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Presence of a frequency-independent maximum and a frequency-dependent shoulder in temperature-frequency dependence of dielectric permittivity are characteristic features of NBT-based solid solution...

Photoluminescence and optical second harmonic generation in Er-doped 0.4Na0.5Bi0.5TiO3-(0.6-x)SrTiO3-xPbTiO3 solid solutions is studied. Earlier, it was shown that upon increasing of PbTiO3 concent...

This work was supported by the Research Council of Lithuania (Project S-LLT-20-4). This work has been supported by Mutual Funds Taiwan–Latvia– Lithuania Cooperation Project Application LV-LT-TW/2020/10., In this paper, we present the dielectric and piezoelectric properties of tetragonal 0.8Na0.5 Bi0.5 TiO3-0.2BaTiO3 modified with NaNbO3 ((1-x)[0.8Na0.5 Bi0.5 TiO3-0.2BaTiO3 ]-xNaNbO3 ). Our experimental study has revealed that the ferroelectric phase in these compositions is suppressed with the increase of sodium niobate concentration. A broad anomaly, resembling relaxor ferroelectrics, appears in the 325–450 K temperature interval. The investigation of the electric field dependence of polarization has indicated that the double hysteresis loop behaviour is character-istic of the modified compositions, which is associated with the 1st order phase transition under the applied electric field. The experiments below room temperature have revealed that the range of stability of the ferroelectric phase is shifted to lower temperatures upon the increase of sodium niobate concentration. The electromechanical displacement in the modified compositions shows a similar maximum displacement in the whole concentration range. The electromechanical response in 0.8Na0.5 B0.5 TiO3-0.2BaTiO3 solid solutions is due to the piezoelectric effect, while, in the mixed compositions, it is related to the jump-like change of the lattice constants in the vicinity of electric field-induced 1st order phase transition. © Lietuvos mokslų akademija, 2022., Mutual Funds Taiwan–Latvia– Lithuania Cooperation Project Application LV-LT-TW/2020/10; Lietuvos Mokslo Taryba S-LLT-20-4; Institute of Solid State Physics, University of Latvia has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2.

Photoluminescence in Er-doped NBT is studied at different temperatures. Remarkable reduction of the luminescence intensity in the green spectral range is found in the poled state comparing with the depoled state. Luminescence spectra at low temperatures reveal continuous wavelength shift of some maxima belonging to the 4 S 3/2 → 4 I 15/2 transition depending on the excitation wavelength, which is explained by large variety of different environments around Er 3+ related to the random distribution of Na + and Bi 3+ in A-sublattice of the ABO 3 perovskite structure. Poling extends the wavelength range where shift of luminescence maxima is observed in the direction of longer excitation wavelengths. This feature can be explained by more ordered structure characteristic to the poled state comparing with the depoled one. Luminescence spectra of Er-doped BaTiO 3 are also measured at low temperatures, and confirm the role of Na + and Bi 3+ ion disorder in the observed spectral features of Er-doped NBT.

Na0.5Bi0.5TiO3 (NBT)-based compositions are among the most promising lead-free ferroelectrics. Although studies of modification of NBT-based compositions’ properties are a hot topic, there has been very little attention paid to their characterization from the standpoint of ceramics and the process of producing them. Here, we report on comprehensive analysis of the influence of sintering temperature across a wide temperature range (1020–1240 °C) on the complete microstructure and chemical content of NBT ceramics produced by solid state sintering, which is dominating in producing of NBT ceramics. Thorough attention is paid to the grain size distribution, porosity, and inhomogeneity. It is demonstrated how the grain size distribution monotonously becomes more diffuse and the average grain size increases, upon sequential increasing of the sintering temperature. Along with high density (reaching 98% of the theoretical value), two types of pores are observed. Macroscopic pores form at high sintering temperatures along with a small concentration of residual pores remaining after densification of ceramics and observed throughout the whole range of sintering temperatures. Two types of inclusions are detected, corresponding to the chemical compositions NaBiTi6O14 and TiO2, as inferred from local energy-dispersive X-ray analysis. Non-intentional non-stoichiometry is not detected in the matrix grains of the NBT ceramics, even if sintered at high temperatures. It is inferred that, instead of changing the composition of the matrix grains, Na and Bi volatilization rather influences the porosity and inhomogeneity of NBT.

