Ferroelectric Phase Transitions in (1-x)K<sub>0.5</sub>Na<sub>0.5</sub>NbO<sub>3</sub>-(x/5)K<sub>2</sub>NaLi<sub>2</sub>Nb<sub>5</sub>O<sub>15</sub> Composite Ceramics

Abstract

Lead-free dielectric and piezoelectric composite ceramics were considered as a mixture of multiple phases coexisting in the alkaline niobates $A$NbO$_{3}$ ($A$ = K, Li and Na). $A$NbO$_{3}$ displayed perovskite, completely filled tetragonal tungsten-bronze, LiNbO$_{3}$, and other structures in the ternary system of KNbO$_{3}$-LiNbO$_{3}$-NaNbO$_{3}$. The respective phases had different melting points and corner sharing oxygen octahedra of NbO$_{6}$. In this report, the composite K$_{0.5}$Na$_{0.5}$NbO$_{3}$ (KNN) and K$_{2}$NaLi$_{2}$Nb$_{5}$O$_{15}$ (KNLN) ceramics, \textit{i.e.}, (1-$x$)KNN-($x$/5)NKLN ($x$ = 0 - 0.1) ceramics, were confirmed to show a composition dependence of the structural phase transition temperature, $T_{T-O}$, from the tetragonal to the orthorhombic structure.