Application of the photoacoustic method for characterization of natural galena (PbS)

Abstract

Electron transport properties of single crystal and polycrystalline natural mineral galena (PbS) samples from the Trepča mine, Yugoslavia, were determined using the photoacoustic frequency transmission technique. Their thermal diffusivity (DT ≈ 0.16 × 10-5 m2 s-1), the coefficient of diffusion (D between 0.15 × 10-2 0.16 × 10-2 m2 s-1) and lifetime of the excess carrier (τ ≈ 35 μs and the front and rear recombination velocity (Sg ≈ 65.5 m s-1 and Sb ≈ 66.4 m s-1, respectively), were calculated by comparing the experimental results and the theoretical photoacoustic amplitude and phase signals. The lattice parameter obtained by X-ray work was a = 5.936 Å. The free carrier concentration of these single-crystal samples was measured using the Hall method (N = 3 × 1018 cm-3). Measurements of the optical reflectivity of the same samples, as a function of wavelength, in the infrared and far infrared ranges, were performed. In the far infrared range a free electron plasma frequency was observed and numerically analyzed, using the least-squares fitting procedure. The values of optical parameters were calculated and the value of the free carrier concentration obtained by the Hall method was confirmed.