Structures, thermal expansion properties and phase transitions of Er xFe 2− x(MoO 4) 3 (0.0 ≤ x ≤ 2.0)

Abstract

Structures, thermal expansion properties and phase transitions of Er x Fe 2− x (MoO 4) 3 (0.0 ≤ x ≤ 2.0) have been investigated by X-ray diffraction and differential thermal analysis. The partial substitution of Er 3+ for Fe 3+ 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(MoO 4) 3, as well as the orthorhombic Er x Fe 2− x (MoO 4) 3 ( x ≤ 0.8) have positive thermal expansion coefficients. However, the linear thermal expansion coefficients of Er x Fe 2− x (MoO 4) 3 ( x = 0.6–2.0) decrease with increasing content of Er 3+ and for x ≥ 1.0, compounds Er x Fe 2− x (MoO 4) 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 × 10 −6/°C in Er 1.0Fe 1.0(MoO 4) 3 is observed in the temperature range of 180–400 °C, and zero thermal expansion is observed in Er 0.8Fe 1.2(MoO 4) 3 in the temperature range of 350–450 °C. In addition, anisotropic thermal expansions are found for all the orthorhombic Er x Fe 2− x (MoO 4) 3 compounds, with negative thermal expansion coefficients along the a axes.