First principles phase diagram calculations for the system NaNbO3–KNbO3: Can spinodal decomposition generate relaxor ferroelectricity?

Abstract

First principles based phase diagram calculations were performed for the system (1−X) NaNbO3–(X) KNbO3. Plane wave pseudopotential calculations of formation energies were used as a basis for fitting a cluster expansion Hamiltonian, and a phase diagram was calculated. The predicted phase diagram has an unusual asymmetric miscibility gap, which suggests that it might be possible to synthesize a lead-free compositionally modulated sample with bulk composition X≈0.23; such a sample is likely to exhibit relaxor characteristics.