Search

Abstract: Crystal structures and thermal expansion properties of Dy2−x Ln x Mo4O15 (Ln=Ho (x =0.0–2.0) and Sm (x =0.0–0.4)) have been investigated by means of X-ray diffraction (XRD). Dy2−x Ln x Mo4O15 (Ln=Ho and Sm) crystallizes in monoclinic lattice with space group P21/c in the 25–500°C temperature range. High-temperature XRD result reveals an anisotropic expansion in the lattice of Dy2−x Ln x Mo4O15 with the expansion of a- and c-axes and contraction of b-axis. Despite the shrinkage of b-axis, the volume thermal expansion coefficient of Dy2−x Ln x Mo4O15 is positive. The thermal expansion behavior of Dy2−x Ln x Mo4O15 is basically related to the temperature-induced expansion of bond Dy(Ln)–O and Mo(2)–O14. [Copyright &y& Elsevier]

Abstract: Three new series of Ho2−x Er x Mo4O15 (x =0.0–2.0), Ho2−x Sm x Mo4O15 (x =0.0–0.6) and Ho2−x Ce x Mo4O15 (x =0.0–0.25) solid solutions have been prepared successfully by solid-state reaction and studied by powder X-ray diffraction. All the XRD patterns of these molybdates can be indexed in monoclinic space group P21/c. Lattice parameters a, b and c of Ho2−x Ln x Mo4O15 decrease linearly with increasing erbium content and increase with increasing samarium or cerium content. Thermal expansion behaviors of Ho2−x Ln x Mo4O15 have been investigated in the 25–500°C temperature range with high-temperature X-ray diffraction. The temperature dependence of Mo(2)–O14 interaction looks like to be responsible for their thermal expansion behaviors. [Copyright &y& Elsevier]

Abstract: Compounds Ho2W3O12, Ho2Mo3O12, Tm2W3O12 and Tm2Mo3O12 have been prepared by conventional solid-state reaction. Their crystal structures and thermal expansion properties were investigated by room temperature and high temperature X-ray diffractions. It is found that, in certain temperature ranges (200–700°C for Ho sample and 200–800°C for the others), Ho2Mo3O12, Tm2W3O12 and Tm2Mo3O12 all adopt orthorhombic structure and show negative thermal expansion whereas Ho2W3O12 adopts monoclinic structure and shows positive thermal expansion. The volume thermal expansion coefficients obtained for Ho2W3O12, Ho2Mo3O12, Tm2W3O12 and Tm2Mo3O12 from high temperature XRD are 29.46×10−6 °C−1, −34.50×10−6 °C−1, −11.85×10−6 °C−1 and −12.09×10−6 °C−1, respectively. Thermogravimetry was used to study their hygroscopicity in air. [Copyright &y& Elsevier]

Abstract: The syntheses and structures of Er2−x Ce x W3O12 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°C whereas samples with 1.5≦ x ≦2.0 crystallize in monoclinic structure. Thermal expansion properties of Er2−x Ce x W3O12 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°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. [Copyright &y& Elsevier]

Abstract: Structures, thermal expansion properties and phase transitions of Er x Fe2−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 Er x Fe2−x (MoO4)3 (x ≤0.8) have positive thermal expansion coefficients. However, the linear thermal expansion coefficients of Er x Fe2−x (MoO4)3 (x =0.6–2.0) decrease with increasing content of Er3+ and for x ≥1.0, compounds Er x Fe2−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 −0.60×10−6/°C in Er1.0Fe1.0(MoO4)3 is observed in the temperature range of 180–400°C, and zero thermal expansion is observed in Er0.8Fe1.2(MoO4)3 in the temperature range of 350–450°C. In addition, anisotropic thermal expansions are found for all the orthorhombic Er x Fe2−x (MoO4)3 compounds, with negative thermal expansion coefficients along the a axes. [Copyright &y& Elsevier]

Abstract: The crystal structural and thermal expansion properties of solid solution Er2−x Sm x W3O12 (0≦ x ≦2.0) have been investigated by X-ray powder diffraction. The XRD patterns indicate that pure phases can form in the composition range of 0.0≦ x ≦0.5 with orthorhombic structure and 0.6≦ x ≦2.0 with monoclinic one. The cell parameters and unit cell volumes increase almost linearly with increasing Sm content. Investigations on the thermal properties show that compounds with 0.0≦ x ≦0.5 exhibit negative thermal expansion in the 200–800°C temperature range and samples with 0.6≦ x ≦2.0 possess normal thermal expansion (25–800°C). It is also found that high samarium content leads to more negative thermal expansion coefficient of Er2−x Sm x W3O12 (0.0≦ x ≦0.5). [Copyright &y& Elsevier]

Abstract: Solid solutions of Nd2−x Er x W3O12 ( and ) have been successfully prepared and their structures have been investigated by X-ray and neutron powder diffraction. The thermal expansion properties of Nd2−x Er x W3O12 (, 0.4, 1.5, 1.7 and 1.9) were studied with high temperature X-ray diffraction. Positive thermal expansions of compounds Nd2−x Er x W3O12 with are found to be anisotropic along the three crystallographic directions where the a -axis expands in the 25–200 °C range and contracts in the 200–800 °C range, while b - and c -axes show expansion in the whole temperature range. Negative thermal expansion coefficient of compounds Nd2−x Er x W3O12 with becomes more negative from to  °C−1 with the neodymium content increasing. [Copyright &y& Elsevier]

Abstract: Crystal structures and thermal expansion properties of solid solutions Ln2−x Dy x W3O12 (Ln=Er and Y) were studied by room and high temperature X-ray diffraction. Rietveld analysis results show that compounds Er2−x Dy x W3O12 with 0≤ x ≤0.7 and Y2−x Dy x W3O12 with 0≤ x ≤1.0 have orthorhombic structures and show negative thermal expansion in temperature range of 200–800°C while compounds Er2−x Dy x W3O12 with 1.2≤ x ≤2.0 and Y2−x Dy x W3O12 with 1.5≤ x ≤2.0 have monoclinic structures and exhibit positive thermal expansion in temperature range of 25–800°C. Thermogravimetric (TG) and differential thermal analysis (DTA) were used to study the hygroscopicity and the phase transition temperature. [Copyright &y& Elsevier]