Dielectric relaxation and polar structures of BaTi1−xSnxO3 ceramics, x=0.10–0.20, are investigated by means of dielectric spectroscopy and piezoresponse force microscopy. A transition regime between “normal” ferroelectric and relaxor behaviors is encountered. In the compositions with x=0.10, a complex domain pattern confirming the ferroelectric state is observed. Strong dielectric relaxation around Tm is attributed to domain wall motion. On the other hand, the dielectric spectra in the sample with x=0.20 are very similar to those observed in relaxor ferroelectrics. Analysis of the relaxation spectra at the intermediate concentration, x=0.15, reveals both domain wall response and an additional contribution related to mesoscale polar structures. The appearance of relaxor behavior in BaTi1−xSnxO3 is discussed within the framework of the random field model.

A high, rounded peak of the permittivity, ${\mathrm{\varepsilon }}_{\max }^{\prime }$≈6×${10}^4$, at T≈18 K evidence a percolative-type phase transition into a random-field-induced ferroelectric domain state of the doped system ${\mathrm{Sr}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Ca}}_{\mathrm{x}}$ ${\mathrm{TiO}}_3$ (x=0.007). Dispersion measurements of the permittivity reveal strong polydispersivity of the system. Deviations from Arrhenius behavior below T=11 K indicate the onset of dissipative quantum tunneling of the ${\mathrm{Ca}}^{2+}$ dipoles between their different off-center positions. Anomalies in both the linear and the nonlinear dielectric permittivity are explained by the presence of two different dissipative cluster contributions. They are attributed to the reorientation of ${\mathrm{Ca}}^{2+}$-centered polar nanometer-scale regions within ferroelastic single domains of the system and to their interaction with coherent acoustic quantum fluctuations of the host lattice, respectively.

Polarized Raman, IR, and time-domain THz spectroscopy of orthorhombic lead zirconate single crystals have yielded a comprehensive picture of temperature-dependent quasiharmonic frequencies of its low-frequency phonon modes. It is argued that these modes primarily involve vibrations of Pb ions and librations of oxygen octahedra. Their relation to phonon modes of the parent cubic phase is proposed. Counts of the observed IR and Raman active modes belonging to distinct irreducible representations agree quite well with group-theory predictions. Analysis of the results yields insight into the phase transition mechanism, involving a soft ferroelectric branch coupled by a trilinear term to another two oxygen octahedra tilt modes.

Complex as-grown nanodomain patterns are studied with piezoresponse force microscopy in ${\mathrm{Sr}}_x{\mathrm{Ba}}_{1-x}{\mathrm{Nb}}_2{\mathrm{O}}_6$ single crystals at variant $\mathrm{Sr}∕\mathrm{Ba}$ molar ratios, $0.4⩽x⩽0.75$. They reflect random-field Ising model (RFIM) ferroelectricity, which crosses over into relaxor behavior at increasing $x$. This is explained by an increase of the polar disorder within the open tungsten-bronze crystal structure giving rise to enhanced quenched random electric fields at simultaneous decrease of the ferroelectric ordering temperature. The strongly anisotropic domain shapes, their fractal properties and size distributions, and their metastable occurrence above the nominal Curie temperature are in accordance with predictions for the RFIM.