Relaxer ferroelectrics as promising materials for IR detectors

The dielectric and pyroelectric properties of a typical relaxer ferroelectric, 0.9PbMg_1/3Nb_2/3O₃-0.1PbTiO₃ (PMN-PT), are studied experimentally. Based on the results obtained, the pyroelectric constant and figure of merit of the material when used in IR detectors are calculated. These parameters are presented as a function of temperature and external electric field. The current and voltage sensitivities and the detectivity of PMN-PT-based IR detectors are evaluated. They are compared with the same properties of pyroelectric detectors and dielectric bolometers that use traditional pyroelectric materials as the active element and also of other uncooled photodetectors.     

The role of the secondary pyroelectric effect in a ferroelectric relaxor 0.72Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>-0.28PbTiO<Subscript>3</Subscript>

The depth profile of the pyroelectric coefficient effective values of a 0.72Pb(Mg_1/3Nb_2/3)O₃-0.28PbTiO₃ (PMN-0.28PT) single crystal is studied. It was shown that owing to high pyroelectric coefficients the secondary pyroelectric effect significally contributes (∼40%) to the total pyroelectric coefficient.     

Kinetic features of the new phase nucleation in the electric field in some lead-containing relaxors

The kinetics and dynamics of the new phase nucleation in an external electric field E in ferroelectric relaxors Pb_1/2Nb_1/2O₃–PbMg_1/3Nb_2/3O_3–x (x = 25 and 32%) and PbMg_1/3Nb_2/3O₃–29PbTiO₃ have been investigated. The joint measurements of optical transmittance at different wavelengths as well as the sound speed and attenuation at different frequencies have been carried out at room temperature. The analysis of the character of the changes of the optical and acoustic properties in different electric fields has been performed with the aim of identifying the mechanisms of such changes under phase transition conditions. The reduction of optical transmission with time is associated only with the size change of nanoregions in the process of phase transition. The observed acoustic anomalies are the consequence of phase transition and conditioned by the lattice increased rigidity, caused by a large piezoelectric effect in the ferroelectric phase.     

Complex Studies of the Kinetics of Induced Phase Transition in [001], [011], and [111]-Oriented Single Crystal Relaxor Solid Solutions

The kinetics of an induced phase transition in single-crystal relaxor solid solutions 33PbIn_1/2Nb_1/2O₃–35PbMg_1/3Nb_2/3O₃–32PbTiO₃ and PbMg_1/3Nb_2/3O₃–29PbTiO₃ under application of an electric field along three directions [001], [011], and [111] at room temperature is studied. Joint measurements of optical transmission at different wavelengths, dielectric properties, and attenuation of sound are carried out. It was found that, even in small fields (E ~ 2 kV/cm) applied in the [011] and [111] directions, the maximum changes in all three characteristics as well as the coincidence of the time dependences of the optical transmission at different wavelengths of light occur in the same time interval. It is established that, in the same interval of fields along the [001] direction, the anomalies of the optical properties do not coincide in time with the anomalies of the acoustic and dielectric properties. The results obtained are explained by the induction of single-domain and multidomain phases.     

E-T phase diagrams of a solid solution of the multicomponent PbZn1/3Nb2/3O3-PbMg1/3Nb2/3O3-PbNi1/3Nb2/3O3-PbTiO3 system near the morphotropic phase boundary

The specific features of the dielectric and pyroelectric responses of a solid solution in the barium-doped multicomponent yPbZn_1/3Nb_2/3O₃-mPbMg_1/3Nb_2/3O₃-nPbNi_1/3Nb_2/3O₃-xPbTiO₃ system of the composition y = 0.0982, m = 0.4541, n = 0.1477, and x = 0.3 near the morphotropic phase boundary have been investigated. It has been assumed that the maxima revealed in the dependences of the reversible permittivity on the electric field strength with both the forward and backward changes in the field (E ₌) are associated with the induced phase transition. Based on the experimental results, the E-T phase diagrams are constructed in the temperature range from ?100 to 150°C for different temperature-field regimes: (i) variation in the electric field E ₌ at a fixed temperature of the sample and (ii) variation in the temperature of the sample at a constant value of E ₌. It has been found that there is a singular point in the E-T phase diagram and that, in the vicinity of this point, the dielectric and pyroelectric responses of the studied ceramics exhibit specific features.     

