Relaxor behavior of SrTiO3-LiNbO3 solid solutions

Ceramic samples of (1 ? x)SrTiO₃-xLiNbO₃ (0 ≤ x ≤ 0.05) solid solutions are synthesized. The dielectric and acoustic properties of the solid solutions are studied in the temperature range from 15 to 300 K. It is revealed that the polar state characterized by the dispersion of the permittivity and the dielectric hysteresis occurs at low temperatures. The results obtained are discussed within the concept of relaxor ferroelectrics.     

Ferroelastic transition and the relaxor state in SrTiO3-PbMg1/3Nb2/3O3

Dielectric and acoustic properties of the (1 ? x)SrTiO₃?xPbMg_1/3Nb_2/3O₃ solid solutions (0 ? x ? 1) have been studied at temperatures ranging from 4.2 to 350 K. It has been found that the improper ferroelastic transition exists up to a concentration x = 0.4 and that the phase transition temperature grows with x increasing from 0 to 0.4. As the concentration of the second component is further increased, the transition becomes suppressed by the relaxor phase forming at x _c ≈ 0.22. The results obtained are discussed in terms of the current concepts of relaxor ferroelectrics.     

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)     

Diffuse ferroelectric phase transitions in cubically sabilized perovskites

Typical examples of ferroelectrics with diffuse phase transitions (relaxor ferroelectrics), like Pb(Mg_1/3Nb_2/3)O₃ are actually non transforming. The paraelectric phase is fully stablized against a ferroelectric phase transition in this case. A phase transition can be induced, however, by an electric field with appropriate orientation below the temperature of the dielectric constant maximum. The analogy with stress-induced martensitic phase transitions in metallic alloys is pointed out. Pecularities of the properties and of the polarization reversal of such systems are demonstrated. Actual diffuse ferroelectric phase transitions in disordered solid solutions and mixed compounds with a partially stabilized parent phase are compared with athermal martensitic transformations. With particular regard to technical ceramics based on PZT, the influence of interfaces between transformed regions and remnants of the parent phase which have to distinguished from domain walls, and of the reduced stability of the ferroelectric phase on the properties of these systems is discussed. Some effects usually explained solely by domain processes may be understood also from this point of view.

Stabilization of a parent phase against an order-disorder-type phase transition is supposed to be caused by glass-like freezing caused by inelastic cooperative interactions between disordered molecular groups.     

Influence of the prehistory of NaNbO3-Gd1/3NbO3 ceramics and single crystals on their dielectric properties

The dielectric properties of a ceramic and a single crystal of the same composition 0.9NaNbO₃-0.1Gd_1/3NbO₃ (NNG10) with different prehistories of the material are investigated in the low-and infralow-frequency ranges. It is revealed that the dielectric aging of the material based on the NaNbO₃ antiferroelectric with a smeared phase transition differs in character from similar phenomena observed in relaxor ferroelectrics.     

Anomalies of polarization processes in relaxor ferroelectrics

The anomalous polarization of relaxor ferroelectrics (relaxors), such as solid solutions of barium-strontium niobate (SBN) and lead magnesium niobate (PMN), is studied in ac low-frequency (up to 10^?4 Hz) and dc electric fields. The results of studying dielectric hysteresis loops, polarization relaxation, the coercive-field distribution spectrum, nonlinear polarization for various scales of inhomogeneities, and polarization in a photosensitive SBN relaxor subjected to illumination are presented. All of the anomalous polarization properties of relaxors substantially distinguish them from ordinary homogeneous ferroelectrics and serve as signs and a measure of structural disorder. This article presents a brief review of our recent studies and some new results obtained as a result of their analysis.     

Dielectric characteristics of the relaxor state of the perovskite ceramics 0.9(Na1 − x K x Bi)1/2TiO3-0.1Bi(ZnTi)1/2O3 near the morphotropic phase boundary

X-ray diffraction investigations have revealed that, in the system of solid solutions 0.9(Na_{1 ? x} K _x Bi)_1/2TiO₃-0.1Bi(ZnTi)_1/2O₃, there is a morphotropic phase boundary in the potassium concentration range of x ≈ 0.25, which separates the regions of compositions with rhombohedral (R3c) and tetragonal (P4mm) structures. It has been shown that, in the vicinity of this boundary, ceramic samples of the studied system exhibit properties of relaxor ferroelectrics. The results of the investigation into the dielectric properties of relaxor ceramics of the composition x = 0.3 with the use of the impedance spectra measured in the frequency range from 25 to 10⁶ Hz at temperatures from 100 to 900 K have been presented. It has been found that, in the temperature region of the existence of the relaxor state lying below the temperature corresponding to the maximum of the real part of the permittivity (T′ _m = 550 K), the dielectric polarization is determined by the sum of the contributions from the matrix and dipole clusters. The temperature dependence of the contribution from the clusters, which is determined by the kinetics of their formation and freezing, is characterized by a curve with the maximum at approximately 400 K. The process of freezing of dipole clusters occurs over an extended temperature range of more than 200 K.     

