PbMg1/3Nb2/3O3dielectric aging in the freezing temperature region.

Aging of the relaxors and PbMg1/3Nb2/3O3in particular was extensively studied in last two decades. Most of the results were related to the low temperature glass-like region. No systematic data around the freezing temperatures were reported. To cover this still missing information we have studied the evolution of the dielectric spectra in the broad frequency region from 10-1 Hz to 106 Hz both below and above the freezing temperatureTf≈240 K. Below freezing temperature the existence of the earlier reported waiting time-frequency scaling at frequencies below ≈50 Hz is confirmed. At higher frequencies this deviation from the scaling is observed that can be tentatively attributed to the complexity of the relaxing entities. AboveTfaging is observed only in the restricted frequency interval below the maximum of the dielectric loss spectrum. The observed effect can be attributed to the hardening and narrowing of the dielectric loss spectra and decreasing of the dielectric strength with time. The explanation is proposed based on the concept of the creation of the degenerate polar nanoregions covering several chemically ordered regions (COR) (multi PNRs-MPNRs). These MPNRs are large compare to the PNRs located at the single CORs and some of them may become frozen resulting in the described spectra changes.

Structural heterogeneity and diffuse scattering in morphotropic lead zirconate-titanate single crystals.

Complementary diffuse and inelastic synchrotron x-ray scattering measurements of lead zirconate-titanate single crystals with composition near the morphotropic phase boundary (x=0.475) are reported. In the temperature range 293 K

Critical scattering and incommensurate phase transition in antiferroelectric PbZrO3 under pressure.

Antiferroelectric lead zirconate is the key ingredient in modern ferroelectric and piezoelectric functional solid solutions. By itself it offers opportunities in new-type non-volatile memory and energy storage applications. A highly useful and scientifically puzzling feature of this material is the competition between the ferro- and antiferroelectric phases due to their energetic proximity, which leads to a challenge in understanding of the critical phenomena driving the formation of the antiferroelectric structure. We show that application of hydrostatic pressure drastically changes the character of critical lattice dynamics and enables the soft-mode-driven incommensurate phase transition sequence in lead zirconate. In addition to the long known cubic and antiferroelectric phases we identify the new non-modulated phase serving as a bridge between the cubic and the incommensurate phases. The pressure effect on ferroelectric and incommensurate critical dynamics shows that lead zirconate is not a single-instability-driven system.

Lattice dynamics in the paraelectric phase of PbHfO3 studied by inelastic x-ray scattering.

We report the results of an inelastic x-ray scattering study of the lattice dynamics in the paraelectric phase of the antiferroelectric lead hafnate PbHfO3. The study reveals an avoided crossing between the transverse acoustic and transverse optic phonon modes propagating along the [1 1 0] direction with [1 -1 0] polarization. The static susceptibility with respect to the generally incommensurate modulations is shown to increase on cooling for the entire Γ-M direction. We consider different approaches to the data analysis that correspond to different models for the temperature evolution of the dynamic susceptibility function. A number of similarities and differences between the lattice dynamics of PbHfO3 and PbZrO3 are described.

The origin of antiferroelectricity in PbZrO3.

Antiferroelectrics are essential ingredients for the widely applied piezoelectric and ferroelectric materials: the most common ferroelectric, lead zirconate titanate is an alloy of the ferroelectric lead titanate and the antiferroelectric lead zirconate. Antiferroelectrics themselves are useful in large digital displacement transducers and energy-storage capacitors. Despite their technological importance, the reason why materials become antiferroelectric has remained allusive since their first discovery. Here we report the results of a study on the lattice dynamics of the antiferroelectric lead zirconate using inelastic and diffuse X-ray scattering techniques and the Brillouin light scattering. The analysis of the results reveals that the antiferroelectric state is a 'missed' incommensurate phase, and that the paraelectric to antiferroelectric phase transition is driven by the softening of a single lattice mode via flexoelectric coupling. These findings resolve the mystery of the origin of antiferroelectricity in lead zirconate and suggest an approach to the treatment of complex phase transitions in ferroics.