Observation of Anion Order in Pb₂Ti₄O₉F₂

The observation of anion order is indispensable for the investigation of oxyfluorides. However, the negligible contrast between O^2– and F^– in both X-ray and neutron diffraction obscures the distinct anion sites for Rietveld refinement. Therefore, the difference in the chemical bonding of M–O^2– and M–F^– is the key to determining anion order. In this study, bond-valence-sum calculations and determination of the electron density distribution by the maximum entropy method illustrated anion order in the newly synthesized oxyfluoride Pb₂Ti₄O₉F₂. These results demonstrate a promising method to determine anion order in mixed anion systems

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

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

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

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