Grain boundary complexion transitions in WO₃- and CuO-doped TiO₂ bicrystals

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• 作者：Shuailei Ma^a ; Patrick R. Cantwell^a ; Timothy J. Pennycook^b ; ^c ; Naixie Zhou^d ; Mark P. Oxley^b ; ^c ; Donovan N. Leonard^c ; ^e ; Stephen J. Pennycook^b ; ^c ; Jian Luo^d ; Martin P. Harmer^a ; ^{mph2@lehigh.edu}
• 关键词：Grain boundaries (GBs) ; Complexions ; Grain boundary segregation ; Sintering ; STEM
• 刊名：Acta Materialia
• 出版年：2013
• 出版时间：March, 2013
• 年：2013
• 卷：61
• 期：5
• 页码：1691-1704
• 全文大小：1K

文摘

Several grain boundary complexions (grain boundary interfacial phases) have been identified in TiO₂ bicrystals by high-resolution transmission electron microscopy (TEM) and aberration-corrected scanning TEM (STEM). An intrinsic grain boundary with no apparent impurity segregation was observed in an undoped TiO₂ bicrystal. In a WO₃-doped TiO₂ bicrystal, WO₃ second-phase particles formed along the boundary, with a nominally clean, intrinsic-type grain boundary in between the particles. In a CuO-doped bicrystal, a remarkable series of three distinct grain boundary complexions with abrupt structural transitions was discovered coexisting at the grain boundary, and the existence of a fourth equilibrium complexion at the annealing temperature was implied. Thus, the WO₃- and CuO-doped TiO₂ bicrystals exhibit dramatically different solute partitioning behavior which can be understood in terms of the relative interphase boundary energies of these two systems. STEM-electron energy loss spectroscopy and energy-dispersive X-ray spectroscopy analysis of the nanoscale lens-shaped films of amorphous material in the CuO-doped TiO₂ bicrystal demonstrated an excess of CuO, as expected, yet also revealed the unintentional presence of SiO_x. The multiple grain boundary complexions in CuO-doped TiO₂ offer an explanation for the CuO-enhanced grain growth and sintering of TiO₂ that has been reported in the literature. Conversely, the intrinsic grain boundary complexion observed in WO₃-doped TiO₂ is consistent with previous work showing that WO₃ has no effect on grain boundary mobility in TiO₂. A phenomenological thermodynamic model is proposed to explain the physical origin of these observed grain boundary complexions and the abrupt, first-order complexion transitions that are believed to occur upon cooling of the CuO-doped TiO₂ bicrystal.