Phase transitions and microwave dielectric properties in the perovskite-like Ca(Al0.5Nb0.5)O3−CaTiO3 system

Phase transitions and microwave dielectric properties in the (1−x)Ca(Al0.5Nb0.5)O3–xCaTiO3 system were analyzed using x-ray and neutron powder diffraction, transmission electron microscopy, Raman spectroscopy, and dielectric measurements at microwave frequencies (2–8 GHz). Rietveld structural refinements demonstrated that both end compounds exhibit similar octahedral tilted frameworks, while in Ca(Al0.5Nb0.5)O3, tilting is superimposed onto NaCl-type ordering of Al and Nb on the B sites. Accordingly, the room-temperature structures of CaTiO3 and Ca(Al0.5Nb0.5)O3 are described by orthorhombic Pbnm and monoclinic P21/n symmetries, respectively, with similar lattice parameters, √2ac×√2ac×2ac (where ac is the lattice parameter of cubic perovskite). The (1−x)Ca(Al0.5Nb0.5)O3–xCaTiO3 system features both cation ordering and octahedral tilting phase transitions. The Ca(Al0.5Nb0.5)O3 structure remains ordered at least up to 1625 °C. However, the temperature of the order/disorder transition decreases rapidly with ...

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