Irena Jankowska-Sumara

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.

Antiferroelectric phase transitions in single crystals PbZrO3:Sn revisited

This paper is a review of earlier results which have been completed with recent investigations on the nature and sequence of phase transitions evolving in the antiferroelectric PbZr1–xSnxO3 single crystals (0 < x < 0.35). It was found that these crystals undergo several first-order phase transitions. To investigate these transitions, five experimental methods were used to characterize the crystal properties: birefringence, Raman light scattering, dielectric, thermodynamic and electromechanical methods, and the atomic force microscopy-piezoresponse force microscopy (AFM-PFM) method to focus also on nanoscale properties. Temperature dependencies have been tentatively measured in a wide range, including a region above TC, where precursor dynamics is observed in the form of non-centrosymmetric regions existing locally in crystal lattices. New experimental data (Raman light scattering and PFM) are presented mainly to revise the phase diagram and, at the same time, to complement other studies on the problem of pre-transitional effects. The phase transition mechanism in PbZr1–xSnxO3 is discussed taking into account the incommensurability of crystal lattices, ferroelastic behavior of multicell cubic phases, electric field influence on antiferroelectric to ferroelectric transformation, and flexoelectric effect.

Phase Transitions in PbZr 1−x Sn x O3 Single Crystals

The phase diagram of PbZr 1−xSnxO3 (0 ≤ x ≤ 0.4) has been investigated for single crystals by dielectric and optic measurements. The stability of the antiferroelectric Pbam phase was observed for 0 ≤ x ≤ 0.05. Au Sn4+ content above x > 0.05 induces another antiferroelectric P2221 phase. At concentrations higher than x = 0.3 a phase of ferroelectric character (R3m) becomes stable. Above x = 0.15 the crossover from sharp to diffuse behaviour of the phase transition takes place. The changes in the phase transitions character and the mechanism leading to the appearance of new anti- and ferroelectric phases are discussed.

Raman scattering in pure and Ti-doped PbHfO3 antiferroelectric crystals

Raman scattering investigations were performed over a large temperature range from 10 to 700 K on pure and Ti-doped PbHfO3 single crystals. The modifications of the Raman spectra were precisely observed in the vicinity of two structural phase transitions occurring in the crystal: an antiferroelectric (A1) to antiferroelectric (A2) phase transition at 436 K and antiferroelectric (A2) to paraelectric (P) phase transition at 484 K. The characteristic parameters of the Raman structures were determined throughout the whole phase transition sequence. The softening of the two lowest-frequency Raman lines seems to have a dominating influence on the slight increase in dielectric permittivity at the A1 to A2 phase transition in both pure and doped samples suggesting a displacive nature for this transition. For Ti-doped samples the form of the A1 to A2 transition is smoother than for undoped samples while the A1 to P transition appears to be unaffected by doping with Ti.

Dielectric and Pyroelectric Properties of Pb((Fe1/3Sb2/3)xTiyZrz)O3 Ceramics

The temperature dependence of pyroelectric and dielectric properties was measured for polycrystalline Pb[(Fe 1/3 Sb 2/3 ) x Ti y Zr z ]O 3 where x = 0.1, y = 0.4–0.5 and x + y + z = 1 in the temperature range from 300 K to 650 K. The total pyroelectric effect was determined by measuring the pyroelectric current. The changes of dielectric permittivity ϵ′ confirmed the temperature points of the phase transitions occurring in Pb[(Fe 1/3 Sb 2/3 ) x Ti y Zr z ]O 3 . Two diffused phase transitions are observed in the system. The paraelectric-ferroelectric transition near T m is demonstrated by a maximum of dielectric permittivity. The anomaly on ϵ′(T) dependence near 530 K for y = 0.43 speaks for ferroelectric(tetragonal)-ferroelectric(rhombohedral) phase transition. For y > 0.44 this transition is definitely diffuse and the coexistence of tetragonal and rhombohedral phases is observed in a wide temperature range around 530 K. The temperature dependences of the pyroelectric coefficient confirmed the diffuse character of phase transitions in Pb[(Fe 1/3 Sb 2/3 ) x Ti y Zr z ]O 3 .

