Structures, thermal expansion properties and phase transitions of ErxFe2-x(MoO4)3 (0.0 ≤ x ≤ 2.0)

Structures, thermal expansion properties and phase transitions of ErxFe2-x,(MoO4)(3) (0.0 <= x <= 2.0) have been investigated by X-ray diffraction and differential thermal analysis. The partial substitution of Er3+ for Fe3+ induces pronounced decreases in the phase transition temperature from monoclinic to orthorhombic structure. Rietveld analysis of the XRD data shows that both the monoclinic and orthorhombic Fe-2(MoO4)(3), as well as the orthorhombic ErxFe2-x(MoO4)(3) (x <= 0.8) have positive thermal expansion coefficients. However, the linear thermal expansion coefficients of ErxFe2-x(MoO4)(3) (x = 0.6-2.0) decrease with increasing content of Er3+ and for x >= 1.0, compounds ErxFe2-x (MoO4)(3) show negative thermal expansion properties. Attempts for making zero thermal expansion coefficient materials result in that very low negative thermal expansion coefficient of -0.60 x 10(-6)/degrees C in Er1.0Fe1.0(MoO4)(3) is observed in the temperature range of 180-400 degrees C, and zero thermal expansion is observed in ErxFe2-x(MoO4)(3) in the temperature range of 350-450 degrees C. In addition, anisotropic thermal expansions are found for all the orthorhombic ErxFe2-x(MoO4)(3) compounds, with negative thermal expansion coefficients along the a axes. (C) 2007 Elsevier Masson SAS. All rights reserved.