Effect of vanadium doping on the electric properties of barium titanate hafnate ceramics

Pure and V-doped barium titanate hafnate (BaHf_0.1Ti_0.9O₃, short for BHT) ceramics were prepared by sol–gel method. The microstructures, dielectric and ferroelectric properties of BaHf_0.1V _x Ti_0.9?x O₃ (x = 0, 0.02, 0.05, 0.08, 0.1) ceramics have been investigated. From the X-ray patterns it implies that V⁵⁺ ions have entered the unit cell maintaining the perovskite structure of solid solution. The a-axis and c-axis lattice constants gradually increase and the tetragonality gradually decreases with the increasing of vanadium content. The content of vanadium has an inconspicuous effect on the grain size and the Curie temperature. The addition of vanadium can decrease the dielectric loss of BHT ceramics. It is found that well-behaved hysteresis loops can be observed in all samples at room temperature. The coercive electric field gradually decreases and then increases with the increasing of vanadium content.     

Oxygen vacancy-related dielectric relaxation and electrical conductivity in La-doped Ba(Zr0.9Ti0.1)O3 ceramics

Ba_1?xLa_x (Zr_0.9Ti_0.1)_1?x/4O₃ (BLZT) ceramics with x = 0.02 (BLZT-1), 0.04 (BLZT-2), 0.06 (BLZT-3) and 0.08 (BLZT-4) were prepared by a solid-state reaction route. Crystal structure of the BLZT ceramics was determined using X-ray diffraction and Raman spectroscopy. While the ceramics for x ≤ 0.04 are pure phase with cubic perovskite structure, pyrochlore La₂Zr₂O₇ appears in the samples with x = 0.06 and 0.08. Dielectric properties as function of temperature and frequency showed more than one dielectric anomaly were found at high temperatures during heating but they weakened or disappeared during cooling. Both dielectric relaxation and electrical conductivity were taken into account in point defect mechanism. The double-ionized and short-range hopping of oxygen vacancy should be mainly responsible for the dielectric anomalies and conduction behavior. Activation energy of conductivity E _con is lower than half of the band gap E _g obtained by UV–Vis spectroscopy, which results from emergency of oxygen vacancies. In visible light region, the ceramics show a strong absorption with band gap of about 3.57 eV.     

High dielectric tunability of ferroelectric (Ba1−x,Srx)(Zr0.1,Ti0.9)O3 ceramics

(Ba_1?x,Sr_x)(Zr_0.1,Ti_0.9)O₃ (BSZT) ceramics with x = 0, 0.05, 0.15, 0.25, 0.35 and 0.45 were prepared by conventional solid state reaction method. The structural characterization with X-ray diffraction and scanning electron microscopy indicate a monotonical drop in lattice constants and grain size with the increase of Sr concentration. Consequently, the Curie temperature and remnant polarization of the ceramics exhibit a strong compositional dependence. A linear relationship between the Curie temperature and Sr concentration is revealed. At x = 0.45, the BSZT ceramics show substantially high tunability of over 55 % under 20 kV/cm dc electric field with very low dielectric loss value of 0.0025 at room temperature, suggesting the BSZT ceramics could be a promising alternative to traditional (Ba,Sr) TiO₃ ferroelectrics for developing high frequency tunable dielectric devices.     

Large electric field-induced strain near AFE/FE phase boundary in (Pb0.97La0.02)(Zr, Sn, Ti)O3 system

(Pb_0.97La_0.02)(Zr, Sn, Ti)O₃ ceramics were prepared by conventional solid state reaction process, and the effects of Zr⁴⁺/Sn⁴⁺ and Zr⁴⁺/Ti⁴⁺ ratios on the crystal structure, dielectric, ferroelectric, and electric field-induced strain properties were systemically investigated. The XRD results showed, with the increase of Zr⁴⁺ and Ti⁴⁺ contents, the stability of the specimens became weakened and a transformation from AFE to FE phase was observed at x = 0.65 and y = 0.12, respectively. In addition, it was observed that the strain first increased with a maximum value in the composition near AFE/FE phase boundary, and then decreased with increasing Zr⁴⁺ and Ti⁴⁺ contents. Further, with the decrease of measuring frequency, the strain continuously increased because the reversal of the domain can be more sufficient. The maximum strain of 0.55 % is obtained in Pb_0.97La_0.02(Zr_0.63Sn_0.26Ti_0.11)O₃ AFE ceramics at 1 Hz measuring frequency which lays a foundation for preparing actuators with high properties.     

