Sphalerite-wurtzite phase transformation in CdS

This is the authors' abstract. We don't add key points for this paper.

An analytical study of the solid-solid phase transformation from the cubic zinc blende or sphalerite (S) metastable modification of CdS ({β}-CdS) to the wurtzite (W) hexagonal stable phase ({α}-CdS) is presented. Polycrystalline CdS layers in the cubic phase were prepared on glass substrates by means of chemical bath deposition. Films were heated in Ar+S₂ in the temperature (T) range 100--550 ^∘{}C. X-ray diffraction data of annealed samples allowed us to observe a process of gradual change from {β}- to {α}-CdS. Optical absorption spectra let us obtain the band-gap energy (Eg) of samples (both as grown and annealed). The unit-cell volume $(V)$ vs T line shape was explained as an interface movement of the S-W interdomain wall driven by T. The Eg vs T plot exhibits a minimum as a sharp peak at 300 ^∘{}C, which is the T value assigned by us to the critical point (Tc) of the experimental structural transformation. The Eg vs V curve indicates an Eg=AV²+BV+C functional behavior. This Eg vs V dependence was explained through a relation between (∂Eg/∂T)P and CP, where CP is the specific heat at constant pressure. The CP against T function was also calculated in the interval 300--800 K.