Phase analysis, thermal and thermoelectric properties of nanocrystalline Na0.15Cu1.85S, Na0.17Cu1.80S, Na0.20Cu1.77S alloys
AUTHORS: M.Kh. Balapanov, M.M. Kubenova, K.A. Kuterbekov, A. Kozlovskiy, S.N. Nurakov, R.Kh. Ishembetov, R.A. Yakshibaev
PAGES: 231 - 241
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−1K−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.
Copper sulﬁde, thermal conductivity, thermoelectric materials, superionic conductors.
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