Doping GeSb2Te4 with Cr3+: Structure and Temperature-Dependent Physical Properties†

The tellurides Ge0.94Cr0.04Sb2Te4 and Ge0.88Cr0.08Sb2Te4 were synthesized in sealed silica glass ampoules. Rietveld refinements show that they crystallize in the 21R-In3Te4 structure type (Rm), similar to undoped GeSb2Te4. The composition and phase purity were confirmed by ICP-AES as well as by SEM and TEM, including EDX measurements. EPR spectroscopy reveals the valence state +III for the Cr atoms (g = 1.990) in Ge0.88Cr0.08Sb2Te4, which agrees well with the Cr3+ content calculated from the inverse magnetic susceptibility. The material exhibits a ferromagnetic fluctuations with a paramagnetic Curie temperature of 70 K ± 20 K and is a metallic conductor. Compared to GeSb2Te4, the electrical conductivity is increased by a factor of 2.5. As Cr doping further leads to a higher Seebeck coefficient, the thermoelectric figure of merit ZT reaches values of up to 0.3 at 500 °C, i.e. three times the value of undoped material.