The long and short range orders in 0.4Na1/2Bi1/2TiO3-(0.6-x)SrTiO3-xPbTiO3 solid solutions were studied by x-ray diffraction and Raman spectroscopy. X-ray diffraction patterns for these composition...

Phase coexistence region is studied by x-ray diffraction for Na1/2Bi1/2TiO3-BaTiO3 solid solutions in the tetragonal phase side from the morphotropic phase boundary. The first order ferroelectric phase transition, determined from a jump in the temperature dependence of dielectric permittivity, is located inside the coexistence region of cubic and tetragonal phases and is below the temperature, where tetragonality disappears. At low BaTiO3 concentrations phase transition into ferroelectric state at cooling is slowly approached in time and is smeared over large temperature range. Rietveld method, applied for more precise evaluation of phase content, reveals large local deformations inside the ferroelectric phase.

Increasing of Sr0.7Bi0.2TiO3 concentration in Na0.5Bi0.5TiO3-Sr0.7Bi0.2TiO3 solid solutions causes increasing of Bi/Na relation and vacancies in the A-site of perovskite structure. In temperature dependence of dielectric permittivity, such a change of composition is reflected by transforming of the frequency-dependent shoulder into a maximum characteristic for relaxor ferroelectrics and diminishing of the frequency-independent maximum characteristic for Na0.5Bi0.5TiO3. Here changes in behavior of dielectric permittivity and polarization are studied if PbTiO3 is added in a certain concentration range of Na0.5Bi0.5TiO3-Sr0.7Bi0.2TiO3 solid solutions. Changes of the characteristic temperatures as a function of PbTiO3 concentration are determined. Behavior of the electrocaloric effect is compared with the results obtained for Na0.5Bi0.5TiO3-SrTiO3-PbTiO3.

A detailed analysis of photoluminescence of Eu-doped Na0.5Bi0.5TiO3 (NBT) is performed using it as a tool for describing the local structure of NBT. The obtained results reveal the low symmetry of the Eu3+ local environment in NBT, as indicated by the observed maximal number of sublevels of the 5D0→7F1 and the 5D0→7F2 luminescence transitions, clearly observed at low temperatures. Approximation of the luminescence spectra by Gaussian peaks provides valuable information about the shift of the involved levels upon change of the excitation wavelength. Variation in the strength of the crystal field in Eu-doped NBT is evaluated. Temperature dependence of the luminescence above room temperature is analyzed for the poled and the unpoled states of the material. The results obtained for Eu-doped NBT are compared with the results for Er-doped NBT reported previously.

The role of substitution in A- and B-sites of perovskite ABO3 structure in phase transitions is evaluated, comparing (1-y)(0.939Na0.5Bi0.5TiO3-0.061BaTiO3)-yKxNa1-xNbO3 solid solutions with x = 0.0, x = 0.5 and x = 1.0. The influence of deviation from a stoichiometric Na/Bi ratio is also studied. The influence of K0.5Na0.5NbO3, NaNbO3 or KNbO3 reduces mainly to suppressing of ferroelectric properties, like in other perovskite ferroelectrics where Ti is replaced by Nb, and development of the relaxor state. Besides the frequency-dependent dielectric permittivity, the relaxor state in the studied compositions is characterized also by a temperature dependence of critical electric fields, corresponding to phase transitions between relaxor and ferroelectric states. The influence of Nb in the above mentioned compositions is compared with the one of compositions far from the morphotropic phase boundary by a study of solid solutions (1-y)(0.80Na0.5Bi0.5TiO3-0.20BaTiO3)-yKxNa1-xNbO3.

