J. Suchanicz

Electrostrictive strain and pyroeffect in the region of phase coexistence in Na0.5Bi0.5TiO3

Abstract Local maxima and other singularities distinguish the temperature range 200-320°C in the electrostrictive versus temperature graph of Na0.5Bi0.5TiO3, known from other experiments as a region of coexistence of phases. Investigation of the pyroeffect in virgin Na0.5Bi0.5TiO3 single crystals reveals the existence of polar microregions.

The low-frequency dielectric relaxation Na0.5Bi0.5TiO3 ceramics

Abstract Dielectric measurements, carried out on Na0.5Bi0.5TiO3 ceramics, revealed behaviour-dependency of both temperature and frequency. Two relaxation processes for frequencies from 20 Hz to 1 MHz are observed. The first relaxation process could be attributed to space charge. The second is low-frequency dipolar relaxation in the frequency range up to 100 kHz at 833 K and close to 0.5 kHz at 493 K, and could be related to the existence of polar regions in Na0.5Bi0.5TiO3.

Behaviour of Na0.5Bi0.5TiO3 ceramics in the a.c. electric field

Abstract The dielectric dispersion and influence of a.c. electric field strength on electric permittivity as well as the hysteresis loops for Na0.5Bi0.5TiO3 ceramics were investigated. The dipolar relaxation of Cole—Cole type below 1 MHz is observed. This relaxation significantly evolves with temperature and is connected with dynamics of polar regions. The increasing strength of a.c. electric field shifts the electric permittivity characteristic towards lower temperatures. This effect can be associated with the reactivation and reversal of the polar regions and mechanical stresses rising because of external field action. Examination of the low-frequency hysteresis loops reveals the occurrence of usual ferroelectric properties below 200°C. The occurrence of deformed hysteresis loops above 200°C is discussed in terms of electro-mechanical interaction between polar regions and nonpolar matrix.

Time dependence of electric permittivity in na0.5Bi0.5TiO3 single crystals

Abstract Performed measurements showed that in Na0.5Bi0.5TiO3 single crystals the long-time variation of the electric permittivity is connected with the existence of polar regions. The size and dynamics of the polar regions change with temperature. These regions may be ordered in an external electric field.

Investigations of the phase transitions in Na0.5Bi0.5TiO3

Abstract The dielectric, pyroelectric, electrostrictive, optical and thermal properties of Na0.5Bi0.5TiO3, in wide temperature range, particularly in the range of 200–340[ddot]C are presented and discussed. The results of investigations show the complicated nature of phase transition occurring in this material.

High temperature X-ray single crystal study of Na1/2Bi1/2TiO3

Abstract For a Na0.5B0.5TiO2 single crystal the intensity variation of the satellite reflection was measured by X-ray diffraction. No hystereses were observed for the phase transitions into both the rhombohedra1 and the tetragonal phases, however there is a coexistence of both phases in the range between ∼250°C and 300°C. By fitting the intensity vs. temperature curve for the tetragonal phase a critical exponent of 2β = 0.39(4) was obtained. The mean square displacement of the probability tensor of the high temperature cubic phase does not vary linearly with temperature which indicates that there is some disorder in this phase.

Peculiarities of phase transitions in Na0,5Bi0,5TiO3

Abstract The measurements of time dependencies of dielectrics and structural properties of Na0,5Bi0,5TiO3 have been performed. The results of this investigations confirm the prior data, that phase transition in Na0,5Bi0,5TiO3 from tetragonal to rhombohedral phase takes place in wide temperature range, in which both phases coexist. Moreover, this phase transition indicate the features of isothermal phase transformation.

Time evolution of the phase transformation in Na0.5Bi0.5TiO3

Abstract For Na0.5Bi0.5TiO3 single crystals the time dependencies of dielectric and structural properties were investigated. The obtained results reveal that phase transformation in Na0.5Bi0.5TiO3 between tetragonal and rhombohedral symmetries disclosed a time dependent character. This transformation was completed after about 300 minutes.

Some properties of NaO0.5Bi0.5TiO3

Abstract The specific heat of Na0.5Bi0.5TiO3 crystal in the temperature range 300–650 K and the changes of spontaneous polarization of Na0.5Bi0.5TiO3 ceramic in the temperature range 4.2–90 K were measured. The calorimetric measurements showed that the anomaly of specific heat exists in the temperature range where the phase transition rate from the rhomhedral phase to the tetragonal phase is utmost. From low-temperature pyroelectric effect a phonon wave number equal to 128 cm−1 was found to have the main share in the temperature changes of spontaneous polarization.

Dielectric and structural relaxation phenomena in Na0.5Bi0.5TiO3 single crystal

Abstract Dielectric permittivity studies of Na0.5Bi0.5TiO3 single crystals in a broad range of frequency up to 10 MHz and temperature 300—823 K are reported. In this temperature range dielectric dispersion below 1 MHz has been found. The obtained data were fitted to the Cole-Cole relation. The mean relaxation time τ is strongly temperature dependent (0.04 − 2.6 × 10−5 s). A remarkable hysteresis effect in the values of τ on cooling and heating took place. The Δe(T) dependence (the maximal value of Δe ∼ 400) is similar to the global e′(T) response at low frequency. An isothermal structural transformation in Na0.5Bi0.5TiO3 was observed by X-ray measurements. The order of the time in which the transformation takes place (∼300 minutes) corresponds to the time in which the strongest time evolution of electric permittivity and time changes of dielectric dispersion were detected.