in the DTA curve,there is a sharp endothermic peak observed at 246.4 and 239.6 for pure and KCl crystals, respectively. these endothermic peaks may be assigned to the melting point or liberation of CO due to decomposition of the sample.
The addition of KCl decreases the decomposition temperature by 7 for doped (0.4 mol%) crystal. this show that the KCl molecules may reside inside the crystal as impurity and might have weakened the lattice partially. same results were observed,when the measurement was repeated several times. the sharpness of this endothermic peak observed in DTA shows good degree of crystallinity and purity of the sample.