Correlation of the piezoelectric and dielectric properties of soft ferroelectric ceramics

The dependences of the piezoelectric (g ₃₃) and electrostriction (Q ₃₃) coefficients of nonpolarized soft relaxor ferroelectric ceramics of the PbMg_1/3Nb_2/3O₃-PbTiO₃ system on electric field E ₃ are calculated and interpreted. The nonmonotonic g ₃₃(E ₃) dependence and negative values of Q ₃₃ were revealed in strong electric fields. These features are shown to be the manifestation of correlation between the piezoelectric and dielectric properties.     

Study of the formation processes of a domain nanostructure in relaxor ferroelectrics

We present the results of an investigation into processes of formation of polar nanoregions and the relaxation dynamics of a cubic relaxor ferroelectric (PbMg_1/3Nb_2/3O₃)_0.9-(pbTiO₃)_0.1 (PMNPT10), selected to be studied as a model compound.     

Evolution of dielectric and optical properties in PbIn1/2Nb1/2O3-PbMg1/3Nb2/3O3-PbTiO3 single crystals in an electric field

A study is reported of various modes of dc electric field application (0 < E < 3 kV/cm) on structural phase transformations and behavior of the phase boundary in [001]-oriented 30PbIn_1/2Nb_1/2O₃-37PbMg_1/3Nb_2/3O₃-33PbTiO₃ single crystals located close to the morphotropic phase boundary. Dielectric methods of investigation have been complemented for the first time with optical methods. It has been found that the number, symmetry, and stability of the phases formed in the field depend on the actual mode of field application. The E-T phase diagrams have been constructed for different field application modes. It has been shown that phase diagrams obtained for the same crystal are different for different field application modes.     

Optical and acoustic properties of 33PbIn1/2Nb1/2O3-35PbMg1/3Nb2/3O3-32PbTiO3 single crystals in an electric field

The influence of different conditions of applying a dc electric field (0 < E < 4 kV/cm) on the behavior of optical transmission and on the acoustic parameters (sound velocity and attenuation) in the [001]- and [011]-oriented single crystals 33Pb(In_1/2Nb_1/2)O₃-35PbMg_1/3Nb_2/3O₃-32PbTiO₃ existing near the morphotropic phase boundary has been investigated. It has been found that the optical transmission, sound velocity, and attenuation sharply change near the phase transition in a narrow range of electric fields for any method of their applying. In the field applied along [001], the change in the sound velocity due to the phase transition is 1.5 times greater than that in the field applied along [011]. This is caused by a larger contribution of the piezoelectric effect to the elastic modulus determining the sound velocity along [001] as compared to [011]. It has been shown that the number, symmetry, and stability of the phases formed in the field depend on the conditions of applying the field.     

Low-frequency dielectric relaxation (1/<Emphasis Type="Italic">f</Emphasis> noise) in relaxors of the (1 − <Emphasis Type="Italic">x</Emphasis>)PMN-(<Emphasis Type="Italic">x</Emphasis>)PZT system

The dielectric properties of relaxor ferroelectric ceramics (1 ? x)PbMg_1/3Nb_2/3O₃-(x)PbZr_0.53Ti_0.47O₃ (PMN-PZT) have been studied at frequencies from 40 Hz to 1 MHz in the temperature range of the diffuse phase transition. It is established that the dielectric relaxation generates 1/f noise, whose spectral density depends on the relaxor composition and temperature.     

