generation, and dielectric measurements. The temperature dependence of the dielectric constant and tangent loss suggested that they exhibit a reversible ferroelectric−paraelectric phase transition of the first order near 950−960 K. The high-temperature phases have space group R3̄m and Z = 3. Thermal analysis revealed the presence of an intermediate phase between the R3c and R3̄m phases in a very narrow temperature range. Magnetic susceptibilities of Sr9Tm(VO4)7 and Sr9Yb(VO4)7 are typical of Tm3+ and Yb3+ ions affected by an octahedral crystal field. The effective magnetic moments were 7.39 μB for Tm3+ and 4.59 μB for Yb3+

Iodide-Iodates M₃[IO₃]₁₂·Ag₄I, M = Bi, Tb, with a Framework Structure and High Second-Harmonic Generation Optical Response

Single crystals of two new iodide-iodates, Bi₃[IO₃]₁₂·Ag₄I and Tb₃[IO₃]₁₂·Ag₄I, are synthesized in hydrothermal systems. The anionic parts in both iodide-iodates are characterized as a complex charged framework of isolated IO₃ umbrella-like groups and large Bi­(Tb)–O polyhedra similar to those previously found in La₃[IO₃]₁₂­[IO₃]­(Pb₃O). Broad channels along the <i>c-</i>axis contain compensators: (Ag₃I)²⁺ umbrella-like groups and additional Ag⁺ ions which form Ag₄⁴⁺ tetrahedral clusters augmented with I^– halogen. New iodates possess significantly higher second-order nonlinear optical characteristics compared to the previously known lead-containing compounds REE₃[IO₃]₁₂­[IO₃]­(Pb₃O), REE = La, Pr, Nd. The difference is related to the polar ordering of umbrella-like (Ag₃I)²⁺ groups in the channels in the new iodide-iodate. Additionally, planar-coordinated Ag atoms add three Ag atoms in umbrellas forming [Ag₄I]³⁺ polar clusters in the channels

BiScO₃: Centrosymmetric BiMnO₃-type Oxide

With neutron powder diffraction, electron diffraction, and second-harmonic generation, we have shown that BiScO3 has a structure closely related to that of multiferroic BiMnO3, but BiScO3 crystallizes in the centrosymmetric space group of C2/c. These results bring up a question about the origin of ferroelectricity in BiMnO3. BiScO3 may serve as a model system to understand the role of Mn3+ ions in the ferroelectricity of BiMnO3