Sequence of phase transitions of Li-Na niobate solid solutions in the high temperature region

Abstract

. Dielectric, thermal expansion and mechanoelastic measurements as a function of the temperature in Lithium Sodium Niobate (LixNa1 −x)NbO3 ceramics in the low Lithium content side, X ≤ 12%, have been performed. The obtained results from the different techniques in the 300 K-1000 K-temperature interval show several reversible anomalies besides that corresponding to the main ferro-paraelectric phase transition at Tc. The anomalies above Tc show a ferroelastic character and those below Tc are of the ferroelectric type. The existence of ferroeleastic phases is non-dependent on the Li content. A secondary ferroelectric phase below Tc (T’ ≈ 560 K) stabilizes only for X ≥ 10%Li content and the anomaly for X < 5% Li content could better considered as a diffusive ferroelectric phase transition. The main ferro-paraelectric phase transition was attributed to Na displacements but the other observed phase transitions are better accounted for NbO6 octahedra tilts.