Description of ferroelectric phase transitions in solid solutions of relaxors in the framework of the random-field theory

A model based on the random-field theory is proposed for calculating the properties of solid solutions of ferroelectric relaxors. The electric dipoles randomly distributed in the system are treated as sources of random fields. The random field distribution function is calculated taking into account the contribution of nonlinear and correlation effects and the differences in the dipole orientations for different solid solution components. The dependence of the phase transition temperature T _c on the concentration of solid solution components is analyzed. Numerical calculations are performed for the lead scandoniobate and lead scandotantalate solid solutions (PbSc_1/2Nb_1/2O₃)_1?x (PbSc_1/2Ta_1/2O₃)_x with different degrees of ordering and the lead magnoniobate and lead titanate solid solution (PbMg_1/3Nb_2/3O₃)_1?x (PbTiO₃)_x. It is shown that the higher transition temperature for more disordered solid solutions of the composition (PbSc_1/2Nb_1/2O₃)_1?x (PbSc_1/2Ta_1/2O₃)_x in the range 0≤x<0.5 is associated with the larger nonlinearity coefficient for PbSc_1/2Nb_1/2O₃ as compared to that for PbSc_1/2Ta_1/2O₃. The theory provides a means for calculating the region of the coexistence of the phases with different symmetry groups in the temperature-composition phase diagram of the (PbMg_1/3Nb_2/3O₃)_1?x (PbTiO₃) solid solution. Numerical calculations with the use of the fitting parameters obtained from the known transition temperatures T _c for the solid solution components adequately describe the experimental phase diagrams for the aforementioned solid solutions of ferroelectric relaxors.     

Elastic properties of cubic relaxor ferroelectrics

Comparative analysis of the elastic properties of PbMg_1/3Nb_2/3O₃ (PMN) and PbMg_1/3Ta_2/3O₃ (PMT) crystals has been performed. The temperature dependences of the elastic moduli C ₁₁, C ₁₂, and C ₄₄ are presented. These curves exhibit anomalies near the Burns temperature for both crystals. Additional anomalies are observed in the vicinity of the suppressed ferroelectric transition (T _C ～ 210 K) in PMN. Nontrivial frequency dispersion of the elastic moduli has been revealed for PMN.     

Quasi-static electric field–temperature diagrams in epitaxial relaxor ferroelectric films

Quasi-static polarization induced by dc electric field was studied in a broad range of temperatures in epitaxial films of relaxor ferroelectric PbMg_1/3Nb_2/3O₃ and PbSc_1/2Nb_1/2O₃. The electric field was applied and the response was measured along the out-of-plane <100> crystal direction of the epitaxial perovskite-structure (001) oriented films. The films remained in the relaxor state in zero-field cooling. A new polar state can be induced by electric field at a critical temperature below 100 K. The critical field and the induced polarization increased on cooling and reached the bulk-like values at 20 K. The orientational anisotropy of thin-film dipolar systems is discussed as a possible reason for the observed stable relaxor state.     

(100) MgAl2O4 as a lattice-matched substrate for the epitaxial thin film deposition of the relaxor ferroelectric PMN-PT

The (100) surface of MgAl₂O₄ is evaluated as a substrate for the thin film deposition of the relaxor ferroelectric PbMg_1/3Nb_2/3O₃(65%)–PbTiO₃(35%). With a lattice mismatch of less than 0.5%, this film-substrate combination presents a geometrical template for growth that is far superior to that formed with other commercially available oxide substrates. Films were deposited using the pulsed laser deposition technique and were characterized in terms of their crystallographic, microstructural, and dielectric properties. From a crystallographic perspective the films show excellent cube-on-cube epitaxy, are highly oriented, and show no evidence of the frequently observed parasitic pyrochlore phase. With the exception of a few faceted surface structures, the film’s microstructure is single-crystal-like, exhibiting a sharp film-substrate interface, a smooth top surface, and no discernable granularity. The dielectric response shows the frequency-dependent diffuse phase transition characteristic of a relaxor material, but with less frequency dispersion and a smaller maximum in the dielectric constant. Taken together, the results suggest that the (100) MgAl₂O₄ substrate could prove to be an effective substrate material, not only for the PbMg_1/3Nb_2/3O₃(65%)–PbTiO₃(35%) system, but also for a number of other important lattice-matched ferroelectric, relaxor, and ferroelectric superlattice systems.     

