B. Mroz

Anomalous changes in the pyroelectric and dielectric properties of LiKSO4 crystals

Abstract The pyro- and dielectric properties of LiKSO4 crystals, grown at 315 K by the dynamical method in isothermal conditions, were studied from 100 up to 300 K. The properties studied were found to exhibit anomalous temperature-dependent variations.

Anomalous changes in the piezoelectric and elastic properties of LiKSO4 crystals

Abstract The piezoelectric and elastic properties of LiKSO4 crystals, grown from aqueous solutions at 315 K, were studied in the temperature range from 100 up to 300 K by means of the dynamical series impedance method and by the low-frequency torsion pendulum technique. The parameters studied were found to exhibit anomalous temperature dependence. This suggests ferroelastic properties of LiKSO4 crystals in the temperature range below 190 K.

Double Brillouin scattering geometry

A procedure to optimize the collection of Brillouin spectra and to allow the simultaneous observation of phonons in two pairs of scattering geometries is proposed. The first geometry is used to observe the bulk phonons in right-angle- and back-scattering. This procedure reduces measurement time and requires the use of only one type of sample. The second geometry is used for simultaneous observation of bulk and surface phonons in transparent materials and can provide some valuable information on the relation between the bulk and surface elastic properties.

Ferroelasticity and internal friction in LiKSO4 crystals

Abstract The elastic properties and internal friction in LiKSO4. crystals were studied in the range from 100 K to 300 K using torsion vibration technique. The anomalies in these properties were found around 190 K and 250 K which are the phase transitions temperatures. Below 190 K LiKSO4 crystals were found to show ferroelastic properties. It was confirmed by mechanical hysteresis loops observed in the relation between strain and stress.

Low temperature ferroelastic phase transition in K3Na(CrO4)2

Abstract Dielectric, thermal and elastic properties of K3Na(CrO4)2 crystals, grown from aqueous solution at 315 K, were studied in the temperature range from 100 to 300 K. The studied properties were found to exhibit anomalous temperature behaviour. At 239 K a structural transition to the ferroelastic phase was observed. The ferroelastic character of this new phase was confirmed by direct observation of the domain structure reorientable under the effect of appropriate mechanical stress, and by a strong decrease in the torsion vibration frequencies related to the acoustic phonon softening. The morphology of the crystal studied and the lack of pyroelectric and piezoelectric properties together with the analysis of the domain structure observed in the polarized light for crystal plates oriented perpendicularly to the main crystallographic directions, lead to the conclusion that, at 239 K, K3Na(CrO4)2 undergoes a ferroelastic phase transition from the trigonal point group 3m to the monoclinic 2/m one.

High resolution Brillouin scattering studies of β-Gd2(MoO4)3; the bulk and surface phase transitions

We present here results of Brillouin scattering from bulk and surface phonons propagating in a well known ferroelectric–ferroelastic crystal β-Gd2(MoO4)3, in the temperature range covering the phase transition. Temperature dependences of the velocity of Rayleigh surface acoustic waves, propagating in a few planes of this crystal, have been calculated. The surface phonon velocities determined experimentally have been found to show a different character of temperature dependences, especially in the phase transition range.

Low-Temperature Phase Transition in K3Na(SO4)2 CRYSTAL

Raman, Brillouin and dielectric measurements have been undertaken to confirm the theoretically predicted low-temperature phase transition in the K3Na(SO4)2 crystal. As follows from our results this phase transition takes place at about 70 K.

Li 2 TiGeO 5 --A Novel Ferroelastic Crystal

Newly discovered phase transition at 233.5 K in the Li 2 TiGeO 5 crystal was studied with various physical methods. Results of dielectric, dilatometric, calorimetric, linear birefringence measurements, ferroelastic domain structure observations, the Brillouin scattering studies demonstrated a ferroelastic character of the second order transition, of 4/mmmFmmm Aizu type.

The ferroelastic phase transition in (NH4)4LiH3(SO4)4: Brillouin scattering studies and Landau theory modeling

High-resolution Brillouin spectroscopy was used to study the elastic properties of (NH4)4LiH3(SO4)4 (ALHS). The temperature dependences of eleven Brillouin modes from acoustic phonons, propagating in the (100), (001), (110) and (101) directions, were measured in the temperature range from 140 to 300 K. The greatest elastic anomaly was observed in the plane perpendicular to the (001) crystallographic axes. The soft elastic constant c2S was found to vanish at T approximately=232 K. A Landau-type free-energy expansion is postulated and discussed, in order to explain the observed elastic anomalies.

Raman studies of lattice vibrations in Rb4LiH3(SO4)4 and K4LiH3(SO4)4 single crystals

The Raman scattering technique was used to study lattice vibrations in single crystals of K4LiH3(SO4)4 from 100 to 295 K covering their 4 to 2 structural phase transitions. All of the Raman modes of K4LiH3(SO4)4 were found not to be affected by the transition. In the case of Rb4LiH3(SO4)4, a slight softening of the B mode (at 31 cm-1) was observed in the paraelastic phase.