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High‐Temperature Structural Phase Transition in Ca 0.7 Ti 0.7 La 0.3 Al 0.3 O 3 : Investigation by Synchrotron X‐Ray Diffraction
Author(s) -
Ravi Guttamindapalli A.,
Azough Feridoon,
Freer Robert,
Cernik Robert J.,
Bell Anthony M. T.
Publication year - 2007
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2007.01995.x
Subject(s) - orthorhombic crystal system , tetragonal crystal system , crystallography , materials science , x ray crystallography , dielectric , crystal structure , space group , phase transition , diffraction , analytical chemistry (journal) , mineralogy , chemistry , condensed matter physics , optics , physics , optoelectronics , chromatography
Mixed‐oxide prepared Ca 0.7 Ti 0.7 La 0.3 Al 0.3 O 3 (CTLA) ceramics (≈96% dense), grain size 6–7 μm, with dielectric properties (at 4 GHz) of ɛ r ≈46, Q × f ≈38 000 GHz, and τ f +13 ppm/°C, were studied at 25°–1300°C using synchrotron X‐ray powder diffraction. At room temperature, CTLA exhibits a distorted orthorhombic structure, with two tilt systems: a =5.40383 (4) Å, b =5.41106 (6) Å, and c =7.64114 (7) Å with space group Pbnm . At 1050°±25°C, there is a transition from orthorhombic ( Pbnm ) to tetragonal ( I 4/ mcm ), with a simpler tilt arrangement. The lattice parameters at 1100°C were: a =5.44285 (4) Å and c =7.68913 (8) Å.