Effects of La-doping on microstructure, dielectric and piezoelectric properties of Ba0.85Ca0.15Ti0.90Zr0.10O3 lead-free ceramics

Lead-free (Ba_0.85Ca_0.15)_1?xLa_2/3xTi_0.90Zr_0.10O₃ + 1 mol% MnO₂ ceramics have been prepared an ordinary sintering technique and the effects of La-doping on the microstructure, dielectric and piezoelectric properties of Ba_0.85Ca_0.15Ti_0.90Zr_0.10O₃ were studied. All the ceramics possess a pure perovskite structure, indicating that La ions are incorporated into Ba_0.85Ca_0.15Ti_0.90Zr_0.10O₃ lattices to form a lead-free solid solution. The ceramics are transformed from coexistence of orthorhombic and tetragonal phases to pseudocubic phase with the doping level of La increasing. After the doping of La, grain growth is inhibited, ferroelectric-paraelectric phase transition temperature (T _C) is decreased and the degree of diffuse phase transition is increased. The ferroelectricity of the ceramics is weakened after the addition of La. Unlike donor-doped lead zirconate titanate ceramics, the piezoelectric properties of the ceramics are degraded after the partial substitution of La³⁺ for (Ba_0.85Ca_0.15)²⁺ because of the weakness or disappearance of coexistence of orthorhombic and tetragonal phases near room temperature. The (Ba_0.85Ca_0.15)_1?xLa_2/3xTi_0.90Zr_0.10O₃ + 1 mol% MnO₂ ceramic with x = 0 exhibit the optimum piezoelectric properties: d ₃₃ = 277 pC/N and k _p = 30.3 %, respectively.     

Crystal structure and optimized microwave dielectric properties of (1 − x) LiZn0.5Ti1.5O4–xTiO2 ceramics for application in dielectric resonator

Microwave dielectric ceramics with the composition of (1?x) LiZn_0.5Ti_1.5O₄ (LZT)–xTiO₂ (0.05 ≤ x ≤ 0.4) were prepared by a solid-state reaction route. XRD patterns revealed that the samples consist of LiZn_0.5Ti_1.5O₄ and rutile TiO₂, and the amount of rutile TiO₂ phase increased with increasing the x values. The microwave measurements show that the dielectric properties of ceramics can be improved with increasing x values. When x = 0.1, the temperature coefficient of resonant frequency (τ _f ) of 0.9LZT–0.1TiO₂ ceramic can be adjusted to a near-zero value of ?1 ppm/°C, and permittivity (ε_r) and Q × f value are 26 and 45,000 GHz, respectively. These results indicate that 0.9LZT–0.1TiO₂ ceramic can be a candidate in microwave dielectric resonators.     

Lead-free (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3-Y2O3 ceramics with large piezoelectric coefficient obtained by low-temperature sintering

Lead-free (Ba_0.85Ca_0.15)(Ti_0.9Zr_0.1)O₃-xwt.%Y₂O₃ (BCZT-xY) piezoelectric ceramics have been synthesized using solid-state reaction technique and the effects of Y₂O₃ addition on the phase structure and piezoelectric properties of the ceramics have been studied. The results reveal that the addition of Y₂O₃ significantly improves the sinterability of BCZT ceramics, resulting in a reduction of sintering temperature from 1,540 to 1,350 °C, and an increase of the Curie temperature T _C from 85 to 95 °C. X-ray diffraction data shows that Y₂O₃ diffuses into the lattice of BCZT-xY ceramics and a pure perovskite phase forms in the ceramics. Scanning electron microscopy images indicate that a small amount of Y₂O₃ addition affects the microstructure, obviously. Main piezoelectric parameters of these ceramics are optimized around x = 0.06 wt % with a large piezoelectric coefficient (d ₃₃  = 560 pC/N), a high planar electromechanical coefficient (k _p  = 53 %) and a low dissipation factor (tan δ = 0.9 %) at 1 kHz. The results indicate that the BCZT-xY ceramics are promising lead-free materials for practical applications.     

