Study of structure and dielectrc properties of non-stoichiometric Bi2O3-ZnO-Nb2O5 ceramics

Bi-based ceramics with pyrochlore structure exhibit interesting dielectric properties such as high dielectric constant and small dielectric loss at high frequency and low firing temperature. Structure and dielectric properties of non-stoichiometric ceramics Bi_1.5?x ZnNb_1.5O_7?1.5x (with x?=??0.25～0.6) were investigated. The compounds departured from stoichiomeric compositions lead to structural parameters change. The second phase appeared when x?≥?0.4. The lattice parameters of cubic pyrochlore Bi_1.5?x ZnNb_1.5O₇ and grain size decreased as x increased. The experimental results show that dielectric constant decrease with increasing of the x value. The dielectric relaxation and defect resulting from non-stoichiometric ceramics Bi_1.5?x ZnNb_1.5O_7?1.5x were discussed.     

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.     

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.     

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.     

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.     

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.     

Excellent dielectric constants observed in heterogeneous conduction Ba(Zr<Subscript>0.25</Subscript>Ti<Subscript>0.75</Subscript>)O<Subscript>3</Subscript> ceramics doped with Sr(Fe<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>)O<Subscript>3</Subscript>

The (1-x)Ba(Zr_0.25Ti_0.75)O₃-xSr(Fe_0.5Nb_0.5)O₃ or (1-x)BZT-xSFN ceramics have been fabricated via a solid-state reaction technique. All ceramics exhibit a pure phase perovskite with cubic symmetry. The addition of a small amount of SFN (x?=?0.1) produces an obvious change in dielectric behavior. Very high dielectric constants (ε_r?>?164,000 at 1 kHz and temperature?>?150°C) are observed and the value is obviously higher than dielectric constants for Ba(Zr_0.25Ti_0.75)O₃ and Sr(Fe_0.5Nb_0.5)O₃ ceramics. The ferroelectric measurement data suggests that the unmodified sample exhibited a ferroelectric behavior. However, a transformation from a ferroelectric to a relaxor-like behavior is noted with increasing x concentration. Impedance Spectroscopy (IS) analysis indicates that the presence of excellent dielectric constants is due to the heterogeneous conduction in the ceramics after adding SFN, which can be explained in terms of the Maxwell-Wagner polarization mechanism.     

Effect of La3+ substitution on microwave dielectric properties of (Pb0.5Ca0.5)(Fe0.5Nb0.5)O3 ceramics

Microwave dielectric properties of the [(Pb_0.5Ca_0.5)_1?x La_2x/3](Fe_0.5Nb_0.5)O₃ and [(Pb_0.5Ca_0.5)_1?x La _x ](Fe_0.5Nb_0.5)O₃ ceramics were investigated as a function of La³⁺ content $ {\left( {0.0 \leqslant \times \leqslant 0.2} \right)} $ . A single perovskite phase was detected in [(Pb_0.5Ca_0.5)_1?x La_2x/3](Fe_0.5Nb_0.5)O₃, while Pb₃Nb₄O₁₃ were detected as a secondary phase in [(Pb_0.5Ca_0.5)_1?x La _x ](Fe_0.5Nb_0.5)O₃ beyond x?=?0.05 due to the excess of unbalanced charge. The amount of Pb₃Nb₄O₁₃ was proportional to the unbalanced charge. Qf value of [(Pb_0.5Ca_0.5)_1?x La_2x/3](Fe_0.5Nb_0.5)O₃ decreased remarkably with La³⁺ substitution due to the increase of oxygen vacancy. For [(Pb_0.5Ca_0.5)_1?x La _x ](Fe_0.5Nb_0.5)O₃ ceramics, dielectric constant and Qf value increased with La³⁺ content up to x?=?0.03 due to an increase of density and grain size. Temperature coefficient of resonant frequency (TCF) was depended on B-site bond valence in single perovskite phase.     

Enhanced piezoelectricity around the tetragonal/orthorhombic morphotropic phase boundary in (Na,K)NbO3–ATiO3 solid solutions

The high density perovskite titanates-modified potassium–sodium niobate solid solutions (1?x)(Na_0.5K_0.5)NbO₃?xBaTiO₃ and (1?x)(Na_0.5K_0.5)NbO₃?xSrTiO₃ have been prepared by the solid state reaction method. The phase diagram summarized from the dielectric property measurement reveals that there exists a tetragonal/orthorhombic morphotropic phase boundary for both the solid solutions. The piezoelectric properties show enhanced behavior at around the tetragonal/orthorhombic morphotropic phase boundary. It is believed that the origin for the high piezoelectric performance (Na,K)NbO₃-based lead-free piezoelectric ceramics is the same as that for the lead zinc niobate-lead titanate solid solution.     