Effect of the la concentration on the dielectric and optical properties of the transparent ferroelectric ceramics 75PbMg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript>-25PbTiO<Subscript>3</Subscript>

The dielectric, optical, and electro-optical properties of transparent ferroelectric ceramics 75PbMg_1/3Nb_2/3O₃-25PbTiO₃ (75PMN-25PT) with different La concentrations (2, 3, and 4 at %) have been studied. It has been shown that all the samples under study undergo a diffuse phase transition, and the degree of diffuseness increases with an increase in the La concentration. The temperature dependences of the optical transmission in different regimes of applying an electric field and the quadratic electro-optical effect have been investigated. It has been found that, at room temperature, the maximum electro-optical effect is observed in the ceramics with a La concentration of 3 at %. This is explained by the fact that the measurement temperature is close to the Vogel-Fulcher temperature at which the minimum electric field is required to induce ferroelectric states from the relaxor phase.     

(1-x)PMN-xPT铁电致冷陶瓷的研究

概括介绍了铁电致冷基本原理，给出了三种电生热效应，即线性电生热效应、二次电生热效应和电场诱导一级相变型电生热效应的表达式，测量了(1-x)Pb(Mg_1/3 Nb_2/3 )O₃-xPbTiO₃［简记为(1-x)PMN-xPT］，当x=0.08, 0.10和0.25时在室温附近的电生热性能，分析了其电生热效应的起源.研究结果表明，(1-x)PMN-xPT铁电固溶体陶瓷在室温附近具有较大的电生热效应；该效应起源于电场诱导一级相变型电生热效应和线性电生热效应；该系列陶瓷可望用于室温附近多级铁电致冷. 关键词：     

Unique features of the crystal structure of the (PbMg1/3Nb2/3O3)0.6-(PbTiO3)0.4 solid solution

An x-ray diffraction study of the paraphase of the (PbMg_1/3Nb_2/3O₃)_0.6-(PbTiO₃)_0.4 solid solution has been found to exhibit a clearly pronounced ferroelectric transition. It is shown that Pb²⁺ ions occupy a special position (000), as opposed to pure PMN and other relaxor ferroelectrics, where they are displaced from it in random directions. The absence of these displacements indicates suppression of frozen-in random electric fields in this compound. Fiz. Tverd. Tela (St. Petersburg) 41, 1282–1285 (July 1999)     

Unusual piezoresponse behavior across the grain boundary of PbMg1/3Nb2/3O3-0.33PbTiO3 thin films

Ferroelectric PbMg_1/3Nb_2/3O₃-0.33PbTiO₃ (PMN-0.33PT) polycrystalline thin film near MPB was grown on Ir with LaNiO₃ buffer layer by pulsed laser deposition technology. Piezoresponse force microscopy (PFM) was employed to investigate the role of grain boundary on the domains formation and their local physical properties in PMN-PT thin film. Unusual piezoresponse behaviors were firstly observed across the grain boundary of PMN-PT thin film via PFM. Such abnormal phenomenon is ascribed to the structural incompatibility-induced local stress across the grain boundary, which gives a deep influence on the local imprint behavior of PMN-PT thin film.     

Electro-optical polarization mode dispersion in PbMg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript> single crystals

The polarization mode dispersion induced by an external ac electric field in PbMg_1/3Nb_2/3O₃ single crystals is studied experimentally at frequencies of 10⁴–10⁷ Hz. It is established that the discovered electro-optical polarization mode dispersion (EPMD) displays anomalous properties related to the orientation of the induced dipole moments in microregions of the crystal. Analytical expressions describing the peculiarities of the physical properties of relaxors giving rise to the EPMD are obtained.     

The theory of morphotropic phase transition in PbZr<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ti<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3</Subscript>

The concept of the mechanism of formation of morphotropic boundaries in T?x phase diagrams of solid solutions of complex oxides with the perovskite structure has been formulated. This concept is illustrated by calculation of the conditions for existence of morphotropic phase transition in a quasy-binary solid solution of the PbZr_{1 ? x} Ti _x O₃ and (1 ? x)PbMg_1/3Nb_2/3O₃ + xPbTiO₃ compositions.