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.     

Ferroelectric phase transitions in Pb0.96Ba0.04Sc0.5Nb0.5O3 and Pb0.94Ba0.06Sc0.5Nb0.5O3 solid-solution single crystals

The optical properties of Pb_0.96Ba_0.04Sc_0.5Nb_0.5O₃ (PBSN-4) and Pb_0.94Ba_0.06Sc_0.5Nb_0.5O₃ (PBSN-6) single-crystal solid solutions were studied for the first time. It was shown that the spontaneous phase transition occurring in PBSN-4 with no electric field present is accompanied by a sharp minimum in optical transmission, which indicates the percolation nature of the transition. No sharp changes were observed in the temperature dependence of optical transmission in PBSN-6 single crystals with no electric field applied. However, a very weak electric field, ～0.4 kV/cm, is sufficient to induce the ferroelectric state in PBSN-6 single crystals. It was shown that the destruction of the induced ferroelectric state is a first-order phase transition which is accompanied by an anomalously narrow peak in the small-angle light scattering intensity (or by a minimum in optical transmission) and occurs through the percolation mechanism.     

Dielectric,ferroelectric and field-induced strain response of lead-free BaZrO3-modified Bi0.5Na0.5TiO3 ceramics

Lead-free piezoelectric ceramics (1 − x)Bi_0.5Na_0.5TiO₃–xBaZrO₃ (BNT–BZ100x, with x = 0–0.10) were prepared using a conventional solid-state reaction method. The crystal structure, microstructure, dielectric, ferroelectric, and piezoelectric properties of BNT–BZ100x ceramics were studied as functions of different BZ content. X-ray diffraction patterns revealed that the BZ completely diffused in the BNT lattice in the studied composition range. An appropriate amount of BZ addition improved the dielectric, ferroelectric, and piezoelectric properties of BNT ceramics. The remanent polarization (P_r) and piezoelectric constant (d₃₃) increased from 22 μC/cm² and 60 pC/N for pure BNT to 30 μC/cm² and 112 pC/N for x = 0.040, respectively. In addition, electric field-induced strain was enhanced to its maximum value (S_max = 0.40%) with normalized strain (d*₃₃ = S_max/E_max = 500 pm/V) at an applied electric field of 8 kV/mm for x = 0.055. The enhanced strain can be attributed to the coexistence of ferroelectric and relaxor ferroelectric phases.     

Evolution from relaxor-like dielectric to ferroelectric in Ba[(Fe0.5Nb0.5)1−xTix]O3 solid solutions

Ba[(Fe_0.5Nb_0.5)_1−xTi_x]O₃ (x=0.2,0.4,0.6,0.8,0.85,0.9 and 0.95) solid solutions were synthesized by a standard solid-state reaction technique. X-ray diffraction at room temperature and dielectric characteristics over a broad temperature and frequency range were evaluated systematically. The structure of Ba[(Fe_0.5Nb_0.5)_1−xTi_x]O₃ solid solutions changed from cubic to tetragonal with increasing x. A Debye-like dielectric relaxation following the Arrhenius law similar to that in Ba(Fe_0.5Nb_0.5)O₃ was observed at lower temperature in the composition range 0.2≤x≤0.8, while the relaxor ferroelectric, diffused ferroelectric and normal ferroelectric behavior were observed for x=0.85,0.9 and 0.95, respectively. The process of the evolution of relaxor-like dielectric to ferroelectric suggested the changing from dilute polar micro-domains to polar micro-domains, polar micro/macro-domains and then polar macro-domains in the present ceramics.     

Optical studies of delayed relaxation in Pb<Subscript>0.94</Subscript>Ba<Subscript>0.06</Subscript>Sc<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>O<Subscript>3</Subscript> (PBSN-6) solid solutions

The temperature dependences of the permittivity, birefringence, optical transmittance, and small-angle light scattering and their variations with time are studied for single crystals of the Pb_0.94Ba_0.06Sc_0.5Nb_0.5O₃ relaxor (PBSN-6) in the heterophase region of coexistence of different phases. It is shown that an electric field induces a phase transition to the ferroelectric state, which manifests itself within some time (delay time τ) after application of the electric field to the crystal. The observed dependence of the temperature of this transition on the heating rate of the sample and the changes in the birefringence and small-angle light scattering intensity with time confirm the kinetic character of the induced transition. Temperature dependences of the delay time τ for different electric fields are constructed. It is revealed that, at low temperatures, the delay time τ decreases with increasing temperature. This agrees with the behavior of τ in classical relaxors. At the Vogel-Fulcher temperature, however, one observes that dτ/dT reverses sign and τ increasing as the temperature continues to increase. This anomalous behavior of τ in the heterophase region is accounted for by the coexistence of the cubic relaxor and rhombohedral macrodomain phases.     