Results of direct measurements of electrocaloric effect and polarization are mutually compared in solid solutions 0.4Na1/2Bi1/2TiO3-(0.6-x)SrTiO3-xPbTiO3. Three temperature regions are distinguished in respect of a phase transition temperature. Above the phase transition, electrocaloric effect is determined by orientation of polar nanoregions by electric field. In wide temperature regions above and below the phase transition temperature, the difference between results, obtained from direct electrocaloric effect measurements and from polarization hysteresis loops, is explained by temperature dependence of concentration of polar nanoregions, oriented by electric field. Existence of a common ΔT(P) curve for all temperatures in the ferroelectric state indicates that polarization can be treated as a parameter, which solely determines electrocaloric effect in this state.

Description of the local symmetry of relaxor ferroelectrics, especially in connection with nature of polar nanoregions, is one of the key questions in research of relaxor ferroelectrics. Unlike such well-known relaxor ferroelectrics as PbMg1/3Nb2/3O3 and (Pb,La)(Zr0.65Ti0.35)O3, ternary solid solutions 0.4Na1/2Bi1/2TiO3-(0.6-x)SrTiO3-xPbTiO3 show clear coexistence of phases of tetragonal and cubic symmetry, which is established by x-ray diffractometry. Since the second-harmonic generation spectroscopy is a sensitive tool in determination of deviation from symmetry, containing a centre of inversion, it is used as an additional method in characterization of structure in 0.4Na1/2Bi1/2TiO3-(0.6-x)SrTiO3-xPbTiO3. Measurements indicate low, increasing intensity of the second-harmonic generation upon decreasing of temperature, for the samples with low concentration of PbTiO3. Whereas an abrupt change is observed at the phase transition between ferroelectric and relaxor states for the samples with higher concentr...

In this work we address the peculiarities of the macroscopic responses in ternary 0.1Na0·5Bi0·5TiO3-0.6SrTiO3-0.3PbTiO3 (0.1NBT-0.6ST-0.3PT) solid solutions. These solid solutions exhibit a spontaneous first order relaxor to normal ferroelectric phase transition. The phase transition is accompanied by a broad dielectric relaxation which expands over 10 orders of magnitude in frequency just above the phase transition temperature. The temperature dependence of polarization shows that non-zero net polarization persists above the phase transition temperature. Below the phase transition temperature, it is not possible to describe the temperature dependence of polarization with a power law function which is valid in normal ferroelectrics. The piezoresponse force microscopy studies reveal that 0.1NBT-0.6ST-0.3PT solids solutions display several local polarization patterns which arise due to the bimodal distribution of grains in the ceramics. We associate the peculiar macroscopic responses to these complex polar structures and their different temperature behaviours.

In this paper we present our measurements of the linear and nonlinear dielectric permittivity of 0.4 Na 0.5 Bi 0.5 TiO 3 – ( 0.6 - x ) SrTiO 3 – xPbTiO 3 solid solutions (x = 0, 0.05, 0.1, 0.15). The dielectric anomaly increases in the system with respect to the concentration of lead, showing that interactions between dipolar entities are modified. The system exhibits dipolar-glass-like behaviour at low values of x ( 0 ⩽ x 0.1 ). Relaxor behaviour emerges in the sample where x = 0.1 . Furthermore, a spontaneous first-order phase transition from relaxor to normal ferroelectric is observed at x ⩾ 0.15 . A few peculiar dispersion regions are observed in the ferroelectric phase, which we attribute to the coexistence of ferroelectric and dipolar glass phases. On the other hand, the nonlinear dielectric response indicates the existence of compressible polar nanoregions as common elementary dipolar entities in both relaxor and glass-like states. Dielectric spectra were approximated with empirical Cole–Cole or Havriliak–Negami equations. It is shown that the temperature dependencies of mean relaxation times, which were obtained from dielectric spectra, follow the Vogel–Fulcher equation in all samples. Moreover, distributions of relaxation times are obtained and a phase diagram is presented.

