Polymorphism in Thermoelectric As2Te3

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• 作者：Cedric Morin ; Serena Corallini ; Julie Carreaud ; Jean-Baptiste Vaney ; Gaelle Delaizir ; Jean-Claude Crivello ; Elsa Branco Lopes ; Andrea Piarristeguy ; Judith Monnier ; Christophe Candolfi ; Vivian Nassif ; Gabriel Julio Cuello ; Annie Pradel ; Antonio Pereira Goncalves ; Bertrand Lenoir ; Eric Alleno
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：October 19, 2015
• 年：2015
• 卷：54
• 期：20
• 页码：9936-9947
• 全文大小：832K
• ISSN：1520-510X

文摘

Metastable 尾-As₂Te₃ (R3虆m, a = 4.047 脜 and c = 29.492 脜 at 300 K) is isostructural to layered Bi₂Te₃ and is known for similarly displaying good thermoelectric properties around 400 K. Crystallizing glassy-As₂Te₃ leads to multiphase samples, while 尾-As₂Te₃ could indeed be synthesized with good phase purity (97%) by melt quenching. As expected, 尾-As₂Te₃ reconstructively transforms into stable 伪-As₂Te₃ (C2/m, a = 14.337 脜, b = 4.015 脜, c = 9.887 脜, and 尾 = 95.06掳) at 480 K. This 尾 鈫?伪 transformation can be seen as the displacement of part of the As atoms from their As₂Te₃ layers into the van der Waals bonding interspace. Upon cooling, 尾-As₂Te₃ displacively transforms in two steps below T_S1 = 205鈥?10 K and T_S2 = 193鈥?97 K into a new 尾鈥?As₂Te₃ allotrope. These reversible and first-order phase transitions give rise to anomalies in the resistance and in the calorimetry measurements. The new monoclinic 尾鈥?As₂Te₃ crystal structure (P2₁/m, a = 6.982 脜, b = 16.187 脜, c = 10.232 脜, 尾 = 103.46掳 at 20 K) was solved from Rietveld refinements of X-ray and neutron powder patterns collected at low temperatures. These analyses showed that the distortion undergone by 尾-As₂Te₃ is accompanied by a 4-fold modulation along its b axis. In agreement with our experimental results, electronic structure calculations indicate that all three structures are semiconducting with the 伪-phase being the most stable one and the 尾鈥?phase being more stable than the 尾-phase. These calculations also confirm the occurrence of a van der Waals interspace between covalently bonded As₂Te₃ layers in all three structures.