Grain Growth Of BaTiO3 Research Articles

Doping behaviors of yttrium, zinc and gallium in BaTiO3 ceramics for AC capacitor application

The doping behaviors of yttrium, zinc and gallium and their effects on the dielectric properties and microstructures of BaTiO3 were investigated. Y3+ dissolved in the lattice of BaTiO3, replacing both Ba2+ site and Ti4+ site; while Zn2+ and Ga3+ tended to occupy Ti4+ site. Compared with Y2O3 and Ga2O3, ZnO suppressed grain growth of BaTiO3 more effectively and promoted greater uniformity of grains, thus reducing the dielectric loss. The addition of Ga2O3 inhibited the appearance of second phase Y2Ti2O7 and enhanced the sinterability, which was ascribed to the compensation mechanism and synergistic effect. Proper amount of Y2O3, Ga2O3 and ZnO significantly improved the dielectric temperature characteristics due to the formation of the core–shell structure in the codoped BaTiO3 ceramics. High performance dielectrics with er of 2,690, tanδ of 1.0 % (at 1 kHz), and alternating current breakdown voltage E > 3.73 kV/mm, were achieved.

Microstructural evolution by in-situ TEM observations of oxides

In-situ observations using high-temperature transmission electron microscopy (TEM) is a promising technique for obtaining new findings and developing phenomenological theory for ceramic materials at high temperatures. By observing the changes in hydrothermal BaTiO3 due to heating, we clarify the vanishing mechanism of internal pores and the mechanism of BaCO3 phase generation/vanishing at high temperatures. Through observations of the grain growth of BaTiO3 prepared by radio-frequency plasma chemical vapor deposition, we calculate the grain-boundary diffusion coefficient, which is an important parameter controlling the sinterability of ceramics. Observations of the shrinkage and disappearance of Ba5Nb4O15, as well as simulations, indicate that high energy and low diffusivity at the grain boundary make grains vanish while maintaining a truncated spherical shape. Finally, observations of the structural changes in layered perovskite BaLn2Mn2O7 (Ln = Gd, Pr, Eu) reveal a first-order phase transition that has not been previously reported.

Low-temperature sintering of BaTiO3 with Mn-Si-O glass

In order to reduce sintering temperature and prevent adverse dielectric effects, pure BaTiO3 powder with the addition of Mn-Si-O glass was sintered in the temperature range of 1175–1300°C. Microstructural observation showed that BaTiO3 grains of the sintered samples only grew from the initial 400 nm to an average of 430 nm between 1175–1275°C for 1 h, or sintered at 1250°C as long as 27 h. Abnormal BaTiO3 grains are not found in the sintered samples. The microstructure and phase analysis showed that the dielectric properties, tetragonality, and grain growth of BaTiO3 are closely controlled by the formation of the liquid phase, newly formed Ba2TiSi2O8 grains, and Mn solid solution in BaTiO3 grains.

Microstructure and dielectric properties of BaTiO3-CeO2-SnO2 ceramics

We have studied the effect of codoping with CeO2 and SnO2 (2 to 3.5 wt %) on the microstructure and dielectric properties of BaTiO3. Doping with CeO2 and SnO2 inhibits grain growth in BaTiO3 and enables the fabrication of ceramic materials with a grain size below 1 μm. The temperature coefficient of permittivity of the ceramics increases with CeO2 + SnO2 content, firing temperature, and firing time.

Influence of CaZrO3 on dielectric properties and microstructures of BaTiO3-based X8R ceramics

The influences of CaZrO3 on the dielectric properties and microstructures of BaTiO3 (BT)-based ceramics have been investigated. The experiment results showed that the dielectric constant at room temperature increased with the addition of CaZrO3 in the range of 0–3.0 mol%, which could be explained by the growth of BT grains. XRD analysis revealed that the tetragonality declined as CaZrO3 concentration increased. XRD patterns of BT ceramics with different amounts of CaZrO3 doping were analyzed by a recently developed procedure-materials analysis using diffraction (MAUD), which was based on the Rietveld method combined with Fourier analysis. The results depicted that the high temperature peak of temperature-capacitance characteristics (TCC) was largely dependent on the micro-strain of samples. Furthermore, more CaZrO3 doping resulted in lower porosity and higher density. It was revealed that proper usage of CaZrO3 could improve the dielectric properties significantly, which was benefit to develop X8R multi-layer ceramic capacitors.

