Enhanced ionic conductivity in pyrochlore and fluorite mixed phase yttrium-doped lanthanum zirconate

A series of yttrium-doped lanthanum zirconate (La1−xYx)2Zr2O7 (0 ≤ x ≤ 1) bulk samples were prepared and their ionic conductivities were studied by impedance spectroscopy. It is found that intermixing of Y and La ions increases the conductivity of the end members pyrochlore-type La2Zr2O7 and fluorite-type Y2Zr2O7. Highest conductivity which is 2-3 orders of magnitude higher than that of La2Zr2O7 and Y2Zr2O7 is achieved in a two-phase sample which consists of both pyrochlore and fluorite phases. The enhanced conductivity in the two-phase sample is attributed to the presence of the pyrochlore-fluorite phase boundary, which has higher conductivity than the pyrochlore and the fluorite phase grains. The effect of the conductive phase boundary has been confirmed by a 2-dimensional finite element modelling.