Physical and dielectric properties of BaTiO3–fluoride–glass systems for nitrogen-fireable embedded capacitors

BaTiO₃-based dielectrics containing the selective additive combinations from Pb-free glasses and fluoride compounds such as AlF₃, BaF₂, CaF₂, LiF and ZnF₂ were studied mainly for a potential N₂-fireable embedded capacitor in printed circuit board with Cu metallization. The physical and dielectric properties, such as dielectric constant (k), loss tangent (tanδ) and T _c, strongly depended on the choice of additive combination. A bismuth borosilicate glass was most promising in terms of the degree of densification and dielectric constant. The samples containing LiF and ZnF₂ and sintered at 950 °C looked most beneficial in that these additives produced high k of >1,200 and low tanδ of < 0.022 at room temperature regardless of sintering atmosphere. As an example, the 95BaTiO₃–2LiF–3(Bi borosilicate) sample exhibited k?~?1,340 and tanδ?~?0.022 at room temperature when fired at 950 °C in N₂.     

Effect of sintering temperature on microstructure and piezoelectric properties of Pb-free BiFeO3–BaTiO3 ceramics in the composition range of large BiFeO3 concentrations

Lead-free (1-x)BiFeO₃–xBaTiO₃ [(1-x)BF-xBT] piezoelectric ceramics in the range of large BF concentrations were prepared by conventional oxide-mixed method at various sintering temperatures. The sintering temperatures have a significant effect on the microstructure of the ceramics, and the composition has a remarkable effect on optimal sintering temperature of the ceramics, which are closely related with piezoelectric properties. The grain size increased with increasing sintering temperature and the optimal sintering temperature increased with increasing BT content. The ceramics with x?=?0.275 sintered at 990 °C exhibit enhanced electrical properties of d ₃₃?=?136pC/N and k _p?=?0.312 due to the polarization rotation mechanisms at MPB and desired microstructure. These results show that the ceramic with x?=?0.275 is a promising lead-free high-temperature piezoelectric material.     

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.     

The effect of Sb on the electrical and magnetic properties of Ni-Zn ferrites prepared by sol–gel autocombustion method

Polycrystalline Ni-Zn ferrites with a well-defined composition of Ni_0.4Zn_0.6Fe_2-xSb_xO₄ synthesized using sol–gel method. Morphological characterizations on the prepared samples were performed by high resolution transmission electron and field emission scanning electron microscopy. The powders were densified using microwave sintering method. The room temperature complex permittivity (ε′ and ε″) and permeability (μ′ and μ″) were measured over a wide frequency range from 1 MHz–1.8 GHz. The real part of permittivity varies as ‘x’ concentration increases and the resonance frequency was observed at much higher frequencies and there is a significant decrease in the loss factor (tanδ). The electrical resistivity and permeability of NiZn ferrites increased with an increase of Sb content. As the concentration of ‘x’ increases from 0 to 0.08 the saturation magnetisation decreases. The saturation magnetization (M_s)?≈?52.211 A.m²/Kg for x?=?0 at room temperature. The room temperature electro paramagnetic resonance (EPR) were studied.     

Effects of doping Y2O3 on the microstructure and electrical properties of ZnO-Bi2O3−based varistor ceramics

ZnO-based varistor ceramics doped with different amount of Y₂O₃ have been made by two-step solid-state reaction route including the pre-calcination and subsequent sintering procedures, using nanosized ZnO powder and corresponding additives as the raw material. The phase composition, microstructure and electrical properties were studied by means of X-ray diffractometry (XRD), scanning electron microscopy (SEM) and direct current electrical measurement. It was found that the electrical properties of the varistor ceramics sintered at 950 °C from the powder pre-calcined at 800 °C were enhanced by doped appropriate amount of Y₂O_3. Particularly, ZnO varistors doped with 1.2 mol% Y₂O₃ possessed the best comprehensive electrical properties with the breakdown field of 2113 V/mm, the nonlinear coefficient of 184.6 and the leakage current of 0.4 μA. Y₂O₃ phase, Y-rich phase and the other secondary phase particles were confirmed to distribute along the grain boundaries of predominant ZnO grains from XRD and SEM analyses. The results illustrated that doping Y₂O₃ should be a promising route to obtain varistor ceramics with excellent electrical properties.

