Synthesis and Structure of Vacancy-Ordered Perovskite Ba₆Ta₂Na₂X₂O₁₇ (X = P, V): Significance of Structural Model Selection on Discovered Compounds

Vacancy-ordered 12H-type hexagonal perovskites Ba6Ru2Na2X2O17 (X = P, V) with a (c’cchcc)2 stacking sequence of [BaO3]c, [BaO3]h, and [BaO2]c’ layers, where c and h represent a cubic and hexagonal stacking sequence, were previously reported by Quarez et al. in 2003. They also synthesized Ba6Ta2Na2V2O17, but structural refinement was absent. Very recently, Szymanski et al. reported 43 new compounds, including 12H-type Ba6Ta2Na2V2O17, using large-scale ab initio phase-stability data from the Materials Project and Google DeepMind with the assistance of an autonomous laboratory. But their structural refinement was very poor. Here, we report the synthesis and structure of Ba6Ta2Na2V2O17, which does not have 12H-type structure but has a vacancy-ordered 6C-type perovskite with a (c’ccccc) stacking sequence of [BaO3]c and [BaO2]c’ layers. We also report the phosphite analogue Ba6Ta2Na2P2O17 as a new compound. We claim an importance of careful structural characterization on newly discovered compounds; otherwise, the database constructed will lose credibility

Structure and Magnetic Properties of BiFe_1–<i>x</i>Co_<i>x</i>O₃ and Bi_0.9Sm_0.1Fe_1–<i>x</i>Co_<i>x</i>O₃

BiFe_1–<i>x</i>Co_<i>x</i>O₃ and Bi_0.9Sm_0.1Fe_1–<i>x</i>Co_<i>x</i>O₃ were synthesized under a high pressure of 4 GPa; 10% Sm substitution for Bi in BiFe_1–<i>x</i>Co_<i>x</i>O₃ (<i>x</i> ≤ 0.20) drastically destabilized the ferroelectric BiFeO₃-type structure and changed it to an antiferroelectric PbZrO₃-type superstructure. In comparison, a ferroelectric BiCoO₃-type tetragonal structure (<i>x</i> ≥ 0.40) was insensitive to the Sm substitution. No decrease in the ferroelectric Curie temperature (<i>T</i>_C) was observed. Weak ferromagnetism with a spontaneous moment of 0.025 μ_B/formula unit (f.u.) was observed for BiFe_1–<i>x</i>Co_<i>x</i>O₃ (<i>x</i> = 0.10 and 0.20) samples, suggesting the change in the spin structure from a cycloidal one. Because of the coexistence of ferroelectricity and ferromagnetism at room temperature, this compound is a promising multiferroic material

Electric-Field-Induced Reorientation of the Magnetic Easy Plane in a Co-Substituted BiFeO₃ Single Crystal

Single crystals of BiFe_0.9Co_0.1O₃ and BiFe_0.892Mn_0.008Co_0.1O₃, room temperature ferroelectric ferromagnets, were successfully grown by a flux method at a high pressure of 3 GPa. Remanent magnetization measurements along 18 crystallographic directions revealed the existence of a magnetic easy plane perpendicular to the electric polarization. Reorientation of the magnetic easy plane occurred in connection with 71° ferroelectric switching by applying an electric field. This is the first demonstration of an electric field affecting the local magnetic moment of Co-substituted BiFeO₃

Crystal and Magnetic Structure in Co-Substituted BiFeO₃

Ultra-high-resolution neutron diffraction studies of BiFe_0.8Co_0.2O₃ show a transition from a cycloidal space modulated spin structure at <i>T </i>= 10 K to a collinear G-type antiferromagnetic structure at <i>T </i>= 120 K. The model of antiparallel directions of Fe³⁺ and Co³⁺ magnetic moments at the shared Wyckoff position describes well the observed neutron diffraction intensities. On heating above RT, the crystal structure of BiFe_0.8Co_0.2O₃ changes from a rhombohedral <i>R</i>3<i>c</i> to a monoclinic <i>Cm</i>. At 573 K only the <i>Cm</i> phase is present. The collinear C-type antiferromagnetic structure is present in the <i>Cm</i> phase of BiFe_0.8Co_0.2O₃ at RT after annealing

High-Pressure Polymorph of NaBiO₃

A new high-pressure polymorph of NaBiO₃ (hereafter β-NaBiO₃) was synthesized under the conditions of 6 GPa and 600 °C. The powder X-ray diffraction pattern of this new phase was indexed with a hexagonal cell of <i>a</i> = 9.968(1) Å and <i>c</i> = 3.2933(4) Å. Crystal structure refinement using synchrotron powder X-ray diffraction data led to <i>R</i>_WP = 8.53% and <i>R</i>_P = 5.55%, and the crystal structure was closely related with that of Ba₂SrY₆O₁₂. No photocatalytic activity for phenol decomposition was observed under visible-light irradiation in spite of a good performance for its mother compound, NaBiO₃. The optical band-gap energy of β-NaBiO₃ was narrower than that of NaBiO₃, which was confirmed with density of states curves simulated by first-principles density functional theory calculation

