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Using first-principles methods, we investigate the joint effects of epitaxial strain and electrostatic coupling on the appearance of oxygen octahedral rotations, O6, in ferroelectric perovskites. We find that by varying the relative content of ferroelectric and paraelectric layers in epitaxially strained superlattices the size of O6 can be efficiently tuned. Keywords: Oxide perovskites, Superlattices, Density functional theory

We analyse the effects of applying an electric field on the critical temperature at which superionicity appears in archetypal fast ion conductor CaF2, by means of molecular dynamics simulations. We find that the onset of superionicity can be reduced by about 100 K when relatively small electric fields of ∼50 KV cm−1 are applied. Under large enough electric fields, however, ionic conductivity is depleted. The normal to superionic phase transition is characterised by a large increase of entropy, thereby sizeable electrocaloric effects can be realised in fast ion conductors that are promising for solid-state cooling applications.