Effect of cooling time on the structural, optical, mechanical, thermal and electrical properties of KCl1−xBrx crystals formed directly on cooling the melt

In order to investigate the effect of cooling time on the properties of crystal formed directly on cooling the melt, we have prepared the KCl1−xBrx crystals [with x = 0.0 (pure KCl), 0.2, 0.4, 0.5, 0.6, 0.8 and 1.0 (pure KBr)] by cooling their melts directly with different cooling times (0, 2, 4, 6, 8, 10, 12 and 14 h) in each case. The prepared crystals have been characterized structurally, optically, mechanically, thermally and electrically by carrying out X-ray diffraction (XRD), atomic force microscopic (AFM), optical absorption, micro-hardness, specific heat capacity and electrical conductivity measurements. XRD analysis indicates halite structure for all the crystals formed. AFM results show an increase of grain size with the cooling time. Optical absorption spectra obtained have illustrated the presence of peak at 229 nm for the KCl crystal and 342.2 nm for the mixed crystals, the peak gradually shifts to shorter wavelengths with the increase of cooling time. Hardness analysis shows nonlinear variation with the cooling time, KCl0.5Br0.5 crystal having the maximum value when the cooling time is 4 h. Temperature and composition have influences on the thermal conductivity, specific heat capacity and thermal diffusivity, while the cooling time has a little influence on the thermal performance. Electrical conductivity measurement indicates a little influence of cooling time and strong influences of temperature and composition on the electrical conductivity and activation energy.