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

Journal article

We present new results on the microscopic nature of the ferroelectricity mechanisms in Ca₃Mn₂O₇ 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 trapping of the soft-mode leads to a large uniaxial negative thermal expansion (NTE) reaching a maximum between 250 - 350 K (3.6 × 10⁻⁶ K⁻¹) representing the only sizable NTE reported for these and related perovskite materials to date. Our results suggest a systematic strategy for designing and searching for ceramics with large NTE coefficients.

Authors: Senn, M; Bombardi, A; Murray, C; Scherillo, A; Luo, X

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Physical Society
• Journal: Physical Review Letters
• Volume: 114
• Issue: 3
• Publication date: 2015-01-22
• Acceptance date: 2014-12-12
• DOI: 10.1103/PhysRevLett.114.035701
• EISSN: 1079-7114
• ISSN: 0031-9007
• Language: English