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

Number 3_Vol.2

AUTHORS: M.Kh. Balapanov, M.M. Kubenova, K.A. Kuterbekov, A. Kozlovskiy, S.N. Nurakov, R.Kh. Ishembetov, R.A. Yakshibaev

DOI: 10.29317/ejpfm.2018020304

PAGES: 231 - 241

DATE: 2018-09-26


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
Na2Cu4S(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.


KEYWORDS

Copper sulfide, thermal conductivity, thermoelectric materials, superionic conductors.


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