Processing and Properties of Strontium Bismuth Vanadate Niobate Ferroelectric Ceramics

The processing conditions, microstructure, and dielectric properties of strontium bismuth niobate vanadate ceramics, SrBi₂(V _x Nb_{1− x} )₂O₉ (SBVN, with 0 ≤ x ≤ 0.3), were systematically studied. A relative density of >90% was obtained for all the samples using a two-step sintering process. XRD showed that a single phase with the layered perovskite structure of SrBi₂Nb₂O₉ (SBN) was formed with a vanadium content of up to 30 at.%. SEM revealed that the average grain size decreased gradually with an increase in vanadium content. The Curie point was found to gradually increase from ∼418°C for SBN to ∼459°C for SBVN with 30 at.% vanadium. Dielectric constants at room temperature and their respective Curie points were found to peak at a composition with 10–15 at.%; vanadium. Moreover, a high concentration of vanadium (>5 at.%) resulted in a significant increase in tangent loss at low frequencies (<1000 Hz). The relationships between chemical composition, processing condition, microstructure, and dielectric properties of SBVN ferroelectric ceramics are discussed.     

Influence of Rare-Earth Dopants on Barium Titanate Ceramics Microstructure and Corresponding Electrical Properties

In this article, ytterbium and erbium oxides are used as doping materials for barium titanate (BaTiO₃) materials. The amphoteric behavior of these rare-earth ions leads to the increase of dielectric permittivity and decrease of dielectric losses. BaTiO₃ ceramics doped with 0.01–0.5 wt% of Yb₂O₃ and Er₂O₃ were prepared by conventional solid-state procedure and sintered at 1320°C for 4 h. In BaTiO₃ doped with a low content of rare-earth ions (0.01 wt%) the grain size ranged between 10 and 25 μm. With the higher dopant concentration of 0.5 wt%, the abnormal grain growth is inhibited and the grain size ranged between 2 and 10 μm. The measurements of capacitance and dielectric losses as a function of frequency and temperature have been carried out in order to correlate the microstructure and dielectric properties of doped BaTiO₃ ceramics. The temperature dependence of the dielectric constant as a function of dopant amount has been investigated.     

Dielectric and Pyroelectric Properties of Cadmium Niobate Ceramics

The low-temperature dielectric and pyroelectric properties of pyrochlore Cd₂Nb₂O₇ ceramics have been investigated over the temperature range from 10 to 300 K. Dielectric data confirmed that two ferroelectric transitions occurred in the Cd₂Nb₂O₇ ceramics at temperatures near 80 and 192 K. The higher-temperature ferroelectric transition is complex, with evidence for three separate transitions occurring within a narrow temperature range. The temperature and frequency dependencies of the dielectric constant were consistent with both second-order (diffuse) and improper ferroelectric (ferroelastic) effects. Pyroelectric data also confirmed the multiple-transition behavior, with anomalies in the pyroelectric coefficient at temperatures corresponding to the onset of the diffuse ferroelectric transition and the ferroelastic effect. Dielectric loss data (analyzed by both Arrhenius and Cole-Cole formalisms) indicated the presence of three separate relaxation-type dielectric loss mechanisms in this temperature range. Unambiguous explanations for the observed dielectric and pyroelectric phenomena could not be made, but domain effects are believed to be responsible for at least part of the complex nature of the ferroelectric transitions in this material.     

Fabrication of Optically Transparent and Electrooptic Strontium Barium Niobate Ceramics

The tetragonal tungsten bronze (TTB) type of Sr _x Ba_{1− x} ^m Nb₂O₆ (SBN) (0.5 ≤ x ≤ 0.75) was synthesized by a mixed-oxide route. Using the two-step densification process of pressureless sintering followed by oxygen HIPing, transparent ceramics were successfully fabricated. Microstructural, dielectric, optical, and electrooptic properties were investigated. All single-phase TTB-type SBN showed the characteristics of relaxor ferroelectrics. The extinction coefficients of the sample with the highest transparency were calculated from transmission spectra to be 30.4, 5.8, and 2.4 cm⁻¹ at 600, 1450, and 2000 nm, respectively. The linear electrooptic coefficients for SBN55, r ₃₃ and r ₁₃, were 46 × 10⁻¹² and 21 × 10⁻¹² m/V at 633 nm, respectively.     

