Effect of Ba₆Ti₁₇O₄₀/BaTiO₃ Interface Structure on {111} Twin Formation and Abnormal Grain Growth in BaTiO₃

Abstract

A structural transition of Ba6Ti17O40/BaTiO3 interfaces from faceted to rough was induced by reducing oxygen partial pressure in the atmosphere. As the oxygen partial pressure decreased, the number densities of {111} twins and abnormal grain decreased. TEM observation showed that the twin formation was governed only by the faceting of the interface. Experimental evidence of {111} twin‐assisted abnormal growth of faceted BaTiO3 grains was also obtained.

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

“…Presence of Ba 6 Ti 17 O 40 secondary phase has a significant influence on microstructure of BaTiO 3 ceramics. 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.…”

Inhibition of abnormal grain growth in BaTiO3 by addition of Al2O3

“…This excess Ti reacts with BaTiO 3 during sintering to form Ba 6 Ti 17 O 40 , 1 which acts as a site for the nucleation of {1 1 1} double twins. 13,16 These twins in turn provide non-vanishing sites for abnormal grain growth. 5,14,15 This is why the series A samples with 0 mol% Al 2 O 3 exhibit AGG.…”

“…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. If the excess TiO 2 is decreased to zero, then AGG is eliminated and normal grain growth occurs.…”

Microstructure transition from normal to abnormal grains for BaTiO3

“…BaTiO 3 specimen in an atmosphere of low oxygen partial pressure. 4,8,17,22 The morphology of abnormal grains also shows strong dependence on the sintering temperature. As the sintering temperature is lower than the eutectic temperature, the abnormal grains with {1 1 1} twin lamellae are formed.…”

“…5,8,19 A liquid phase is formed instead at a temperature higher than the eutectic temperature. 3,4,14,21,22 The presence of impurity, especially SiO 2 , can lower the eutectic temperature to a temperature ∼1260 • C. 20 The formation of abnormal grains can be suppressed by sintering or annealing * Corresponding author. Tel.…”