Relaxor Behaviour and Ferroelectric Properties of （Li0.12Na0.88） （Nb0.9-xWa0.10Sbx）O3 Lead-Free Ceramics

New lead-free ceramics （Lio.12Na0.88） （Nbo.9-x Ta0.10 Sbx） 03 （0.01 × 0.06） are synthesized by solid-state reaction method. The dielectric, piezoelectric and ferroelectric properties of the ceramics are studied. The dielectric constant dependence with temperature and frequency of the ceramic specimen with x = 0.04 shows typical characteristics of relaxor ferroelectrics, and the Vogel-Fulcher relationship is fulfilled. The dielectric behaviour and its relation to the phase transition phenomena are discussed. The polarization hysteresis loops at room temperature are also measured.     

Acoustic anomalies in SrTiO<Subscript>3</Subscript>−BiFeO<Subscript>3</Subscript> solid solutions

The results of acoustic investigations of solid solutions SrTiO₃?BiFeO₃ in the temperature range from 100 to 650 K have been presented. The measurements of the velocity and attenuation of the longitudinal ultrasonic mode at a frequency of 10 MHz were carried out by the pulse-echo method. The observed anomalies in velocity and attenuation correlate with the maxima of the dielectric constant in the temperature range of the relaxor state. In addition, the attenuation peaks in the temperature range 400–600 K, which define Burns and T* temperatures, which are characteristic of relaxors, have been identified. The obtained results have allowed the clarifying of the phase diagram of the solid solution system SrTiO₃?BiFeO₃.     

Ferroelectricity in SrTiO3 nanocrystalline disks

SrTiO₃ and CaTiO₃ conventional bulk materials are incipient ferroelectrics. In this note, we report for the first time that ferroelectricity could occur in SrTiO₃ nanocrystalline disks even at room temperature. The peak in the temperature dependence of permittivity for a CaTiO₃ nanocrystalline disk at a low temperature is also observed. The observed ferroelectricity (or permittivity peak) in SrTiO₃ (or CaTiO₃) nanocrystalline disks could be attributed to the strain effect.     

Phase transition, structural and electrical properties of Pb(Zn1/3Nb2/3)O3-doped Pb(Ni1/3Nb2/3)O3-PbTiO3 ceramics prepared by solid-state reaction method

Phase pure perovskite (1−x−y)Pb(Ni_1/3Nb_2/3)O₃-xPb(Zn_1/3Nb_2/3)O₃-yPbTiO₃ (PNN-PZN-PT) ferroelectric ceramics were prepared by conventional solid-state reaction method via a B-site oxide mixing route. The PNN-PZN-PT ceramics sintered at the optimized condition of 1185 °C for 2 h exhibit high relative density and rather homogenous microstructure. With the increase of PbTiO₃ (PT) content, crystal structure and electrical properties of the synthesized PNN-PZN-PT ceramics exhibit successive phase transformation. A morphotropic phase boundary (MPB) is supposed to form in (0.9−x)PNN-0.1PZN-xPT at a region of x=32-36 mol% confirmed by X-ray diffraction (XRD) measurement and dielectric measurement. The MPB composition can be pictured as providing a “bridge” connecting rhombohedral ferroelectric (FE) phase and tetragonal one since crystal structure of the MPB composition is similar to both the rhombohedral and tetragonal lattices. Dielectric response of the sintered PNN-PZN-PT ceramics also exhibits successive phase-transition character. 0.64PNN-0.1PZN-0.26PT exhibits broad, diffused and frequency dependent dielectric peaks indicating a character of diffused FE-paraelectric (PE) phase transition of relaxor ferroelectrics and 0.40PNN-0.1PZN-0.50PT exhibits narrow, sharp and frequency independent dielectric peaks indicating a character of first-order FE-PE phase transition of normal ferroelectrics. The FE-PE phase transition of 0.56PNN-0.1PZN-0.34PT is nearly first-order with some diffused character, which also exhibits the largest value of piezoelectric constant d₃₃ of 462pC/N.     

Polarization characteristics of the relaxor ceramics of multicomponent system with PbNb2/3Zn1/3O3, PbNb2/3Mg1/3O3, and PbTiO3

The phenomenon of dielectric hysteresis in the relaxor ceramics of multicomponent system with PbNb_2/3Zn1/₃O₃, PbNb_2/3Mg_1/3O₃, PbTiO₃ has been studied. The influence of different modifiers on polarization characteristics is examined and the correlations of these properties with the phase and chemical composition of the ceramics are investigated. The results obtained can be used to predict relaxor properties.     

Investigating the structure and dielectric properties of ceramic solid solutions of the SrTiO3-BiScO3 system

Ceramic samples of (1 − x)SrTiO₃-(x)BiScO₃ system with x = 0, 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5 were synthesized. Neither of the end members of this system are ferroelectric materials. X-ray diffraction analysis reveals that at room temperature, the samples with x = 0.2, 0.3, 0.4, and 0.5 consisted of a mixture of two phases: a cubic center-symmetric Pm3m phase and a tetragonal polar P4mm phase. Dielectric permittivity and dielectric losses measurements of these compositions showed anomalies associated with the diffuse phase transition characteristic of ferroelectrics.     