铌酸锶钡/钛酸锶钡复相陶瓷形成过程研究

应用粉末-溶胶工艺合成出铌酸锶钡/钛酸锶钡复相陶瓷(SBN/SBT)。采用X射线衍射技术研究了不同预烧温度的原始粉料、不同烧结温度和不同保温时间得到的铌酸锶钡/钛酸锶钡复相陶瓷。研究表明:钨青铜相和钙钛矿相共存于体系之中。复相陶瓷形成过程中形成了TiO2、BaNb2O6(BN)、SrNb2O6(SN)等中间相,增加烧结温度至1250℃,形成了铌酸锶钡/钛酸锶钡复相陶瓷。     

Microstructure and Dielectric Properties of Barium Strontium Magnesium Niobate

Dielectric properties and their related microstructural characteristics in solid solutions of (1 – x )Ba(Mg_1/3Nb_2/3)O₃– x Sr(Mg_1/3Nb_2/3)O₃ (BMN–SMN, or BSMN) were investigated by measuring the relative permittivity (ɛ_r), Q values, and temperature coefficient of resonator frequency (τ_f), and by observing microstructure using transmission electron microscopy. When the tolerance factor ( t ) was >0.99 in BSMN with composition 0 < x < 0.5, where the tilting of oxygen octahedra was not involved, the microstructure included only 1:2 ordered phase. In the region where 0.99 > t > 0.97 with 0.7 < x < 1.0, the phase due to the antiphase tilting of oxygen octahedral, the disordered phase, and the 1:2 ordered phase were also present. In a few of the grains, core–shell-type structures, whose main components were dislocations and stacking faults, were found in the solid solution of BSMN.     

Microstructure Development and Dielectric Properties of Potassium Strontium Niobate Ceramics

Sintering of a KSr₂Nb₅O₁₅ powder compact at 1350°C resulted in a duplex structure. Prefiring of the compact between 1200° and 1300°C inhibited the abnormal grain growth responsible for the duplex structure. The Curie temperature and dielectric constant were dependent on the microstructure.     

Effect of the Strontium:Barium Ratio and Atmosphere on the Sintering Behavior of Strontium Barium Niobate

The sintering behavior of Sr _x Ba_{1− x} Nb₂O₆ (SBN) ( x = 0.5, 0.6, and 0.7) was studied. The densification rate increased and the evaluated activation energy of SBN decreased as the Sr:Ba molar ratio increased. Also, when SBN50 (SBN where x = 0.5) was sintered at <1300°C, the densification rate decreased as the oxygen partial pressure increased, and, at 1300°C, the oxygen partial pressure had insignificant influence on the densification. The relationship of sintering behavior and structure of SBN has been discussed, and the niobium ion was suggested as being the rate-limiting species when sintering SBN.     

铌酸锶钡的结构和制备工艺研究进展

铌酸锶钡(Sr1-xBaxNb2O6,简称SBN)是一种重要的滤波压电陶瓷,具有重要的实际应用价值。本文综述了铌酸锶钡的结构,从烧结温度、制备方法、掺杂等方面分析了铌酸锶钡的研究进展,评述了制备工艺和掺杂等对铌酸锶钡的结构和性能的影响,并指出了铌酸锶钡研究领域内尚待解决的问题。     

铌酸锶钡/钛酸锶钡介电常数预测模型研究

首次应用粉末-溶胶工艺合成出铌酸锶钡/钛酸锶钡复相陶瓷(SBN/SBT)。以Clausius(克劳修斯)-Mosotti(莫索缔)方程为基础,采用混合对数法则,通过实验得到的复合材料的晶格参数和铌酸锶钡、钛酸锶钡的理论极化率,建立了描述铌酸锶钡/钛酸锶钡复相陶瓷的介电常数预测模型,通过数学模型得到的预测数值与实验数值吻合。     

Effect of Acceptor and Donor Dopants on the Dielectric and Tunable Properties of Barium Strontium Titanate

The effects of different concentrations of Mn²⁺, Mg²⁺, Al³⁺, Fe³⁺, La³⁺, and Nb⁵⁺ on the dielectric and tunable properties of Ba_0.6Sr_0.4TiO₃ ceramics were investigated. It was found that doping in small amounts with acceptor ions such as Mg²⁺, Fe³⁺, and Al³⁺ could meliorate the dielectric properties clearly. Decrease of dielectric loss was attributed to the formation of compensating defects originating from acceptor substitution. It was concluded that the tunability was linked to both the dielectric constant and the grain size. A higher figure of merit was obtained by doping the ceramics with smaller ions of Al and Fe, compared to Ti.     

Piezoresistance and Piezocapacitance Effects in Barium Strontium Titanate Ceramics

A large piezoresistance response to hydrostatic pressure is reported for a series of ceramic compositions in the system barium strontium lanthanum titanate (Ba, Sr, La)TiO₂. This property appears to be closely associated with the Curie region (cubic-tetragonal phase transition) and the phenomenon of a positive temperature coefficient of resistance for these same compositions. The piezoresistance coefficient, similar to the temperature coefficient of resistance, is positive in the Curie region, and is found to range up to the order of 700 X 10 ⁻¹² sq. cm. per dyne. Consistent with the observed piezoresistance effect, a positive piezocapacitive effect, ranging up to the order of 700 x 10⁻¹² sq. cm. per dyne, is observed in these compositions in the absence of the lanthanum impurity which produces semiconduction. It is suggested that these materials may be of interest in pressure-sensitive devices such as acoustic transducers and pressure-sensing elements and in techniques for measuring force and displacement.     

