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Article Dans Une Revue Inorganic Chemistry Année : 2015

Polymorphism in Thermoelectric As2Te3

Jean-Baptiste Vaney
Judith Monnier
Christophe Candolfi
Vivian Nassif
Gabriel J. Cuello
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Bertrand Lenoir
Eric Alleno

Résumé

Metastable β-As2Te3 (R3̅m, a = 4.047 Å and c =29.492 Å 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 β-As2Te3 could indeed be synthesized with good phase purity (97%) by melt quenching. As expected, β-As2Te3 reconstructively transforms into stable α-As2Te3 (C2/m, a = 14.337 Å, b = 4.015 Å, c = 9.887 Å, and β = 95.06°) at 480 K. This β → α 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, β-As2Te3 displacively transforms in two steps below TS1 = 205−210 K and TS2 = 193−197 K into a new β′-As2Te3 allotrope. These reversible and first-order phase transitions give rise to anomalies in the resistance and in the calorimetry measurements. The new monoclinic β′-As2Te3 crystal structure (P21/m, a = 6.982 Å, b = 16.187 Å, c = 10.232 Å, β = 103.46° 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 β-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 α-phase being the most stable one and the β′-phase being more stable than the β-phase. These calculations also confirm the occurrence of a van der Waals interspace between covalently bonded As2Te3 layers in all three structures.
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Dates et versions

hal-01219302 , version 1 (08-03-2023)

Identifiants

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Cédric Morin, Serena Corallini, Julie Carreaud, Jean-Baptiste Vaney, Gaëlle Delaizir, et al.. Polymorphism in Thermoelectric As2Te3. Inorganic Chemistry, 2015, 54 (20), pp.9936. ⟨10.1021/acs.inorgchem.5b01676⟩. ⟨hal-01219302⟩
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