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首页> 外文期刊>Physical review. B, Condensed Matter And Materials Physics >β phase and γ-β metal-insulator transition in multiferroic BiFeO_3
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β phase and γ-β metal-insulator transition in multiferroic BiFeO_3

机译：多铁性BiFeO_3中的β相和γ-β金属-绝缘体转变

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摘要

We report on extensive experimental studies on thin film, single crystal, and ceramics of multiferroic bismuth ferrite BiFeO_3 using differential thermal analysis, high-temperature polarized light microscopy, high-temperature and polarized Raman spectroscopy, high-temperature x-ray diffraction, dc conductivity, optical absorption and reflectivity, and domain imaging, and show that epitaxial (001) thin films of BiFeO_3 are clearly monoclinic at room temperature, in agreement with recent synchrotron studies but in disagreement with all other earlier reported results. We report an orthorhombic order-disorder β phase between 820 and 925 (±5) ℃, and establish the existence range of the cubic γ phase between 925 (±5) and 933 (±5) ℃, contrary to all recent reports. We also report the refined Bi_2O_3-Fe_2O_3 phase diagram. The phase transition sequence rhombohedral-orthorhombic-cubic in bulk [monoclinic-orthorhombic-cubic in (001)BiFeO_3 thin film] differs distinctly from that of BaTiO_3. The transition to the cubic y phase causes an abrupt collapse of the band gap toward zero (insulator-metal transition) at the orthorhombic-cubic β-γ transition around 930 ℃. Our band structure models, high-temperature dc resistivity, and light absorption and reflectivity measurements are consistent with this metal-insulator transition.
机译：我们使用差热分析，高温偏振光显微镜，高温和偏振拉曼光谱，高温X射线衍射，直流电导率，对薄膜，单晶和多铁酸铋铁氧体BiFeO_3的陶瓷进行了广泛的实验研究。 ，光吸收和反射率以及畴成像，表明BiFeO_3的外延（001）薄膜在室温下显然是单斜晶的，这与最近的同步加速器研究一致，但与所有其他先前报道的结果不一致。与最近的所有报道相反，我们报告了820至925（±5）℃之间的正交相的无序β相，并确定了925（±5）与933（±5）℃之间的立方γ相的存在范围。我们还报告了改进的Bi_2O_3-Fe_2O_3相图。块状六面体-斜方立方的相变序列[（001）BiFeO_3薄膜中的单斜方-斜方立方]与BaTiO_3的相变顺序明显不同。向立方y相的转变导致在930℃左右的正交-立方β-γ跃迁带隙突然向零崩溃（绝缘体-金属跃迁）。我们的能带结构模型，高温直流电阻率以及光吸收率和反射率测量值与这种金属-绝缘体的转变相一致。

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