{111} Twin Formation and Abnormal Grain Growth in Barium Strontium Titanate

Abstract

Two series of experiments were performed to study the experimental conditions for the formation of {111} twins and related microstructures in barium strontium titanate ((Ba, Sr)TiO3). In the first series, the phase equilibria in the BaTiO3–SrTiO3–TiO2 system were determined. XRD and WDS analysis, done in the BaTiO3‐rich region, of 45(Ba,Sr)TiO3–10TiO2 samples annealed at 1250°C for 200 h in air showed that (Ba,Sr)TiO3 was in equilibrium with Ba6Ti17O40 (B6T17) and Ba4Ti13O30 phases with strontium solubility (Sr/(Ba + Sr)) of ∼0.02 and 0.20, respectively. In the second series the microstructures of samples consisting of a mixture of (Ba,Sr)TiO3 and 2.0 mol% TiO2, were observed after sintering at 1250°C for 100 h in air. {111} twins formed only in the samples with faceted B6T17 second phase particles, similar to the case of BaTiO3. In these samples, abnormal grain growth occurred in the presence of the {111} twins. In contrast, no {111} twins formed and no abnormal grain growth occurred in the samples containing second phase particles other than B6T17. With an increased substitution of strontium for barium, the aspect ratio of abnormal grains containing {111} twin lamellae was reduced. This result was attributed to a reduction in the relative stability of the {111} planes with the strontium substitution.

Dielectric and ferroelectric properties of BST ceramics obtained by a hydrothermally assisted complex polymerization method

“…Rios [26], Lin [27] and Jung et al [28] observed abnormal grain growth and formation of elongated twinned grains when BaTiO 3 is sintered below the BaTiO 3 -Ba 6 Ti 17 O 40 eutectic temperature of 1332 1C. Lee at al [13] investigated abnormal grain growth and required conditions for twin formation in (Ba, Sr)TiO 3 samples sintered at 1250 1C. Authors concluded that growth of elongated twinned grains form only when (Ba, Sr)TiO 3 grains grow around Ba 6 Ti 17 O 40 secondary phase.…”

“…In spite of numerous publications on the dielectric and ferroelectric properties of the solid solution BST, only small number of studies have been reported which consider correlation between secondary phases formed during sintering processes and the dielectric and ferroelectric properties [13,14]. Lee et al [13] studied the effect of second phase, particularly Ba 6 Ti 17 O 40 and Ba 4 Ti 13 O 30 on microstructure in (Ba, Sr)TiO 3 system, but without their impact on dielectric and ferroelectric properties.…”

“…Lee et al [13] studied the effect of second phase, particularly Ba 6 Ti 17 O 40 and Ba 4 Ti 13 O 30 on microstructure in (Ba, Sr)TiO 3 system, but without their impact on dielectric and ferroelectric properties. Lee at al [14] investigated the dielectric properties of BaTiO 3 ceramics as a function of Ba/Ti ratio, and found that in the Ti-excess BaTiO 3 samples abnormal grain growth occurred and dielectric constant decreased, but ferroelectric properties were similar to those of stoichiometric BaTiO 3 ceramics.…”

Synthesis and characterization of nanocrystalline Barium Strontium Titanate powder via sol-gel processing

“…The peaks of the dissociated phases are obtained even at 950°C indicating that the dissociation of the parent phase starts at a temperature lower than 950°C. B. K. Lee and his coworkers [26] reported the presence of Ba 4 Ti 13 O 30 in BST powder synthesized by ball milling. They observed an increase in the content of Ba 4 Ti 13 O 30 phase with the increase in the ratio of Sr:(Sr+Ba) from 0.245 to 0.70 for BST powder sintered at 1,200°C.…”

Inhibition of abnormal grain growth in BaTiO3 by addition of Al2O3

“…13 These twins provide growth sites for abnormal grains by the twin-plane re-entrant edge mechanism. 5,14,15 For {1 1 1} twins to nucleate, the Ba 6 Ti 17 O 40 phase must be faceted (atomically smooth). 13,16 Excess TiO 2 is often added to BaTiO 3 as a sintering aid.…”