Subsolidus solubility of lithium niobate in sodium niobate: metastability of segnetoelectric perovskite phases

Using the methods of annealing and hardening and by X-ray phase analysis the region of perovskite solid solutions Nasub(1-x)Lisub(x)NbOsub(3) has been studied. Annealed from 10O0 deg C solid solutions at 20 deg C have rhombic distortion at 0 <x <= 0.05; rhombohedrical - at 0.12 <= x <= 0.27, and in the range 0.05 < x < 0.12 both phases coexist. Equilibrium solubility polytherm of lithium niobate in sodium niobate is described by the equation lg x=1.62-2760/T, i. e. over the whole range of ferroelectric properties existence the solid solutions are metastable. Discrepancy of literature data is explained by their uncontrolled decomposition. The decomposition rate at 800 deg C is limited by diffusion and increases sharply during heterovalency alloying