Fast ion conduction in the defect pyrochlore system KBxW2−xO6(B = Al,Ti and Ta)

K⁺ ionic conductivity has been measured by the complex impedence method for the defect pyrochlore type compounds of the general formula K(B^y+_xW⁶⁺_2?x)O₆, (x=1/(6?y)) where B=Al³⁺, Ti⁴⁺ and Ta⁵⁺. Thermogravimetric analysis showed the compounds to be hydrated at room temperature with from ∽0.2 mole for the Al compound to ∽1 mole of water for the Ta substituted phase. There is a correlation between the lattice parameter and amount of water present in the cavities. The ionic conductivity of 5.2×10^?3ω^?1cm^-1 at 300°C for KAl_0.33W_1.67O₆ is found to be best among known KB₂O₆ type pyrochlores. High ionic conductivity has been explained on the basis of occupancy of K⁺ ions in the available sites and polarization of the B₂X₆ network.