On thermal stability of nanocrystalline Ag–Cu-S powders

The nanocrystalline semiconducting compounds based on the AgCuS system are considered as low-cost candidates of thermoelectric materials with improved thermal stability. The nanocrystalline Ag–Cu—S powders were prepared from metal nitrates and sulphur powder in tetraethylene glycol (TEG) solvent by reductive agent NaBH4. The crystallite sizes of the observed phases were in the range between 60 and 80 nm. The chemical compositions of the as-received samples were analysed by the ICP-AES method and their phase compositions were evaluated by XRPD. The investigation was supplemented by DSC and in situ HTXRD thermal analysis. A more detailed in situ experiment was performed for a sample containing ternary phases. The nucleation and growth of silver micro-wires were first observed on the substrate involving ternary phases at isothermal heat treatment. The formation of silver wires and semi-conductive ternary thermoelectric phase (stromayerite τ3) is explained by observed phase transformation. The obtained results are complemented by microscopy (LM, SEM, TEM).