Dielectric properties and defect mechanisms of (1-<Emphasis Type="Italic">x</Emphasis>)Ba(Fe<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>)O<Subscript>3</Subscript> -<Emphasis Type="Italic">x</Emphasis>BiYbO<Subscript>3</Subscript> ceramics

(1-x)Ba(Fe_0.5Nb_0.5)O₃ -xBiYbO₃ (BFN-xBY) ceramics were prepared by a conventional solid-state reaction method. The dielectric properties and relaxation behavior of BFN-xBY ceramics were analyzed according to dielectric and impedance spectroscopy. Dielectric permittivity of the ceramics increases with increasing temperature below 500 K then remains unchanged up to 700 K, while corresponding loss factor decreases with the increase of temperature below 500 K then increase slowly. Defect compensation mechanism of this system was analyzed in detail. The giant dielectric behavior of the ceramics arises from the internal barrier layer capacitor (IBLC) effect. Polarization effect at insulating grain boundaries between semiconducting grains accompanied by a strong Maxwell-Wagner (MW) relaxation mode. The characteristic of grain boundaries was revealed using impedance spectroscope and the universal dielectric response law.     

The microstructures and dielectric properties of xSrZrO3–(1−x)SrTiO3 ceramics

In this paper, the microstructures and the dielectric properties of xSrZrO₃–(1?x)SrTiO₃ (x?=?0.01, 0.03, 0.05, and 0.07) ceramics were investigated. The composition can form a single-phase structure solid solution as x increases from 0.01 to 0.07, and the average grain size decreases from 15 to 2 μm with the x increasing. With the variation of SrZrO₃ content, dielectric constant, dielectric loss, and breakdown strength (BDS) of xSrZrO₃–(1?x)SrTiO₃ samples are changed. When x?=?0.05, the samples exhibit high BDS more than 14 kV/mm and low dielectric loss about 1?×?10^?3 with dielectric constant of 330. It can be a candidate material of energy storage for pulsed power application.     

Study of the electrical properties of Pb(Zn,Ni)1/3Nb2/3O3–PbTiO3 ceramics across the morphotropic phase boundary

Structure and electrical properties of (1???x)Pb(Zn_0.2Ni_0.8)_1/3Nb_2/3O₃–xPbTiO₃ ceramics with x?=?0.24–0.38 were examined in detail. X-ray diffraction measurements reveal that all samples are in pure perovskite phase, and most of them lie within the morphotropic phase boundary (MPB) region. The dielectric behaviors of all compositions are characterized with diffuse phase transition and frequency dispersion. The variable power law and the Vogel–Fulcher relation have been used to describe such dielectric behaviors. The highest dielectric constant and the largest piezoelectric coefficient are simultaneously observed when x?=?0.30. The variation of the ferroelectric property with PT content is also discussed.     

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.     

Dielectric,ferroelectric and bipolar electric field induced strain properties of MPB composition of NBT-xKNN system

(1-x) (Na_0.5Bi_0.5TiO₃)-xK_0.5Na_0.5NbO₃/NBT-xKNN [x?=?0.07, 0.06, 0.05] ferroelectric ceramics were prepared by solid state synthesis route (SSSR). The effects of KNN contents on the microstructure, dielectric, piezoelectric and ferroelectric properties of the NBT-xKNN system were investigated in detail. For single perovskite phase formation, the calcination temperature was optimized at 800 °C for 6 h. From the XRD study, the morphotropic phase boundary (MPB) was confirmed for x?=?0.07 composition. For better densification, the sintering temperature was optimized for 1150 °C for 4 h. SEM micrographs illustrate the closely packed and non-uniform distribution of grains. Diffusive type of behaviour was observed in all the ceramics. Polarization (P) vs. electric field (E) study confirmed the ferroelectric nature of the NBT-xKNN ceramics. The bipolar field-induced strain measurement for all the ceramic samples showed butterfly-shaped loops indicating their piezoelectric nature. Among all the different compositions in MPB region, high dielectric constant (ε_r) of?~?3011, high remnant polarization (P _r ) of 17.88μC/cm² and high strain % of 0.41, were obtained in NBT-xKNN system with x?=?0.07 confirming the existence of MPB at this composition.     

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.     

Effect of Mg doping on dielectric properties of sol-gel derived (Pb0.7Sr0.3)Mg x Ti1–x O3–x thin film

(Pb_0.7Sr_0.3)Mg _x Ti_1–x O_3–x (x?=?0?～?0.3) thin films were successfully prepared on ITO/glass substrate by sol-gel technique. The crystalline phase structures were measured through X-ray diffraction (XRD). The dielectric properties were measured by a precision impedance analyzer. Results show that the perovskite phase was stable in (Pb_0.7Sr_0.3)Mg _x Ti_1–x O_3–x thin film. Its lattice constant was found to decrease with the increase of x when x?<?0.1 and increase when x?>?0.1.The crystalline phase formation and the dielectric properties of the (Pb_0.7Sr_0.3)Mg _x Ti_1–x O_3–x thin film depend on Mg doping content. The phase formation ability was decreased below x?=?0.1 and then increased above x?=?0.1 with the increase in x. The dielectric constant of the thin film is correspondingly changed. The tunabilities of about 35%?～?63% were obtained at 10 kHz. The highest tunability and the lowest dielectric loss of the thin films appeared at x?=?0.2. The FOM of the thin film with Mg doping of x?=?0.2 is about three times higher than that of x?=?0.1 under applied frequency of 10 kHz.     

