Crystallographic Characterization of (Sr2-xCax)(MgTe)O6 Double Perovskite via Electron Diffraction

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Dr. Rick Ubic


Complex perovskite oxides [(A,A’)(B,B’)O3] are ubiquitous in electronic applications. An understanding of such structures and the mechanisms which affect them is essential in predicting and controlling the material properties. Structural distortions away from the ideal cubic aristotype may include tilting or deformation of the oxygen octahedra, chemical ordering or displacement of cations, or defect-induced lattice strain. Each of these mechanisms can alter the symmetry of the perovskite, resulting in a doubled supercell, with a corresponding effect on properties. By investigating the appearance of superlattice reflections in electron diffraction patterns, a summary of the octahedral tilting (tilt system) of the structure can be identified, cation ordering inferred, and space group symmetry established. In the case of the (Sr2-xCax)(MgTe)O6 system, a phase transformation occurs from a tetragonal I4/m symmetry at x = 0 (Sr2MgTeO6) to monoclinic P21/n symmetry for x ≥ 0.5; however, B-site cation ordering causes ½{odd,odd,odd} type reflections in all compositions, complicating the crystallographic characterization.

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