Ferroelectric Bi4Ti3O12 and Bi4−x La x Ti3O12 ceramics prepared by a new sol-gel route

Ceramics of bismuth titanate, Bi₄Ti₃O₁₂ (BIT) and the La-doped series, Bi_4?x La _x Ti₃O₁₂ (xBLT) with x?=?0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, and 0.75, have been synthesized by a new sol-gel process based on ethylene glycol. La-doping is found to reduce the temperature of the formation of pure Bi-layer-structured phase from 600 °C in BIT and low La-doped xBLT (x?=?0.1–0.3) to 500 °C in high La-doped xBLT (x?=?0.4–0.75). Increasing the La-content in the xBLT ceramics decreases the contribution of the space charge polarization to the apparent dielectric permittivity. The ceramics of xBLT prepared by this sol-gel route exhibit improved dielectric properties, with a higher room temperature dielectric constant and lower losses up to high temperatures.     

Correlation between crystal structure and properties of ultra-high dielectric constant ceramics x SrCO3-Bi2O3-Ag(Nb,Ta)O3

The correlation between crystal structure and properties of x wt% SrCO₃-4.5?wt.%Bi₂O₃-Ag(Nb_0.8Ta_0.2)O₃ (x SrCO₃-Bi₂O₃-ANT) (x?=?0.5?~?3.0) dielectric ceramics was investigated. The permittivity was significantly influenced by the redshift of three typical vibration modes of A_1g(Ag), F_2g(Nb/Ta) and A_1g(O). The dielectric loss was optimized by the restraint of the second phase AgNbO₃, and a minimum value was obtained when x?=?2.0. Changes of c/a value, which indicate the degree of lattice distortion, reflected the temperature coefficient of relative permittivity (τ_ε) was highly correlated with the crystal structure and a near zero τ_ε value was achieved with 2.0?wt.% Sr concentration. The Bi₂O₃-doped ANT ceramics containing 2.0?wt.% SrCO₃ sintered at 1150°C showed excellent dielectric properties: an ε_r value of 841, a tan δ value of 0.00119 and a near zero (?23.7?ppm/°C) τ_ε value.     

La2O3–B2O3–TiO2 Glass/BaO–Nd2O3–TiO2 ceramic for high quality factor low temperature co-fired ceramic dielectric

A conventional BaO–Nd₂O₃–TiO₂ ceramic of microwave dielectric material was added to rare-earth derived borate glasses (La₂O₃–B₂O₃–TiO₂) for use as LTCC (low temperature co-fired ceramic) materials. The sintering behavior, phase evaluation, and microwave dielectric properties were investigated. It was found that increasing the sintering temperature from 750 to 850 °C led to increases in shrinkage and microwave dielectric properties (≈15 for ?_r , >10,000 GHz for Q*f₀ and >94 ppm/ °C for τ _f at 7–8 GHz for resonant frequency). The results suggest that a composite with suitable additives for τ _f could feasibly be developed as a material for LTCC applications.     

Ferroelectric and piezoelectric properties of (Bi1/2K1/2)TiO3 ceramics fabricated by hot-pressing method

Bismuth potassium titanate, (Bi_1/2K_1/2)TiO₃ (BKT), ceramics were prepared by the hot-pressing (HP) method without dopant and with dopants of Bi₂O₃, La₂O₃ and MnCO₃. The relative density of BKT ceramics hot-pressed at 1,060 and 1,080 °C (hereafter abbreviated to BKT-HP1060°C and BKT-HP1080°C) and x mass% Bi₂O₃, La₂O₃ and MnCO₃ doped BKT ceramics hot-pressed at 1,060 °C (hereafter abbreviated as BKTBix; x?=?0.1–0.6, BKTLax; x?=?0.1–0.6 and BKTMnx; x?=?0.1–0.3) were all higher than 97%. In this study, the ferroelectric properties of BKT ceramics were successfully obtained, and the remanent polarization P _r and coercive field E _c of BKT-HP1080°C were 22.2 μC/cm² and 52.5 kV/cm, respectively. A small amount of La tends to increase P _r, and the P _r of BKTLa0.1 was 19.2 μC/cm². The piezoelectricities were improved to optimize poling conditions, and the electromechanical coupling factor k ₃₃ and piezoelectric constant d ₃₃ of BKT-HP1080°C were 0.34 and 82.8 pC/N, respectively.     

