Regularity of thermal characteristics, thermoelectric properties of EuLnCuSe3 compounds (Ln = La–Lu)

https://doi.org/10.1140/epjp/s13360-024-05155-6

The temperatures and enthalpies of the decomposition of EuLnCuSe₃ compounds (Ln = La–Lu) are determined for the first time as functions of the Ln³⁺ ionic radius (rLn³⁺). The EuLnCuSe₃ compounds with Ln = La and Ce decompose in the course of a solid-phase reaction to form EuSe, Ln₂Se₃, and Cu_2−xSe, whereas those with Ln = Tb, Dy, Ho, Tm, and Lu melt incongruently to form EuSe and a melt, for example, T_decay = 1175 K and ΔH_decay = 2.66 kJ/mol for EuLaCuSe₃, while T_melt = 1576 K and ΔH_melt = 2.69 kJ/mol for EuTbCuSe₃. When plotted as functions of rLn³⁺, the temperatures of thermal effects of these compounds exhibit a periodic dependence and a tetrad effect. The temperature dependence of electrical resistivity and that of the Seebeck coefficient are measured from 300 to 600 K. It is shown that the studied compounds are p-type semiconductors with bandgaps ranging from 0.4 to ~ 1 eV.