On the stability of calcium and cadmium based Ruddlesden–Popper and double perovskite structures

Abstract

This paper presents ab initio calculations on stability properties and phase diagrams of Ca- and Cd-related hybrid improper ferroelectric materials, with the Ruddlesden–Popper (RP) and double perovskite (DP) structures. The results show that enthalpy relations favor the decomposition of Cd-based RP compounds, indicating that experimental synthesis may be nontrivial. Thus, pure Cd-related RP compounds are not stable. The RP Ca₃B₂O₇ (B = Ti, Mn) systems, however, admit the incorporation of certain percentages of Cd replacing Ca, providing a possible route for tuning ferroelectric properties through chemical substitution. In addition, the stability results indicate that the Ca₂TiO₄ RP is not stable, in agreement with previous investigations. Searching for alternative stable phases, we found that the forsterite structure might be stable at room temperature and a new structure for this material. Moreover, the results reveal that the Cd-based DP CaCdTi₂O₆ is dynamically stable, therefore, a possible new hybrid improper ferroelectric.