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 °C with an expansion coefficient of 10.4 × 10⁻⁶ °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 × 10⁻⁶ °C⁻¹. In EuF₂ the lattice constant increases non-linearly upto 140 °C. At higher temperatures, the lattice constant decreases with increasing temperature with a negative expansion coefficient of −29 × 10⁻⁶ °C⁻¹ over the range 170–235 °C. The cause of the anomalous behaviour observed in EuF₂ is yet to be understood.