Dielectric Properties and Phase Transitions of Ferroelectric Sodium-Strontium Niobates

Solid solution was observed in the system Na1‐xSrx/2NbO3 between 0 ≤x≤ 0.50. Between 0 ≤x≤ 0.30 the structure at 25°C was that of a multiple‐cell perovskite having a monoclinic subcell. Between 0.30 ≤x≤ 0.50 the subcell had tetragonal symmetry with c/a > 1. Compositions for which x < 0.10 were nonferroelectric in the virgin state. Application of an electric field of sufficient intensity transformed these compositions to a ferroelectric state as evidenced by the appearance of electrical hysteresis loops. A pseudorhombohedral phase existed over a limited temperature and compositional range at this point in the system. Poisson's ratio for these materials was about 0.22. High‐temperature X‐ray studies revealed several transitions in these materials. The structure of all these compositions transformed to a small‐cell cubic perovskite when the subcell edge attained a length of 3.941 ± 0.002 A. This transformation temperature decreased with an increase in x in the system.