Diffuse phase transition and possible dipole glass in perovskite solid solutions

Abstract

Various phases and associated phase transitions between them have been investigated in the complex pseudobinary perovskite solid solutions, $(1-x)Pb (Fe \frac{1}{2} Ta \frac{1}{2}) O_3 -xPb(Mg \frac{1}{2} W \frac{1}{2}) O_3$ and $(1-x) Pb (Fe \frac{1}{2} Nb \frac{1}{2}) O_3-xPb(Mg \frac{1}{2} W \frac{1}{2}) O_3$, with dielectric susceptibility, differential scanning calorimeter, and thermal expansion measurement. The apparent antiferroelectric transition temperature decreases linearly with the increase of the solute ferroelectric $Pb(Fe \frac{1}{2} Ta \frac{1}{2})$ concentration in the high antiferroelectric $Pb(Mg \frac{1}{2} W \frac{1}{2}) O_3$ concentration range. Further increase of $Pb(Fe \frac{1}{2} Ta \frac{1}{2}) O_3$ concentration past x=0.82 no longer decreases the transition temperature linearly and the apparent transition temperature in the mid composition range of the solid solution remains relatively constant with respect to a compositional change. In the high $Pb(Fe \frac{1}{2} Ta \frac{1}{2}) O_3$ concentration range, transition temperature decreases linearly with the increase of $Pb(Mg \frac{1}{2} W \frac{1}{2}) O_3$ until x=0.2 is reached. This transition behavior is in good agreement with the so called GLP (glass like phase) random bond model or the phase diagram of $Rb_{1-x}(NH_4)_x H_2PO_4$ which hints that the low temperature phase in the mid composition range is possibly the dipole glass phase. Using this observation and the concept of percolation and proposed block Hamiltonian, the author shows that the normal antiferroelectric or ferroelectric phase does not appear for $0.20<x<0.82$. The percolation thresholds for the possible dipole glass are therefore pinned at x=0.2 and x=0.82. Specific heat anomaly and thermal expansion discontinuity diminish with the increasing ferroelectric content in the antiferroelectric range, and then eventually disappear at the threshold concentration x=0.82. Low frequency dispersion ($f<10kHz$) of the dielec...