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 Fe2(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 -0.60X10-6/ deg C in Er1.0Fe1.0(MoO4)3 is observed in the temperature range of 180-400 deg C, and zero thermal expansion is observed in Er0.8Fe1.2(MoO4)3 in the temperature range of 350-450 deg 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.