Domain state properties of weakly doped SrTiO₃:Ca

Abstract

Linear birefringence, Raman scattering, dielectric, and second-harmonic generation (SHG) studies on Sr_1-xCa_x TiO₃, x=0.007, reveal a smeared transition into a ferroelectric-improper ferroelastic phase at T_c=18 K. Polar disorder persists on a nanometric scale as a consequence of the percolative nature of the transition under the constraint of quenched random fields. The ferroelectric nanoregions exhibit superparaelectric response to an external ac field and interact piezoelectrically with acoustic quantum fluctuations of the host lattice, SrTiO₃. Their morphology is probed by interface SHG, the angular dependence of which is incompatible with the global orthorhomic symmetry of the ferroelectric phase.

Key Words:

• Quantum paraelectric
• linear birefringence
• dielectric permittivity
• Raman scattering
• secondharmonic generation
• polar domains