Negative thermal expansion in hybrid improper ferroelectric Ruddlesden-Popper perovskites by symmetry trapping.

@article{Senn2015NegativeTE,
  title={Negative thermal expansion in hybrid improper ferroelectric Ruddlesden-Popper perovskites by symmetry trapping.},
  author={Mark S Senn and Alessandro Bombardi and Claire A Murray and C. Vecchini and Antonella Scherillo and Xuan Luo and S. W. Cheong},
  journal={Physical review letters},
  year={2015},
  volume={114 3},
  pages={035701}
}
We present new results on the microscopic nature of the ferroelectricity mechanisms in Ca3 Mn2O7 and Ca3Ti2O7. To the first approximation, we confirm the hybrid improper ferroelectric mechanism recently proposed by Benedek and Fennie for these Ruddlesden-Popper compounds. However, in Ca3Mn2O7 we find that there is a complex competition between lattice modes of different symmetry which leads to a phase coexistence over a large temperature range and the "symmetry trapping" of a soft mode. This… CONTINUE READING