Effect of Glass Composition on the Dielectric Properties of a Liquid‐Phase‐Sintered MgO‐Doped BaTiO3

A series of BaTiO3–MgO–glass mixtures has been sintered via liquid‐phase sintering in a reducing atmosphere at 1280°C by controlling MgO/CaO ratio in an aluminum borosilicate glass composition, and the subsequent microstructure, phase evolution, and dielectric properties have been investigated. The growth of BaTiO3 grains was inhibited in all of the prepared specimens with the evidence of Mg incorporation to the BaTiO3 lattice from the glass. The change in MgO/CaO ratio in the glass notably modified the dielectric properties: a high MgO/CaO ratio in the glass resulted in a decreased dielectric constant, a decreased phase transition temperature, a broadened temperature range of phase transition, a decreased temperature coefficient of capacitance, and increased electrical resistivity.

Abnormal Grain Growth in Barium Titanate Doped with Alumina

The effect of additions of ≤1 mol% Al2O3 on abnormal grain growth in BaTiO3 sintered for periods of ≤60 min at 1350°C has been studied. Addition of ≤0.2 mol% Al2O3 caused an increase in the nucleation and growth rates of abnormal grains, with further additions causing a decrease. This behavior is explained by interface‐controlled growth. Dopant adsorption reduces both the edge free energy and the step velocity of a grain, causing the nucleation and growth rates of abnormal grains to increase, pass through a maximum, and then decrease with increasing dopant concentration.

Critical Grain Size for Abnormal Grain Growth of BaTiO3 in Air

The critical average size of matrix BaTiO3 grains for {111} twin-assisted abnormal grain growth in air was determined through the use of bi-layer samples of large BaTiO3 grains with {111} twin lamellae and fine matrix grains of various sizes. Plates with large BaTiO3 grains containing {111} twin lamellae were prepared by sintering 0.4 mol%-TiO2-added BaTiO3 powder compacts at 1250°C for 20 h in air. Additionally, plates with matrix grains having various grain sizes were prepared by sintering BaTiO3 powder compacts at 1300°C for 0.5, 2, 8 and 48 h in H2. Abnormal growth of the twin-containing large grains into matrix grains occurred for the matrix grain size of 4.1 μm and did not occur for that of 5.6 μm. It appears, therefore, that the critical size for abnormal grain growth is approximately 5 μm, which correspond to a critical driving force of 4.6 J/mol. The commonly observed abnormal grain growth during sintering of undoped BaTiO3 in air is, hence, understood to result from much higher driving forces of fine powders than the critical value.

Texture Development in Barium Titanate and PMN–PT Using Hexabarium 17‐Titanate Heterotemplates

Bulk BaTiO3 ceramics with 〈111〉‐texture have been prepared by the modified templated grain growth method, using platelike Ba6Ti17O40 particles as templates, and the mechanism of texture development is examined. The Ba6Ti17O40 particles induce the abnormal growth of BaTiO3 grains, and a structure similarity between {001} of Ba6Ti17O40 and {111} of BaTiO3 gives 〈111〉‐texture to abnormally grown BaTiO3 grains. Thus, the 〈111〉‐texture develops in the BaTiO3 matrix. The use of platelike Ba6Ti17O40 particles has been extended to a 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 matrix, but the matrix phase is decomposed by extensive chemical reactions between the matrix and template phases.

Grain‐Growth Behavior during Stepwise Sintering of Barium Titanate in Hydrogen Gas and Air

To study the effect of oxygen partial pressure on grain growth in BaTiO3, TiO2‐excess samples have been sintered in air with and without a prior H2 heat treatment. Without prior H2 treatment, abnormal grain growth occurs below and above the eutectic temperature (Te). An introduction of H2 treatment before air sintering, however, increases the average grain size and suppresses the formation of abnormal grains during subsequent air sintering below and above Te. This H2 treatment effect has been explained in terms of a decrease of the driving force for the growth of faceted grains below a critical value for formation of abnormal grains. The observed grain‐growth behavior under various atmospheres demonstrates the possibility of having various microstructures via control of oxygen partial pressure and initial grain size.

Barium titanate derived from mechanochemically activated powders

A high-energy ball milling process was applied to a mixture with equal molar ratio of BaCO3 and TiO2. X-ray diffraction data indicated that there was no reaction happening during the milling process although the particle size was greatly reduced. The effect of post-annealing on the phase formation and grain growth of BaTiO3 was investigated by thermal analysis (DTA/TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). No reaction was observed in the sample annealed at 600°C. Ba2TiO4 was found as the mixture annealed at 700°C. An 800°C-annealing led to single phase BaTiO3 with a cubic structure. The temperature at which BaTiO3 phase was derived is lower than required by the solid-state reaction process, which could be attributed to the refined grains/particles of the mixture as a result of high-energy ball milling. Tetragonal structured BaTiO3 was formed at 1150°C together with a sharp increase in grain size.

