Brillouin light scattering in niobium doped lead zirconate single crystal.

Brillouin light scattering experiments were performed for lead zirconate single crystals doped with niobium. Special attention was paid to the elastic mode softening near phase transition temperatures. The results are compared with data obtained by Raman light scattering experiments. We observed that the interaction between acoustic and optic modes is responsible for symmetry breaking far above TC, leading to polar regions' appearance. No changes in the acoustic mode frequency and its damping are observed at TC, where ε(T) exhibits a maximum value. The absence of these changes and the central peak observed in Raman experiments suggest that the phase transition at TC is mainly of the order-disorder type. The origin of other phase transitions is discussed as well.

Local properties and phase transitions in Sn doped antiferroelectric PbHfO3 single crystal.

Pb(Hf1-x Sn x )O3 single crystals with x = 0.23 were characterized using single-crystal x-ray diffraction in the wide temperature range. The information on the structure of two intermediate phases, situated between low temperature antiferroelectric and high temperature paraelectric phases, has been obtained. The lower-temperature intermediate AFE2 phase is characterized by incommensurate displacive modulations in the Pb sublattice. The higher temperature intermediate IM phase is characterized by rotations of oxygen octahedra, primarily in the form of anti-phase tilts, which are also present in the lower-temperature AFE2 phase. For the same crystal, 119Sn Mossbauer effect in the temperature range from 300 K to 600 K has been used to study phase transitions mechanism. Two kinds of quadruple splitting have been found. It implies that two different environments of the central Sn ion exist. The observed two kinds of quadruple splitting do not disappear in the whole investigated temperature range which confirm that even far above T C the structure of paraelectric phase is locally non-centrosymmetric.

Crystallographic and optical study of PbHfO3 crystals.

The symmetry of the intermediate high-temperature phase of PbHfO3 has been determined unambiguously to be orthorhombic using a combination of high-resolution X-ray diffraction and birefringence imaging microscopy measurements of crystal plates. While lattice parameter measurements as a function of temperature in the intermediate phase are consistent with either orthorhombic or tetragonal symmetry, domain orientations observed in birefringence imaging microscopy measurements utilizing the Metripol system are only consistent with orthorhombic symmetry with the unit cell in the rhombic orientation of the pseudocubic unit cell.

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.

Phase transition of displacive type in PbZr(0.94)Ti(0.06)O(3).

In this paper the electrostrictive properties above T(εmax), represented by the field-related M and polarization-related Q coefficients, have been reported for Pb(Zr(1-x)Ti(x))O(3) ceramics with x = 0.03-0.10. Among M(11)(T) and Q(11)(T) dependences, those found for Pb(Zr(0.94)Ti(0.06))O(3) have been clearly distinguished. In this case, the Q(11)(T) dependence is linear in the whole temperature range above T(εmax). Experimental and theoretical analysis of the M(11)(T) dependences has shown that the phase transition to the ferroelectric phase in Pb(Zr(0.94)Ti(0.06))O(3) ceramics seems to be of the displacive type.