Relaxor behaviour of (Ba0·5Sr0·5)(Ti0·6Zr0·4)O3 ceramics

Ba_0·5Sr_0·5Ti_0·6Zr_0·4O₃ ceramic has been prepared through solid state reaction route. X-ray diffraction shows that the sample has cubic perovskite structure with space group Pm-3m at room temperature. Temperature dependent dielectric study of the ceramic has been investigated in the frequency range 50 Hz-1 MHz. The density of the sample is determined using Archimedes’ principle and is found to be ∼99% of X-ray density. The dielectric study revealed diffuse phase transition of second order. A broad dielectric anomaly coupled with the shift of dielectric maxima toward a higher temperature with increasing frequency indicates the relaxor-type behaviour in the ceramics. The index of relaxation (γ) and the broadening parameter (Δ) were estimated from a linear fit of the modified Curie-Weiss law. The value of γ ∼ 1·72 indicates the strong relaxor nature of the ceramic. A remarkably good fit to the Vogel-Fulcher relation further supports such a relaxor nature.     

Temperature dependence of dielectric and piezoelectric properties of (1?x)(BiScO3–0.64PbTiO3)–xLiNbO3 high-temperature relaxor ferroelectric ceramics

(1−x)(0.36BiScO₃–0.64PbTiO₃)–xLiNbO₃ (BSPT64–xLN) high-temperature relaxor ferroelectric ceramics near the morphotropic phase boundary (MPB) composition were investigated. X-ray diffraction showed a change in symmetry from MPB phase to rhombohedral phase with LiNbO₃ content increasing. A change from normal ferroelectric features to relaxor ferroelectric features was observed with LiNbO₃ substitution up to x = 0.06, while high-temperature dielectric relaxation was exhibited at T _max ~230 to 383°C for 0.02 ≤ x ≤ 0.06. The BSPT64–xLN ceramics with x = 0.02 LiNbO₃ exhibited good piezoelectric properties compared with BS–0.64PT ceramics: piezoelectric coefficients d ₃₃ = 505pC/N, planar electromechanical coupling factors k _p = 0.47, and remnant polarization P _r = 40 μC/cm², respectively. The annealing temperature dependence of piezoelectric response for BSPT64–xLN ceramics was measured and it was found that the piezoelectric properties decreased slightly before 210°C for x = 0.02 and 0.04, showing excellent thermal stability, which indicated that BSPT64–xLN relaxor ferroelectric ceramics can be used in the range of high temperature compared to Pb-based relaxor ferroelectrics.     

Dielectric properties and relaxation of Bi<Subscript>0·5</Subscript>Na<Subscript>0·5</Subscript>TiO<Subscript>3</Subscript>-BaNb<Subscript>2</Subscript>O<Subscript>6</Subscript> lead-free ceramics

A new member of lead-free piezoelectric ceramics of the BNT-based group, (1 − x)Bi_0·5Na_0·5TiO_3−x BaNb₂O₆, was prepared by conventional solid state reaction and its dielectric properties and relaxation was investigated. X-ray diffraction showed that BaNb2O6 diffused into the lattice of Bi_0·5Na_0·5TiO₃ to form a solid solution with perovskite-type structure. A diffuse character was proved by the linear fitting of the modified Curie-Weiss law. The temperature dependence of dielectric constant at different frequencies revealed that the solid solution exhibited relaxor characteristics different from classic relaxor ferroelectrics. The samples with x = 0·002 and 0·006 exhibited obvious relaxor characteristics near the low temperature dielectric abnormal peak, T _f, and the samples with x = 0·010 and 0·014 exhibited obvious relaxor characteristics between room temperature and T _f. The mechanism of relaxor behaviour was also discussed according to the macro-domain to micro-domain transition theory.     

The effects of CuO-doping on dielectric and piezoelectric properties of Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>–Ba(Zr,Ti)O<Subscript>3</Subscript> lead-free ceramics

CuO-doped lead-free ceramics based on bismuth sodium titanate (Bi_0.5Na_0.5TiO₃, BNT) and barium zirconate titanate (Ba(Zr_0.07Ti_0.93)O₃, BZT) were prepared via a multi-step solid-state reaction process. The BNT–BZT with CuO dopant ceramics sintered at 1150–1180 °C for 2 h in air showed a pure perovskite structure. SEM images reveal that a small amount of CuO (<2 mol%) play a significant role on the microstructure to improve its sintering attributes, while it will degrade when the dopant is added beyond 2 mol%. The dielectric and piezoelectric properties of CuO-doped BNT–BZT ceramics were evaluated. At room temperature, the sample doped with 2 mol% CuO shows quite good properties such as a high piezoelectric constant (d ₃₃ ∼156.5 pC/N) and a high electromechanical coupling factor (k _t ∼52%). The depolarization temperature increased dramatically and the maximum permittivity temperature decreased slightly.     