セラミック材料 ジルコニウムアルコキシドを用いたＺｒＯ２‐コーティングＢａＴｉＯ３複合粒子の合成と評価

Chemical processing of ZrO2-coated BaTiO3 composites was investigated with the surface modification through the hydrolysis of zirconium alkoxide on the surfaces of BaTiO3 particles. It was clarified from the BET measurement and the SEM observation that original BaTiO3 particles were homogeneously coated with zirconium hydroxide fine particles.2mass%ZrO2-coated BaTiO3 (BT-05) bodies sintered at 1275°C exhibited a flattened dielectric temperature dependence (dielectric constants of 3600 to 4700) with lower loss (tanδ of<5% in the temperature range of -30 to 110°C), indicating a relaxor characteristics. The microstructure of ZrO2-added BaTiO3 (BT-05) sintered bodies consisted of grains of several 0.9μm which are much smaller than ones of non-added BaTiO3 sintered bodies, suggesting that the grain growth of BaTiO3 was suppressed by zirconia existing at the grain boundaries.

Effect of Silver on the Sintering and Grain‐Growth Behavior of Barium Titanate

Silver and its alloys frequently are used as electrode material for BaTiO3‐based dielectrics. In the present study, a small amount of fine silver particles have been intimately mixed with BaTiO3 powder. The sintering and grain‐growth behavior of the silver‐doped BaTiO3 in air are investigated. The solubility of silver in BaTiO3, as revealed by lattice‐parameter measurement, electrical measurement, and electron probe microanalysis, is &lt;300 ppm. The densification of BaTiO3 is slowed slightly by the addition of silver inclusions. However, the presence of a small amount (&lt;0.3 wt%) of silver increases the amount and size of abnormal grains. When the silver content is &gt;0.3 wt%, the grain growth of BaTiO3 then is prohibited by the silver inclusions.

Control of {111| twin formation and abnormal grain growth in BaTiO3

To investigate the experimental conditions for {111| twin formation and abnormal grain growth in BaTiO3, various powder compacts with and without excess TiO2 were sintered either in an oxidizing atmosphere (air) or in a reducing atmosphere (95N2-5H2). In all the samples sintered in 95N2-5H2, no twins formed and no abnormal grain growth occurred. On the other hand, when the samples with excess TiO2 were sintered in air, abnormal grain growth occurred and all the abnormal grains contained {111| twins. X-ray diffraction analysis showed that, during sintering, the excess TiO2 formed a Ba6Ti17O40 phase with the space group A2/ a in air and a Ba6Ti17O40-x phase with the space group C in 95N2-5H2. These results show that the {111| twins form and the abnormal grain growth occurs only when the powder compact contains excess TiO2 to form a Ba6 Ti17O40 phase and is sintered in an oxidizing atmosphere. The results may also suggest that the Ba6Ti17O40 phase acts as the nucleation site of {111| twins. The suggestion has been further confirmed via a TEM observation.

Effect of sintering temperature on the secondary abnormal grain growth of BaTiO3

When BaTiO3 specimens containing a small amount of excess TiO2 were sintered for more than 15 h, some grains grew abnormally to several millimeters in size. This phenomenon may be referred to as the secondary abnormal grain growth (SAGG) because it occurred from a large and uniform grain structure (average grain size: 70 μm) after completion of primary abnormal grain growth. SAGG was observed only at a very narrow temperature range between 1360 and 1370°C, where the solid–liquid interface structure was atomically smooth. Almost all the secondary abnormal grains contained the (111) double twin, which provides the persistent twin-plane re-entrant edge (TPRE). During SAGG, the growth of matrix grains was strongly suppressed and material transfer occurred preferentially to the grains with a (111) double twin.

Diffusion Induced Grain-Boundary Migration and Enhanced Grain Growth in BaTiO3

The effect of diffusion induced grain-boundary migration (DIGM) on grain growth has been studied in a model system of BaTiO3-PbTiO3. When sintered BaTiO3 samples of two different grain sizes were heat-treated in contact with PbTiO3, DIGM occurred in the coarse-grained samples (∼200 μm in average size) while fast grain growth was observed in the fine-grained samples (∼4 μm). Energy dispersive spectroscopy (EDS) analysis confirmed that the fast growth of BaTiO3 grains was accompanied by the alloying of Pb and thus related to DIGM. A calculation of coherency strain energy for the BaTiO3-PbTiO3 system showed that the coherency strain energy of a coherent (Ba0.8Pb0.2)TiO3 layer on BaTiO3 was between 2 and 3 MJ/m3 depending on the surface orientation. The calculated coherency strain energy values are much higher than the capillary energy due to the grain boundary curvature of 4 μm grains in the fine-grained sample. The observed enhancement of grain growth appears therefore to be a result of DIGM. Such grain growth enhancement by DIGM is thought to occur in materials processing under chemical inhomogeneity or inequilibrium, for example, in the sintering of powder mixtures and in the annealing of chemically inhomogeneous polycrystals.

