High-temperature ferroelastic phase transitions in Li-Na niobate compounds

Measurements of mechanoelastic properties as a function of the temperature of (LixNa1-x) NbO3 (x less than or equal to 0.12) ceramics in the paraelectric phase show a sequence of anomalies in the complex Young's modulus Y*. These anomalies are associated with structural phase transitions of the ferro - ferroelastic and ferro - paraelastic type, where strong elastic softening due to the order- parameter - spontaneous- strain coupling of linear quadratic character takes place. The existence of NbO6 octahedra tilts and the lack of significant volume change in the phase transition temperatures of the studied compositions allows considering the order parameters in the same way as that invoked in the case of the strontium titanate. (C) 2003 American Institute of Physics.