     

Effect of Zr/Ti ratio on piezoelectric and dielectric properties of PNW–PMS–PZT ceramics

(Pb_0.95Sr_0.05)[(Ni_1/2W_1/2)_0.02(Mn_1/3Sb_2/3)0.06(Zr_XTi_Y)_0.92]O₃ piezoelectric ceramics (abbreviated as PNW–PMS–PZT) with 1%mol excess PbO, 0.25 wt% CeO₂ and 0.2 wt% MnO₂ were prepared by traditional ceramics process. The phase structure of ceramics sintered at 1150°C were analyzed. Results show that the pure perovskite phase was in all ceramics specimens, the phase structure of PNW–PMS–PZT piezoelectric ceramics was transformed from tetragonal to rhombohedral, with Zr/Ti ratio increased in system; Effect of Zr/Ti ratio on piezoelectric and dielectric properties was investigated. Results show that ? _r , tanδ, k _p and d ₃₃ increased with an increase of Zr/Ti ratio and reached the maximum values at Zr/Ti ratio of 50/50, then decreased with further increase of Zr/Ti ratio, whereas the variation of Q _m with an increase of Zr/Ti ratio showed the opposite trend, T _c showed a tendency to decrease with an increase of Zr/Ti ratio. The piezoelectric ceramics with Zr/Ti ratio of 50/50 was applied in high-power multilayer piezoelectric transformer, and properties parameter were ? _r ?=?2100, tanδ?=?0.006, k _p ?=?0.613, Q _m ?=?1300, d ₃₃ ?=?380pC/N, T _c ?=?205 °C.     

Effect of Bi3+ ion on piezoelectric properties of K x Na1−x NbO3

This paper describes the material preparation and characteristics of potassium sodium niobate, K _x Na_{1? x} NbO₃ (KNN), with Bi³⁺ doping. Some physical properties including density, dielectric constant, loss tangent and ferroelectric hysteresis, were examined. The samples were characterized by using X-ray diffraction method and the grain size was measured by using SEM micrographs. Dielectric constant, loss tangent, and electromechanical coupling coefficient of samples were measured at different frequencies. The changes in physical properties are remarkable when KNN is doped with Bi³⁺ ions.     

Effect of additive SrWO4 on microwave dielectric properties of SrTiO3–Sr(Mg1/3Nb2/3)O3 ceramics

The crystal structure and the properties of a new microwave dielectric ceramics x SrTiO₃–(1???x)Sr(Mg_1/3Nb_2/3)O₃ have been investigated. With x?=?0.025, The new microwave dielectric ceramic achieves the dielectric properties of a dielectric constant ? _r ～27.8, a Q?×?f value ～26,800, and a τ _f value ～7.4 ppm/°C. When the SrWO₄ is added, the sintering temperature of x SrTiO₃–(1???x)Sr(Mg_1/3Nb_2/3)O₃ ceramics will fall to 1350 °C, and its Q?×?f value can be improved further and the τ _f value becomes smaller. When the SrWO₄ is added by 0.07 mol, the specimen acquires the following microwave properties: a dielectric constant ? _r ～30.3, a Q?×?f value ～29,500, and a τ _f value of approximately ?0.4 ppm/°C.     

The effect of La-substitution on the energy-storage properties of NBT–BT lead-free ceramics

Journal of Electroceramics - The energy-storage properties have been investigated as a function of the temperature and frequency in (Bi0.5Na0.5)0.92Ba0.08-3x/2LaxTiO3 lead-free ceramics, where...     

Optimizing design of the microstructure of sol–gel derived BaTiO3 ceramics by artificial neural networks

Modeling and application of artificial neural network (ANN) technique to the formulation design of BaTiO₃-based ceramics were carried out. Based on the homogenous experimental design, the results of BaTiO₃-based ceramics were analyzed using a three-layer back propagation (BP) network model. Then the influence of sintering temperatures, holding time, donor additives (La₂O₃, MnO₂, Ce₂O₃) and sintering aids (Al₂O₃–SiO₂–TiO₂ (AST)) on the average grain size (d _a), the degree of grain uniformity given by the ratio of the maximal grain size to the average grain size (d _max/d _a), and the relative density (D _r) of doped BaTiO₃ ceramics system was investigated. The optimized results and experiment data were expressed and analyzed by intuitive graphics. Based on input data and output data, the sintering behavior of BaTiO₃ nano-powder was explained well. Furthermore, the fine and uniform microstructure of sol–gel derived BaTiO₃ ceramics with d _a?≤?3 μm, d _max/d _a?≤?1.20, and D _r?≥?98% was obtained.     

