Novel features of Sr1-xCaxTiO3 phase diagram:: Evidence for competing antiferroelectric and ferroelectric interactions

Structural and dielectric evidences are advanced to show that the Sr1-xCaxTiO3 (SCT) system undergoes an antiferroelectric (AFE) phase transition in the composition range 0.18 less than or equal to x less than or equal to 0.40. Stabilization of the AFE phase. instead of the ferroelectric (FE) phase known for 0 < x < 0.12, 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 CaTiO3 substitution in the incipient FE matrix of SrTiO3 leads to the smearing of the epsilon'(T) response in SCT for 0.002 < x < 0.12 akin to dipole glasses and relaxer ferroelectrics.