Thermal expansion of alkali halides above 300°K

The lattice parameter of NaCl, KCl, KBr, RbCl, RbBr, RbI, CsCl, CsBr and CsI from room temperature to near melting temperature, and of LiF, NaF and KI from room temperature to near 750°K, are measured using high temperature X-ray diffractometry. An orthogonal polynomial of second order with least square error approximation is fitted to the lattice parameter versus temperature data to obtain the thermal expansion coefficient. The Grüneisen's parameter is calculated using the available data, and in five salts it is found to increase gradually with temperature.