Strontium Barium Niobate Ceramics Research Articles

Investigation of the electrocaloric effect in strontium barium niobate (SBN) ceramics with rare-earth dopants

In ceramics, based on a solid solution of strontium barium niobate (0.7SBN) doped with cerium and gadolinium in various concentrations, an investigation was made of dielectric constant, electrical polarization, and the electrocaloric effect. For 0.7SBN ceramics, it was found that the addition of cerium (0.2%) leads to a decrease in the electrocaloric effect compared to pure 0.7SBN, and the addition of gadolinium (˂1%) to an increase in the electrocaloric effect.

Induced anisotropic behavior and enhanced electrical properties on hot-pressed strontium barium niobate ceramics

Sr0.30Ba0.70Nb2O6 (SBN30) ferroelectric ceramics were fabricated by conventional sintering (CS) and by hot-pressing sintering (HP) and their crystal structure, microstructure, dielectric, ferroelectric and pyroelectric properties were studied and compared. Preferred orientation of the HP ceramics was detected through X-ray diffraction. Dense microstructure virtually free of pores has been achieved in HP samples. Moreover, the HP samples manifested prominent anisotropy in electrical properties. Besides, the relative permittivity (εr), saturated polarization (Ps), pyroelectric coefficient (p) in the direction perpendicular to the pressing axis were much higher than those of the randomly oriented CS samples. The HP samples sintered under 200MPa show excellent pyroelectric properties in the direction perpendicular to the pressing axis, with pyroelectric coefficient of 2.38×10−8C/cm2K and pyroelectric figure of merit of Fi=1.13pm/V, Fv=1.89m2/C and Fd=0.63 μPa−1/2，which roughly triple the values obtained in CS samples. These results indicate that hot-pressing is a viable option for accessing single-crystal-like anisotropy as well as enhanced electrical properties in polycrystalline ceramics, thus unveiling the distinctive potential of HP SBN30 ceramics for infrared detector applications.

Enhanced energy storage properties of strontium barium niobate ceramics by glass addition

Strontium barium niobate (SBN) ceramics with BaO-B2O3-SiO2 (BBS, 0–5 wt%) glass additive were prepared by the solid state reaction method, and the sintering behavior, crystal structure, microstructure, dielectric property and energy-storage density were investigated. The results show that the sintering temperature of SBN ceramics can be reduced from 1325 to 1175 °C by BBS addition. The BBS-added SBN ceramic materials adopt a single tetragonal tungsten-bronze structure. The addition of BBS can improve densification and refine grain size of the SBN ceramics. The breakdown strength of the SBN ceramics is greatly improved by BBS addition. The SBN ceramic material with 2 wt% BBS additive has the optimal electrical properties: the dielectric constant (er) is 1598, the breakdown strength is 279 kV/cm, and the energy storage density (J) is 5.39 J/cm3, which is improved by 2.3 times as compared with that of the pure SBN ceramics. This study provides the BBS added SBN ceramic as an attractive candidate for making high-energy density capacitors.

The structural and electrical properties of SrxBa(1−x)Nb2O6 (SBN) ceramic with varied composition

Strontium barium niobate (SBN) with the stoichiometric formula of SrxBa(1−x)Nb2O6 was synthesized using the solid-state reaction method. The compositions were varied as x=0.25, 0.30, 0.50, 0.51, 0.53, 0.55, 0.57 and 0.60 to identify the composition with the optimum structural and electrical properties. The structural properties of the SBN ceramic were studied using X-ray diffraction spectra, while the morphology of the sintered grain was monitored by a field emission scanning electron microscope (FESEM) measurement. The dielectric behavior and the main features of the diffuse phase transition of the SBN ceramics with relaxor behavior were carefully investigated. The increment of the x composition gives rise to continuous decrease of the temperature of the maximum dielectric constant. The effect of the diffuse phase transition and relaxation feature of the SBN can be attributed to the Sr2+ (variation of x composition) site distribution. The SBN ceramic with composition x=0.53 showed a saturated hysteresis loop at an applied field of 50kV/cm, showing the highest remnant polarization of 8.17μC/cm2 with a coercive field of ~11kV/cm. The leakage current densities of the SBN samples were ranged between 0.1 and 1×10−5A/m2 over a voltage range from 100V to 6kV. From these findings, the composition of x=0.53 gives the best electrical and structural properties compared to the rest of the compositions investigated and has potential application for practical lead free ferroelectric sensors.