Orientation dependence of electromechanical properties of relaxor based ferroelectric single crystals

The orientation dependence of electromechanical properties of relaxor based ferroelectric single crystals Pb(Zn_1/3Nb_2/3)O₃–(6–7)%PbTiO₃ and Pb(Mg_1/3Nb_2/3)O₃–33%PbTiO₃ has been calculated by coordinate transformation. Different from previous studies, the optimum cutting orientations have been predicted in terms of their piezoelectric responses in the corresponding crystal planes. The calculation results indicated that the anisotropic piezoelectric effects of [001] _c and [011] _c poled multi-domain crystals mainly come from the intrinsic contribution. However, the strong dielectric anisotropy of [001] _c poled multi-domain crystals mainly comes from extrinsic domain and domain wall contributions. For [011] _c poled multi-domain crystals, the intrinsic orientation effect enhances the dielectric anisotropy.     

Effect of composition on dielectric and electrical properties of the Sr1 −x La x Ti1 −x Co x O3 system

Valence compensated perovskite system Sr_{1 −x} La _x Ti_{1 −x} Co _x O₃ shows dielectric relaxor behaviour with very high value of dielectric constant in the composition range 0·20 <x < 0·40. In this paper the effect of composition on microstructure and the resulting electrical behaviour is reported. The compositions withx = 0·25, 0·30, 0·33, 0·35 and 0·37 have been synthesized by solid state ceramic method and dielectric measurements were made in the temperature range of 300–500 K and frequency range of 100 Hz to 1 MHz. Grain boundaries played an important role in their dielectric behaviour. Complex plane impedance and modulus techniques were used to separate out the contributions of grain and grain-boundaries to the resulting dielectric behaviour. It was observed that the bulk resistivity as well as the grain boundaries resistance decreased with increasingx. Furthermore, impedance analysis demonstrated that extremely high value of dielectric constant observed in these materials was due to barrier layers formation at grain-grain-boundaries interfaces. Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995     

Microwave dielectric properties of 3Li2O–Nb2O5–3TiO2 ceramics with Li2O–V2O5 additions

A new Li₂O–Nb₂O₅–TiO₂ (LNT) ceramic with the Li₂O:Nb₂O₅:TiO₂ mole ratio of 3:1:3 has been investigated. The compound is composed of two phases, the Li₂TiO₃ and “M-phase” solid solution phase. The microwave dielectric ceramic has low sintering temperature (∼1100 °C) and good microwave dielectric properties of a relatively high permittivity (∼51), high Q × f value up to 8700, and small temperature coefficient (∼37 ppm/°C). The low-amount doping of 0.83Li₂O–0.17V₂O₅ (LV) can effectively lower the sintering temperature from 1100 to 900 °C and induce no obvious degradation of the microwave dielectric properties. Typically, the 1 wt.% LV-doped ceramic sintered at 900 °C has better microwave dielectric properties of ε_r = 51.3, Q × f = 7235 GHz, τ _f  = 22 ppm/°C, which suggests that the ceramics can be applied in microwave LTCC devices.     

Piezoelectric properties and equivalent circuits of ferroelectric relaxor single crystals

Temperature dependent piezoelectric properties of ferroelectric relaxor single crystals, particularly the cerium-doped strontium barium niobate compositions (SBN60: Ce), were investigated by resonance and anti-resonance technique. Characteristic resonant frequencies (f_r−f_a, f_s−f_p, and f_m−f_n) were studied using equivalent circuit simulation. Piezoelectric resonance in a relaxor resonator persists into temperatures much higher than Tm (the temperature at which dielectric constant, κ, has a maximum at 1 kHz) in comparison with the normal ferroelectrics such as TGS. The parameters in an equivalent circuit, however, are phenomenally different from a normal resonator like a TGS, near and above the transition temperature region. The significance and understanding of the piezoelectric resonance characteristics in ferroelectric relaxor are discussed. This revised version was published online in November 2006 with corrections to the Cover Date.     

