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Stabilizing n‐Type Cubic GeSe by Entropy‐Driven Alloying of AgBiSe 2 : Ultralow Thermal Conductivity and Promising Thermoelectric Performance
Author(s) -
Roychowdhury Subhajit,
Ghosh Tanmoy,
Arora Raagya,
Waghmare Umesh V.,
Biswas Kanishka
Publication year - 2018
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201809841
Subject(s) - materials science , orthorhombic crystal system , solid solution , band gap , thermoelectric effect , condensed matter physics , cubic crystal system , semiconductor , thermal conductivity , electrical resistivity and conductivity , atmospheric temperature range , lattice constant , phonon scattering , crystal structure , crystallography , thermodynamics , chemistry , diffraction , optics , optoelectronics , physics , metallurgy , composite material , quantum mechanics
The realization of n‐type Ge chalcogenides is elusive owing to intrinsic Ge vacancies that make them p‐type semiconductors. GeSe crystallizes into a layered orthorhombic structure similar to SnSe at ambient conditions. The high‐symmetry cubic phase of GeSe is predicted to be stabilized by applying 7 GPa external pressure or by enhancing the entropy by increasing to temperature to 920 K. Stabilization of the n‐type cubic phase of GeSe at ambient conditions was achieved by alloying with AgBiSe 2 (30–50 mol %), enhancing the entropy through solid solution mixing. The interplay of positive and negative chemical pressure anomalously changes the band gap of GeSe with increasing the AgBiSe 2 concentration. The band gap of n‐type cubic (GeSe) 1−x (AgBiSe 2 ) x (0.30≤x≤0.50) has a value in the 0.3–0.4 eV range, which is significantly lower than orthorhombic GeSe (1.1 eV). Cubic (GeSe) 1−x (AgBiSe 2 ) x exhibits an ultralow lattice thermal conductivity (κ L ≈0.43 W m −1 K −1 ) in the 300–723 K range. The low κ L is attributed to significant phonon scattering by entropy‐driven enhanced solid‐solution point defects.