Abstract:
Synthesis, X-ray phase analysis, electron microscopy and investigations of the thermoelectric and thermal properties of nanocrystalline copper sulfide alloys contained sodium are presented. At room temperature, the alloys are a mixture of three phases of copper sulfide - the monoclinic phase of Na2Cu4S3 ,
the hexagonal phase of Cu2S and the cubic phase of Cu9S5 (digenite). The predominant phase is
Na2Cu4S3 (with content from 57 to 85 volume %). The particle sizes in the compacted samples lie in
the range from 20 to 400 nm. For all samples DSC studies revealed a first-order phase transition in
the (370-380) K region with enthalpies from 5234 to 11720 J/kgK. The heat capacity varies within the
range (0.15-0.48) J/(gK). The electrical conductivity, Seebeck coefficient and thermal conductivity were
measured in the temperature range from 290 to 590 K. A very low thermal conductivity of the samples
was observed in the interval of (0.1-0.6) Wm −1 K −1
. The Seebeck coefficient has a value higher than
0.2 mV/K for Na 0.15 Cu 1.85 S composition, but a low electrical conductivity about 10 S/cm limits the
maximum dimensionless thermoelectric efficiency ZT of the material at 0.3 in the temperature range
290-590 K.