Enhanced piezoelectric properties of 0.55Pb(Ni1/3Nb2/3)O3-0.135PbZrO3- 0.315PbTiO3 ternary ceramics by optimizing sintering temperature

0.55Pb(Ni_1/3Nb_2/3)O₃-0.135PbZrO₃-0.315PbTiO₃ (PNN-PZ-PT) ternary piezoelectric ceramics with excess 1.0 wt.% PbO were synthesized by the conventional solid-state reaction method at 1175–1300 °C for 2 h, respectively. The influence of sintering temperature (T _s) on microstructure, piezoelectric, dielectric, and ferroelectric properties were systematically investigated. The results of XRD and Raman scattering spectra demonstrated that a typical perovskite structure with mainly rhombohedral symmetry near the MPB region were obtained for all the samples. The tetragonal phase content was increased slightly with the increase of sintering temperature. In addition, with increasing T _s the average grain size increases while the density decreases were also found. The results of electrical measurements confirmed that piezoelectric constant, dielectric constant, remnant polarization were firstly increased and then decreased with the increase of sintering temperature. The optimum and remarkable enhanced electrical properties of d ₃₃?=?1070 pC/N, k _p?=?0.69, ε _r?=?8710, tanδ?=?0.026, P _r?=?24.08 μC/cm², and E _c?=?3.2 kV/cm were obtained for the sample sintered at 1250 °C for 2 h. Meanwhile, the sample exhibits a typical relaxor ferroelectric behavior with the maximum dielectric constant ε _m =24541 at Curie temperature T _c?=?113.3 °C at 1 kHz.     

Ionic Doping Effects in SrBi2Nb2O9 Ferroelectric Ceramics

Ionic doping effects of various ions in Bi-layered ferroelectric SrBi₂Nb₂O₉ (SBN) ceramics were studied. Un-doped and doped SBN ceramics with Ba²⁺, Pb²⁺, Ca²⁺, Bi³⁺, La³⁺, Ti⁴⁺, Mo⁶⁺, and W⁶⁺ ions were made with solid state reactions. Temperature dependent dielectric constants were measured. Ferroelectric transition temperature (T_C) decreased with Ba²⁺ and Pb²⁺ ions but increased with Ca²⁺ ion which substitutes the 12-coordinated Sr²⁺ site. T_C increased with Ti⁴⁺, Mo⁶⁺, and W⁶⁺ ions which substitute the 6-coordinated Nb⁵⁺ sites. With trivalent Bi³⁺ and La³⁺ ions, T_C increased with Bi³⁺ ion but much decreased with La³⁺ ion. These results showed that the ion size plays an important role in ferroelectricity of SBN ceramics.     

Piezoelectric properties of the high temperature MPB xPbTiO3 - (1−x)[BiScO3 + Bi(Ni1/2Ti1/2)O3] composition

The ternary perovskite xPbTiO₃ - (1?x)[BiScO₃ + Bi(Ni_1/2Ti_1/2)O₃] (PT-BS-BNiT), where x?=?0.54 is the morphotropic phase boundary composition, was studied for high temperature ferroelectric applications. Polycrystalline ceramics were prepared using the standard solid-state methods. The stoichiometric ceramic was found to have room temperature dielectric permittivity and loss values at 1 kHz of 1490 and 0.049 respectively. Piezoelectric properties, of the stoichiometric composition, measured included: P_r?=?31.0 μC/cm², E_c?=?25.0 kV/cm, d₃₃?=?340 pC/N, d₃₃ ^*?=?896 pm/V, and a bipolar electromechanical strain of 0.25 %. From these data, the Curie temperature was T_C?=?370 °C and the depoling temperature was T_D?=?325 °C. Processing ceramics with excess bismuth improved the low field piezoelectric coefficients with a maximum of d33?=?445 pC/N, while increasing the lead content increased the transition temperatures. The depoling and Curie temperatures of all compositions were measured to be between 275 and 400 °C.     

