Phase analysis, thermal and thermoelectric properties of nanocrystalline Na0.15Cu1.85S, Na0.17Cu1.80S, Na0.20Cu1.77S alloys

• Main Authors: M.Kh. Balapanov, M.M. Kubenova, K.A. Kuterbekov, A. Kozlovskiy, S.N. Nurakov, R.Kh. Ishembetov, R.A. Yakshibaev
• Format: Article
• Language: English
• Published: L.N. Gumilyov Eurasian National University 2018-09-01
• Series: Eurasian Journal of Physics and Functional Materials
• Subjects: copper sulfide; thermal conductivity; thermoelectric materials; superionic conductors
• Online Access: http://ephys.kz/files/2018-09-26_2018020304.pdf

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.