Figs. 2a, b and c illustrate the increase of the a, b and c lattice parameters as a function of increasing temperature and 2d shows the calculated thermal expansion coefficients (TEC) for all three compositions. As expected, the unit cell parameters show a linear increase throughout the temperature range. On close examination of the data, it is evident that the c parameter showed a significant increase when compared to both the a and b parameters, thereby reflecting the cumulative effect of stacking of layers across the crystallographic c direction. The c parameter was more responsive to the changes in temperature than the a parameter because the expansion along the c axis is less restricted by the expansion of the rock-salt layers . Also evident from Fig. is the relatively higher increase in a lattice parameter compared with the b lattice parameter, which points towards an increase in orthorhombic strain with increasing temperature as argued by us in our earlier reports .