Structure family and polymorphous phase transition in the compounds with soft sublattice: Cu2Se as an example,The Journal of Chemical Physics

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Structure family and polymorphous phase transition in the compounds with soft sublattice: Cu2Se as an example
The Journal of Chemical Physics ( IF 3.1 ) Pub Date : 2016-05-16 11:15:55 , DOI: 10.1063/1.4948609
Wujie Qiu _{1,

2} , Ping Lu _{2,

3} , Xun Yuan _{2,

3} , Fangfang Xu ₂ , Lihua Wu ₂ , Xuezhi Ke ₁ , Huili Liu _{2,

3} , Jiong Yang ₄ , Xun Shi _{2,

3} , Lidong Chen _{2,

3} , Jihui Yang ₅ , Wenqing Zhang _{2,

4}

Affiliation

Quite a few interesting but controversial phenomena, such as simple chemical composition but complex structures, well-defined high-temperature cubic structure but intriguing phase transition, coexist in Cu₂Se, originating from the relatively rigid Se framework and “soft” Cu sublattice. However, the electrical transport properties are almost uninfluenced by such complex substructures, which make Cu₂Se a promising high-performance thermoelectric compound with extremely low thermal conductivity and good power factor. Our work reveals that the crystal structure of Cu₂Se at the temperature below the phase-transition point (∼400 K) should have a group of candidate structures that all contain a Se-dominated face-centered-cubic-like layered framework but nearly random site occupancy of atoms from the “soft” Cu sublattice. The energy differences among those structures are very low, implying the coexistence of various structures and thus an intrinsic structure complexity with a Se-based framework. Detailed analyses indicate that observed structures should be a random stacking of those representative structure units. The transition energy barriers between each two of those structures are estimated to be zero, leading to a polymorphous phase transition of Cu₂Se at increasing temperature. Those are all consistent with experimental observations.

中文翻译：

具有软亚晶格的化合物的结构族和多态相变：以Cu2Se为例

Cu ₂ Se共存于Cu ₂ Se中，这是一些有趣但有争议的现象，例如化学成分简单，结构复杂，定义明确的高温立方结构但有趣的相变，这源于相对刚性的Se骨架和“软” Cu亚晶格。但是，这种复杂的子结构几乎不会影响电传输性能，这使Cu ₂ Se具有极低的热导率和良好的功率因数成为一种有前途的高性能热电化合物。我们的工作表明，Cu ₂的晶体结构低于相变点（〜400 K）的温度下的硒应具有一组候选结构，这些候选结构均包含以硒为主的面心立方状层状骨架，但来自“软”原子的位置几乎是随机的铜亚晶格。这些结构之间的能量差异非常低，这意味着各种结构共存，因此基于Se的框架具有固有的结构复杂性。详细的分析表明，观察到的结构应该是那些代表性结构单元的随机堆叠。这些结构中的每两个之间的跃迁能垒估计为零，从而在温度升高时导致Cu ₂ Se的多态相变。这些都与实验观察一致。

更新日期：2016-05-17

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