Thermoelectricity in Ag/Cu based complex crystal structure minerals with inherent low thermal conductivity

Inherently poor lattice thermal conductivity (κL) is highly desired for applications like thermoelectricity, thermal management in electronics, thermal barrier coatings and refractories. Recently, complex crystalline materials have drawn serious scientific attention because of various interesting underlying physical phenomena which explain the unique thermal properties. In this review, we have discussed various interesting concepts and their consequences leading to ultralow κL in complex bulk chalcogenide minerals having multiple scattering channels for heat carrying phonons. The primary focus of this review is on the Ag and Cu based large unit cell structures with low heat capacity and a liquid-like superionic conduction of cations. The Ag/Cu sublattice of these materials that followed the phonon-liquid electron crystal concept strongly reduces the transportation of phonons and enhances the scattering process. The presence of large number of atoms in the unit cell result in low acoustic phonons cut-off frequency, robust acoustic-optical phonons scattering, poor sound velocity and strong crystal anharmonicity inside the crystalline lattice.