X-RAY STUDIES OF SOME EUROPIUM COMPOUNDS AT ELEVATED-TEMPERATURES

The temperature variation of the lattice constants of europium iron garnet (Eu3Fe5O12), europium sulphide (EuS) and europium fluoride (EuF2) has been studied using an X-ray powder diffractometer. The lattice constant of Eu3Fe5O12 increases linearly upto 800-degrees-C with an expansion coefficient of 10.4 x 10(-6)degrees-C-1. In the case of EuS, the lattice constant increases non-linearly with temperature. At room temperature the expansion coefficient has a value of 14.3 x 10(-6)degrees-C-1. In EuF2 the lattice constant increases non-linearly upto 140-degrees-C. At higher temperatures, the lattice constant decreases with increasing temperature with a negative expansion coefficient of -29 x 10(-6)degrees-C-1 over the range 170 - 235-degrees-C. The cause of the anomalous behaviour observed in EuF2 is yet to be understood.