Sintering and dielectric properties of Bi1.5ZnNb1.5O7 cubic pyrochlore ceramics via high-energy milling technology

The dense Bi_1.5ZnNb_1.5O₇ cubic pyrochlore ceramics is synthesized by high-energy milling technology from the coarse Bi_1.5ZnNb_1.5O₇ cubic pyrochlore powders prepared by solid state route. The sintering and dielectric properties of the Bi_1.5ZnNb_1.5O₇ cubic pyrochlore ceramics are investigated, which show that the sintering temperature of the prepared ceramics could be effectively lowered to 800°C and the bulk density reach 6.889 g/cm³ approximately 97% of the theoretical density of Bi_1.5ZnNb_1.5O₇ cubic pyrochlore ceramics. The excellent dielectric properties of the ceramics sintered at 850°C has been obtained with the relative permittivity of 160 and the dielectric loss of 10^?4. This route would be a low-cost and mass production for lowering the sintering temperature of the Bi_1.5ZnNb_1.5O₇ cubic pyrochlore ceramics without sintering aids.     

Studies on dielectric relaxation and high temperature conductivity of Bi1.5Zn1−x Nb1.5O7−x ceramics

The dielectric properties of cubic pyrochlore Bi_1.5Zn_1?x Nb_1.5O_7?x (BZN) ceramics with high dielectric constant, low dissipation factor are strongly affected by their lattice defects. The dielectric properties of BZN sintered in various atmosphere including ambient, N2, and O2 are investigated. The equilibrium high temperature conductivity was examined.     

Relaxor-like behavior of bismuth-based pyrochlores containing Sn

Dielectric relaxation studies have been made in pyrochlore (Bi_1.5Zn_0.5)(Zn_0.5?x/3Sn _x Nb_1.5?2x/3)O₇ ceramics where 0?≤?x?≤?1.5. The measurements of dielectric constant (?) and dielectric loss (tanδ) are made in the frequency range from 1 to 1,000 kHz at low temperatures from 100 to 450K. Frequency dispersion associated with dielectric relaxation phenomena in polycrystalline cubic pyrochlore is analyzed. The effect of Sn on the dielectric relaxation behavior and the physical mechanism giving polarization is briefly discussed.     

Investigation of the physical properties of Bi1.5-xCdxZn0.92Nb1.5O6.92-x/2 pyrochlore ceramics

For the purpose of dielectric parameters tuning Bi_1.5Zn_0.92Nb_1.5O_6.92 (BZN) pyrochlore ceramics were subject to cadmium doping in accordance to the chemical formula; Bi_1.5-xCd_xZn_0.92Nb_1.5O_6.92-x/2 for 0.10 ≤ x ≤ 0.50. The main physical properties of the doped samples were investigated by means of X-ray diffraction, scanning electron microscopy associated with energy dispersion spectroscopy, temperature dependent dielectric constant and temperature dependent electrical resistivity to obtain the crystalline structure, the lattice parameter, the relative density, the surface morphology and chemical composition. Optimization of single phase Cd doped samples were possible for x?≤?0.14, beyond this limit, ZnO and Zn₃Nb₂O₈ minor phases grow through the structure of the BZN. For samples which exhibit single BZN phase, the dielectric constant, the electrical resistivity and the resistivity activation energy increased with increasing Cd content. The maximum obtainable dielectric constant as 259 and 224 with high signal quality factor of 690 and 1090 at 25 and 200 °C, respectively, was for the sample doped with 0.14 Cd. These values are promising for implantation of BZN in RF and microwave technology as a resonator with high quality signal.     

Structural disorder in BZN-based pyrochlores

Careful structural investigations have been carried out on the Bi_1.5ZnNb_1.5O₇ based dielectric system (of A ₂ B ₂O₇ pyrochlore structure type) in an attempt to understand the origin and tolerance of relaxor behavior in such materials. A highly structured, characteristic diffuse intensity distribution was observed in electron diffraction patterns, which arises from static disordering caused by local short range ordering of Bi and Zn ions on the pyrochlore A sites and associated structural relaxation of the O’A ₂ sub-structure. This structural disordering is not affected by B site substitution of the Nb⁵⁺ ions by Sn⁴⁺ or Ti⁴⁺ ions. The result is of significance for optimizing the dielectric properties of bismuth-based advanced ceramics.     

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.     

Co-Modification of Ba5NdTi3Ta7O30 Dielectric Ceramics by Substitution and Introducing Secondary Phase

Co-modification of Ba₅NdTi₃Ta₇O₃₀ dielectrics ceramics was investigated through Pb substitution for Ba and introducing Bi₄Ti₃O₁₂ secondary phase. The dielectric constant increased from 150 to 283, the temperature coefficient of the dielectric constant decreased from –2500 ppm/°C to –1279 ppm/°C, and the dielectric loss decreased to 0.0007 at 1 MHz. Meanwhile, the bi-phase ceramics were investigated to achieve temperature stable ceramics with high dielectric constant and low dielectric loss. As the composition x varied from 0.4 to 0.7 for (1 – x)(Ba_0.8Pb_0.2)₅NdTi₃Ta₇O₃₀/xBi₄Ti₃O₁₂, the temperature coefficient of the dielectric constant changed from negative to zero to positive.     

