An analytical study of the solid-solid phase transformation from the cubic
zinc blende or sphalerite (S) metastable modification of CdS (beta -CdS) to
the wurtzite (W) hexagonal stable phase (alpha -CdS) is presented. Polycry
stalline CdS layers in the cubic phase were prepared on glass substrates by
means of chemical bath deposition. Films were heated in Ar + S-2 in the te
mperature (T) range 100-550 degreesC. X-ray diffraction data of annealed sa
mples allowed us to observe a process of gradual change from beta- to alpha
-CdS. Optical absorption spectra let us obtain the band-gap energy (E-g) o
f 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 dr
iven by T. The E-g vs T plot exhibits a minimum as a sharp peak at 300 degr
eesC, which is the T value assigned by us to the critical point (T-c) of th
e experimental structural transformation. The E-g vs V curve indicates an E
-g = AV(2) + BV+ C functional behavior. This E-g vs V dependence was explai
ned through a relation between (partial derivativeE(g)/partial derivativeT)
(P) and C-P. where C-P is the specific heat at constant pressure. The C-P a
gainst T function was also calculated in the interval 300-800 K.