Crystallization behavior and microwave dielectric characteristics of ZnO-(La, Nd)2O3-B2O3-based dielectrics

Crystallizable zinc borate glasses modified with different contents of La₂O₃ or Nd₂O₃ were investigated as a potential low loss dielectric with respect to their crystallization behavior and microwave dielectric characteristics. The glasses were admixed with Al₂O₃ filler and fired at 850°C for 30 min in air to prepare low temperature dielectrics. Crystallization behavior and microwave dielectric properties of the resulting samples strongly depended on the relative content of La₂O₃ or Nd₂O₃ in the glass. As a promising result, the composition of 0.15ZnO-0.25Nd₂O₃-0.6B₂O₃ exhibited k?～?6.5 and Q?～?1194 at the resonant frequency of 18.9 GHz. Near zero temperature coefficient of frequency (TCF) was obtained by additional modification of the composition with ～10 wt.% of TiO₂ filler. Crystallization kinetics of the samples was studied based on the differential thermal analysis (DTA) curves obtained with different heating rates. Correlation of the observed dielectric properties to the crystallization behavior is the main subject of this work.     

Dielectric and piezoelectric properties of (K0.5Na0.5)(Nb0.97Sb0.03)O3 ceramics doped with Bi2O3

In this study, to develop the optimal composition of ceramics for low loss piezoelectric actuator and ultrasonic motor applications, (K_0.5Na_0.5)(Nb_0.97Sb_0.03)O₃?+?0.009 K_5.4Cu_1.3Ta₁₀O₂₉?+?0.1wt%Li₂CO₃?+?xwt%Bi₂O₃(x?=?0?~?0.9) lead-free piezoelectric ceramics with a fixed quantity of 0.009 K_5.4Cu_1.3Ta₁₀O₂₉ (abbreviated as KCT) were manufactured using the conventional solid-state solution processes. The effects of Bi₂O₃ addition on the dielectric and piezoelectric properties were then investigated. From the X-ray diffraction analysis result the specimens demonstrated orthorhombic symmetry when Bi₂O₃ was less 0.6?wt%, a pseudo-cubic phase appeared when Bi₂O₃ was 0.9?wt%. SEM images indicate that a small amount of Bi₂O₃ addition affect the microstructure. The piezoelectric properties of (K_0.5Na_0.5)(Nb_0.97Sb_0.03)O₃ ceramics were greatly improved by a certain amount of Bi₂O₃ addition. Excellent properties of density?=?4.54?g/cm³, relative densities?=?98.5?%, k _p?=?0.468, Q _m?=?1,715 and d ₃₃?=?183 pC/N were obtained with a composition of 0.3?wt% Bi₂O₃     

Liquid phase effect of La2O3 and V2O5 on microwave dielectric properties of Mg2TiO4 ceramics

Dielectric ceramics of Mg₂TiO₄ (MTO) were prepared by solid-state reaction method with 0.5–1.5 wt.% of La₂O₃ or V₂O₅ as sintering aid. The influences of La₂O₃ and V₂O₅ additives on the densification, microstructure and microwave dielectric properties of MTO ceramics were investigated. It is found that La₂O₃ and V₂O₅ additives lowered the sintering temperature of MTO ceramics to 1300 °C and 1250 °C respectively, whereas the pure MTO exhibits highest density at 1400 °C. The reduction in sintering temperature with these additives was attributed to the liquid phase effect. The average grain sizes of the MTO ceramics added with La₂O₃, and V₂O₅ found to decrease with an increase in wt%. The dielectric constant (ε_r) was not significantly changed, while unloaded Q values were affected with these additives, and the values were in the range of 92,000–157,550 GHz and 98,000–168,000 GHz with the addition of La₂O₃ and V₂O₅, respectively. The dielectric properties are strongly dependent on the densification and the microstructure of the MTO ceramics. The decrease in Q×f _o value at higher concentration of La₂O₃ and V₂O₅ addition was owing to inhomogeneous grain growth and the liquid phase which is segregated at the grain boundary. In comparison with pure MTO ceramics, La₂O₃ and V₂O₅ additives effectively improved the densification and dielectric properties with lowering of sintering temperature. The proposed loss mechanisms suggest that the oxygen vacancies and the average grain sizes are the influencing factors in the dielectric loss of MTO ceramics.     

