A study of the phase diagram of (K,Na,Li)NbO3 determined by dielectric and piezoelectric measurements, and Raman spectroscopy

A composition-temperature phase diagram of the system (1−x)(K0.5Na0.5)NbO3–xLiNbO3 is presented for 0⩽x⩽0.1. Using dielectric and piezoelectric resonance measurements, and Raman spectroscopy, ceramic samples containing 2%–10% LiNbO3 were studied over a temperature range of 7–770K showing a complex sequence of phase transitions. Analysis of the different Raman, piezoelectric, and dielectric data shows distinct transitions from cubic to tetragonal to orthorhombic to rhombohedral phase for x=0.02–0.05. The symmetries of the phases were assigned using analogy to phase diagram of (K0.5Na0.5)NbO3 single crystals and ceramics (x=0). At x>0.07 only one transition between ferroelectric phases occurs where tetragonal phase transforms to another phase, possibly of rhombohedral, orthorhombic, or monoclinic symmetry. In the region between x=0.05 and x=0.08, the phase transition sequence is more complex. Below 100K this phase with unidentified symmetry creates a vertical boundary with the rhombohedral phase present near 5% Li. A triple point between the tetragonal, orthorhombic, and the new phase is identified.