Exploring the origin of low thermal conductivity in thermoelectric Cu2ZnGeSe4

Diamond-like quaternary chalcogenides, including Cu2ZnGeSe4, are attracting considerable interest for their potential as absorbers for solar cells and for thermoelectric energy recovery. Cu2ZnGeSe4 exhibits an electronic transition at 473 K. Analysis of variable-temperature neutron diffraction data has revealed that an order-disorder transition, accompanied by the onset of copper ion mobility, occurs at this temperature. This transition results in a significant reduction in the lattice thermal conductivity of Cu2ZnGeSe4. Here, we seek to gain a better understanding of the effect of copper ionic mobility on the lattice thermal conductivity and the vibrational phonon modes of this material.