Magneto- and thermal-transport properties of Ge₂Sb₂Te₅

The chalcogenide Ge₂Sb₂Te₅ (GST225) and related ternary systems are exemplars of the sensitive interplay of structure, chemical composition, electronic and thermal properties. Here experimental details and numerical results on properties of bulk poly-crystalline GST225 will be presented. We find that the zero field (B=0) resistivity r(T) decreases with decreasing temperature, which can be quantitatively described by the Block- Gruneisen formula with a Debye temperature (Q_D) around 120 K. A positive magnetoresistance i.e., increase in resistance with applied B and a modest one order of magnitude raise between 0 - 18 T is noted. Remarkably, the field dependence of the magnetoresistance (∆ρ(B)/ρ(0)) is neither quadratic nor linear in B. Instead, ∆ρ(B)/ρ(0) is a sublinear concave function of B. Furthermore, even in the sub-kelvin range and field up to 18 T, ∆ρ(B)/ρ(0) does not saturate. The Seebeck coefficient increases from ~5mV/K at 600 mK to about 35 mV/K around room temperature following an S~T^1/2 behavior. The implication of these results will be discussed.