Diffusion phase transition and impedance spectroscopy of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>/CuO co-doped BCZT lead-free ceramics

Perovskite type (Ba_0.85Ca_0.15?2x Bi_2x )(Zr_0.1Ti_0.9?x Cu _x )O₃ lead-free ceramics were prepared via a conventional solid-state reaction method. The phase structure, dielectric, ferroelectric properties and complex impedance were investigated in detail. XRD and dielectric measurements determined that single orthorhombic phase displayed in (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ at room temperature. With the introduction of Bi₂O₃/CuO, the phase structure exhibited the mixture of orthorhombic and tetragonal phases, and then turned to single tetragonal phase. In contrast to the sharp dielectric transition of (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ ceramics, a broad dielectric peak coupled with a slight decrease in Curie temperature was observed in (Ba_0.85Ca_0.15?2x Bi_2x )(Zr_0.1Ti_0.9?x Cu _x )O₃ ceramics with increasing x. The observed diffuse phase transition behavior was further confirmed by a couple of measurements with polarization loops and polarization current density curves. The structural and the composition fluctuations induced by ions doping should be responsible for the diffuse phase transition behavior. Furthermore, physical mechanisms of the conduction and relaxation processes were revealed by using impedance spectroscopy analyses. It was concluded that the conduction and relaxation processes were thermally activated, which was closely linked with the singly and doubly ionized oxygen vacancies.     

Synthesis, structure and dielectric characterization of Ln2Ti2−2xM2xO7(Ln=Gd, Er; M=Zr, Sn, Si)

The progress in wireless communications and information access has demanded the use of electronic ceramics exhibiting desired properties. To further our understanding of these properties, compounds in the Ln₂Ti_2-2xM_2xO₇ (Ln=Gd, Er; M=Zr, Sn, Si) systems were synthesized by ceramic methods and characterized by powder X-ray diffraction. The ZrO₂-doped Gd₂Ti_2−2xZr_2xO₇ compounds adopt the pyrochlore structure type and form a complete solid solution. Er₂Ti_2−2xZr_2xO₇ forms a pyrochlore solid solution for x<0.1. However, stoichiometric Er₂Zr₂O₇ does not form; instead Er₄Zr₃O₁₂ forms a with defect fluorite structure. The Sn-doped Ln₂Ti_2−2xSn_2xO₇ (Ln=Gd, Er) compounds form complete solid solutions, and the Si compounds adopt the pyrochlore structure up to x=0.05. At ambient temperature, dielectric constants range from 10 to 61 for Er₂Ti_2−2xZr_2xO₇ and 16-31 for Gd₂Ti_2−2xZr_2xO₇ with low dielectric loss (1×10⁻³) at 1 GHz.     

Synthesis of High-Phase Purity SrTi1–xZrxO3 Ceramics by Sol-Spray Pyrolysis Method

SrTi₁–_xZr_xO₃ (0 ≤ x ≤ 1.0) ceramics were synthesized from powders generated by sol-spray pyrolysis. Crystal symmetry, morphology, and the band gap of the prepared ceramics were investigated as a function of Ti/Zr ratio. Substitution of Zr⁴⁺ for Ti⁴⁺ in the solid solution markedly effects crystal symmetry and grain growth and results in an increased band gap. Single-phase products with good crystallinity and dense microstructure were obtained after sintering at 1250°C.     

Effects of cobalt and sintering temperature on electrical properties of Ba0.98Ca0.02Zr0.02Ti0.98O3 lead-free ceramics