Piezoelectric and ferroelectric properties of new Pb9Ce2Ti12O36 and lead-free Ba2NdTi2Nb3O15 ceramics

In this paper, measurements of the nonlinear ferroelectric, piezoelectric and dielectric properties of Pb₉Ce₂Ti₁₂O₃₆ (Pb₉CTO) and Ba₂NdTi₂Nb₃O₁₅ (BNTN) ferroelectric ceramics are presented. Hysteresis P(E) loops were measured as a function of applied electric field, frequency and temperature. The coercive field (E _c) and remnant polarization (P _r) displayed temperature and frequency dependence. Lead-free BNTN ceramics exhibited a coercive field E _c?>?2.4 kV mm^?1 and a piezoelectric coefficient d ₃₃?=?2 pC N^?1. The hysteresis loop was pinched above 110°C and a linear response was observed at 155°C, typical of a paraelectric material. Pb₉CTO was shown to be ferroelectric with coercive field E _c?=?1.2 kV mm^?1 and a d ₃₃?=?65 pC N^?1. The frequency dependences of the impedance of the Pb₉CTO discs were analyzed.     

Relaxor behavior of piezoelectric Pb(Yb1/2Nb1/2)O3-PbTiO3 ceramics sintered at low temperature

A (100-x)Pb(Yb_1/2Nb_1/2)O₃-xPbTiO₃ [PYN-PTx] solid solution system with 49.0????×????51.0 was prepared using a conventional ceramics process and sintered at low temperature. When excess PbO was added into the PYN-PTx system, all samples were sintered at temperatures as low as 800°C with good dielectric and piezoelectric properties. It is suggested that a liquid phase with excess PbO was formed during the sintering and improved the densification of PYN-PTx ceramics at low temperatures. For the PYN-PTx binary system, it was found that the temperature dependence of the relative permittivity follows a Curie?CWeiss Law above the deviation temperature (T_D) at high temperatures. Good piezoelectric properties of d ₃₃ ?=?510 pC/N, ?? _r ?=?2800 at RT, k _p?=?0.57, and k _t?=?0.42 with T_c?=?373°C were obtained for PYN-PT49.5 ceramics sintered at 800°C for 8 h.     

Structural and Multiferroic Properties of Bi3.4La0.6Ti3O12/CoFe2O4 Composite Thin Films

Bi_3.4La_0.6Ti₃O₁₂ and CoFe₂O₄ were synthesized by chemical solution route, and Bi_3.4La_0.6Ti₃O₁₂/CoFe₂O₄ multilayers were deposited by spin coating on Pt substrate. X-ray diffraction of multilayer structures reveals composite-like polycrystalline film. Leakage current is less than 10^?5 A at electric field < 90 KV/cm and follows the Ohmic behavior. Dielectric response shows relaxation and the loss (tan δ) is below 3% at 10⁶ Hz. Room temperature ferrroelectric polarization (P_r) = 20.2 μC/cm² and ferromagnetic memory (M_r) = 46.5 emu/cm³ has been obtained. Co-existence of FE and FM response can be attributed to stress and different permeability and permittivity involved in multilayer structures.     

