Synthesis and negative thermal expansion properties of solid solutions Yb_(2-x)La_xW_3O_(12) (0 <= x <= 2)

摘要

A new series of rare earth solid solutions Yb_(2-x)La_xW_3O_(12) were successfully synthesized by the solid-state method. Effects of substituted ion lanthanum on the microstructures and thermal expansion properties in the resulting Yb_(2-x)La_xW_3O_(12) ceramics were investigated by X-ray diffraction (XRD), thermogravimetric analyzer (TGA), field emission scanning electron microscope (FESEM) and thermal mechanical analyzer (TMA). Results indicate that the structural phase transition of the Yb_(2-x)La_xW_3O_(12) changes from orthorhombic to monoclinic with increasing substituted content of lanthanum. The pure phases can form in the composition range of 0 < =x < 0.5 with orthorhombic structure and 1.5 < x < =2 with monoclinic one. High lanthanum content leads to a low hygroscopicity of Yb_(2-x)La_xW_3O_(12). Negative thermal coefficients of the Yb_(2-x)La_xW_3O_(12) (0 <= x < =2) also vary from -7.78 x 10~(-6) K~(-1) to 2.06 x 10~(-6)K~(-1) with increasing substituted content of lanthanum.