Lead-free (Ba_0.98Ca_0.02)(Zr_0.02Ti_0.98)O₃-xmol% (x = 0–1.6) cobalt ceramics (BCZT-xCo) have been fabricated by the traditional solid-state reaction technique and the effects of Co and sintering temperature on ferroelectric, dielectric and piezoelectric properties of (Ba_0.98Ca_0.02)(Zr_0.02Ti_0.98)O₃ lead-free ceramics have been studied systematically. The orthorhombic–tetragonal (T _O–T) transition shift towards lower temperature with increasing Co addition, while Curie temperature (T _c) remained at relatively high value of 107 °C. And the Main piezoelectric parameters are optimized at x = 0.8 mol% with a high piezoelectric coefficient (d ₃₃ = 330 pC/N), a planar mode electromechanical coupling factor (k _p = 46.7 %), a high dielectric constant (ε _r = 2,675) and a low dielectric loss (tanδ = 0.90 %) at 1kHZ. Besides these, high remnant polarization (P _r) and low coercive field (E _c) of 11.5 μC/cm², 0.31 kV/cm are also obtained at (Ba_0.98Ca_0.02)(Zr_0.02Ti_0.98)O₃-0.8 mol%Co lead-free ceramics. Furthermore, greatly enhanced temperature stability of the piezoelectric properties was obtained in the temperature range from 20 to 90 °C. The above results indicate that BCZT-Co ceramics are promising lead-free materials for practical applications.     

Dielectric properties of Ba(Ti1 − xZrx)O3 solid solutions

This paper reports the structural and dielectric properties of Ba(Ti_1 − xZr_x)O₃ (x = 0-0.3) ceramics. Single-phase solid solutions of the samples were determined by X-ray diffraction. Microscopic observation by scanning electron microscope revealed dense, single-phase microstructure with large grains (20-60 μm). The evolution of dielectric behavior from a sharp ferroelectric peak (for x ≤ 0.08) to a round dielectric peak (for 0.15 ≤ x ≤ 0.25) with pinched phase transitions and successively to a ferroelectric relaxor (for x = 0.3) was observed with increasing Zr concentration. Compared with pure BaTiO₃, broaden dielectric peaks with high dielectric constant of 25,000-40,000 and reasonably low loss (tanδ: 0.01-0.06) in the Ba(Ti_1 − xZr_x)O₃ ceramics have been observed, indicating great application potential as a dielectric material.     

Synthesis,structure, and properties of solid solutions based on bismuth ferrite

Solid solutions of Bi_{1 ? x} Pb _x Fe_{1 ? x} Zr _x O₃ (x = 0.1?0.2) are synthesized by the methods of liquid-phase and modified solid-phase synthesis. Also, solid solutions of [Bi_0.9(Pb_0.9Ln_0.1)_0.1][Fe_0.9(Zr_0.65Ti_0.35)_0.1]O₃, and [Bi_0.9(Pb_0.9Ln_0.1)_0.1][Fe_0.9(Zr_0.53Ti_0.47)_0.1]O₃ (Ln - La, Pr, Gd, Yb) are made, including synthesis of their precursors with organic ligands. Comprehensive investigations involving thermal analysis, IR spectroscopy, X-ray powder diffraction, atomic force microscopy, dielectric and magnetic measurements, and neutron powder diffraction are performed. The full-profile analysis of X-ray and neutron diffraction patterns by the Rietveld method shows that, over the whole temperature interval of 10–700 K under study, the Bi_0.9Pb_0.1Fe_0.9Zr_0.1O₃ and Bi_0.8Pb_0.2Fe_0.8Zr_0.2O₃ compounds are characterized by the perovskite structure (space group R3c). The magnetic measurements reveal an antiferromagnetic phase transition in the Bi_0.9Pb_0.1Fe_0.9Zr_0.1O₃ and Bi_0.8Pb_0.2Fe_0.8Zr_0.2O₃ solid solutions. The Néel temperature (T _N ) decreases considerably with growing PbZrO₃ concentration as compared to the Néel point in pure BiFeO₃ (T _N = 633 K). The perovskite structure with a hexagonal distortion is found in lanthanide-substituted solid solutions and specific features of the surface morphology of the ceramics are analyzed. The magnetic measurements suggest the presence of an antiferromagnetic phase transition in the solid solutions under study, with a considerable drop of T _N in the Ln-alloyed compound as compared to the T _N value in pure BiFeO₃     

High piezoelectric coefficient of Ba0.85Ca0.15Ti0.90Zr0.10O3−Sr(Cu1/3Ta2/3)O3 ceramics

The (Ba_0.85Ca_0.15) (Zr_0.1Ti_0.9)O₃ ? x   wt% Sr(Cu_1/3Ta_2/3)O₃ [BCZT ? x  wt% SCT, x = 0–0.3] lead-free ceramics were prepared by the conventional solid-state method. The phase structure was investigated by X-ray diffraction. The results show that only a tetragonal phase is observed in these ceramics. The sintering behavior of BCZT ceramics is also improved by using SCT as a sintering aid. The ceramic with x  = 0.2 wt% SCT demonstrates good piezoelectric properties:d₃₃ ~ 577 pC/N and k_p ~ 59.1 %, Furthermore, the Curie temperature of the ceramics also increases and reaches 97 °C.     

