Sr1-xCaxTiO3: An XY Quantum Ferroelectric with Transition to Randomness

A series of twenty homogeneous Sr1-xCaxTiO3 mixed crystals has been measured dielectrically between 4.2 and 300 K. In the tetragonal phase, the dielectric constant perpendicular to the c axis becomes peaked above xc=0.0018, the quantum mechanical onset for displacive ferroelectricity. The polarization Šc can be switched between the two equivalent a axes, i.e., the system is an XY, n=2, quantum ferroelectric. Above xr=0.016±0.002, the μ(T) peaks round in a distinct manner which we attribute to the onset of a random-field-induced domain state. © 1984 The American Physical Society.