Compositional dependence of structural and electrical properties in (1 − x)[PMN–PT(65/35)]–xPZ solid solutions

Perovskite types (1 − x)[PMN–PT(65/35)]–xPZ (with x = 0, 0.1, 0.3, 0.5, 0.7 and 0.9) piezoelectric ceramics were prepared by a modified columbite precursor method. The lattice parameters of the (1 − x)[PMN–PT(65/35)]–xPZ ceramics increase with the addition of larger Zr⁴⁺ ion compared to that of other B-site ions. The SEM photographs of all the samples with different PZ content exhibit homogeneous and dense microstructure. The P–E loops indicate the PMN–PT–PZ ternary system has excellent ferroelectric properties. Both d ₃₃ and k _p dependences in PZ content show similar variation. Introduction of a small amount of PZ content in the PMN–PT(65/35) ceramics enhanced the relaxor behavior, which was confirmed by studying frequency and temperature-dependent dielectric behavior. The increasing values of diffuseness parameter obtained from the fit of a modified Curie–Weiss law established the relaxor nature.     

Structure and electrical properties of Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–BiCoO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x − y)Bi_0.5Na_0.5TiO₃–xBi_0.5K_0.5TiO₃–yBiCoO₃ (x = 0.12–0.24, y = 0–0.04) have been fabricated by a conventional solid-state reaction method, and their structure and electrical properties have been investigated. The XRD analysis shows that samples with y ≤ 0.03 exhibit a pure perovskite phase and very weak impurity reflections can be detected in the sample with y = 0.04. With x increasing from 0.12 to 0.24 and y increasing from 0 to 0.04, the ceramics transform gradually from a rhombohedral phase to a tetragonal phase and rhombohedral–tetragonal phase coexistence to a pseudocubic phase, respectively. The morphotropic phase boundary (MPB) of the system between rhombohedral and tetragonal locates in the range of x = 0.18–0.21, y = 0–0.03. The ceramics near the composition of the MPB have good performances with piezoelectric constant d ₃₃ = 156 pC/N and electromechanical coupling factor k _p = 0.34 at x = 0.21 and y = 0.01, which attains a maximum value in this ternary system. Adding content of BiCoO₃ leads to a disappearance of the response in the curves of dielectric constant-temperature to the ferroelectric–antiferroelectric transition. The temperature dependence of dielectric properties suggests that the ceramics are relaxor ferroelectrics. The results show that (1 − x − y)Bi_0.5Na_0.5TiO₃–xBi_0.5K_0.5TiO₃–yBiCoO₃ ceramics are good candidate for use as lead-free ceramics.     

Dielectric behaviour of MgFe2O4 prepared from chemically beneficiated iron ore rejects

Chemically beneficiated high silica/alumina iron ore rejects (27–76% Fe₂O₃) were used to synthesize iron oxides of purity 96–98% with SiO₂/Al₂O₃ ratio reduced to 0.03. The major impurities on chemical beneficiations were Al, Si, and Mn in the range 2–3%. A 99.73% purity Fe₂O₃ was also prepared by solvent extraction method using methyl isobutyl ketone (MIBK) from the acid extracts of the ore rejects. The magnesium ferrite, MgFe₂O₄, prepared from these synthetic iron oxides showed high resistivity of ∼ 10⁸ ohm cm. All ferrites showed saturation magnetization, 4πM_s, in the narrow range of 900–1200 Gauss and the Curie temperature,T, _cof all these fell within a small limit of 670 ± 30 K. All ferrites had low dielectric constants (ε′), 12–15, and low dielectric loss, tan δ, which decreased with the increase in frequency indicating a normal dielectric dispersion found in ferrites. The presence of insignificant amount of polarizable Fe²⁺ ions can be attributed to their high resistances and low dielectric constants. Impurities inherent in the samples had no marked influence on the electrical properties of the ferrites prepared from the iron ore rejects, suggesting the possibility of formation of ferrite of constant composition, MgFe₂O₄, of low magnetic and dielectric losses at lower temperatures of 1000°C by ceramic technique.     