Microstructure and relaxor ferroelectric properties of Bi2O3-doped strontium barium niobate ceramics

(1 − x) Sr0.4Ba0.6Nb2O6–xBi2O3 (0.00 ≤ x ≤ 0.20) ceramics were prepared by conventional solid-state reaction method. The microstructure, dielectric properties and P–E hysteresis loops of ceramics were investigated via X-ray diffraction, scanning electron microscope (SEM), Agilent E4980A and modified Sawyer–Tower circuit, respectively. XRD results showed the obtained ceramics were of tungsten bronze structure, and second phase Sr0.4Ba0.6Bi2Nb2O9 was detected at high doping concentration. SEM results showed suitable Bi2O3 addition could reduce the sintering temperature and assist the grain growth. The dielectric characteristics exhibited diffuse phase transition phenomena, which were verified by linear fitting of the modified Curie–Weiss law. Besides, the relaxor ferroelectric properties of ceramics followed the Vogel–Fulcher relationship well. The P–E hysteresis loops became slimmer with increasing the Bi2O3 addition, leading to a gradually decrease in both remnant polarization (Pr) and coercive field (Ec).

Influence of Sr/Ba ratio on the dielectric, ferroelectric and pyroelectric properties of strontium barium niobate ceramics

SrxBa1−xNb2O6 (with x=0.50, 0.45, 0.40 and 0.30) ceramics were synthesized by conventional solid-state method and sintered at 1350°C for 3h. The phase structure, microstructure, dielectric, ferroelectric and pyroelectric properties of obtained ceramics were systematically investigated. Pure tungsten bronze phase could be obtained in all ceramics. The dielectric characteristics showed that SBN ceramic was a relaxor with strong diffuse phase transition and weak frequency dispersion. As Sr molar fraction x increases from 0.30 to 0.50, the transition temperature TC decreased linearly while the diffusivity parameter γ declined from 1.88 to 1.68. The saturated polarization, remnant polarization and pyroelectric coefficient were also found to be enhanced in SBN ceramics with increasing Sr content. The pyroelectric coefficient of about 2×10−8C/cm2K can be obtained for polarized SBN50 ceramics at room temperature.

Sintering behavior and dielectric properties of Ce doped strontium barium niobate ceramics with silica sintering additive

Sr0.5Ba0.5Nb2O6 ceramics with and without CeO2 dopant were prepared by a partial co-precipitation method and a liquid phase sintering process. The cooperative effects of Ce doping and silica sintering additive on the sintering behaviors and the dielectric properties of Sr0.5Ba0.5Nb2O6 ceramics was investigated. It was observed that the lattice parameters of a-axis and c-axis of Sr0.5Ba0.5Nb2O6 ceramics decrease with the increase of Ce dopant, namely contraction of crystal cell volume occurs. Amorphous silica used for sintering additive can effectively restrain abnormal grain growth and prevent the rise of sintering activation energies caused by Ce doping, but Ce doping has more effect on the average size of the grains and the dielectric properties than the silica sintering additive when the Ce dopant and the silica sintering additive are introduced. Both the Curie temperatures and the maximum of dielectric constant at Tc decrease as the Ce3+ concentration increases.

Fabrication of c-axis oriented strontium barium niobate ceramics by rotating magnetic field orientation

Highly c-axis oriented Sr0.6Ba0.4Nb2O6 (SBN60) ceramics was prepared with the recent orientation method based on rotating magnetic field. Drastic improvement of piezoelectricity was noted by the c-axis orientation. The orientation increased in the sintering process through grain growth. Anisotropic microstructure was noted in the ceramics.

Effect of silica sintering additive on the sintering behavior and dielectric properties of strontium barium niobate ceramics

Sr 0.5Ba 0.5Nb 2O 6 powders were prepared in the partial coprecipitation method. Using amorphous SiO 2 as the sintering additive, Sr 0.5Ba 0.5Nb 2O 6 ceramics were sintered at different temperatures and the effects of the additive on the sintering behaviors and dielectric properties were studied. The phase structure, microstructure and dielectric properties of the samples were investigated in X-ray diffraction (XRD), SEM and LCR analyzer respectively. The results indicated that the amorphous SiO 2 additive could accelerate the pore elimination, shorten the sintering time and enhance the density for Sr 0.5Ba 0.5Nb 2O 6 ceramics. The well development of microstructure promoted by the additives can result in the improvement of the dielectric constant and the weakening of the relax behavior. With the help of the additive of 1.5 wt.%, the relative density of the sample sintered at 1300 °C only for 2 h can reached 94.3% and the dielectric constant was up to 4322.

