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Structural Transformations during Formation of Quasi-Amorphous BaTiO3

机译：准非晶态BaTiO3形成过程中的结构转变

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A model of structural transformations of amorphous into quasi-amorphous BaTiO_3 is suggested. The model is based on previously published data and on X-ray photoelectron spectroscopy data presented in the current report. Both amorphous and quasi-amorphous phases of BaTiO_3 are made up of a network of slightly distorted TiO_6 octahedra connected in three different ways: by apices (akin to perovskite), edges, and faces. Ba ions in these phases are located in the voids between the octahedra, which is a nonperovskite environment. These data also suggest that Ba ions compensate electrical-charge imbalance incurred by randomly connected octahedra and, thereby, stabilize the TiO_6 network. Upon heating, the edge-to-edge and face-to-face connections between TiO_6 octahedra are severed and then reconnected via apices. Severing the connections between TiO_6 octahedra requires a volume increase, suppression of which keeps some of the edge-to-edge and face-to-face connections intact. Transformation of the amorphous thin films into the quasi-amorphous phase occurs during pulling through a steep temperature gradient. During this process, the volume increase is inhomogeneous and causes both highly anisotropic strain and a strain gradient. The strain gradient favors breaking those connections, which aligns the distorted TiO_6 octahedra along the direction of the gradient. As a result, the structure becomes not only anisotropic and non-centrosymmetric, but also acquires macroscopic polarization. Other compounds may also form a quasi-amorphous phase, providing that they satisfy the set of conditions derived from the suggested model.
机译：提出了非晶态向准非晶态BaTiO_3结构转变的模型。该模型基于先前发布的数据和当前报告中提供的X射线光电子能谱数据。 BaTiO_3的非晶相和准非晶相均由稍微扭曲的TiO_6八面体网络组成，该网络以三种不同方式连接：顶点（类似钙钛矿），边缘和面。这些相中的钡离子位于八面体之间的空隙中，这是非钙钛矿环境。这些数据还表明，Ba离子可补偿由随机连接的八面体引起的电荷不平衡，从而稳定TiO_6网络。加热后，将TiO_6八面体之间的边对边和面对面的连接断开，然后通过顶点重新连接。切断TiO_6八面体之间的连接需要增加体积，对其进行抑制可以使某些边对边和面对面的连接保持完整。在穿过陡峭的温度梯度期间，发生非晶薄膜向准非晶相的转变。在此过程中，体积增加是不均匀的，并且会引起高度各向异性的应变和应变梯度。应变梯度有利于破坏这些连接，从而使变形的TiO_6八面体沿着梯度方向对齐。结果，该结构不仅变为各向异性和非中心对称的，而且获得了宏观极化。其他化合物也可以形成准非晶相，只要它们满足从建议模型中得出的一组条件即可。

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