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Abstract: The structural transition of grain boundaries in BaTiO3 and related grain growth behavior have been investigated with changing Nd2O3 dopant concentration and oxygen partial pressure. A correlation among total vacancy concentration, grain boundary structure and grain growth behavior was found. When the total vacancy concentration was low by any means, grain boundaries were well faceted and abnormal grain growth occurred in the presence of {111} double twins. However, as the total vacancy concentration increased, the fraction of faceted grain boundary gradually decreased and the formation of {111} twins was suppressed. Further increase in the total vacancy concentration resulted in a change in grain boundary structure from faceted to rough and suppression of abnormal grain growth. These observed changes in grain growth behavior, including a grain growth anomaly with donor doping, can therefore be attributed to a change in boundary mobility with grain boundary structure, which was governed by the total vacancy concentration. [Copyright &y& Elsevier]

Abstract: The effect of boundary faceting on densification has been studied in a 5mol.% TiO2–excess BaTiO3 model system. It was possible to inhibit grain growth during sintering in moderately reducing atmospheres after a hydrogen presintering treatment and, thus, to exclude the effect of grain growth on densification. For a given oxygen partial pressure () there was a saturated relative density which decreased with increasing and boundary faceting. The fraction of small pores was also higher in the samples sintered under high than in those sintered under low . These experimental observations demonstrate the presence of a critical driving force for densification in systems with faceted boundaries and its dependence on boundary faceting, i.e. the critical driving force is larger for systems with greater faceting. The result further confirms that a faceted boundary, either fully or partially faceted, is an imperfect atom source for densification; this idea is in contrast to the conventional understanding. [Copyright &y& Elsevier]

Abstract: The structural relaxation and formation energies of intrinsic vacancies in cubic-BaTiO3 were studied by using a first-principles plane-wave-based pseudopotential calculation. The calculated defect formation energies and the atomic relaxations were compared with previously reported data for SrTiO3 [Tanaka T, Matsunaga K, Ikuhara Y, Yamamoto T. Phys Rev B 2003;68:205213]. It was found that the formation energies of the partial Schottky species, and , are the lowest in the oxidized condition. In contrast, as the oxygen chemical potential decreased, namely the reduced condition, the O vacancy becomes dominant in cubic-BaTiO3. Concerning the atomic relaxation, it was found that BaTiO3 and SrTiO3 show a difference in magnitude. It was also found that the overall vacancy formation energy in BaTiO3 is higher than that in SrTiO3. [Copyright &y& Elsevier]