Quantum paraelectric and induced ferroelectric states in SrTiO3

Nominally pure SrTiO3 has been studied by dielectric spectroscopy using small (linear regime) as well as large electrical fields (non-linear regime) up to 1 kV mm(-1). In addition measurements of the specific heat and its field-dependent contribution have been carried out. The field dependence of the dielectric constant and the specific heat can be well described by the transverse Ising Hamiltonian including tunnelling and external field terms. It gives evidence for the existence of polar clusters at low temperatures which are supposed to be associated with the quantum paraelectric state below T-q approximate to 37 K in accord with recent free-energy calculations. The low-field third-harmonic susceptibility which measures the polar correlations exhibits anomalies near T-q. At high fields an aligned domain state is induced. These results as well as those on the remanent polarization and the dielectric loss have allowed us to deduce a complex E, T-phase diagram. The assignment of the various phases is discussed in connection with the recent proposal of the appearance of a macroscopic quantum state.