Competing structural phase transition scenarios in the giant tetragonality ferroelectric BiFeO3-PbTiO3: Isostructural vs multiphase transition
Competing structural phase transition scenarios in the giant tetragonality ferroelectric BiFeO3-PbTiO3: Isostructural vs multiphase transition
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DOI：
10.1063/1.4792215
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发表时间：
2013-02-28
影响因子：
3.2
通讯作者：
Ranjan, Rajeev
中科院分区：
文献类型：
--
作者：
Kothai, V.;Senyshyn, Anatoliy;Ranjan, Rajeev
对巨四方多铁性（1-x）BiFeO 3-（x）PbTiO 3的系统X射线和中子粉末衍射研究表明，在从立方相冷却时，接近准同型相界的成分呈现两种不同的结构相变情景：（i）立方->四面体（T-2）+四面体（T-1）->四面体（T-1）和（ii）立方->四面体（T-2）+四面体（T-1）+菱形（R3 c）->四面体（T-1）+菱形（R3 c）。与共存的同构T-2相相比，T-1相的相对较大的四方性（c/a - 1）被示出是Pb/Bi-6s和Ti/Fe-3d与O-2 p轨道的重叠程度显著大于T-2相中的结果。次要亚稳菱面体相的形成/抑制似乎受局部动力学因素的微妙影响。在小菱面体（R）相与四方相一起沿着形成的情况下，其能够适应由于四方相的形成而在体系中产生的大的转变应力，并且防止固体在烧结后分解成粉末。当亚稳菱面体相未形成时，大的转变应变使晶界破裂，导致致密固体破碎成粉末。(C)2013年美国物理学会。[http：//dx.doi.org/10.1063/1.4792215]
A systematic x-ray and neutron powder diffraction study of the giant tetragonality multiferroic (1-x) BiFeO3-(x) PbTiO3 have revealed that the compositions close to the morphotropic phase boundary present two different structural phase transition scenarios on cooling from the cubic phase: (i) cubic -> tetragonal (T-2) + tetragonal (T-1) -> tetragonal (T-1) and (ii) cubic -> tetragonal (T-2) + tetragonal (T-1) + rhombohedral (R3c) -> tetragonal (T-1) + rhombohedral (R3c). The comparatively larger tetragonality (c/a - 1) of the T-1 phase as compared to the coexisting isostructural T-2 phase is shown to be a result of significantly greater degree of overlap of the Pb/Bi-6s and Ti/Fe-3d with the O-2p orbitals as compared to that in the T-2 phase. The formation/suppression of the minor metastable rhombohedral phase seems to be governed by subtle play of local kinetic factors. In the scenario when the minor rhombohedral (R) phase is formed along with the tetragonal phases it is able to accommodate the large transformation stress in the system due to formation of the tetragonal phases, and prevent the solid from disintegration into powder after sintering. When the metastable rhombohedral phase is not formed, the large transformation strain ruptures the grain boundaries leading to fragmentation of the dense solid to powder. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4792215]