Stabilization of the ferroelectric phase and relaxor-like behaviour in low Li content sodium niobates

Studies of dielectric permittivity as a function of the temperature and frequency on Li-Na niobate ceramics in the x = 0-5% Li compositional range have been performed. The results obtained for compositions with 0 ≤ x ≤ 4% have revealed small wide anomalies below the temperature of the main peak corresponding to a ferroelectric (FE) or antiferroelectric (AFE)-paraelectric (PE) or antiferroelectric-antiferroelectric phase transition. The x = 5% Li composition does not show peaks below the temperature of the dielectric constant main peak. The behaviour of the real and imaginary parts of dielectric permittivity of these anomalies as a function of the temperature and measuring frequency together with their Vogel-Fulcher-Tamman like relaxation process gather the characteristics of a relaxor-like behaviour for 1 ≤ x ≤ 4% Li-content compositions, but not in the case of x = 0 composition. The evolution of the Raman spectrum in the 50-180 cm-1 region evidences small structural changes in the 450-560 K temperature interval that indicate the coexistence of two close structural phases with similar energies that should correspond to a ferroelectric Q phase and an antiferroelectric P phase. These obtained results support the assumption of diffusive AFE-FE and FE-AFE phase transitions for x = 0% Li-content and a relaxor-like AFE-FE for 1 ≤ x ≤ 4 %content compositions with maxima in the dielectric permittivity in that temperature interval. The results for x = 5% Li-content composition suggest that a single ferroelectric Q-like phase is stabilized. An attempt at a phase diagram is proposed