Structural properties of the thermoelectric material CuCrS2 and of deintercalated CuxCrS2 on different length scales: X-ray diffraction, pair distribution function and transmission electron microscopy studies

We report on the structural alterations of the thermoelectric material CuCrS2 introduced by the removal of 1/3 of the Cu+ ions which are located between CrS2 layers. X-ray diffraction (XRD) and pair distribution function (PDF) analyses revealed a newly formed Cu0.66CrS2 phase with monoclinic symmetry and a 3a superstructure. Simultaneously, a distortion of CrS6 octahedra is observed strongly indicating the oxidation of Cr3+ -> Cr4+ leading to a Jahn-Teller distortion. The structural features extracted from XRD indicate a pronounced disorder in the cationic sub-lattice at moderate temperatures (400 K). Transmission electron microscopy (TEM) examination elucidates the formation of a second Cu0.66CrS2 phase without the superstructure, caused by incipient Cu+ mobility upon beam irradiation. The synergetic combination of high temperature XRD and TEM investigations unveiled the complete mechanism of the phase transition occurring at 503 K, where a transformation into the spinel CuCr2S4 and stoichiometric CuCrS2 occurs.

我们报道了通过去除位于CrS₂层之间的1/3的Cu⁺离子而在热电材料CuCrS₂中引入的结构变化。X射线衍射（XRD）和对分布函数（PDF）分析揭示了一种新形成的具有单斜对称性和3a超结构的Cu₀.₆₆CrS₂相。同时，观察到CrS₆八面体发生畸变，这强烈表明Cr³⁺氧化为Cr⁴⁺，从而导致了姜 - 泰勒畸变。从XRD中提取的结构特征表明，在中等温度（400 K）下阳离子亚晶格存在明显的无序。透射电子显微镜（TEM）检查阐明了由于电子束照射时初期的Cu⁺迁移率而形成的第二种没有超结构的Cu₀.₆₆CrS₂相。高温XRD和TEM研究的协同结合揭示了在503 K时发生的相变的完整机制，此时会转变为尖晶石CuCr₂S₄和化学计量的CuCrS₂。