This work has been supported by the National Research Program in the framework of the project “Multifunctional Materials and composites, photonics and nanotechnology (IMIS2).”, Direct and indirect studies of the electrocaloric effect were carried out in poled and depoled Na0.5Bi0.5TiO3. For this purpose, polarization and electrocaloric effect temperature change measurements were made at different electric field pulses as a function of temperature. The applicability of the widely used indirect electrocaloric effect determination method, using the Maxwell relation, was critically analyzed with respect to the reliable direct measurements. Quantitative differences were observed between the results obtained by both approaches in the case of the poled Na0.5Bi0.5TiO3 sample. These differences can be explained by the temperature-dependent concentration of domains oriented in the direction of the applied electric field. Whereas in depoled Na0.5Bi0.5TiO3, which is characterized by the electric field dependence of polar nanoregions embedded in a nonpolar matrix, the Maxwell relation is not applicable at all, as it is indicated by the obtained results. Possible mechanisms which could be responsible for the electrocaloric effect in the relaxor state were considered. The results of this study are used to evaluate the numerous results obtained and published by other authors, using the Maxwell relation to indirectly determine the electrocaloric effect. The reason for the negative values of the electrocaloric effect, obtained in such a way and widely discussed in the literature in the case of Na0.5Bi0.5TiO3, has been explained in this study., National Research Program (IMIS2); Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²

This work has been supported by National Research Program in the framework of project “Multifunctional Materials and composites, photonics and nanotechnology (IMIS2)”., (1 − x)Na0.5Bi0.5TiO3–xCdTiO3 solid solutions in the whole concentration range (0.0 ≤ x ≤ 1.0) were studied by means of X-ray diffraction, dielectric spectroscopy and polarization measurements. The study was mainly focused on crystalline structure of the compositions, depending on their place in the phase diagram. The solid solution system exhibits at least four different phases at room temperature, giving rise to paraelectric, ferroelectric and relaxor ferroelectric behaviour. There were proposed appropriate space groups for each of these phases, using Rietveld refinement method for analysis of the X-ray diffraction patterns and taking into account polarization measurement results. Unexpected and unusual octahedral tilt systems—a + a + a + and a + b + c +—were found in certain CdTiO3 concentration ranges. The tilt system a + b + c +, which was detected in the ferroelectric phase, was evidenced for the first time, as it has been theoretically predicted, but never experimentally observed before in any material. It was shown that ferroelectricity in (1 − x)Na0.5Bi0.5TiO3–xCdTiO3 solid solutions arises not only from the Ti+4 displacements, but also from the polar distortions in square planar and cubooctahedral cation A-sites. Upon heating, at a phase transition from the ferroelectric to the paraelectric state, a + b + c + tilt system transforms into a + a + a +. The studied compositions were compared with (1 − x)Na0.5Bi0.5TiO3–xCaTiO3 solid solution system, as CdTiO3 and CaTiO3 are crystallographically very similar. It was revealed that both constituents behave very differently. CaTiO3 in (1 − x)Na0.5Bi0.5TiO3–xCaTiO3, even in low concentrations, stabilizes solid solutions in its Pnma space group, unlike its counterpart CdTiO3 in the studied materials., National Research Program (IMIS2); Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²

Dielectric properties, polarization and x-ray diffraction are studied for (1-x)Na1/2Bi1/2TiO3-xBaTiO3 solid solutions in a concentration range above the morphotropic phase boundary. It is showed that all the studied compositions have tetragonal structure with maximal tetragonality slightly above the morphotropic phase boundary. Ferroelectric relaxor behavior is observed in a wide concentration range of BaTiO3. Stability of the relaxor state decreases with increasing BaTiO3 concentration, but only for compositions with low Na1/2Bi1/2TiO3 content the normal ferroelectric-paraelectric phase transition, which is characteristic to pure BaTiO3, occurs. Mechanisms, which influence the change of the phase transition character and promote the appearance of the relaxor state, are discussed. The phase diagram of (1-x)Na1/2Bi1/2TiO3-xBaTiO3 is revised.

In this paper we present dielectric spectroscopy results of NBT-(0.6-x)ST-xPT with x = 0.2 solid solution. Dielectric investigations clearly showed a relaxor—normal ferroelectric phase transition at TPT = 419 K and low temperature and low frequency dispersion similar to coexistence of dipolar glass and ferroelectric phase. The mean relaxation time above the phase transition follows Vogel—Fulcher law with following parameters: E A = 0.179 eV, τ 0 = 3.39·10−14 s, T VF = 223 K.

