Synthesis of solid solution Er2−xCexW3O12 and studies of their thermal expansion behavior

The syntheses and structures of Er{sub 2-x}Ce{sub x}W{sub 3}O{sub 12} were studied. It was found that pure phases could form only for 0.0 {le} x {le} 0.4 and 1.5 {le} x {le} 2.0. Compounds with 0 {le} x {le} 0.4 have the hydrated orthorhombic structure at room temperature and transform to unhydrated orthorhombic one above 135 C whereas samples with 1.5 {le} x {le} 2.0 crystallize in monoclinic structure. Thermal expansion properties of Er{sub 2-x}Ce{sub x}W{sub 3}O{sub 12} were studied with high temperature X-ray powder diffraction. Samples with 0 {le} x {le} 0.4 exhibit negative thermal expansion in temperature range of 200-800 C and higher cerium content leads to more negative thermal expansion coefficient. However, compounds with 1.5 {le} x {le} 2.0 show positive thermal expansion owing to the edge-sharing polyhedra.