Pre-Transitional Effect and an Intermediate Phase in the Antiferroelectric PbZr0.80Sn0.20O3 Single Crystal

The temperature dependences of electrostrictive strain and birefringence for a PbZr0.80Sn0.20O3 single crystal have been measured with a high accuracy close to the high temperature phase transitions into the paraelectric phase. Characteristic features are the existence of local maxima on M 11(T) dependence and irregular Δn(T) dependences that indicate existence of an intermediate phase between the antiferroelectric and paraelectric phase. Above TC a local Δn(T) maximum appears on heating caused probably by interactions of polar regions embedded in the non-polar cubic matrix. The existence of these regions could be accounted for by a disorder of Sn ions in the lead zirconate lattice.

Soft and hybrid-doped Pb(Zr,Ti)O3 ceramics under stress, electric field, and temperature loading

We investigated the influence of uniaxial pressure (0–1000 bars) applied parallelly or perpendicularly to the ac or dc electric field (in a one-dimensional or two-dimensional manner) on dielectric and ferroelectric properties of selected soft and hybrid-doped PZT ceramics (1 mol. % Gd, 1 mol. % La and 1 mol. % (La+Fe)-doped Pb(Zr0.54Ti0.46) O3). Applying uniaxial pressure leads to a reduction of the peak intensity of the electric permittivity (ɛ), of the frequency dispersion, and of the dielectric hysteresis. The peak intensity of ɛ becomes diffused and shifts to a higher temperatures with increasing pressure. Simultaneous application of uniaxial pressure and dc electric field (perpendicular to each other) in the poling process implies in improvement of the ferroelectric properties, indicating a new possibility for poling materials with a high coercive field and/or high electric conductivity. It was also found that simultaneous application of uniaxial pressure and dc electric field (perpendicular to each ...

Dielectric and optic properties of PbZr1−xSnxO3 single crystals (0≤x≤0.2)

Temperature variations of linear birefringence Δn have been studied on flux-grown pure PbZrO3 and PbZr1−xSnxO3 (PZS-for short) single crystals (x=0.01, 0.025, 0.05, 0.075, 0.1, 0.15, 0.2) in the range of temperature between 80 and 500 K. Linear birefringence was measured by means of polarising microscope using Senarmonte compensator. In the same samples changes of dielectric permittivity e′ was also measured in order to confirm temperature points of the phase transitions occurring in PZS crystals. In PZS with x≥0.05, two phase transitions Tc (P-paraelectric to A2-antiferroelectic) and T1 (A1 to A2 both antiferroelectric) were detected. For the concentrations of x<0.05 PZS undergoes one phase transition (P–A1) as in pure PbZrO3. The optical studies were mainly performed in order to determine the character of the phase transitions in PZS.

Antiferroelectric and ferroelectric phase transitions of the displacive and order-disorder type in PbZrO3 and PbZr1-xTi x O3 single crystals

Abstract For PbZrO3 and PbZr0.99Ti0.01O3 single crystals the first order Raman light scattering spectra in the paraelectric phase have been analysed. In lead zirconate two kinds of crystals, with and without a transient phase, were investigated. It was found that temperature dependence of the defect-induced soft mode frequency in the paraelectric phase has a negligible contribution to the low-frequency dielectric response. From the point of view of strong dielectric relaxation in the range of 106–109 Hz, which originates in a disorder of the lead sites, crossover of the order-disorder and displacive type of antiferroelectric phase transition in lead zirconate is considered: the phase transition mechanism is neither purely displacive nor order-disorder. Contribution of physical phenomena responsible for the ε(ω,T) dielectric response at low frequencies of an external electric field are described.

Dielectric spectroscopy of the antiferroelectric PbHfO3

Abstract Dielectric studies of a PbHfO3 (lead hafnate) single crystal undergoing two structural phase transformations at about 163°C (436 K) and 209°C (482 K) were performed in broad frequency and temperature range. Special attention was paid to the paraelectric phase. Investigations of the complex dielectric permittivity in the frequency range 10 Hz to 10 MHz revealed two relaxations of polydispersive and nearly monodispersive (Debye-like) character connected with space charge behaviour. In the frequency range of 106-109Hz a polar relaxation mode has been found and related to a disorder in the Pb sublattice. Temperature dependence of the dielectric step of this relaxation corresponds to a sharp anomaly of the ε(T) function at the phase transition from the paraelectric to antiferroelectric state. Analysis of temperature evolution of the first order Raman light scattering spectra showed existence of a soft line at this transformation. Crossover of the displacive and order-disorder type of the transformation mechanism is thus postulated.