High-Pressure Polymorph of NaBiO₃

A new high-pressure polymorph of NaBiO₃ (hereafter β-NaBiO₃) was synthesized under the conditions of 6 GPa and 600 °C. The powder X-ray diffraction pattern of this new phase was indexed with a hexagonal cell of <i>a</i> = 9.968(1) Å and <i>c</i> = 3.2933(4) Å. Crystal structure refinement using synchrotron powder X-ray diffraction data led to <i>R</i>_WP = 8.53% and <i>R</i>_P = 5.55%, and the crystal structure was closely related with that of Ba₂SrY₆O₁₂. No photocatalytic activity for phenol decomposition was observed under visible-light irradiation in spite of a good performance for its mother compound, NaBiO₃. The optical band-gap energy of β-NaBiO₃ was narrower than that of NaBiO₃, which was confirmed with density of states curves simulated by first-principles density functional theory calculation

Crystal and Magnetic Structure in Co-Substituted BiFeO₃

Ultra-high-resolution neutron diffraction studies of BiFe_0.8Co_0.2O₃ show a transition from a cycloidal space modulated spin structure at <i>T </i>= 10 K to a collinear G-type antiferromagnetic structure at <i>T </i>= 120 K. The model of antiparallel directions of Fe³⁺ and Co³⁺ magnetic moments at the shared Wyckoff position describes well the observed neutron diffraction intensities. On heating above RT, the crystal structure of BiFe_0.8Co_0.2O₃ changes from a rhombohedral <i>R</i>3<i>c</i> to a monoclinic <i>Cm</i>. At 573 K only the <i>Cm</i> phase is present. The collinear C-type antiferromagnetic structure is present in the <i>Cm</i> phase of BiFe_0.8Co_0.2O₃ at RT after annealing

Crystal and Magnetic Structure in Co-Substituted BiFeO₃

Ultra-high-resolution neutron diffraction studies of BiFe_0.8Co_0.2O₃ show a transition from a cycloidal space modulated spin structure at <i>T </i>= 10 K to a collinear G-type antiferromagnetic structure at <i>T </i>= 120 K. The model of antiparallel directions of Fe³⁺ and Co³⁺ magnetic moments at the shared Wyckoff position describes well the observed neutron diffraction intensities. On heating above RT, the crystal structure of BiFe_0.8Co_0.2O₃ changes from a rhombohedral <i>R</i>3<i>c</i> to a monoclinic <i>Cm</i>. At 573 K only the <i>Cm</i> phase is present. The collinear C-type antiferromagnetic structure is present in the <i>Cm</i> phase of BiFe_0.8Co_0.2O₃ at RT after annealing

Crystal and Magnetic Structure in Co-Substituted BiFeO₃

Ultra-high-resolution neutron diffraction studies of BiFe_0.8Co_0.2O₃ show a transition from a cycloidal space modulated spin structure at <i>T </i>= 10 K to a collinear G-type antiferromagnetic structure at <i>T </i>= 120 K. The model of antiparallel directions of Fe³⁺ and Co³⁺ magnetic moments at the shared Wyckoff position describes well the observed neutron diffraction intensities. On heating above RT, the crystal structure of BiFe_0.8Co_0.2O₃ changes from a rhombohedral <i>R</i>3<i>c</i> to a monoclinic <i>Cm</i>. At 573 K only the <i>Cm</i> phase is present. The collinear C-type antiferromagnetic structure is present in the <i>Cm</i> phase of BiFe_0.8Co_0.2O₃ at RT after annealing

Crystal and Magnetic Structure in Co-Substituted BiFeO₃

Ultra-high-resolution neutron diffraction studies of BiFe_0.8Co_0.2O₃ show a transition from a cycloidal space modulated spin structure at <i>T </i>= 10 K to a collinear G-type antiferromagnetic structure at <i>T </i>= 120 K. The model of antiparallel directions of Fe³⁺ and Co³⁺ magnetic moments at the shared Wyckoff position describes well the observed neutron diffraction intensities. On heating above RT, the crystal structure of BiFe_0.8Co_0.2O₃ changes from a rhombohedral <i>R</i>3<i>c</i> to a monoclinic <i>Cm</i>. At 573 K only the <i>Cm</i> phase is present. The collinear C-type antiferromagnetic structure is present in the <i>Cm</i> phase of BiFe_0.8Co_0.2O₃ at RT after annealing