A study of the phase diagram of (K,Na,Li)NbO_3 determined by dielectric and piezoelectric measurements, and Raman spectroscopy

摘要

A composition-temperature phase diagram of the system (1-x)(K_(0.5)Na_(0.5))NbO_3-xLiNbO_3 is presented for 0≤x≤0.1. Using dielectric and piezoelectric resonance measurements, and Raman spectroscopy, ceramic samples containing 2%-10% LiNbO_3 were studied over a temperature range of 7-770 K 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 (K_(0.5)Na_(0.5))NbO_3 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 100 K 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.