Grain Growth of BaTiO3

The perovskite oxide BaTiO{sub 3} is a ferroelectric whose electrical properties have been studied extensively because of its many technical applications, as sensors, transducers, and actuators, for example. The technological importance of BaTiO{sub 3} has been demonstrated repeatedly, and its physical properties in ceramic form have been thoroughly investigated. Knowledge of high-temperature processes, such as creep, sintering, and grain growth is very important in optimizing processing to achieve satisfactory properties. The purpose of this letter is to investigate the grain growth of BaTiO{sub 3} and to compare results with those of high-temperature creep tests. The activation energy value of 720 {+-} 70 kJ mol{sup -1}, measured for coarse-grained BaTiO{sub 3}, agrees well with the value of {approx}800 kJ mol{sup -1} determined in a higher-stress region in superplastic flow of fine-grained BaTiO{sub 3}. However, creep for BaTiO{sub 3} single crystals oriented to glide on {l_brace}0 0 1{r_brace} planes showed an activation energy of 469 {+-} 27 kJ mol{sup -1}. The activation energy for creep shows a disparity among the tests. Therefore, grain-growth studies can help to clarify the interpretation of creep results.

EFFECT OF CUO-BAO MIXTURE CONTENT ON THE GRAIN GROWTH OF BATIO3

The present work has been aimed at studying the effect of processing variables such as amount of additions, sintering temperature, and duration on the density, microstructure, and grain growth of BaTiO3/CuO–BaO ceramics. Grain growth of BaTiO3 during liquid-phase sintering is investigated for CuO–BaO (mole ratio, CuO/BaO=2.5) mixture additions from 0.5 wt% to 2 wt%. Sintering in air for 1 to 16 h at 950 °C to 1250 °C is studied. BaTiO3 with 0.5 wt%, 1 wt%, 1.5 wt%, and 2 wt% CuO–BaO mixture additions, the average grain growth exponents are 5.3, 4.3, 5.9, and 9.2 and the activation energies are 605±60, 348±19, 650±50, and 810±110 kJ mol-1, respectively. For all compositions, the grain growth exponents decrease with increasing sintering temperature. © 1998 Chapman & Hall

Exaggerated Growth of Hexagonal Barium Titanate under Reducing Sintering Conditions

The influence of reducing sintering conditions on anisotropic grain growth in BaTiO3 was studied above the BaTiO3‐Ba6Ti17O40 eutectic temperature. The morphology and structure of exaggeratedly grown grains was examined by X‐ray powder diffractometry, scanning electron micros‐copy, and high‐resolution transmission electron microscopy. The results show that all anomalously grown anisotropic grains were hexagonal BaTiO3 in the form of platelike crystals with a/c ratios up to 10. The direction of preferential growth of hexagonal grains is crystallographically analogous with that of parallel (111) twins in a cubic phase. Ti3+ ions, induced by reducing atmosphere, play an important role in the formation of hexagonal stacking.

粉末プロセスの制御と製品評価 Ｉ 金属アルコキシド法によるＮｂ２Ｏ５−コーティングＢａＴｉＯ３複合粒子の合成と評価

Chemical processing of Nb2O5-added BaTiO3 composites was investigated with the surface modification through the hydrolysis of niobium alkoxide on the surface of BaTiO3 particles.BaTiO3 particles were coated with niobium hydroxide particles formed by preferential hydrolysis of niobium pentaethoxide on the surfaces of BaTiO3 particles, which can lead to the preparation of highly homogeneous composite particles of Nb2O5BaTiO3.It was clarified from the BET measurement, the SEM&TEM observation and Zeta-potential measurment that original BaTi03 particles were homogeneously coated with niobium hydroxide particles.Iwt%Nb2O5-added BaTiO3 bodies sintered at 1250-1300°C exhibited a flattened dielectric temperature dependence (dielectric constants of 2200 to 2400) with lower loss(tan δ<1.0%) in the temperature range of -30 to 80°C, indicating a relaxor characteristics. The microstructure of Nb2O5-added BaTiO3 sintered bodies consisted of grains of several μ m which are much smaller than ones of non-added BaTiO3 sintered bodies, suggesting that the grain growth of BaTiO3 was inhibited by niobium existing at the grain boundaries.