Influence of moderate substitution of Na by monovalent metals Li, K and Ag on structure, phase transitions and dielectric properties of 0.4Na1/2Bi1/2TiO3-0.4SrTiO3-0.2PbTiO3 is studied. Substitution by Li increases, while substitution by K and Ag decreases tetragonality of unit cell. Li increases, Ag decreases while K weakly influences phase transition temperature. The characteristic for the parent phase relaxor state with Tt approaching Tm in case of substitution by K and Li transfers into diffused phase transition without Tm dependence on frequency and extended region of thermal hysteresis.

Thermal expansion and electromechanical properties are studied for compositions Na1/2Bi1/2TiO3-SrTiO3-PbTiO3, belonging to various locations in the phase diagram. The main purpose of the studies is to extend the range of physical properties, which characterise the relaxor state and could be used for comparison with other relaxors. Possibility to evaluate Burns temperature from thermal expansion is discussed. The obtained results are compared to the well-know relaxor ferroelectric PLZT.

Behaviour of ferroelectric properties in Na1/2Bi1/2TiO3-CdTiO3 solid solutions correlates with dependence of lattice symmetry versus concentration of constituents. However, some overlapping is observed in concentration range close to the morphotropic phase boundary. The properties of dielectric permittivity, characteristic for relaxor ferroelectrics, diminish, if concentration of CdTiO3 increases, but it is not influenced by the change of crystallographic symmetry. The electromechanical properties are mostly pronounced in the range of cubic-tetragonal morphotropic phase boundary.

The addition of NaNbO3 and PbMg1/3Nb2/3O3 to 0.4Na1/2Bi1/2TiO3-0.4SrTiO3-0.2PbTiO3 causes transfer from ferroelectric state to relaxor. The opposite was observed when concentration of PbTiO3 is increased in (1-x-y)Na1/2Bi1/2TiO3-xSrTiO3-yPbTiO3. The studied solid solutions represent the case of very complex mixing of different ions in the same positions of crystallographic lattice. The weakening of ferroelectric properties is considered to be an important reason developing of relaxor state.

Vogel-Fulcher law, traditionally applied to describe dispersion of dielectric permittivity in relaxor ferroelectrics, requires introduction of two different relaxation mechanisms above and below freezing temperature correspondingly. Extending distribution function of relaxation times, previously known for low-temperature region, allows creating common description of relaxation in all range, where distribution function of relaxation times can be regarded as wide, without freezing at certain temperature.

All sequential steps of transfer from relaxor to normal ferroelectric phase transition are found in Na1/2Bi1/2TiO3-SrTiO3-PbTiO3 if concentration of PbTiO3 increases. The relaxor properties in Na1/2Bi1/2TiO3-SrTiO3-PbTiO3 solid solutions are described by the power law and Vogel-Fulcher relationship. Concentration dependence of the relevant parameters is discussed. Stability of relaxor and ferroelectric phases is discussed by analyzing behaviour of critical electric fields.

The existing situation in prospects of application of electrocaloric effect (ECE), related to finding ferroelectrics exhibiting high values of ECE, is discussed. Besides 1st order ferroelectric-paraelectric phase transitions, which were most promising till recent time with respect to high values of ECE, there are other approaches, related to ECE in high field range in relaxors and polymers. The restrictions of application of traditional indirect evaluation of ECE in ferroelectrics are discussed.

Studies of nature of polarization in ternary solid solutions of Na1/2Bi1/2TiO3-SrTiO3-PbTiO3 were done, using measurements of dielectric properties and polarization hysteresis loops. Various stages of relaxor behavior depending on concentration of PbTiO3 were established and compared with other known ferroelectric relaxors.

The dielectric, elastic and electromechanical properties, electrocaloric effect and thermal expansion of poled and depoled Pb0.99Nb0.02(Zr0.75Sn0.20Ti0.05)O3 samples are presented to evaluate the nature of polar phases existing in the solid solution above room temperature. The Kittel's free energy expansion is used to explain some essential features of physical properties.

Field induced deformation and electrocaloric effect are investigated in the vicinity of phase transition at 163°C. The sharp increase of electrostriction below Tc is explained by the field induced ferroelectric to antiferroelectric phase transition. The antiferroelectric phase appears and remains stable below Tc in the absence of field. Elastic compliance and thermal expansion as functions of temperature are studied.