Effect of annealing on the dielectric permittivity of strontium titanate films in the SrTiO3/Al2O3 structure

The paper reports an experimental study of the structure of a strontium titanate film on a sapphire substrate and of the dielectric properties of capacitors based on a SrTiO₃/Pt/Al₂O₃ multilayer system before and after a high-temperature anneal. The macro-and microstructure of SrTiO₃ films and its variation induced by the annealing have been investigated. The temperature and field dependences of the dielectric permittivity of strontium titanate films have been determined, and their comparison with similar data for single crystals carried out. The mechanisms by which annealing can affect the capacitor capacitance and the properties of SrTiO₃ films are discussed. Fiz. Tverd. Tela (St. Petersburg) 40, 1473–1478 (August 1998)     

Low- and infralow-frequency dielectric properties of the Pb(Mg1/3Nb2/3)O3 + 2 wt % Li2O ceramics

A dielectric response of the Pb(Mg_1/3Nb_2/3)O₃ ferroelectric ceramics with impurity of 2 wt % Li has been studied. The phase transition has been found to exhibit a relaxor character, as is the case in PMN without Li. However, unlike pure PMN, the dielectric response dispersion in PMN + 2 wt % Li₂O has been described by the Cole-Cole equation at temperatures below the temperature of the low-frequency maximum of the permittivity. An analysis of the dispersion parameters in a wide temperature range has demonstrated that it can be due to the relaxation of domain walls in PMN + 2 wt % Li₂O that appear most likely because of the existence of anomalously coarse grains in PMN + 2 wt % Li₂O.     

Evolution of phase transitions in SrTiO3-BiFeO3 solid solutions

The dielectric and acoustic properties of (1 ? x)SrTiO₃?xBiFeO₃ solid solutions (0 ≤ x ≤ 1) have been studied in the temperature range from 4.2 to 850 K. Evolution of the antiferrodistortive transition and its suppression in the concentration range 0.1 < x < 0.2 have been revealed. X-ray diffraction data obtained at room temperature, as well as the observed acoustic anomalies combined with dielectric measurements, have been used to estimate the concentration range of the existence of the relaxor state, as well as of the formation and coexistence of the antiferromagnetic and ferroelectric phases at high BiFeO₃ concentrations.     

Transparent ferroelectric ceramics PbMg1/3Nb2/3O3-xPbZr0.53Ti0.47O3: Dielectric and electro-optical properties

Lanthanum-free high-transparency ferroelectric ceramics PbMg_1/3Nb_2/3O₃?xPbZr_0.53Ti_0.47O₃ (PMN-xPZT) have been prepared for the first time by a two-stage sintering method. The dielectric and electro-optical properties of the PMN-xPZT ceramics of different compositions, with the values of x both far from the morphotropic phase boundary (x = 10, 16, 23%) and close to it (x = 33%), have been studied. It has been shown that, in compositions lying closer to the morphotropic phase boundary (x = 23 and 33%), one observes, with no electric field applied, a first-order phase transition to a macrodomain ferroelectric phase, whereas the compositions far from the boundary (x = 10, 16%) persist in the relaxor cubic phase down to the low-temperature domain. It has been found that, in the ceramic with x = 33%, the quadratic electro-optical coefficients have at high temperatures (T > 340 K) the largest value among the relaxor systems, which expands the temperature interval of applicability of these solid solutions in industry.     

Polarized Raman mapping study of the microheterogeneity in 0.67PbMg1/3 Nb2/3O3‐0.33PbTiO3 single crystal

Polarized micro‐Raman spectroscopy was carried out on the (001) face of a 0.67PbMg_1/3Nb_2/3O₃‐33%PbTiO₃ (PMN‐33%PT) single crystal. The Raman images revealed the spatial variations of the intensity of the Raman bands, suggesting that the structure in the PMN‐33%PT single crystal varied from one micro‐area to another. When changing the polarization direction of the incident light with respect to the selected crystalline axes, the intensities of the Raman modes varied periodically. According to the Raman selection rules (RSRs), the angular dependences of the Raman modes indicated that the PMN‐33%PT single crystal is in the monoclinic phase. Furthermore, the color patterns in the Raman images were associated with the coexistence of the M_A‐ and M_C‐type monoclinic phases in the PMN‐33%PT single crystal. Our results provide useful information for understanding the microheterogeneity of the relaxor PMN‐xPT single crystals with compositions near the morphotropic phase boundary region. Copyright © 2010 John Wiley & Sons, Ltd.     

Properties of strontium titanate in the SrTiO3/CeO2/Al2O3 multilayered structure

Studies of the crystal structure, elemental composition, and dielectric properties of strontium titanate films in SrTiO₃/CeO₂/Al₂O₃ multilayered structures are reported. Data on the crystal lattice and impurity contents have been obtained, and temperature and electric field dependences of the dielectric properties of SrTiO₃ films in the microwave range have been measured. An analysis of the results is made to establish the reason for the nonmonotonic dependence of the small-signal dielectric permittivity of SrTiO₃ films on temperature. Fiz. Tverd. Tela (St. Petersburg) 39, 1024–1029 (June 1997)