Jirka Hlinka

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<T<400 K a highly anisotropic quasielastic diffuse scattering is observed. Above 400 K this scattering disappears. Its main features can be reproduced by the model of inhomogeneous lattice deformations caused by inclusions of a tetragonal phase into a rhombohedral or monoclinic phase. This observation supports the idea that PZT at its morphotropic phase boundary is essentially structurally inhomogeneous.

Resolved E-symmetry zone-centre phonons in LiTaO3 and LiNbO3

E-symmetry optical phonons at the Γ point of LiNbO3 and LiTaO3 were experimentally resolved in spectra measured by infrared and Raman spectroscopy. For this purpose, congruent and nearly stoichiometric crystals of LiNbO3 and LiTaO3, and mixed LiNb1−xTaxO3, crystals were studied. The results show that some of the E modes have weak intensities in Raman or infrared spectra. Thus the complete assignment of E-symmetry modes has been achieved by comparing Raman and infrared data. In addition, this assignment has been confirmed by Raman measurements at low temperatures.

Mobility of Ferroelastic Domain Walls in Barium Titanate

Phenomenological theory of dissipation-limited motion of ferroelectric domain walls under external bias field is applied to the case of 90-degree domain wall in a defect-free BaTiO3 crystal. Quantitative estimation for the limiting mobility (μE∼ 5 × 10− 4 m2/Vs at room temperature) is obtained in the framework of Landau-Khalatnikov equation of motion and generalized Ginzburg-Landau-Devonshire model, using model parameters estimated from results of independent experiments.

Order-disorder versus soft mode behaviour of the ferroelectric phase transition in

This paper explains the coexistence of the displacive and the order-disorder features of the ferroelectric phase transition in crystals. Both have been observed in experiments. The height of the potential barrier hindering the order parameter fluctuations, estimated from experimental data, shows that the phase transition in is actually very close to the theoretical case of the order-disorder versus displacive crossover. Moreover, previously performed model calculations can be used for the analysis of the temperature dependence of dielectric susceptibility and other physical properties which do not obey the predictions of standard Landau theory.

A neutron diffuse scattering study of PbZrO3 and Zr-rich PbZr1–xTixO3

A combined neutron diffuse scattering study and model analysis of the antiferroelectric crystal PbZrO3 is described. Following on from earlier X-ray diffuse scattering studies, supporting evidence for disordering of oxygen octahedral tilts and Pb displacements is shown in the high-temperature cubic phase. Excess diffuse scattering intensity is found at the M and R points in the Brillouin zone. A shell-model molecular dynamics simulation closely reproduces the neutron diffuse scattering pattern. Both in-phase and antiphase tilts are found in the structural model, with in-phase tilts predominating. The transition between disordered and ordered structure is discussed and compared with that seen in Zr-rich PbZr1−xTixO3.

Computer Simulations of Frequency-Dependent Dielectric Response of 90-Degree Domain Walls in Tetragonal Barium Titanate

Dissipation-limited motion of 90-degree domain walls in a defect-free BaTiO 3 crystal under external electric field is investigated by computer simulations in the framework of Landau-Khalatnikov equation of motion and generalized Ginzburg-Landau-Devonshire model. Domain wall mobility determined directly from simulation of frequency dependent dielectric response is shown to be in a reasonable agreement with simple analytical estimates.

Electric-field influence on the neutron diffuse scattering near the ferroelectric transition of Sr0.61Ba0.39Nb2O6

ABSTRACT Uniaxial relaxor ferroelectric Sr0.61Ba0.39Nb2O6 single crystal has been investigated in the vicinity of its phase transition using neutron scattering and dielectric spectroscopy. A global-type thermal hysteresis is evidenced by both techniques in the ferroelectric phase and up to about 15 K above Tc. In addition, a part of the transverse neutron diffuse scattering in the 001 Brillouin zone, presumably related to static nanodomain structure, can be suppressed by prior poling the crystal in electric field of 3 kV/cm. The remaining part of the transverse neutron diffuse scattering and the real part of permittivity show a similar temperature dependence. The temperature position of the maximal scattering intensity Tmax depends significantly on the scattering wave vector. Tmax shifts monotonically to higher temperature with the increasing wave vector in all investigated cooling and heating regimes. It is concluded that the critical fluctuations have space correlations which depend on frequency and wave vector.

Domain Walls of BaTiO3 and PbTiO3 Within Ginzburg-Landau-Devonshire Model

The origin of the considerable thickness of the 90-degree head-to-tail domain wall in BaTiO 3 is discussed in the framework of the phenomenological Ginzburg-Landau-Devonshire theory. For this purpose, domain wall widths of 90-degree and 180-degree domain walls in BaTiO 3 and PbTiO 3 are compared. It is argued that the ratio of the 90-degree and 180-degree domain wall widths is primarily determined by the polarization gradient term, which happens to be strongly anisotropic in the BaTiO 3 case.

Wanted: Amplitudon mode in raman spectra of BCCD

Abstract Polarised Raman scattering by the low-frequency totally symmetric modes in modulated phases of deuterated Betaine Calcium Chloride Dihydrate was measured in order to identify the amplitudon mode. The spectra are similar to those of non-deuterated compound. Detailed analysis based on fitting the coupled-mode lineshape to the experimental data allows to suggest the temperature dependence of the bare amplitudon mode, as well as to ascribe the previously observed sharp intensity minimum to the coupling of the amplitudon with the activated transverse acoustic mode.

Amplitudon Mode in Deuterated Thiourea by Raman Scattering

Polarised Raman study of the amplitudon mode in the deuterated thiourea enabled us to determine temperature dependence of both damping and frequency of the amplitudon mode. In combination with recent inelastic neutron scattering experiment [J. Hlinka, J. Petzelt, B. Brezina and R. Currat: Phys. Rev. B 66, 132302 (2002).], the dispersion of the phason mode oscillatory frequency could be estimated.