The jump of dielectric permittivity as function of bias field applied after various duration of storage at the measurement temperature is investigated. The influence of storage time on ϵ(E=) depends on the value of bias field and frequency of measuring field. It is found that ϵ(E=) depends on the path of how particular field value is reached.

Continuous transfer from relaxor to normal ferroelectric phase transition is found in Na1/2Bi1/2TiO3-SrTiO3-PbTiO3 if concentration of PbTiO3 increases. The relaxor properties in NBT solid solutions are described by the power law and Vogel-Fulcher relationship, and concentration dependence of the relevant parameters is discussed. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The structure-properties relationships and phase transitions in perovskite ceramics, and films of PLZT, PLZST, PST, PSN, PMNT compounds are discussed with regard to ordering, relaxor behaviour, pronounced ferroelectric, electromechanical and electrocaloric properties. The theoretical approach is extended to the time dependent Ginsburg-Landau model. The evolution of dielectric properties in relaxors after the change of temperature and electric field creating an increase of dielectric permittivity is found to follow a logarithmic law of decay. A strong electromechanical response is observed in a number of thin films of different compositions.

The electrostriction in lead scandium tantalate PST ceramics with various degree of ordering in the B sublattice as well as Pb deficiency is investigated in the region of phase transition. The coefficient of electrostriction Q11 was found to be unaffected by the degree of ordering. The behavior of the field-induced deformation in PLZT 12/50/50 and PLZT 6/80/20 ceramics belonging to different regions of the phase diagram, is explained by the different characters of the phase transition in both cases

The time evolution of dielectric properties after a temporary change of temperature and electric field is investigated. It is found, that below the temperature of ˛' maximum Tm the change of temperature and electric field creates an increase of dielectric permittivity followed by logarithmic decay when the change of these parameters is finished. At every temperature the dielectric properties are characterized by a unique ˛'(t) independent on previous thermal history. If the applied electric field is E< Ec, the state of polarization is not affected. The dependence on dielectric constant of storage time under field as well as field intensity is determined.

Optical spectra and dielectric parameters are used to study PLZT X/65/35 (X=4.5−11 at.% La) and PSN ceramics subject to gamma- electron-, and neutron irradiation. In neutron-irradiated ceramics stable defects, maintained at annealing up to 700 °C are manifested by a gradual shift of extinction edge near the fundamental absorption to longer wavelengths and by reduced polarization values. The thermal dependence of the extinction edge in reference samples of PLZT and PSN has been determined to be ca. 0.10 nm/deg (0.9 meV/deg) and 0.125 nm/deg, respectively in the range 20-500°C. In PLZT 6.5-8/65/35 ceramics a defect enforced phase transformation from the initial rhombohedral structure to “quasicubic” with essential broadening of the phase transition takes place.

The deformation as a function of polarization was measured in PLZT 8-10/65/35 in the region of diffused phase transition. A different behaviour of deformation in the region of double hysteresis loops was observed corresponding to ferroelectric and nonpolar phases as well as to the field induced phase transition region. In the ferroelectric phase the results are described by electrostriction. The decrease of volume as well as small longitudinal deformations at the field induced transition to ferroelectric state are explained by large remanent deformations, existing in the nonpolar phase. Since description of deformation in the framework of electrostriction cannot be motivated in the nonpolar phase, the influence of reorientation of polar microregions on deformation is discussed.

Dielectric properties, polarization and x-ray diffraction are studied for (1−x)Na 1/2 Bi 1/2 TiO 3 -xBaTiO 3 solid solutions in a concentration range above the morphotropic phase boundary. It is showed that all the studied compositions have tetragonal structure with maximal tetragonality slightly above the morphotropic phase boundary. Ferroelectric relaxor behavior is observed in a wide concentration range of BaTiO 3 . Stability of the relaxor state decreases with increasing BaTiO 3 concentration, but only for compositions with low Na 1/2 Bi 1/2 TiO 3 content the normal ferroelectric-paraelectric phase transition, which is characteristic to pure BaTiO 3 , occurs. Mechanisms, which influence the change of the phase transition character and promote the appearance of the relaxor state, are discussed. The phase diagram of (1−x)Na 1/2 Bi 1/2 TiO 3 -xBaTiO 3 is revised.