Ni–Mn–Fe–Cr–O negative temperature coefficient thermistor compositions: Correlation between processing conditions and electrical characteristics

A study has been carried out to correlate the effect of sintering temperature on the microstructural, electrical and reliability aspects of Ni_0.75Mn_{(2.25−x−y)}Cr _x Fe _y O₄ (x = 0 to 0.3 and y = 0 to 0.3) negative temperature coefficient thermistor compositions prepared by solid-state route. The calcined and sintered compositions were characterized by X-ray diffraction and Scanning Electron Microscopy. The existence of cubic spinel single-phase region was determined by sintering Ni_0.75Mn_{(2.25−x−y)}Cr _x Fe _y O₄ samples in air at temperatures 1150 to 1250 °C. X-ray diffraction patterns of samples sintered above 1200 °C shows additional Bragg reflections of a rock salt structured NiO phase besides normal cubic spinel. A maximum B-value of 4044 K was obtained for Ni_0.75Mn_1.95Cr_0.25Fe_0.05O₄ composition at a sintering temperature 1250 °C/3 h. The reliability of the thermistor compositions were evaluated by performing accelerated ageing based on thermal cycling test. We found that chromium enhances the reliability of Ni_0.75Mn_{(2.25−x−y)}Cr _x Fe _y O₄ (x = 0 to 0.3 and y = 0 to 0.3) based NTC thermistor compositions. A maximum reliability of +0.25% resistance drift was observed at sintering temperature 1200 °C for 0.25 mol% chromium content. Excellent reliability of Ni_0.75Mn_{(2.25−x−y)}Cr _x Fe _y O₄ NTC thermistor compositions makes it ideal candidates for high-performance thermal sensor applications.     

Synthesis of (Ba0.5Sr0.5)(Ti1 − x Zr x )O3 ceramics: Effect of Zr content on room temperature electrical properties

The phase formation behavior and room temperature dielectric properties of bulk perovskite solid solution composition (Ba_0.5Sr_0.5)(Ti_1 − x Zr _x )O₃ have been investigated. The samples with different Zr-content were prepared through solid state reaction. The XRD investigation showed that Zr⁺⁴ is systematically dissolved in Ba_0.5Sr_0.5TiO₃ lattice up to about 60 atm.% substitution, having cubic Pm3m structure. Eighty atom percent Zr substituted composition showed to contain a cubic phase similar to that of x = 0.6 composition and a tetragonal (I4/mcm) phase. That is the solid solution breaks around at 80 atm.% Zr substitutions. Ba_0.5Sr_0.5ZrO₃ was having orthorhombic Imma structure. Decrease in grain sizes were observed with increase in Zr content. The permittivity of the ceramics decreased with the increase in Zr substitution. The frequency dependency of dielectric loss in the frequency range 10 Hz to 10 MHz, were improved with Zr substitution in the ceramics. The room temperature ac and dc conductivity also decreased significantly with the increase in Zr-content.     

Effect of heating rate on the structure evolution of (K0.5Na0.5)NbO3–LiNbO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x)(K_0.5Na_0.5)NbO₃–xLiNbO₃ (abbreviated an KNLN) have been synthesized by traditional ceramics process. Effects of heating rate on the phase structure, microstructure evolution and piezoelectric properties of (1 − x)(K_0.5Na_0.5)NbO₃–xLiNbO₃ were investigated. Results show that the heating rate has no effects on the phase structures. However, the fracture surface of the 0.94(K_0.5Na_0.5)NbO₃ −0.06 LiNbO₃ ceramics transforms from intergranular fracture mode to a typical transgranular fracture mode with the increasing of the heating rate. This result is ascribed to the presence of agglomerates of grains which exhibit different sintering behavior at diverse heating rates. The 0.94(K_0.5Na_0.5)NbO₃–0.06LiNbO₃ ceramic sintered at 1080°C with heating rate of 5°C/min shows the optimum piezoelectric properties(d ₃₃ = 210 pC/N, k _p = 0.403 and k _t = 0.498).     

