Thermal and Electrical Transport Properties in bulk Ge₂Sb₂Te₅

The remarkable ability of certain solids, the Phase Change materials (PCM), to reversibly and rapidly switch between amorphous and crystalline states with large differences in electrical, thermal and optical properties was discovered exactly half a century ago [S.R. Ovshinsky PRL, 21,1450 (1968)]. Currently ambient temperature operable PCM’s are used in electronic flash memory as well as optical data storage. Ge₂Sb₂Te₅ is such a PCM alloy; in which, we have previously reported Noritheim-Gorter like scaling between Seebeck coefficient (S) and electrical conductivity (s). Here we report that in the room temperature regime, thermal conductivity (κ) of this material is a linear function of temperature with a slope ~ 1e-3 W/mT²; whereas, electrical conductivity falls off with rising temperature; Remarkably, despite this deviation from Wiedemann-Franz Law, the value of Lorenz number estimated from the experimental (κ and s) data ranges between 2-2.47 e-8 WWK^-2, not much off from the ideal kinetic theory value of 2.44e^-8. Further experimental details and results will be discussed.