The syntheses and structures of Er2-xCexW3O12 were studied. It was found that pure phases could form only for 0.0 <= x <= 0.4 and 1.5 <= x <= 2.0. Compounds with 0 <= x <= 0.4 have the hydrated orthorhombic structure at room temperature and transform to unhydrated orthorhombic one above 135 degrees C whereas samples with 1.5 <= x <= 2.0 crystallize in monoclinic structure. Thermal expansion properties of Er2-xCexW3O12 were studied with high temperature X-ray powder diffraction. Samples with 0 <= x <= 0.4 exhibit negative thermal expansion in temperature range of 200-800 degrees C and higher cerium content leads to more negative thermal expansion coefficient. However, compounds with 1.5 <= x <= 2.0 show positive thermal expansion owing to the edge-sharing polyhedra. (c) 2007 Elsevier Ltd. All rights reserved.