THERMOELECTRIC AND OPTICAL PROPERTIES OF SOLID SOLUTION CRYSTALS ACROSS THE Pb4Ga4GeSe12-Pb4Ga4GeS12 SECTION

Abstract

The paper presents the results of studies on the thermoelectric and optical properties of Pb4Ga4GeSe12– Pb4Ga4GeS12 crystals. The Pb4Ga4GeSe12–Pb4Ga4GeS12 crystals corresponded to the compositional content of 10, 20, and 30 mol.% Pb4Ga4GeS12.The aim of the study was to experimentally determine the specific electrical conductivity, conductivity type, Seebeck coefficient, estimate the band gap width, and calculate the thermoelectric power of Pb4Ga4GeSe12–Pb4Ga4GeS12 crystals.All studies were conducted at room temperature (T≈300 K). The highest values of specific electrical conductivity (σ≈170 Ω⁻¹·m⁻¹) were observed in Pb4Ga4GeSe12–Pb4Ga4GeS12 crystals with a 20 mol.% Pb4Ga4GeS12 content. High values of σ may indicate that the materials are in a state close to degeneracy. Thermoelectric methods have established that Pb4Ga4GeSe12–Pb4Ga4GeS12 crystals belong to n-type semiconductors. The Seebeck coefficient values were 205 µV/K, 220 µV/K, and 240 µV/K for Pb4Ga4GeSe12–Pb4Ga4GeS12 crystals with 10, 20, and 30 mol.% Pb4Ga4GeS12 content, respectively. Having high Seebeck coefficient values, Pb4Ga4GeSe12–Pb4Ga4GeS12 compounds are promising materials for the fabrication of sensitive thermal sensors. It has been established that the highest values of thermoelectric power (α²·σ=8.2×10⁻⁶ W/m·K²) are characteristic of Pb4Ga4GeSe12–Pb4Ga4GeS12 crystals with a 20 mol.% Pb4Ga4GeS12 content.To estimate the band gap width, light absorption spectra were studied in the region of the fundamental absorption edge.The band gap values estimated from the optical absorption spectra were 1.89 eV, 1.92 eV, and 1.95 eV for Pb4Ga4GeSe12– Pb4Ga4GeS12 solid solutions with 10, 20, and 30 mol.% Pb4Ga4GeS12, respectively. It was established that the investigated crystals are indirect band gap semiconductors.