Phase formation mechanism and characteristics of strontium barium niobate ceramics

Ceramic powders of (1 − x)BaNb 2O 6– xSrNb 2O 6 (0 ≤ x ≤ 1) composition were prepared by solid-state reaction. Thermal analysis data revealed that SrNb 2O 6 was formed at a lower temperature, compared with BaNb 2O 6. Ba 1− x Sr x Nb 2O 6 mixtures show an intermediate thermal behaviour. For the samples thermally treated at 1000 °C/3 h, X-ray diffraction data pointed out single phase compositions for x = 0.4–0.6, which means that SrNb 2O 6 completely dissolves into BaNb 2O 6 lattice in this composition range The temperature increase at 1150 °C leads to partial decomposition and supplementary demixing phenomena for all the mixtures analyzed. At 1300 °C, solid-state reactions progress and a structural rearrangement occurs, so that the same phase composition identified at 1000 °C was found again. A slight increase of the isomorphy limit of SrNb 2O 6 into BaNb 2O 6 lattice was also noticed. Single-phase compositions were identified for the samples with x = 0.3–0.6.

Effect of ceria doping on random-field-related polarization reversal in strontium barium niobate ceramics

Polarization reversal has been investigated in undoped and Ce3+-doped Sr0.5Ba0.5Nb2O6 in terms of a power-law random-field model. The random fields, excess polarization, and the volume contribution to the excess polarization were evaluated and found to be linearly dependent on the concentration of Ce doping. The origin of the random fields arising form Ce doping is discussed.

Structural and microwave dielectric properties of Sr1-xBaxNb2O6ceramics at microwave frequencies

Microwave dielectric properties and crystal structure of Sr1-xBaxNb2O6 ceramics (x = 0·39, 0·45, 0·50, 0·55, 0·57, 0·60, 0·65) have been investigated. The microwave cavity perturbation technique was employed for the study of dielectric properties. Parameters such as complex permittivity and conductivity of strontium barium niobate ceramics were determined at the S band by measuring changes in the resonant frequencies and Q values of the cavity resulting from the introduction of the sample. The real part of the complex permittivity of all samples shows an increase with frequency, whereas the imaginary part of permittivity decreases as frequency increases. The effects of composition and sintering temperature on crystal structure and microstructure were studied by X-ray powder diffraction and scanning electron microscopy. Most compositions show preferred orientations along the c axis, as is evident from the relatively high intensity of (001) and (002) peaks. The microstructure contains ferroelectric domainlike structures with increasing barium content.

Microstructure and dielectric properties of strontium barium niobate ceramics synthesized by partial coprecipitation

Abstract Strontium Barium Niobate, Sr0.5Ba0.5Nb2O6 (SBN50), has been synthesized, for the first time, by partial coprecipitation of SrCl2 and BaCl2 on Nb2O5. Powder X-ray diffraction study shows tetragonal tungsten bronze phase formation at 1200 °C. Particle morphology and size of calcined powder has been examined using Transmission Electron Microscopy. The particle size of calcined powder ranges between 250 and 300 nm. The green compacts have been sintered at 1250, 1300 and 1350 °C and at each temperature for 6, 12 and 24 h, respectively. Effect of sintering time and temperature on dielectric properties has been investigated. Scanning electron microscopy has been used for grain morphology studies. Grains have been found to be tetragonal in shape and show variation in size for different sintering conditions. Highest dielectric constant (e) has been observed for the pellet sintered at 1350 °C for 6 h. A variation in Tc from 93 to 119 °C has also been observed.