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.     

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.     

Dispersion and rheology of BaTiO3 nanoparticles in ethanol–isopropanol solvents

Barium titanate (BaTiO₃) nanoparticles were dispersed in ethanol–isopropanol mixtures and their rheological behaviors were examined in terms of surfactant concentration (0–5 wt.% of the solids) and volumetric solids loading () over a shear-rate () range 1 to 1,000 s⁻¹. An oxyethylene-based polymeric surfactant was used to facilitate the nanoparticle dispersion. A pronounced viscosity reduction, >95% when compared to the suspensions without the dispersant, resulted with a surfactant concentration of 4 wt.% at a constant shear rate of 100 s⁻¹. This finding was in parallel with a simultaneous reduction in the mean “floc” size of the suspensions. Shear-thinning flow character resulted over most of the shear-rate range examined, especially for the concentrated suspensions with ϕ ≥ 0.25. The concentrated suspensions were indeed flocculated. This increased instability was partly due to the compression of electrical double layer as the particulate solids became more crowded in the carrier solvents, and also to the increased “effective” solids concentration because of the preferential adsorption of the surfactant molecules on the nanoparticle surface.     

Effect of Fe – substitution on phase transformation,optical, electrical and dielectrical properties of BaTiO<Subscript>3</Subscript> nanoceramics synthesized by sol-gel auto combustion method

The structural, microstructural, optical, electrical and dielectrical properties of nanocrystalline Fe substituted BaTiO₃ synthesized by sol-gel auto combustion have been investigated. The X-ray diffraction (XRD) analysis revealed the existence of the tetragonal phase for lower Fe content (x = 0.0–0.3) whereas, coexistence of the tetragonal and hexagonal structure of higher Fe content (x = 0.4 and 0.5). The lattice constant (a and c) and unit cell volume (V) increases with increase in Fe content; and an average crystallite size (t) was recorded in the range of ~14–20 nm. The surface morphology as examined using field emission scanning electron microscopy (FESEM) and the compositional stoichiometry was confirmed by energy dispersive spectrum (EDS) analysis. The UV-Vis spectra showed that the band gap energy sensitively depends on the Fe concentration x. DC-electrical conductivity (σ) was recorded in the temperature range of 333–714 K which was found to be increases with increasing temperature and Fe concentration; indicating that an electrical conduction was a thermally activated process. The type of temperature dependent DC conductivity indicates that the electrical conduction in the material is a thermally activated process. The dependencies of the conductivity contributions were predicted from the simple defect model presented, in which oxygen vacancies charge compensate Fe substitution of Ti. Dielectrical property was measured as a function of frequency in the range 50 Hz - 5 MHz at room temperature which was found to be higher at lower frequencies. Dielectric constant (ε’) and loss tangent (tan δ) shows strong compositional as well as frequency dependences.     

Fabrication and electrical properties of barium strontium titanate thick films by modified sol–gel method

A modified sol–gel method has been developed to prepare for the barium strontium titanate (Ba_0.6Sr_0.4TiO₃, BST) thick films. The films were deposited on either Pd–Ag electroded alumina substrates (Pd–Ag/Al₂O₃) or silver electroded alumina (Ag/Al₂O₃) substrates by spin coating technique or screen printing technique. The thickness of the film was in the range of 2–10 μm. The key point of the process is to disperse fine-grained BST ceramic powders prepared by high energy ball mill into BST sol solution to form a slurry for spin coating and screen printing. In order to enhance the stability of the slurry and to avoid crack formation of the thick film, organic macromolecular poly-vinylpyrrolidone (PVP) was added to the sol solution. The structure and surface morphology of the films were studied by X-ray diffraction and Scanning Electron Microscope (SEM) techniques. It is revealed that the thick films exhibit pure perovskite phase and are crack-free, dense and homogeneous. The dielectric constant and loss tangent of the thick films are about 1200 and 0.01, at 10 °C and 1 KHz, respectively.