Dielectric properties and morphotropic phase boundaries in the xPb(Zn1/3Nb2/3)O3−(1−x)Pb(Zr0.5Ti0.5O3 pseudo-binary system

Ceramics in the xPb(Zn_1/3Nb_2/3)O₃−(1−x)Pb(Zr_0.5Ti_0.5)O₃ [xPZN–(1−x)PZT] solid solution system are expected to display excellent dielectric, piezoelectric, and ferroelectric properties in compositions close to the morphotropic phase boundary (MPB). The dielectric behavior of ceramics with x = 0.1−0.6 has been characterized in order to identify the MPB compositions in this system. Combined with X-ray diffraction results, ferroelectric hysteresis measurements, and Raman reflectivity analysis, it was consistently shown that an MPB exists between x = 0.2 and x = 0.3 in this binary system. When x ≤ 0.2, the tetragonal phase dominates at ambient temperatures. In the range of x ≥ 0.3, the rhombohedral phase dominates. For this rhombohedral phase, electrical measurements reveal a profound frequency dispersion in the dielectric response when x ≥ 0.6, suggesting a transition from normal ferroelectric to relaxor ferroelectric between 0.5 ≤ x ≤ 0.6. Excellent piezoelectric properties were found in 0.3PZN–0.7PZT, the composition closest to the MPB with a rhombohedral structure. The results are summarized in a PZN–PZT binary phase diagram.     

High temperature electronic properties of BaTiO3 – Bi(Zn1/2Ti1/2)O3 – BiInO3 for capacitor applications

Solid solutions xBaTiO₃ – (1-x)(0.5Bi(Zn_1/2Ti_1/2)O₃ – 0.5BiInO₃), where x?=?0.95–0.60, were prepared by conventional mixed oxide method. The single phase perovskite structure was obtained for the composition with x?≥?0.75. Phase transformation from tetragonal to pseudocubic was observed from x-ray diffraction patterns when x decreased from 0.95 to 0.75. In tetragonal phase region, x?≥?0.90, the increase of Bi(Zn_1/2Ti_1/2)O₃ – BiInO₃ content decreased the tetragonality and the temperature at which the relative permittivity is maximum (T_max). The increase in lattice parameter and T_max were observed in the pseudocubic phase region, x?<?0.90. Additionally, a highly broad and diffuse phase transition was observed from the dielectric data in the pseudocubic phase region. The introduction of Ba vacancies in compositions with x?=?0.80 and 0.75 also improved dielectric loss at high temperatures. The incorporation of BiInO₃ into the BaTiO₃ – Bi(Zn_1/2Ti_1/2)O₃ compound was also found to improve the temperature coefficient of the relative permittivity, with values as low as approximately ?1,000?ppm/K. Overall, ternary perovskite solid solutions based on adding Bi(Zn_1/2Ti_1/2)O₃ – BiInO₃ to BaTiO₃ shows excellent potential for high temperature capacitor applications     

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.     

Effect of Ba2+ – Sr2+ co-substitution on the structural and dielectric properties of Lead Titanate

Growing interest in developing new materials for device applications led to study of ferroelectric oxides in a wide range and variety of compositions. In the present work, polycrystalline samples of lead barium strontium titanate (Pb_1-xBa_0.5xSr_0.5xTiO₃) solid solution system have been synthesized. Phase formation studies and crystal structure analysis were carried out by X ray diffractometry at room temperature, which suggested formation of single phase compound with tetragonal structure up to x?=?0.8 and cubic structure for x?=?1.0. The XRD pattern has been analyzed by employing Rietveld method. The phase transition in the system was confirmed by Differential Scanning Calorimetry (DSC). Samples with 0.0????x????0.8 are in ferroelectric state whereas with x?=?1.0 is found to be in paraelectric state at room temperature. Co-substitution of Ba²⁺ and Sr²⁺ into lead titanate shows reduction in anisotropy as well as porosity. The dielectric studies of the system as a function of temperature and frequency were carried out in the range 323?K to 773?K and 100?Hz to 1?MHz respectively. Variation of dielectric constant and loss tangent with temperature shows peaking effect near Curie temperature. Frequency dependant dielectric studies clearly show that the dielectric constant and loss tangent decrease exponentially with increased frequency.