Synthesis and characterization of negative thermal expansion HfW2−xVxO8−x/2 solid solutions

Cubic HfW2−xVxO8−x/2 (c-HfW2−xVxO8−x/2) solid solutions, where x is up to 0.34, were synthesized using a process of acidic steam hydrothermal (ASH)-thermal dehydrating precursors. The process is studied detailedly. The results reveal tetragonal HfW2−xVxO7−x/2(OH)2(H2O)2 precursors are synthesized after ASH treatment and they produce orthorhombic HfW2−xVxO8−x/2 in dehydrating. Then c-HfW2−xVxO8−x/2 are obtained at higher temperature. The crystal structures of c-HfW2−xVxO8−x/2 are characterized as α-HfW2O8 and β-HfW2O8 structure for 0≤x≤0.30 and x=0.34, respectively. All the c-HfW2−xVxO8−x/2 show excellent negative thermal expansion property. The relationships between the properties, such as ordered degree parameter, crystal lattice parameter, phase transition temperature and linear average thermal expansion coefficient, and the V content are also discussed.