Synthesis, X-ray phase analysis and differential thermal analysis of nanocrystalline superionic KxCu1.85S (x<0.05) copper sulfides

Abstract

Superionic semiconductor chalcogenides with mixed electronic-ionic conductivity have very low lattice thermal conductivity and are excellent thermoelectrics. Doping with other elements is one of the methods for optimizing the useful properties of a material. In this work, nanosized polycrystalline alloys of nonstoichiometric Cu1.85S copper sulfide with a low content of potassium are studied. The paper presents the results of X-ray phase analysis, differential thermal analysis (DTA) and electron microscopy of differential thermal analysis of KxCu1.85S alloys. The resulting alloys are a mixture of phases, in which the main share is djurleite - non-stoichiometric copper sulfide of the composition Cu1.97÷1.93S , in addition, depending on the composition of the alloy, there are impurities of monoclinic and hexagonal chalcocite Cu2S , roxbyite Cu1.81S , anilite Cu1.75S , traces of metallic copper. All alloys contain inclusions of Cu2O copper oxide. DTA detected a superionic phase transition from an ordered low-symmetry djurleite phase to a disordered superionic hexagonal phase of copper sulfide at about 373-383 K. In addition, DTA revealed two thermal effects at about 433 K and 460 K, which are absent in binary copper sulfide. The reason for the effects may be the redistribution of impurity potassium ions in the copper sulfide lattice.