Synthesis and characteristics of KTa0.5Nb0.5O3 thin films

KTa_0.5Nb_0.5O₃ thin films were synthesized via a metal-organic solution. Characteristics were measured, such as X-ray diffraction pattern, surface morphology and roughness, and electric properties. The synthesized films have a (100) preferential growth orientation on Si (100) substrate. The homogeneous microstructure and smooth surface benefit to the good electric properties of the thin films. The current density-voltage characteristic shows an unexpected feature of the transition from linear to nonlinear, which can be explained by the space-charge-limited mode. Dielectric constant and loss of the thin films decrease with the increase of frequency. The decrease of dielectric loss is related to the decrease of net polarization in material. The decrease of dielectric constant can be explained by Debye formula. The phase transition temperature T _c is about 102 °C for KTa_0.5Nb_0.5O₃ materials.     

Chromium-and manganese-doped TlInS<Subscript>2</Subscript>—A new relaxor ferroelectric

The dielectric, pyroelectric, and polarization properties of TlInS₂ crystals doped with 0.1 mol % Cr and Mn are investigated. It is shown that TlInS₂ compounds doped with chromium and manganese can be assigned to the class of relaxor ferroelectric materials. The temperature range of existence of the stable relaxor (nanodomain) state and the temperature of the phase transition from this state to the ferroelectric (macrodomain) state are determined. The temperature dependence of the pyroelectric current is characterized by an anomaly in the range of the phase transition.     

Properties of the solid solution (1−x)Na0.5Bi0.5TiO3-(x)BiFeO3

This study shows that remarkable electric and magnetic properties are encountered within the (1−x)Na_0.5Bi_0.5TiO₃ (NBT)-(x)BiFeO₃ (BF) solid solution. Dual ferroelectric and magnetic properties are observed in the BF-rich part of the solid solution implying intrinsic multiferroic character of the compounds. In addition, a relaxation phenomenon is evidenced within the overall compositional domain of the solid solution. This study emphasizes that in the NBT-rich part, the relaxor behaviour is very similar to that of NBT, while beyond x=0.5, it turns to a different mechanism of relaxation probably induced by the presence of oxygen vacancies resulting from the mixed valence of the iron cations.     

Phase diagram of (1−x%)(0.89Bi0.5Na0.5TiO3–0.06BaTiO3–0.05K0.5Na0.5NbO3)–x%MnO2 lead-free anti-ferroelectric ceramics

A phase diagram for the lead-free ceramics in the (1?x%)(0.89Bi_0.5Na_0.5TiO₃–0.06BaTiO₃–0.05K_0.5Na_0.5NbO₃)–x%MnO₂ (BNBKN-x%Mn) binary system is constructed for the first time based on the ferroelectric and dielectric measurements. The ferroelectric behaviors under different temperatures suggest that the ceramics are basically of relaxor anti-ferroelectric nature near room temperature. The temperature dependent dielectric properties show that when the addition of MnO₂ increases, the relaxor anti-ferroelectric phase can be stabilized to be close to the Curie point, which corresponds to a relaxor anti-ferroelectric to paraelectric phase transition.     

Ferroelectric-relaxor behavior of (Na0.5K0.5)NbO3-based ceramics

We report that ferroelectric-relaxor behavior is induced by doping of SrO and TiO₂, or BaO and TiO₂ into classic ferroelectric (Na_0.5K_0.5)NbO₃. It is found that [(Na_0.5K_0.5)_0.9Sr_0.1](Nb_0.9Ti_0.1)O₃ ceramics exhibit a pronounced ferroelectric-relaxor behavior, comparable to that of [(Na_0.5K_0.5)_0.9Ba_0.1](Nb_0.9Ti_0.1)O₃ ceramics. Our results indicate that the relaxor behavior is closely related to the appearance of micropolar regions in these systems. The relaxor behavior should arise from the dynamic response of micropolar clusters. Raman spectra of [(Na_0.5K_0.5)_1−xSr_x](Nb_1−xTi_x)O₃ ceramics measured in the wavenumber range from 100 to 1200 cm⁻¹ confirm that the first order scattering is dominant in phonon bands should result from both short-range ordered region (micropolar regions) and disordered matrix. The frequency dependence of dielectric permittivity measurements show that the relaxor behavior of SrO and TiO₂, or BaO and TiO₂ doped (Na_0.5K_0.5)NbO₃ ceramics is not a Debye type in the radio frequency range.     

Dielectric and optical properties of Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)<Subscript>0.8</Subscript>Ti<Subscript>0.2</Subscript>O<Subscript>3</Subscript> (PMNT-0.2) ferroelectric relaxor single crystals

The dielectric and optical (optical transmission, small-angle light scattering, birefringence) properties of PMNT-0.2 single crystals and their variation induced by a dc electric field have been studied. The birefringence was found to increase anomalously at the transition from the rhombohedral ferroelectric to the inhomogeneous relaxor phase (the spontaneous ferroelectric transition temperature T_sp). Below T_sp, the dielectric and optical properties were observed to exhibit anomalies originating from reorientation and growth of domains in size. Unlike ferroelectric relaxors of the type of PbB′_1/3B′_2/3O₃ and PbB′_1/2B′_1/2O₃, in PMNT-0.2 neither induction of the ferroelectric phase by an electric field nor thermally stimulated destruction of the ferroelectric state occurs through the percolation mechanism (i.e., they are not accompanied by anomalously narrow maxima in small-angle light scattering). This is attributed to the inhomogeneous structure of the relaxor phase, as a result of which the phase transition does not take place simultaneously in various regions of the crystal.     

