Properties of nonstoichiometric sodium niobate

Stoichiometric and nonstoichiometric sodium niobate of the composition Na_1−x NbO_3−x/2 (0≤x≤0.2) is obtained by the two-stage solid-phase reaction technique. X-ray diffraction study reveals the homogeneity region for compositions below x=0.1. At higher x, the samples become two-phase. The phase transition is found to occur at x=0.04. It is accompanied by a change in the multiplicity of the monoclinic subcell of the sodium niobate rhombic unit cell, as well as by the anomalous behavior of its structural and electrophysical characteristics. From the study of the dielectric and piezoelectric properties of the material, it is concluded that the stability of the antiferroelectric phase is enhanced, whereas the ferroelectric phase becomes less stable, as the nonstoichiometry in terms of Na₂O increases.