Temperature-dependent dielectric and structural properties of Li-doped (Na, K) NbO3 near the morphotropic phase region

In this study, pellet samples of (Na0.5K0.5)(1-)yLiyNbO3, (NKLN) y <= 0.06, were prepared using a conventional solid-state reaction method with double sintering. The temperature-dependent dielectric constant and high-temperature X-ray diffraction characteristics of the prepared compositions were observed. Four consistent distinct phases were determined according to the observations as follows. For the compositions where y <= 0.02, the phases exhibited monoclinic symmetry between room temperature and about 200 degrees C, tetragonal between about 200 degrees C and 400 degrees C, tetragonal with different symmetry between about 400 degrees C and 460 degrees C (the so-called X phase), and cubic symmetry above about 460 degrees C. For the compositions with higher Li concentrations (y) between 0.03 <= y <= 0.06, the X phase was not observed and two distinct phase transitions were observed from monoclinic to tetragonal at around 200 degrees C, and from tetragonal to cubic at around 460 degrees C.