Electric-field-induced phase transition in single-crystal lead zinc niobate

The behavior of lead zinc niobate, a relaxor ferroelectric, in electric fields has been studied by dielectric, optical transmittance, and small-angle light scattering techniques. A field-induced transition from an averaged cubic to macrodomain ferroelectric phase has been found. A comparison is made with the properties of the phase induced in lead magnoniobate, a classical relaxor. Fiz. Tverd. Tela (St. Petersburg) 40, 527–530 (March 1998)     

Evolution of domain processes during the transition from classical ferroelectric to relaxor ferroelectric

Dependences of the relative permittivity on the external bias electric field of ceramics of the yPZN-mPMN-nPNN-xPT (x = 0.25?C0.40) system have been studied. The evolution of domain processes during the concentration transition from classical ferroelectric to relaxor ferroelectric has been shown. Tentative conclusions on the mechanisms of electric field-induced transitions from the relaxor state to the ??normal?? ferroelectric state have been drawn.     

Optical properties of cubic and tetragonal KTa0.5Nb0.5O3 by density functional theory

Using density functional methods, optical properties of KTa_0.5Nb_0.5O₃ (KTN) are investigated. The imaginary part of dielectric function ε₂(ω), the optical absorption coefficient I(ω) and the reflectivity R(ω) of KTN in the cubic (paraelectric) and tetragonal (ferroelectric) phases are calculated. The origin of the different behavior of the optical spectra between the two phases is discussed.     

Ferroelectric relaxor properties of (1 − x)K0.5Na0.5NbO3–xBa0.5Ca0.5TiO3 ceramics

The Ba_0.5Ca_0.5TiO₃ (BCT) composition dependent dielectric and structural properties of (1?x)K_0.5Na_0.5NbO₃–xBa_0.5Ca_0.5TiO₃ powders were investigated. Room temperature x-ray diffraction revealed the powder structure to transform from orthorhombic to cubic with increasing BCT composition. The frequency dependent dielectric constant measurements revealed a shift in the temperature of the maximum dielectric constant for at frequencies, suggesting that the system exhibits ferroelectric relaxor behavior. The system containing 15% BCT showed the closest calculated Curie–Weiss exponent to 2, which the exponent for a relaxor ferroelectric.     

Dielectric properties Ca-substituted barium strontium titanate ferroelectric ceramics

The dielectric and ferroelectric properties of Ba_1−xSr_xTiO₃ (BST) (x=0.10,0.20,0.30,0.40 and 0.60) ceramics and Ba_1−2xSr_xCa_xTiO₃ (BSCT) (x=0.10,0.20,0.30) ceramics have been investigated. The low temperature phase transitions of BST ceramics vanish after Ca²⁺ substitution while the high temperature transition is diffused and relaxed, which becomes more obvious with increasing x. Ca²⁺ substitution obviously decreases the dielectric constant maximum, K_m, of BST ceramics and changes the temperature of dielectric constant maximum, T_m, of BST ceramics. The shift of T_m in BST is attributed mainly to the Sr²⁺ and Ba²⁺ concentration. BST ceramics exhibit almost normal ferroelectric characteristics, while a typical relaxor behavior was observed in BSCT ceramics. The relaxor behavior observations may be understood by a random electric field induced domain state.     

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.     

Reverse dependences of the permittivity of xPZN − (1 − x)PSN ferroelectric ceramics on the bias electric field

The effect of bias electric fields E ₌ on the dielectric response of xPZN ? (1 ? x)PSN ferroelectric solid solutions with PZN contents x = 0, 0.05, 0.20, and 0.50 is investigated in the temperature ranges corresponding to the smeared phase transitions of the studied compounds. It is concluded that an increase in the PZN content in this system leads to a narrowing of the temperature range of existence of the relaxor phase.     

Bi-fluctuation in Na0.5Bi0.5TiO3 ferroelectric ceramics with abnormal relaxor behaviour

ABSTRACT

The existence of Bi-fluctuation dispersing in Na_0.5Bi_0.5TiO₃ (NBT) relaxor ferroelectric is hinted in other recent studies. However, this fluctuation has not been directly observed yet. We introduce the Bi-rich nano-regions with different sizes in a series of NBT ceramics by the slight excess of Bi³⁺ content. The crystal symmetries of the Bi-rich nano-regions and the NBT matrix are rhombohedral. The lattice parameters of the nano-regions are larger than those of the matrix in NBT ceramics, which were confirmed by the X-ray diffraction Rietveld refinement, TEM techniques and first-principles calculation. Also, the disorder-induced nano-regions appearing as Bi-fluctuation are associated with the complex phase transitions and the high-frequency relaxor behaviour of NBT suggested by the dielectric measurements and Raman spectra.