The onset of copper-ion mobility and the electronic transitions in kesterite, Cu2ZnGeSe4

Mangelis, P., Vaqueiro, P. ORCID: https://orcid.org/0000-0001-7545-6262, Smith, R. I. and Powell, A. V. (2021) The onset of copper-ion mobility and the electronic transitions in kesterite, Cu2ZnGeSe4. Journal of Materials Chemistry A, 9 (48). pp. 27493-27502. ISSN 0959-9428 doi: 10.1039/D1TA08642A

Abstract/Summary

Kesterite-related phases have attracted considerable interest as earth-abundant photovoltaic and thermoelectric materials. For the kesterite Cu2ZnGeSe4, we have established a direct link between anomalies in the temperature dependence of transport properties and an order -disorder transition. Powder neutron diffraction as a function of temperature reveals an order-disorder transition at 473 K, involving disordering of copper and zinc cations over three crystallographic positions. Vacancies are simultaneously created on the copper-ion sublattice, indicative of the concomitant onset of copper-ion mobility. Differential scanning calorimetry data show a weak thermal signature in this temperature region, typical of a second-order phase transition, which is consistent with the absence of anomalies in the temperature dependence of the unit cell volume. The partial melting of the copper-ion sublattice induces a transition in the electrical-transport properties. The changes in electrical resistivity and Seebeck coefficient suggest this involves a transition from a conventional, activated semiconductor, to a degenerate semiconductor. The entry of an increasing fraction of the copper-ion sub-lattice into a liquid-like state is reflected in a reduction in thermalconductivity above 473 K. The order-disorder phase transition identified here has consequences for the performance of photovoltaic and thermoelectric devices based on kesterites.

Item Type	Article
URI	https://reading-clone.eprints-hosting.org/id/eprint/101473
Item Type	Article
Refereed	Yes
Divisions	Life Sciences > School of Chemistry, Food and Pharmacy > Department of Chemistry Interdisciplinary centres and themes > Chemical Analysis Facility (CAF) > Thermal Analysis (CAF) Interdisciplinary centres and themes > Chemical Analysis Facility (CAF) > Xray (CAF)
Uncontrolled Keywords	Thermoelectric, photovoltaic, kesterite
Publisher	Royal Society of Chemistry
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