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 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.
@article{arxiv.1906.01384,
title = {Mapping the structural transitions controlled by the trilinear coupling in Ca3-xSrxTi2O7},
author = {Marie Kratochvilova and Fei-Ting Huang and Maria-Teresa Fernandez Diaz and Milan Klicpera and Sarah J. Day and Stephen P. Thompson and Yoon-Seok Oh and Bin Gao and Sang-Wook Cheong and Je-Geun Park},
journal= {arXiv preprint arXiv:1906.01384},
year = {2019}
}