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Spanish Agencia Estatal de Investigacion supported this work through grants PID2019- 105325RB-C32, PID2021-122585NB-C21-2, PGC2021-125518NB-I00 and RED2022-134388-T cofinanced by EU FEDER funds. A.O.R. acknowledges the European Union NextGenerationEU/PRTR for grants TED2021-129457B-I00 and CNS2023-144958. JSR acknowledges the Spanish Ministry of Science and Innovation, through the predoctoral contract PRE2020-096178. His research has also been partially funded by the Eurofusion Enable Research grant CfP-FSD-AWP21-ENR-01. The authors thankfully acknowledgethe computer resources and technical support provided by MareNostrum5 (RES-AECT-2024-2-0010), the Malta-Consolider Supercomputing center, and the Centre for Supercomputation and Visualisation in Madrid (CeSViMa).

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Solving Static and Dynamic Disorder in Cu4TiTe4: Crystal Structure and Thermodynamic Properties

Publicated to:Inorganic Chemistry. 64 (7): 3223-3234 - 2025-02-07 64(7), DOI: 10.1021/acs.inorgchem.4c04585

Authors: Suarez-Recio, Jorge; Lobato, Alvaro; Izquierdo-Ruiz, Fernando; Franco, Ruth; Otero-de-la-Roza, Alberto; Recio, J Manuel

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Abstract

Cu4TiTe4 shows positional disorder because one of the copper atoms does not occupy a precise position in the unit cell. This fact complicates the development of simple and reliable crystalline models capable of capturing the promising thermodynamic and optical properties of Cu4TiTe4. Here, we select practical supercells accounting for the different Cu atomic environments in the crystal and identify nonequivalent structural configurations. Their electronic energies and thermodynamic properties are calculated by coupling DFT and the quasi-harmonic approximations. Average values corresponding to the experimentally observed Cu4TiTe4 structure are obtained introducing Boltzmann weights based on the total energy of these configurations. For Cu4TiTe4, differences in the calculated properties among the 16 nonequivalent configurations of its 2 x 2 x 1 supercell demonstrate the inadequacy of focusing just on a single configuration. After calculating the energy barriers associated with the diffusion of the disordered copper atoms among its four equivalent positions (lower than 0.5 eV), we evidence the importance of taking into account this dynamic disorder, which reveals a negative thermal expansion for this telluride at low temperatures, not found under the static disorder approach.

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