Synthesis, structure and negative thermal expansion of cubic zrw_(2-w)v_xo_(8-x/2) solid solutions

摘要

A novel cubic ZrW_(2-x)V_xO_(8-x/2) solid solution series was found to possess similar negative thermal expansion property like the extensively studied ZrW_2O_8. A tetragonal hydrate ZrW_(2-x)V_xO_(7-x/2)(OH)_2(H_2O)_2 up to x = 0.30 was first prepared through acidic steam hydrothermal synthesis, this precursor dehydrates at moderate temperature and converts to an intermediate orthorhombic phase then transforms to corresponding solid solutions at higher temperature. At room temperature cubic ZrW_(2-x)V_xO_(8-x/2) (x = 0-0.24) has α-ZrW_2O_8 type and ZrW_(1.70)V_(0.30)O_(7.85) has p-ZrW_2O_8 type disordering. X-ray diffraction, neutron diffraction and Raman spectroscopy studies support an average crystal structure model of ZrW_(2-x)V_xO_(8-x/2) as a superposition of respective cubic ZrW_2O_8 and ZrV_2O_7 structures. The lattice parameters of cubic ZrW_(2-x)V_xO_(8-x/2) solid solutions, the value of orientation order parameter ω and order-disorder phase transition temperature of the solid solutions all decrease with increasing substitution content x. The maximum solid solubility of cubic ZrW_(2-x)V_xO_(8-x/2) solid solution reaches 16% according to the Vegard's law.