Phase transition and UV-vis spectra of Al₂Mo₃O₁₂-related compounds

Abstract

(Co, Zr)-substituted Al₂Mo₃O₁₂-related compounds with various chemical compositions were synthesized by a solid-state reaction. All of the synthesized compounds with a single phase were identified as Al₂Mo₃O₁₂ or Al₂W₃O₁₂-related compounds by XRD. High-temperature XRD and DTA analysis clarified that the structural phase-transition temperature of the synthesized Co_0.05Zr_0.05Al_1.9Mo_3-yW_yO₁₂ (0≦y≦3) decreased with increasing the W content. High temperature XRD also revealed that the synthesized Co_0.05Zr_0.05Al_1.9Mo_0.9W_2.1O₁₂ had a discontinuous thermal expansion around 333 K. The UV-vis-NIR spectra of the synthesized compound at each temperature of 303 to 373 K were investigated. Although the diffusion-reflectance ratio almost unchanged until 333 K, it began to decrease at 343 K. The spectral change corresponded to the discontinuous thermal expansion of the synthesized Co_0.05Zr_0.05Al_1.9Mo_0.9W_2.1O₁₂. Furthermore, it was found that the synthesized (Co, Zr)-substituted compounds had the optical property with the ΔL* luminance decreasing in the range of R.T. to 373 K due to its structural phase transition.