Effect of attrition milling on the piezoelectric properties of Bi0.5Na0.5TiO3-based ceramics

Bismith sodium titanate (BNT)-based powders were prepared by conventionally mixed-oxide method using Bi₂O₃, Na₂CO₃ and TiO₂. The La₂O₃ was added as the modifier to the BNT composition for easily poling and reducing an abnormal dielectric loss at high temperatures. In this study, the investigated compositions were Bi_0.5Na_0.5TiO₃ and Bi_0.5Na_0.485La_0.005TiO₃. The powders were calcined at 900 °C for 2 h by slow heating rate at 100 °C/h. The calcined BNT-based powders were then attrition-milled for 3 h with a high speed at 350 rpm. After drying, the fine powders were uniaxially pressed and then cold-isostatically pressed (CIP) at 240 MPa for 10 min. All pressed pellets were sintered at 1000–1100 °C for 2 h in air atmosphere. The microstructure of sintered pellets was investigated by SEM. Results of dielectric and piezoelectric property measurement were also reported.     

Dielectric behavior of Bi2/3Cu3Ti4O12 ceramic and thick films

The paper reports on synthesis, sintering and microstructure of Bi_2/3Cu₃Ti₄O₁₂, a lead-free, high-permittivity material with internal barrier layer capacitor behavior. Complex impedance and capacitance of the ceramic and thick films were studied as a function of frequency (10 Hz–2 MHz) and temperature (−170 to 400°C). Dc electrical conductivity of the samples was measured in the temperature range 20–400°C. Broad and high maxima of dielectric permittivity versus temperature plots were observed reaching 60,000 for ceramic and 5,000 for thick films. The maxima decrease and shift to higher temperatures with increasing frequency. Two arcs ascribed to grains and grain boundaries were found in the plots of imaginary part versus real part of impedance. Analysis of the impedance spectra indicates that Bi_2/3Cu₃Ti₄O₁₂ ceramic could be regarded as electrically heterogeneous system composed of semiconducting grains and less conducting grain boundaries. The developed thick film capacitors with dielectric layers based on Bi_2/3Cu₃Ti₄O₁₂ exhibit dense microstructure, good cooperation with Ag electrodes, high permittivity up to 5,000 and relatively low temperature coefficient of capacitance in the temperature range 100–300°C. Broad maxima in the dielectric permittivity versus temperature curves may be attributed to Maxwell–Wagner relaxation.     

Effect of B2O3 addition on the microwave dielectric properties of Li2ZnTi3O8 ceramic

Li₂ZnTi₃O₈ ceramics doped with B₂O₃ were prepared by the conventional solid-state reaction. The effects of B₂O₃ additions on the sintering characteristic, phase composition, microstructure and microwave dielectric properties of Li₂ZnTi₃O₈ ceramics were investigated. The addition of B₂O₃ reduces the sintering temperature of the Li₂ZnTi₃O₈ ceramic from 1075 °C to 925 °C. Only a single phase Li₂ZnTi₃O₈ forms in the Li₂ZnTi₃O₈ ceramic with less than 2.0 wt% B₂O₃ sintered at 925 °C. However, when the addition of B₂O₃ exceeds 2.0 wt%, the second phase Li₂B₄O₇ appears in the Li₂ZnTi₃O₈ ceramic. Li₂ZnTi₃O₈ ceramic doped with 1.5 wt% B₂O₃ addition sintered at 925 °C reaches a maximum relative density of 94.5 % and exhibits good microwave dielectric properties of ε_r?=?24.96, Q×f?=?49,600 GHz and τ_f?=??11.3 ppm/°C.     

Structure and dielectric properties of Bi5−x La x Nb3O15 ceramics

Bi_5?x La _x Nb₃O₁₅ (x?=?0–?1.25) ceramics prepared by conventional solid-state reaction were studied using X-ray diffraction (XRD), electron probe microanalysis (EPMA) and dielectric spectroscopy techniques. The XRD analysis indicated single phase solid solution of Bi_5?x La _x Nb₃O₁₅ is formed for x?≤?1.25. EPMA showed good densification and homogeneous microstructures for the ceramics. With increasing x, the dielectric constant decreases monotonously and can vary from 258 to 158 at 300 kHz. The frequency dependence of dielectric constants indicated these ceramics are promising candidates for high frequency applications.     

