Temperature Dependence of Tetragonal Distortion and Crystal Field Splitting in CuGaS₂

Abstract

The lattice parameters and crystal field splitting of the uppermost valence band in CuGaS2 are measured as a function of temperature. The linear thermal expansion coefficients along the "a" and "c" axes are estimated to be 11.2×10-6 and 4.1×10-6 respectively, and the axial ratio, c/a, changes with a coefficient of -9.0×10-6. This result indicates an "increase" in tetragonal distortion, (2-c/a), with temperature, and hence, an increase in crystal field splitting is expected. However, the apparent crystal field splitting shows a slight "decrease" with temperature. An attempt to explain this contradictory feature is discussed using the concept of the p-d hybridization effect on crystal field splitting.