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Ehre, David
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Topics
Publications (8/8 displayed)
- 2024Local Environment of Sc and Y Dopant Ions in Aluminum Nitride Thin Filmscitations
- 2024A Gd-doped ceria/TiOx nanocomposite as the active layer in a three terminal electrochemical resistivity switch.citations
- 2022C-Axis Textured, 2–3 μm Thick Al0.75Sc0.25N Films Grown on Chemically Formed TiN/Ti Seeding Layers for MEMS Applicationscitations
- 2021Local Piezoelectric Properties of Doped Biomolecular Crystalscitations
- 2020Surface Piezoelectricity and Pyroelectricity in Centrosymmetric Materials: A Case of α-Glycinecitations
- 2016CH3NH3PbBr3 is not pyroelectric, excluding ferroelectric-enhanced photovoltaic performancecitations
- 2008X-ray photoelectron spectroscopy of amorphous and quasiamorphous phases of BaTi O3 and SrTi O3citations
- 2007Structural transformations during formation of quasi-amorphous BaTiO 3citations
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article
Structural transformations during formation of quasi-amorphous BaTiO 3
Abstract
<p>A model of structural transformations of amorphous into quasi-amorphous BaTiO<sub>3</sub> 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<sub>3</sub> are made up of a network of slightly distorted TiO<sub>6</sub> 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<sub>6</sub> network. Upon heating, the edge-to-edge and face-to-face connections between TiO<sub>6</sub> octahedra are severed and then reconnected via apices. Severing the connections between TiO<sub>6</sub> 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<sub>6</sub> 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.</p>