First Order Phase Transition in Quantum Paraelectrics

We discuss the nature of pressure induced phase transitions in standard Quantum Paraelectrics near quantum critical point. From a microscopic theory we first show that near the critical point the transition temperature $T_c(p)$ varies as $ (1-p/p_c)^\xi$ with $\xi={1/2}$. Within the Landau scheme, it is shown that for $\xi \leq 1$, a condition satisfied by most quantum paraelectrics the transition is inevitably first order in nature. The present analysis is valid for non-polar impurity induced transitions in these materials and is supported by some recent experiment.