Composition Inhomogeneity due to Alkaline Volatilization in Li-Modified (K, Na)NbO3 Lead-Free Piezoceramics



Alkaline volatilization during sintering in (K, Na)NbO3 (KNN)-based lead-free piezoceramics is a problem that causes non-stoichiometry and hence affects the phase structures and properties. This work investigated the depth-dependent distributions of alkaline elements in Li-modified KNN ceramics using X-ray photoelectron spectroscopy and Raman spectroscopy. It was found that Li evaporated more severely than Na and K, consequently almost no Li elements remained on the as-sintered surface, while its content became stable at the depth over 55 μm from the outmost surface. In addition, X-ray diffraction results suggested the phase structure might show discrepancy at the pellet surface and the interior part due to the textured surface grains.