Effects of ZnO–xV2O5 substitution on the microstructure and microwave dielectric properties of ZnNb2O6 ceramics

The ZnO–xV₂O₅ substituted ZnNb₂O₆ ceramics with chemical formula Zn(Nb_0.9V _x )₂O_5.5+5x (0?<?x?≤?0.10) were prepared by solid-state reaction route. The densities, microstructures and microwave dielectric properties were investigated according to the different substitution amount of V₂O₅ and sintering temperature. A small amount of substitution of ZnO–xV₂O₅ was effective to lower sintering temperature of ZnNb₂O₆ ceramics from 1,150 °C to 900 °C. The V₂O₅ substitution led to growth of rod-like grains with the help of liquid phase formed from ZnO and V₂O₅. The dielectric properties depended largely on the amount of V₂O₅ substitution and sintering temperature. The dense ceramics with x?=?0.05 were obtained at 950 °C, which had excellent dielectric properties: ?_r?=?24, Q?×?f?=?72,800 GHz and τ_f?=??63.5 ppm/°C. The interface analysis for cofired multilayer composites composed of the present LTCC and metal Ag demonstrated good co-firing chemical compatibility at co-sintering temperature.     

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.     

Sputter target stoichiometry dependent dielectric properties of Bi2O3-ZnO-Nb2O5 pyrochlore system

Tunability of Bi₂O₃-ZnO-Nb₂O₅ (BZN) pyrochlore systems can be varied widely, even among isostructural phases (e.g., α-BZN crystals), because of the nonstoichiometry. Therefore, the tunability of BZN pyrochlore paraelectric thin films was reinvestigated. Using nonstoichiometric BZN targets, films with either cubic or monoclinic structure and a second phase devoid of Zn were obtained. Owing to the low sputtering yield of Bi, (Bi_1.5Zn_0.5)(Zn_0.5Nb_1.5)O₇ (α-BZN) was obtained by sputtering α-BZN targets and also targets with Bi-enriched monoclinic composition, i.e., Bi₂(Zn_0.33Nb_0.66)₂O₇ (β-BZN) targets. However, α-BZN films sputtered from β-BZN targets exhibited far better tunability than do those sputtered from α-BZN targets, proving the significance of Bi enrichment of targets. Furthermore, α-BZN films were continuously deposited even when the target composition, Bi:Zn:Nb, increased from the stoichiometry ratio of 3:1:2 to nonstoichiometric 4:1:2. At a target composition of 3.2:1:2, the dielectric properties maximized with a dielectric constant of 184; loss tangent of 0.008; and maximum tunability of 42 % at 1.2 MV/cm of dc-bias field under 1 MHz. The properties minimized at the target composition of 4:1:2, at which β-BZN films formed. For the composition mid-range, Bi₅Nb₃O₁₅ phases occurred along with the α-BZN phase and showed synergetic effects on the properties of the α-BZN films.     

Enhanced dielectric properties of Bi1.5ZnNb1.5O7 thick films via cold isostatic pressing

Dense Bi_1.5ZnNb_1.5O₇ thick films were prepared on Ag/Al₂O₃ substrates using screen-printing technology at a lower temperature of 825?°C. A novel pretreatment of cold isostatic pressing was introduced to enhance the quality of thick films. After cold isostatic pressing prior to sintering, the microstructure of thick films was improved with a more compact morphology and better dielectric properties, and the permittivity and dielectric loss of thick films sintered at 900?°C were about 160 and 0.006. The obvious tunability of thick films was also observed, and the tunability value reached about 3?% for thick films sintered at 900?°C under 400?kV/cm. The enhanced properties and low-temperature sintering made this compound a potential candidate for Low Temperature Co-fired Ceramic (LTCC).     

Effect of Ca substitution on structure and dielectric properties of bismuth-based microwave ceramics

The effect of the chemical substitution of Ca cation on the microstructure and microwave dielectric properties of bismuth-based pyrochlores has been investigated. Broad ranges of solid solutions based on (Bi_3x Zn_2?3x )(Zn _x Nb_2?x )O₇ (x?=?0.56–0.64) were obtained with Ca cation substitution of Zn at A site. The XRD patterns revealed that the substitution of Ca for Zn led to the α–β pyrochlore phase transformation and pure β pyrochlore structure were obtained. The dielectric constants (? _r ) varied slightly with x increasing. The quality factor Q was significantly improved by Ca substitution. The temperature coefficient of resonant frequency (τ _f ) was negative and increased with x increasing. (Bi_3x Ca_2?3x )(Zn _x Nb_2?x )O₇(x?=?0.58) ceramic, sintered at 960 °C, exhibits the optimal microwave dielectric properties of ? _r ?～?74, Qf value ～6,457 (at 4.8 GHz), and τ _f ?～??143 ppm/°C.     