Properties of sol-gel derived strontium barium niobate ceramics and the effect of V2O5 additive

Strontium barium niobate, SrxBa1−xNb2O6, (SBN) ceramics with a range of Sr/Ba ratios were fabricated using a solution chemistry approach with alkoxides dissolved in acetic acid. Powders obtained from dried gels were calcined at 800°C for three hours, a heat treatment that produced fully crystalline powders. After preparing bulk ceramics from these powders by sintering at 1200°C for 1–24 hours, the tetragonal tungsten bronze (TTB) phase was present in all compositions between 0 ≤ x≤ 1, although not predicted by the phase diagram for BaNb2O6and SrNb2O6. Vanadium pentoxide (V2O5) additions increased the densification, the amount of tungsten bronze phase, and the dielectric constant for all compositions except for Sr0.65Ba0.35Nb2O6(SBN65) ceramics.

Pyroelectric properties of rare earth doped strontium barium niobate ceramics from 20K to 450K

Pyroelectric properties of rare earth doped strontium barium niobate ferroelectric ceramics (SBN + yRE2O3, where RE = La, Nd, and Gd) were carefully investigated in the temperature range of 20K to 45 OK. The temperature dependence of the remanent polarization showed the existence of three distinct depolarization regions for all compositions. In addition, the overall behavior of the pyroelectric properties was highly dependent of doping element and its content.

Effect of different cations on the ferroelectric properties of modified strontium barium niobate ceramics

Strontium barium niobate (SBN) is a ferroelectric solid solution with tetragonal tungsten bronze structure [1, 2]. The structure consists of a framework of oxygen octahedra sharing corners in such a way that there are three different types of interstitial sites A, B and C. The common formula is (A1)2(A2)4(C)4(B1)2(B2)8030, where positions At , A2, BI, B2 and C can be filled by different-valency cations or may be partially empty. In tungsten bronze niobates BI and B 2 are filled by Nb 5+ . As, A2 and C could be filled by alkali and alkaline-earth metal ions from which crystals and solid solutions could be prepared with a variety of cations introduced into the structure. In many of these materials diffuse phase transition has been reported. In the work of Jimenez et al. [3] on SBN ceramics a large decrease in the Curie temperature of nearly 50 °C was reported when doped with Fe, Mn, Cr and La. Hence, in this work by doping with suitable cations we have tried to enhance Tc and decrease the dielectric loss. When the interstitial vacancies are filled partially or fully with alkali elements, Tc is raised. Hence, for filling the structure Na + was introduced. With the introduction of Na +, Aposition vacancies result from the volatility of Na. It is well known that A-position vacancies aid the sintering process. Lattice vacancies may be expected to be effective promoters of sintering because sintering is basically diffusion-controlled. Also, the ionic radius of Na + is smaller than that of Sr or Ba. This difference in ionic size is enough of a defect to cause marked lattice reconstruction by diffusion. The effect of different cations Cr 6+ , Zn 2+ and y3+ on the lattice parameters and ferroelectric properties of SrBaNb20 6 ceramics are reported in this letter. Polycrystalline solid solutions of the following compositions are prepared by the conventional ceramic processing: (Sr0.6Ba0.4)0.s RyNa0.4Nb206

A photoacoustic study of phase transition in modified strontium barium niobate ceramics

Abstract Strontium barium niobate (SBN) of the tetragonal tungsten bronze structure is a well known dielectric relaxor. In the present paper, the relaxor behavior which is a manifestation of the diffuse phase transition (DPT) characteristics is further pursued in a La-substituted SBN ceramics by the photoacoustic (PA) technique. An abrupt change of the PA signal of the pure and modified specimens shows another transition below the para-ferroelectric transition. Besides the diffuse ferroelectric phase transition the corresponding dielectric transition is located near room temperature in the modified SBN ceramics under a dc bias.

Ferroelectric properties of tungsten bronze ceramics

Abstract Modified strontium barium niobate and lead potassium niobate ceramics with tungsten bronze structure were prepared by the conventional ceramic techniques. The effect of various dopants on the properties of strontium barium niobate ceramics have been investigated. Curie temperature decreases with the increase of the ionic radius of dopant. The properties of filled and unfilled structures are compared. The effect of La3+ on Lead Potassium Niobate is discussed.

Ferroelectric properties of modified strontium barium niobate ceramics

Modified Strontium Barium Niobate ceramics with tungsten bronze filled structure were prepared by the conventional ceramic techniques. The dielectric constant is measured at 1 MHz as a function of temperature. The ferroelectric transition temperature is considerably lowered by the introduction of rare-earth Nd3+. The dielectric constant is found to be lower in Lithium composition.