Abstract
This paper presents the comparative data on thermal properties of five compounds of nanocrystalline copper sulfides KxCu1.85S (0 < x < 0.05) at the temperature range from 300 to 700 K. X-ray phase analysis shows that Cu31S16 (or Cu1.9375S) monoclinic djurleite phase are found as prevailing in all KxCu1.85S samples (0.01< x < 0.05). Also in all samples there are oxygen oxide Cu2O and orthorhombic anilite Cu7S4 (Cu1.75S). Variable components of the alloys are monoclinic and hexagonal chalcocite, triclinic roxbyite. The sizes of crystallites in the alloys estimated from half-width of X-ray lines are in the range from 11 to 265 nm at room temperature. Differential scanning calorimetry revealed considerable endothermic thermal effect in the temperature range from 370 to 375 K for all compounds, obviously caused by the superionic phase transition from monoclinic djurleite to hexagonal chalcocite. The thermal conductivity of alloys decreases to 0.16 ÷ 0.25 W K−1m−1 in the temperature range of 450 – 600 K due to an increase in the amount of potassium (for x = 0.04, 0.05). This favors the achievement of high thermoelectric figure of merit of the material. The obtained results are important for semiconductor materials used in the field of thermoelectric devices.