BaFe2Se3晶体结构与温度和压力的关系：相变现象和Landau势的高阶展开
Crystal Structure of BaFe2Se3 as a Function of Temperature and Pressure: Phase Transition Phenomena and High-Order Expansion of Landau Potential
摘要：
BaFe 2Se 3（Pnma，CsAg 2 I3型结构），最近被认为在~ 11 K下表现出超导性，在60 kbar左右表现出与压力相关的结构转变为CsCu 2Cl 3型结构（Cmcm空间群），这一点从与压力相关的同步辐射粉末衍射数据中得到了证明。随温度变化的同步辐射粉末衍射数据表明，在加热时的室温BaFe 2Se 3结构向高对称性CsCu 2Cl 3形式的演变。在425 K左右，BaFe 2Se 3发生可逆的一阶等结构转变，这一结果得到了差示扫描量热法的支持。的温度依赖性的结构变化发生在两个阶段中，所确定的FeSe 4四面体和Ba原子的位置的相应调整的对齐。在660 K时，观察到了Cmcm结构的二级相变。一个相当不寻常的同构和二阶相变的组合参数化的唯象理论假设高阶扩展的朗道潜力。在参数化的基础上，提出了一种映射观测结构的通用相图。
英文摘要：
BaFe2Se3 (Pnma, CsAg2I3-type structure), recently assumed to show superconductivity at ~ 11 K, exhibits a pressure-dependent structural transition to the CsCu2Cl3-type structure (Cmcm space group) around 60 kbar, as evidenced from pressure-dependent synchrotron powder diffraction data. Temperature-dependent synchrotron powder diffraction data indicate an evolution of the room-temperature BaFe2Se3 structure towards a high symmetry CsCu2Cl3 form upon heating. Around 425 K BaFe2Se3 undergoes a reversible, first order isostructural transition, that is supported by the differential scanning calorimetry data. The temperature-dependent structural changes occur in two stages, as determined by the alignment of the FeSe4 tetrahedra and corresponding adjustments of the positions of Ba atoms. On further heating, a second order phase transformation into the Cmcm structure is observed at 660 K. A rather unusual combination of isostructural and second-order phase transformations is parameterized within phenomenological theory assuming high-order expansion of Landau potential. A generic phase diagram mapping observed structures is proposed on the basis of the parameterization.
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