Phase transition, dielectric and piezoelectric properties of K0.5Na0.5NbO3–CaTi0.9Zr0.1O3 lead-free ceramics

Lead-free (1 − x)K_0.5Na_0.5NbO₃–xCaTi_0.9Zr_0.1O₃ + 0.75 mol%MnO₂ piezoelectric ceramics have been prepared by an ordinary sintering technique and their phase transition, dielectric and piezoelectric properties have been studied. The results of X-ray diffraction show that CaTi_0.9Zr_0.1O₃ diffuse into K_0.5Na_0.5NbO₃ lattices to form a solid solution with a perovskite structure. After the addition of CaTi_0.9Zr_0.1O₃, both the cubic–tetragonal and tetragonal–orthorhombic phase transition temperatures decrease, and a relaxor behavior is induced. Coexistence of the orthorhombic and tetragonal phases is formed in the ceramics with 0.03 < x < 0.07 at room temperature. Owing to the higher number of possible polarization states resulting from the coexistence of the two phases, the piezoelectric properties of the ceramics are enhanced significantly. The ceramic with x = 0.05 exhibits the following optimum properties: d ₃₃ = 203 pC/N, k _p = 45.0%, and T _C = 342 °C.     

Dielectric behaviour and a.c. conductivity in Cu x Fe3−x O4 ferrite

The dielectric properties (dielectric constant and loss) for the system Cu _x Fe_3−x O₄ with x = 1.0, 0.8, 0.6, 0.4 and 0.2, were studied in the temperature range 300 ∼ 800 K and also in the frequency range 1 kHz ∼ 1 MHz. A.c. conductivity was derived from dielectric constant and loss tangent data. The conduction in this system is interpreted as due to small polaron hopping. The dielectric relaxation was observed for the compositions with tetragonal structure whereas normal behaviour was observed for cubic structure.     

Dielectric and piezoelectric properties of Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>–BaNb<Subscript>2</Subscript>O<Subscript>6</Subscript> lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x)Bi_0.5Na_0.5TiO₃–xBaNb₂O₆ (BNT–BN100x), a new member of the BNT-based group, was prepared by conventional solid state reaction. X-ray diffraction showed that BaNb₂O₆ (BN) diffused into the lattice of Bi_0.5Na_0.5TiO₃ to form a solid solution with perovskite-type structure. The temperature dependence of dielectric constant ε_r revealed that the solid solution underwent two phase transitions from ferroelectric to anti-ferroelectric and anti-ferroelectric to paraelectric. Both the transition temperature T _d and T _m were shifted to lower with the increasing content of BaNb₂O₆. The temperature dependence of dielectric constant at different frequency revealed that the solid solution exhibited obviously dielectric relaxation characteristics. The sample with x = 0.6 mol% exhibited excellent electrical properties, piezoelectric constant d ₃₃ = 94 pC/N; electromechanical coupling factor k _p = 0.185. The results showed that BNT–BN100x ceramics were good candidates for use as lead-free piezoelectric ceramics.     

Effect of Zn2TiO4 and ZnB2O4 additions on the microstructure and dielectric properties of AgNb1 ? xTaxO3 solid solutions

We report the preparation and characterization of AgNb_0.6Ta_0.4O₃ (ANT) based materials. The addition of Zn₂TiO₄ and ZnB₂O₄ influences the sintering temperature, phase composition, and microstructure of ANT ceramics. ANT doped with 1 wt % Zn₂TiO₄ or ZnB₂O₄ has high dielectric permittivity (400–470), low dielectric losses (tanδ ∼ 10⁻³), and a nonlinearity coefficient n _R ≅ 3–9% (at a field strength E = 3 × 10⁶ V/m).     

Phase transition and dielectric study in Ba<Subscript>0·95</Subscript>Dy<Subscript>0·05</Subscript>TiO<Subscript>3</Subscript> ceramic

Temperature and frequency dependence dielectric permittivity of Ba0·95Dy0·05TiO₃ ceramic has been studied in the temperature range of 100–350 K at the frequencies, 1 kHz, 10 kHz, 100 kHz and 1 mHz. Diffuse phase transition and frequency dispersion is observed in the permittivity-vs-temperature plots. This has been attributed to the occurrence of relaxor ferroelectric behaviour. The observed relaxor behaviour has been quantitatively characterized based on phenomenological parameters. A comparison with the Zr doped BaTiO₃ has also been presented. The microstructure of as-sintered samples shows a dense and almost uniform micrograph without any impurity phases; the grains are almost spherical with random orientation.     

Preparation and properties of ceramics based on (Na0.5Bi0.5)1 ? xAxTiO3 (A = Sr, Cd) solid solutions

This paper describes the preparation and properties of (Na_0.5Bi_0.5)_{1 − x} A _x TiO₃ (A = Sr, Cd) lead-free ferroelectric ceramics. The (0.63–0.66)Na_0.5Bi_0.5TiO₃ · (0.37–0.34)Sr_0.7Bi_0.2TiO₃ ceramics are shown to have the best dielectric and piezoelectric properties: tanδ = 0.013–0.009, ɛ_RT = 1200–1500, d ₃₁ = (370–400) × 10⁻¹² C/N, and k _ρ = 0.4–0.58. The cadmium-containing ceramics offer low dielectric losses and high dielectric permittivity at room temperature.     

