Novel Features of ${\mathrm{Sr}}_{1-\mathit{x}}{\mathrm{Ca}}_{\mathit{x}}{\mathrm{TiO}}_3$ Phase Diagram: Evidence for Competing Antiferroelectric and Ferroelectric Interactions

Structural and dielectric evidences are advanced to show that the ${\mathrm{Sr}}_{1-x}{\mathrm{Ca}}_x{\mathrm{TiO}}_3$ (SCT) system undergoes an antiferroelectric (AFE) phase transition in the composition range $0.18\le x\le 0.40$. Stabilization of the AFE phase, instead of the ferroelectric (FE) phase known for $0<x<\mathrm{}0.12\mathrm{}$, is shown to be intimately linked with the nonpolar antiferrodistortive phase transitions driven by the $R$ and $M$ point instabilities preceding the AFE transition. It is proposed that the disorder and frustration introduced by $\mathrm{Ca}{\mathrm{TiO}}_3$ substitution in the incipient FE matrix of ${\mathrm{SrTiO}}_3$ leads to the smearing of the ${\varepsilon }^{\prime }\left(T\right)$ response in SCT for $0.002<x<\mathrm{}0.12\mathrm{}$ akin to dipole glasses and relaxor ferroelectrics.