High piezoelectric properties of (Ba,Ca)TiO3-0.04LiF ceramics sintered at a low temperature

Lead-free piezoelectric ceramics are strongly needed to replace the lead-based piezoelectric ceramics with increasing environmental concerns. Barium titanate (BaTiO₃) systems are one of the most promising candidates due to excellent electrical properties. However, the sintering temperature for traditionally sintered BaTiO₃ ceramics are about 1300°C, which restricts the applications of BaTiO₃ ceramics. It is necessary to develop high piezoelectric properties of BaTiO₃ based ceramics which are able to sinter at low temperature. The (Ba_0.94Ca_x)Ti_0.94O_δ-0.04LiF (x?=?0.00?~?0.05 mol) ceramics were synthesized by a conventional sintering method at 1050°C. All the samples show high relative densities over 90%. X-Ray Diffraction pattern indicated that the crystallographic structure of the samples (x?=?0.00 and 0.01 mol) are orthorhombic phase and changes to pseudocubic one with increasing Ca content to x?=?0.03 mol. Two-phases with orthorhombic and pseudocubic symmetries coexisted at x?=?0.02 mol, which contributes the excellent properties, in which the piezoelectric constant d ₃₃?=?361 pC/N, the planar electromechanical coupling coefficient k_p?=?41.2%, the Curie temperature Tc?=?70°C, the temperature of phase transition T _O-PC?=?34°C near the room temperature, the relative permittivity ε _r?=?4028 and the remanent polarization P _r?=?9.39 μC/cm².     

Effects of doping Bi and Nd on the phase transition and electric properties of (Bi1/2Na1/2)0.94Ba0.06TiO3 ceramics

(Bi_1/2Na_1/2)_0.94Ba_0.06TiO₃ (BNBT6) ceramics with 3 wt.% Bi₂O₃ and xwt.%Nd₂O₃ (x?=?0, 1.5, 4.5, 6.0) doping were prepared by solid state reaction. The phase transition behaviors and electric properties of ceramics were investigated. The results showed that with doping of 3 wt.% Bi₂O₃, an antiferroelectric (AFE) phase was induced in ferroelectric BNBT6 ceramics at room temperature. It was attributed to disruption of the ferroelectric coupling between [BO₆] octahedra since the generation of A-site vacancies. The AFE (Bi_1/2Na_1/2)_0.94Ba_0.06TiO₃-3wt.%Bi₂O₃ (BNBT6-3B) ceramics showed a high phase transition temperature (T _m?~?320 °C), corresponding to the AFE - paraelectric (PE) phase transition. Low Nd₂O₃ (x?=?1.5, 4.5) doping was helpful to strengthen the AFE phase of BNBT6-3B, while high Nd₂O₃ (x?=?6.0) resulted in a stronger frequency dispersion due to the enhancement of A-site cation disorder. With increasing temperature, the ceramics with low Nd₂O₃ underwent a relaxor AFE - AFE - PE phase transition, while only relaxor AFE - PE phase transition was presented in high Nd₂O₃-doped ceramics. An excellent dielectric properties (ε _max?=?2916) was obtained in x?=?1.5 sample.     

Fabrication and electrical properties of textured Na1/2Bi1/2TiO3-BaTiO3 ceramics by reactive-templated grain growth

The <001> fiber-textured Na_1/2 Bi_1/2TiO₃-BaTiO₃ (6 mol% BaTiO₃) ceramics were fabricated by reactive-templated grain growth (RTGG), using plate-like Bi₄Ti₃O₁₄ (BiT) particles prepared by a molten salt method as templates. The effects of sintering conditions on texture development and microstructure evolvement were both studied, and the mechanisms of grain orientation and densification were discussed. High Lotgering factor (≥96%) and high density (≥96% theoretic density) textured Na_1/2 Bi_1/2TiO₃-6BaTiO₃ ceramics were prepared by using the max templates concentration supplying 100% Bi in the final product, and sintering at 1200 °C for 10 h. The NBT-6BT obtained exhibited good piezoelectric performance with piezoelectric coefficient d ₃₃ ?=?241pC/N, and electromechanical coupling factor k _p ?=?41.2%, k _t ?=?66.5% at room temperature.