Diffuse Phase Transition of Tantalum-Bearing Strontium Barium Niobate

The dielectric constants, ε' and ε", of tantalum-bearing strontium barium niobate (SBNT) ceramics were measured as functions of temperature and frequency. The phase transition of SBNT became ambiguous by adding Ta and the apparent Curie temperature determined from the maximum of ε' had a linear relation with the axial ratio c/a. A dielectric loss peak was observed in the phase transition region of SBNT, and its peak frequency increased with temperature. The loss peak was attributed to dielectric relaxation by the jump between two states with different polarizing directions as a preliminary phenomenon of the phase transition. A model based on the local variation from one unit cell to the next rather than the macroscopic compositional fluctuation in the crystal was proposed for the mechanism of diffuse phase transition.     

Phase Stability and Ferroelectric Properties of Lead Strontium Zirconate Titanate Ceramics

The effect of compositional modifications on the field-induced phase-transition behavior and dielectric properties of strontium-doped lead zirconate titanate (PZT) ceramics was studied. PZT compositions with different strontium and titanium contents, within the general formula Pb_{1– x} Sr _x (Zr_{1– y} Ti _y )O₃ and located in the tetragonal antiferroelectric (AFE) and rhombohedral ferroelectric (FE) phase fields were prepared by tape casting and sintering. X-ray diffraction and polarization measurements were used to locate compositions suitable for investigation of the field-induced AFE–FE phase transition. The results indicated that a higher Sr²⁺ content decreased the polarization and hysteresis and increased the switching field; a lower Ti⁴⁺ content decreased the polarization and increased the switching field and hysteresis. A high room-temperature dielectric constant was obtained for compositions near the phase boundary. These results suggest that a combination of both A -site and B -site modifications can be used to tailor ferroelectric properties, such as the switching field and hysteresis, of these strontium-doped PZTs displaying a field-induced AFE–FE phase transition.     

钛酸铜锶钡陶瓷晶相结构及介电性能研究

采用溶胶-凝胶法制备(Ba0.5Sr0.5)1-xCuxTiO3高介电性能陶瓷,用X射线衍射和LCR分析仪对不同x取值和烧结温度制备陶瓷的晶相组分和介电性能进行分析对比,结果表明,x=0.1可以得到比较好的固溶体;随着Cu2比例上升,陶瓷中出现氧化铜杂相;并且,烧结温度升高,陶瓷中氧化铜相含量也增加.氧化铜相含量的增加使陶瓷的介电系数获得明显提升,可达104数量级,但与此同时,氧化铜相也使陶瓷的介电损耗有所增大.     

Optical Properties of Barium Strontium Titanate (BST) Ferroelectric Thin Films

Barium strontium titanate (Ba_0.05Sr_0.95TiO₃) ferroelectric thin films have been prepared on single crystal [001] MgO substrates using the pulsed laser deposition method. The X-ray diffraction (XRD) analysis show the films were oriented with the [001] direction perpendicular to the plane of the substrate. The refractive index of Ba_0.05Sr_0.95TiO₃ is determined from model fitting with the calculated data of the reflectivity of Ba_0.05Sr_0.95TiO₃ in the wavelength 1450-1580 nm at the room temperature. The dispersion curve decreases gradually with increasing wavelength. The average value of the refractive index is found to be 1.985 in the wavelength 1450-1580 nm which is important for optoelectronic device applications.     

Effect of Aliovalent Substituents on the Ferroelectric Properties of Modified Barium Titanate Ceramics - Relaxor Ferroelectric Behavior

Structure–property relationships were investigated to reveal the generic influence of various substituents on ferroelectric BaTiO₃. Compositional modifications of ferroelectric BaTiO₃ were systematically investigated for La³⁺ and Nb⁵⁺ substituents. A generic influence of charged point defects in breaking down the ferroelectric domains into polar clusters was demonstrated. In both types of modified BaTiO₃, relaxor ferroelectric behavior was induced for higher concentrations of substituents.     

Effect of Barium Titanate on Microstructural Evolution and Properties of Lead Zinc Magnesium Niobate Ceramics

BaTiO₃ (BT) addition vastly alters the dielectric behavior of lead zinc magnesium niobate (PZMN) relaxor ferroelectrics. Heat treatment, including the sintering process, influences the dielectric properties through changes in the distribution of heterogeneous compositions and in the extent of diffused phase transition. With more than 15 mol% BaTiO₃ addition, two cubic phases composed of Ba-rich and Ti-rich PZMN substances exist. The destruction of the BaTiO₃ phase and reconstruction of Ba-rich and Ti-rich regions are initiated during heat treatment, and the extent of destruction and reconstruction determines the dielectric properties of the PZMN ceramics. The BT-rich PZMN phase, which occurs with higher BaTiO₃ addition, plays a less important role in the present investigation.     

钛酸锶钡陶瓷材料的掺杂改性

钛酸锶钡(BST)是一种重要的具有钙钛矿结构的铁电材料。顺电态下,其介电损耗较小,结构稳定。因此对顺电态下的BST进行掺杂改性是近年来铁电材料的研究热点之一。本文简要介绍了目前国内外科研工作者利用稀土、碱土氧化物进行掺杂时对BST的微观结构、介电损耗、介电常数以及可调率方面的影响。