Local Structure Analysis of Bi(Mg0.5Ti0.5)O3 Grown by High Pressure Synthesis
$B$-site mixed bismuth perovskite oxide of Bi(Mg 0.5 Ti 0.5 )O 3 (BMT) was grown by high-pressure and high-temperature synthesis to achieve a morphotropic phase boundary induced by pressure. Two types of BMT crystal were obtained: one has an orthorhombic structure and the other has a rhombohedral st...
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| Published in | Jpn J Appl Phys Vol. 50; no. 9; pp. 09NE06 - 09NE06-6 |
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| Main Authors | , , |
| Format | Journal Article |
| Language | English Japanese |
| Published |
The Japan Society of Applied Physics
25.09.2011
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| Online Access | Get full text |
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| Summary: | $B$-site mixed bismuth perovskite oxide of Bi(Mg 0.5 Ti 0.5 )O 3 (BMT) was grown by high-pressure and high-temperature synthesis to achieve a morphotropic phase boundary induced by pressure. Two types of BMT crystal were obtained: one has an orthorhombic structure and the other has a rhombohedral structure. In situ high-pressure and high-temperature X-ray diffraction measurements were performed. It was clarified that the orthorhombic structure is stabilized in the ambient-pressure phase and the rhombohedral structure is stabilized in the high pressure phase. We also performed local structure analysis by atomic pair-distribution function analysis. The similarity of local structures in the orthorhombic and rhombohedral BMT crystals was revealed, and this similarity enables phase transition under pressure. |
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| Bibliography: | X-ray diffraction profiles of recovered BMT synthesized at 6 GPa. Perovskite BMT crystals can be obtained at growth temperatures of 800 and 1000 °C, but it decomposes at 1200 °C. Result of Rietveld refinement of (a) rhombohedral and (b) orthorhombic BMT crystals. Fitting was performed by considering the space groups $R3c$ and $Pnnm$. The obtained parameters of the orthorhombic BMT, such as atomic positions, are essentially the same as those reported in ref. . (a) X-ray diffraction profiles of BMT crystal obtained by in situ high-pressure X-ray diffraction experiments. (b) Pressure dependences of the difference angles of (400) and (212) Bragg peaks indexed by orthorhombic structure. Temperature was fixed at RT. The structure phase transition from the orthorhombic phase to the rhombohedral phase occurred at approximately 2 GPa. Temperature dependences of (a) peak width at half maximum and (b) intensity of (012) reflection indexed by rhombohedral structure. Pressure was fixed at 7 GPa. Phase diagram of BMT obtained by in situ X-ray diffraction measurements under high pressure. Temperature evolutions of $F(Q)$s of (a) rhombohedral and (b) orthorhombic BMT crystals. Peak intensity increased with decreasing temperature owing to the temperature factor, but no phase transition was observed down to 5 K. Temperature evolutions of PDFs of (a) rhombohedral and (b) orthorhombic BMT crystals at low temperatures. The data were off-set for clarify. The lowest PDF is calculated by assuming an average structure. The rhombohedral BMT can be reproduced by the rhombohedral model, but there is large deviation when the orthorhombic BMT was fit with the orthorhombic model. (a) Comparison of $G(r)$ of the rhombohedral and orthorhombic BMT crystals at 5 K. These BMT crystals have similar local structures, but the PDF amplitude of the rhombohedral BMT is larger than that of the orthorhombic BMT, indicating the ordered structure of the rhombohedral BMT. (b) The local structure of the orthorhombic BMT was fit by assuming the orthorhombic structure (upper solid line) and rhombohedral structure (lower dashed line). Open circles in both the upper and lower show the observed PDF at 5 K. The local structure of the orthorhombic BMT can be reproduced by the rhombohedral model. Atomic positions of (a) rhombohedral and (b) orthorhombic BMT crystals. Large circles show Bi atoms and octahedra show Ti 0.5 Mg 0.5 O 6 . Thin solid squares show the unit cells. The orthorhombic BMT shows a more disordered feature than the rhombohedral BMT when it compared in thick solid squares. Octahedral tilting occurs owing to the Bi displacement. The average structure of BMT coincides with the orthorhombic structure in the disorder system. |
| ISSN: | 0021-4922 1347-4065 |
| DOI: | 10.1143/JJAP.50.09NE06 |