The physical background of field-induced first-order ferroelectric-paraelectric, antiferroelectric-ferroelectric phase transitions and diffused phase transition in modified lead-containing perovskite ceramic compositions is discussed. Examination of radiation effects has proven to be useful in finding ways to control the properties of perovskites. Some specific applications of the materials are considered.

Selected optical (absorption coefficient), dielectric (polarization) and electrooptical (quadratic electrooptical coefficient) parameters of PLZT X/65/35 and PSN ceramics exposed to various radiation environments (γ-rays, electrons, neutrons) have been studied. The observed property changes depend on the type of radiation, the dose and, in the case of the dielectric properties, on the state of sample polarization. Special features observed upon annealing the irradiated samples are discussed.

Bulk and film samples have been prepared of composite YBa2Cu3O7-x-BaTiO3. The X-ray diffraction, SHG, resistivity and magnetic susceptibility investigations have been performed. The superconductive phase transition is broadened towards lower temperatures in the presence of BaTiO3, the resistivity of the normal phase being increased. Changes in behaviour of the composite films can be partly explained by weak contacts between particles of YBa2Cu3CV7-x during the preparation.

The transformation of the hysteresis loops in PLZT x/65/35 in the region of diffuse phase transition is discussed in relation to the behaviour of dielectric permittivity. The Vogel-Fulcher type dielectric relaxation is used to describe the discussed phenomena.

Despite wide studies of Na0.5Bi0.5TiO3, structure of this material and its connection with the observed physical properties still raise numerous questions due to mutually contradicting results obtained. Here, structure and dielectric properties of poled and unpoled Na0.5Bi0.5TiO3-CaTiO3 solid solutions are studied, projecting the obtained concentration dependence of structure and dielectric properties on pure Na0.5Bi0.5TiO3 as the end member of this material group. X-ray diffraction patterns for Na0.5Bi0.5TiO3-CaTiO3 solid solutions reveal dominating of an orthorhombic Pnma phase, even for the compositions approaching the end composition (Na0.5Bi0.5TiO3), whereas structure of pure Na0.5Bi0.5TiO3 can be considered, assuming coexistence of rhombohedral and orthorhombic phases. This allows one to avoid appearance of a large difference of rhombohedral distortions between the unpoled and poled Na0.5Bi0.5TiO3, if the rhombohedral distortion is calculated as for single R3c phase. Features of dielectric permittiv...

Results of comprehensive studies of the (A’A“)(B’B”)O3-ferroelectric perovskites are reported. Examined compositions include Pb1-xLax(Zr0.65Ti0.35)1-x/4O3(PLZT), PbSc0.5Nb0.5O3(PSN), PbSc0.5Ta0.5O3(PST), and PMNT, PSNT and PLuNT pseudo-binary systems exhibiting pronounced dielectric, electrooptical, and electromechanical properties. Degree of ordering in the materials has been varied by chemical composition (modification, isomorphic ion substitution), by variation of technology (hot-pressing, specific thermal treatment, thin films), and by irradiation of different kind and intensity (γ-rays, electrons, neutrons).

The influence on the relaxor state and phase transitions are studied when Sr in 0.4Na1/2Bi1/2 TiO3-0.4SrTiO3-0.2PbTiO3 is gradually replaced by Ca. The concentration dependence of the tetragonal cell volume confirms replacement of Sr by Ca in the lattice, while tetragonality remains independent of Ca concentration in a certain concentration range. The stability of the relaxor state and temperature of phase transition is also weakly dependent on Ca at low concentrations of Ca, and steeply increases starting from a certain Ca concentration. The stability of the phase transition and polarization at low concentrations of Ca and simultaneous steep decreasing of dielectric permittivity values with increasing Ca content is explained assuming that in this concentration range Ca resides inside polar nanoregions, preventing their reorientation in weak external electric field.