Mapping the structural transitions controlled by the trilinear coupling in Ca3-xSrxTi2O7

• Published in: Journal of applied physics 2019-06, Vol.125 (24)
• Main Authors: Kratochvilova, Marie, Huang, Fei-Ting, Diaz, Maria-Teresa Fernandez, Klicpera, Milan, Day, Sarah J., Thompson, Stephen P., Oh, Yoon-Seok, Gao, Bin, Cheong, Sang-Wook, Park, Je-Geun
• Format: Article
• Language: English
• Subjects: Applied physics; Coupling; Ferroelectric materials; Ferroelectricity; High temperature; Hybrid systems; Mapping; Orthorhombic phase; Phase diagrams; Phase transitions; Strontium; X ray powder diffraction; X-ray diffraction
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.5089723

We present the results of the high-temperature neutron and x-ray diffraction experiments on the Ca3–xSrxTi2O7 (x = 0.5, 0.8, 0.85, 0.9) compounds. The ferro- to paraelectric transition in these hybrid improper ferroelectric materials arises from the so-called trilinear coupling. Depending on the strontium content, various structures and phase transitions, different from theoretical predictions, emerge. The in situ x-ray powder diffraction indicates a direct ferro- to paraelectric transition between the orthorhombic A21am and the tetragonal undistorted I4/mmm phase for x ≤ 0.6. We identified a reduction in the trilinear coupling robustness by increasing the Sr-doping level to lead to the emergence of the intermediate tetragonal P42/mnm phase and the gradual suppression of the orthorhombic phase. The observed character of the structure transitions and the Ca3–xSrxTi2O7 phase diagram are discussed in the framework of theoretical models of other related hybrid improper ferroelectric systems.