Rietveld analysis, magnetic, vibrational and impedance properties of (Bi1−xPrx)(Fe1−xZrx)O3 ceramics

(Bi_1?xPr_x)(Fe_1?xZr_x)O₃ ceramics with x = 0.03, 0.06 and 0.10 were prepared via solid state reaction route. X-ray diffraction and Raman spectra of the ceramics were recorded for calculating its lattice parameters and structural analysis. Magnetic studies indicated a significant enhancement in magnetization of (Bi_1?xPr_x)(Fe_1?xZr_x)O₃ ceramics with maximum remnant magnetization of 0.12 emu g^?1 for x = 0.06 sample. Fourier transform infrared spectra and Rietveld analysis confirmed the change in bond length arising due to Pr and Zr codoping. Dielectric measurements showed dielectric anomaly around Neel temperature, indicating magnetoelectric coupling in the samples as well as the dielectric relaxation for higher doping. The effect of Pr and Zr codoping on the impedance and modulus behavior of BiFeO₃ lattice is discussed. The frequency dependence of electric modulus and impedance of the material show the presence of non-Debye relaxation in the samples. All samples showed energy band gap in the range 2.16–2.0 eV, indicating possibility of optical activity in visible range and making it suitable for photocatalytic applications.     

Effect of Zr substitution on microwave dielectric properties of Zn2SnO4 ceramics

The microwave dielectric properties of Zn₂(Sn_(1?x)Zr_x)O₄ ceramics were examined with a view to their exploitation for mobile communication. The Zn₂(Sn_(1?x)Zr_x)O₄ ceramics were prepared by the conventional solid-state method with various amount of Zr substitution. The diffraction peaks of Zn₂(Sn_(1?x)Zr_x)O₄ ceramics did not vary significantly as x varied. A density of 6.10 g/cm³ was obtained for Zn₂(Sn_0.99Zr_0.01)O₄ ceramic, sintered at 1,225 °C for 4 h. Dielectric constant (? _r ) of 9.6, quality factor (Q × f) of 87,000 GHz, and temperature coefficient of resonant frequency (τ _f ) of ?51 ppm/°C were obtained for Zn₂(Sn_0.99Zr_0.01)O₄ ceramics that were sintered at 1,225 °C for 4 h.     

Enhanced giant dielectric response in Sr[(Fe0.5Nb0.5)1−xTix]O3 solid solutions

In the present work, the modified dielectric relaxations with extended giant dielectric constant step were observed in Sr[(Fe_0.5Nb_0.5)_1?x Ti _x ]O₃ solid solutions. The structure of Sr[(Fe_0.5Nb_0.5)_1?x Ti _x ]O₃ solid solutions changed from orthorhombic to cubic with increasing x. A dielectric relaxation following Arrhenius law of Sr[(Fe_0.5Nb_0.5)_1?x Ti _x ]O₃ solid solutions was observed at lower temperature. The dielectric constant of Sr[(Fe_0.5Nb_0.5)_1?x Ti _x ]O₃ solid solutions decreased firstly and then increased with increasing SrTiO₃ content at 1 kHz, while the dielectric loss was suppressed monotonically. At x = 0.8, the dielectric loss at room temperature and 1 kHz was 0.16 which was much smaller than that for x = 0 (tanδ = 0.37), while the dielectric constant was increased to 6,815, and the temperature stability was also improved. This indicated that the dielectric characteristics of Sr(Fe_0.5Nb_0.5)O₃ ceramics could be significantly improved by forming solid solution with SrTiO₃.     