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.     

The effect of sintering atmosphere on V2O5 substituted BiNbO4 microwave ceramics

In multiplayer passive devices, low sintering temperature dielectric materials were needed to co-fire with low melting point inner electrode such as copper or silver, a major problem of base metal electrode (BME) was that the devices must be fired under low oxygen partial pressure atmosphere to protect Cu from oxidation. In this paper, dielectric properties of Bi(V_xNb_1?x)O₄ (x?=?0.001, 0.004, 0.008, 0.016, 0.048) microwave ceramics sintered under air and N₂ atmosphere have been investigated. The densification temperature sintered in different atmosphere decreased from 1010 to 830°C with the amount of V₂O₅ increasing from 0.001 to 0.048. Due to the increasing vacancy defects, the density of ceramics sintered in N₂ was smaller than that sintered in air. The ceramics sintered under N₂ have similar dielectric constant, and its Qf values are higher while x?<?0.016.     

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.     

Control of the ferroelectric and electrical properties of Nd substituted bismuth titanate ceramics

Nd-doped bismuth titanate Bi_4?x Nd _x Ti₃O₁₂ ceramics were prepared by a solid state reaction method. The effects of Nd doping on ferroelectric and electrical properties were investigated. With Nd substitution for Bi ion, a BNdT single-phase with Bi-layered perovskite was confirmed. The Nd doping decreased the dissipation factor (tanδ) and the dc conductivity, and increased the dielectric constant and the remanent polarization. A small Nd doping on Bi₄Ti₃O₁₂ leads to a higher remanent polarization and improves the ferroelectric properties.     

Evolution of Structure and Dielectric Properties on Bismuth-Based Pyrochlore with TiO2 Incorporation

The lattice constant and thermal expansion of the pyrochlore oxides (Bi_1.5Zn_0.5)(Zn_0.5–x/3Ti_x Sb_1.5–2x/3)O₇ (0 x 1.5) were studied by X-ray powder diffraction, SEM and IR spectra, respectively. The average grain size is enhanced as the Ti-doping level is increased. The XRD results indicate that all samples have a cubic structure (Fd3m space group) with the lattice parameter decreasing with rising Ti content. The variation of lattice parameters with composition was found to obey Vegard's law. The assignments for the absorption bands in the IR spectra of the series of samples have also been given. The results of diffraction patterns and IR spectra demonstrated that these compounds have the cubic pyrochlore structure. The dielectric properties of the samples were systematically studied. Dielectric constant and temperature coefficient of dielectric constant exhibit strong dependence on the Ti concentration. Dielectric constant varies sharply from 30 when x = 0 to 115 when x = 1.5.     

The sintering behavior and microwave dielectric properties of Mg4(Nb,Sb)2O9 ceramics

The sintering behavior, microstructure and microwave dielectric properties of Mg₄(Nb_2?x Sb _x )O₉ (0?≤?x?≤?2) solid solutions were investigated systematically by X-ray diffraction(XRD), scanning electron microscopy(SEM) and a network analyzer. The solid solutions of Mg₄(Nb_2?x Sb _x )O₉ was formed with x value being no more than 1.6. The dielectric constant (?) of the sintered ceramics decreased from 13.06 to 6.28 with Sb content x from 0 to 1.6. With a substitution of Sb⁵⁺ for Nb⁵⁺ (0.04?≤?x?≤?0.08), the sintering temperature of Mg₄Nb₂O₉ ceramics was decreased from 1400 to 1300 °C without degradation of the Qf values. The optimum microwave dielectric properties of ??～?12.26, Qf?～?168,450 GHz, and τ _f?～??56.4 ppm/°C were obtained in the composition of Mg₄(Nb_1.6Sb_0.4)O₉ sintered at 1300 °C.     

Sintering and dielectric properties of (Ta2O5)1−x (TiO2) x polycrystalline ceramics

(Ta₂O₅)_1?x (TiO₂) _x system ceramics has been studied intensively as a promising dielectric material for next generation of high density dynamic random access memories instead of SiO₂ and Si₃N₄. It is found that the dielectric permittivity of (Ta₂O₅)_1?x (TiO₂) _x ceramics was dependent of fabrication process. But in the previous work, their calcining and sintering time were too long, generally for 24 h or even more. A relatively quick sintering process was provided which calcining and sintering time can be decreased to 12 h at 1200°C and 1 h at 1550°C, respectively. This kind of sintering process can save a lot of energy and time that is in favor of the industrial production. Under this sintering process, the composition dependent dielectric properties of (Ta₂O₅)_1?x (TiO₂) _x ceramics have been studied in a wide range of composition (0.01?≤?x?≤?0.20), and the dielectric constants of most compositions can be drastically enhanced. The maximum dielectric value can reach 216 at composition x?=?0.04. In the meantime, the mechanism of improvement of ceramic dielectric constants sintered at 1550°C was also discussed.     

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