Microstructure,electrical properties of CeO<Subscript>2</Subscript>-doped (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)NbO<Subscript>3</Subscript> lead-free piezoelectric ceramics

CeO₂-doped K_0.5Na_0.5NbO₃ lead-free piezoelectric ceramics have been fabricated by a conventional ceramic fabrication technique. The ceramics retain the orthorhombic perovskite structure at low doping levels (<1 mol.%). Our results also demonstrate that the Ce-doping can suppress the grain growth, promote the densification, decrease the ferroelectric–paraelectric phase transition temperature (T _C), and improve the dielectric and piezoelectric properties. For the ceramic doped with 0.75 mol.% CeO₂, the dielectric and piezoelectric properties become optimum: piezoelectric coefficient d ₃₃ = 130 pC/N, planar electromechanical coupling coefficient k _p = 0.38, relative permittivity ε_r = 820, and loss tangent tanδ = 3%.     

Effect of simultaneous double doping in Ba and Ti sites on dielectric and ferroelectric properties of sol–gel synthesized nano-BaTiO<Subscript>3</Subscript>

Lead free (Ba_(1−3x)Nd_(2x))(Ti_(1−y)Zr_y)O₃ (x = 0, 0.025, y = 0, 0.025, 0.05) ceramics were prepared successfully using sol–gel method. The effect of Nd, Zr content on dielectric and polarisation properties of BaTiO₃ were studied using dielectric and hysteresis measurements. SEM analysis proved that the particle size of compounds as prepared were in the order of 30–60 nm. The ferroelectric phase transition from tetragonal to cubic phase was observed around 130 °C for pure BaTiO₃. With the addition of Nd (2.5 mol%) and increasing content of Zr (2.5 and 5 mol%), it was observed that transition temperature (T_c) shifts to lower temperatures (70–50 °C), but didn’t show any relaxor behaviour. Dielectric measurements showed an increase in the values at room temperature in all the doped samples. The synthesized ceramics exhibited typical P–E hysteresis loops at room temperature accompanied by saturation polarisation (P_s) and remanent polarisation (P_r). Behaviour of polarisation phenomena in these compounds showed interesting results with increasing temperature.     

Characterization of La1 −x Sr1 +x Cu5 −x Fe x O12 + δ (0 ≤x ≤ 1·0) by dc electrical conductivity,magnetic susceptibility and EPR measurements(0 ≤x ≤ 1·0) by dc electrical conductivity,magnetic susceptibility and EPR measurements

The DC electrical resistivity results of La_{4 −x} Sr_{1 +x} Cu_{5 −x} Fe _x O_{12 + δ} (0 ≤x ≤ 1·0) showed that for S1 (x = 0) and S2 (x = 0·25) the temperature coefficient of resistivity (TCR), dρ/dT, is positive and slightly increases with increasing temperature in the range 20–270 K. This shows the metallic nature of S1 and S2. For the samples S3(x = 0·5) and S4 (x = 0·75), TCR slightly increases in the range 20–270 K, with change in sign from negative to positive at ∼ 80 K and ∼ 130 K, respectively. These results show the metal-insulator type transition in S3 and S4. For the sample S5 (x = 1·0), the TCR is negative and gradually increases in the range 20–270 K, which shows its semiconductor-like behaviour. The activation energy for S5 is found to be 0·21 × 10⁻² eV. Furthermore, the DC resistivity results of S1–S5 in the range 350–660 K are in conformity with the low temperature results. The very weak temperature dependence of magnetic susceptibility results of S1–S3 show Pauli-paramagnetic behaviour in the range 77K–400 K, while S4 and S5 exhibit Pauli-paramagnetic behaviour in the range 77–850 K. Long-range antiferromagnetic interaction is observed in S5 (x = 1·0) belowT _c ∼ 100 K. The room temperature EPR lineshapes gradually improve from metallic S1 (x = 0) to semiconductor-like S5(x = 1·0). Negativeg-shift is observed in the samples S2–S5 with increasing trend ing _iso-values of 1·880 in S2 to 1·961 in S5. However, theg _iso-value for S1 could not be observed due to very poor lineshape.