Microwave dielectric properties and low temperature sintering of Li2Zn(Ti1−xSnx)3O8 (x ≤ 0.20) ceramics with B2O3–CuO addition

In the present work, the influence of Sn substitution for Ti on the phase composition and microwave dielectric properties of the Li₂Zn(Ti_1?xSnx)₃O₈ (x ≤ 0.20) ceramics was studied. It was found that the Sn did not occupy the Ti site in the Li₂Zn(Ti_1?xSn_x)₃O₈ system but existed in the form of SnO₂ as a secondary phase. With the increase of Sn amount, the best microwave dielectric properties with ε_r = 23.3, Q × f = 71,000 GHz and TCF = ?21.7 ppm/°C were obtained in the Li₂Zn(Ti_0.9Sn_0.1)₃O₈ ceramic sintered at 1,120 °C. The sintering temperature of Li₂Zn(Ti_0.9Sn_0.1)₃O₈ ceramic can be can effectively lowered to below 960 °C by the addition of 0.4B₂O₃–0.6CuO and this materials is chemically compatible with silver. This makes the Li₂Zn(Ti_1?xSn_x)₃O₈ ceramics good candidates for low temperature co-fired ceramics technology.     

Effects of La3+ addition on the phase transition,microstructure, dielectric and piezoelectric properties of Ba0.9Ca0.1Ti0.9Zr0.1O3 ceramics prepared by hydrothermal method

Lead-free Ba_0.9Ca_0.1Ti_0.9Zr_0.1O₃–xLa (x = 0.000, 0.005, 0.010, 0.015, 0.020, 0.025) ceramics were prepared by hydrothermal method and were assisted by fast microwave sintering. The effects of La³⁺ addition on the phase transition, microstructure, dielectric and piezoelectric properties were investigated. Single orthorhombic phase was observed in the composition of x ≤ 0.010 and the coexistence of orthorhombic and tetragonal phase were detected at x = 0.015 and 0.020, which is characterized by the broadening of (002)/(200) peaks at around 2θ ~ 45°. The ceramics show cubic phase when the x was increased to 0.025. The grain size was affected significantly by the La³⁺ content, reaching a maximum value of ~8.2 μm at x = 0.010. The dielectric constant decreases with the addition of small amount of La³⁺ and then increases sharply at x ≥ 0.015, exhibiting a PTC behavior at x = 0.020, while no T _C was observed at x = 0.025. The Curie temperature (T _C ) always decrease with the introduction of La³⁺ and the dielectric loss shows a minimum value at x = 0.015. The piezoelectric constant (d ₃₃ ) measured at 50 °C of the ceramics were increased after the partial substitution of La³⁺ because of the enhancement of coexistence of orthorhombic and tetragonal phases at this temperature. Ferroelectric and piezoelectric properties can not be detected when x was increased to 0.02 while they were observed again with further addition.     

The electrostrictive effect and dielectric properties of lead-free 0.5Ba(ZrxTi1−x)O3–0.5(Ba0.75Ca0.25)TiO3 ceramics

Lead-free 0.5Ba(Zr_xTi_1?x)O₃–0.5(Ba_0.75Ca_0.25)TiO₃ (x = 0.25, 0.30, 0.35, 0.40) ceramics have been synthesized by a conventional solid state sintering method. The room temperature ferroelectric and electrostrictive properties of these ceramics were studied. Based on the measured properties, these ceramics showed a typical relaxor behavior. The Curie temperature of BZT–BCT ceramics decreases with increasing the Zr content. The largest electrostrictive strain and electrostrictive coefficient are founded in BZT–BCT ceramic with x = 0.25, the value is 0.16 % and 0.079 m⁴ C^?2, respectively. The polarization, electrostrictive strain and electrostrictive coefficient (Q ₁₁) decrease with increase in Zr concentration. For samples with low Curie temperature, which have large room temperature dielectric constant (ε), electrostrictive coefficient increases (Q ₁₁) is smaller. Because doping can disrupt the long range cation order, and electrostrictive (Q ₁₁) coefficient increases with cation order from disordered, through partially-ordered, simple relaxor and then ordered perovskites, ferroelectrics with a disordered structure have a huge permittivity, but a small electrostrictive coefficient (Q ₁₁).