Investigation of structural transition in molybdates CuMo1-xWxO4 prepared by polymeric precursor method

Solid solutions (CuMo1-x WxO4 where 0 <= x <= 0.12) were synthesized by using a polymeric precursor method. The crystallization process of the polymeric precursors was investigated using TG-DTA, FTIR and XRD techniques. Crystallization of the CuMo1-xWxO4 powders was detected at 300 degrees C, and entirely completed at 420 degrees C. XRD patterns revealed that the polymorphic variety was dependent upon the tungsten content. For x <= 0.075, the solid solutions were isostructural to alpha-CuMoO4 whereas, for 0.075 < x <= 0.12, they were isostructural to gamma-CuMoO4. The obtained homogeneous powders are constituted of relatively spherical grains with sizes in the range 0.5-2.0 mu m. The phase transition of the as-synthesized CuMo1-xWxO4 powders was investigated by X-ray diffraction at elevated temperature and dilatometry. The temperature of the structural transition gamma -> alpha during heating was dependent upon the tungsten content.