Semiconductors

The problems of increasing the thermoelectric figure of merit of polycrystalline misfit layered compounds on (Gd$_x$Dy$_{1-x}$S)$_z$NbS$_2$ example

V. V. Bakovets, A. V. Sotnikov

Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia

Abstract: The lattice disorder of different architecture and dimensions influence on the thermoelectric properties (Seebeck coefficient $S$, resistivity $\rho$, total thermal conductivity $\kappa_{\mathrm{tot}}$, power factor $S^2/\rho$, figure of merit $ZT$) of the polycrystalline ternary sulfides MTS$_3$ was studied. The high-temperature misfit layered compounds (MS)$_z$NbS$_2$ (MS is Gd$_x$Dy$_{1-x}$S solid solutions) were chosen as objects of the study. The variation of gadolinium concentration along the series $x$ = 0.0, 0.1, 0.2, 0.5, 1.0 allowed one to alter the short-range and the long-range order of the crystal lattice and to study their effect on thermoelectric parameters of (Gd$_x$Dy$_{1-x}$S)$_z$NbS$_2$. At low concentration of $x$ = 0.1 the crystallite size increases, cause the deformation stresses decrease and, thereby, leads to an abnormal changes of $S$, $\rho$, $\kappa_{\mathrm{tot}}$ values and $ZT$ decrease. An increase of the gadolinium concentration ($x$ = 0.2 – 0.5) alters the electronic structure and the interatomic bonding character of the incommensurate subsystems [Gd$_x$Dy$_{1-x}$S] and [NbS$_2$]. In this case, $S$ and $\rho$ values remains practically unaffected, while the thermal conductivity value decreases by 40% and $ZT$ increases by 2 times. The nature of this phenomenon and the anisotropy of the thermoelectric properties were discussed.

Keywords: misfit layers compounds, thermoelectric properties, lattice disorder, solid solution, crystallite boundaries.

Received: 27.10.2022
Revised: 30.11.2022
Accepted: 30.11.2022

DOI: 10.21883/FTT.2023.02.54290.508

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