X-Ray Study of the Thermal Expansion Anisotropy in AgGaS2 and AgInS2 Compounds over the Temperature Range from 80 to 650 K

The lattice parameters α and c of the AgGaS2 and AgInS2 compounds are determined as a function of temperature by X-ray diffraction method in the temperature range from 80 to 650 K. The data are used to evaluate the coefficients of thermal expansion, perpendicular (α⟂) and parallel (α∥) to the principal axis, and the thermal expansion of the AC (αAC) and BC (αBC) bonds. It is found that for the two compounds almost over the whole investigated temperature range the coefficients of expansion α∥ and αBC are negative while the coefficients α⟂ and αAC are positive.