A Chemical, High-Temperature Way To Ag1.9te Via Quasi-Topotactic Reaction Of Stuetzite-Type Ag1.54te: Structural And Thermoelectric Properties

Semiconducting silver tellurides gained reasonable interest in the past years due to its thermoelectric, magneto-caloric, and nonlinear optic properties. Nanostructuring has been frequently used to address quantum-confinement effects of minerals and synthetic compounds in the Ag-Te system. Here, we report on the structural, thermal, and thermoelectric properties of stuetzite-like Ag1.54Te (or Ag4.63Te3) and Ag1.9Te. By a quasi-topotactic reaction upon tellurium evaporation Ag1.54Te can be transferred to Ag1.9Te after heat treatment. Crystal structures, thermal and thermoelectric properties of stuetzite-like Ag1.54Te (or Ag4.63Te3) and Ag1.9Te were determined by ex situ and in situ experiments. This method represents an elegant chemical way to Ag1.9Te, which was so far only accessible electrochemically via electrochemical removal of silver from the mineral hessite (Ag2Te). The mixed conductors show reasonable high total electric conductivities, very low thermal conductivities, and large Seebeck coefficients, which result in a significant high thermoelectric figure of 0.57 at 680 K.