SrTiO3: An intrinsic quantum paraelectric below 4 K

The dielectric constants ε110 and their change with uniaxial 11̄0 stress in monodomain 001 SrTiO3 samples have been measured as a function of temperature. Between 4 K and 0.3 K these quantities are independent of temperature. In one sample ε(T) was measured to 0.035 K and found to be constant. This proves the quantum-mechanical stabilization of the paraelectric phase below 4 K with a very high dielectric constant ε. The crossover from classical to quantum behavior on lowering the temperature is discussed, and it is shown that the coupling of the ferroelectric mode to acoustic ones is important. The ε(T) dependence is compared to earlier and recent theories. The former, yielding a coth (ΩkT) term, are found to be inadequate for the crossover region. A recent biquadratic ferroelectric mode-coupling theory fits the data better. © 1979 The American Physical Society.