Diffuse phase transition in potassium lithium niobate ferroelectric crystals

The tungsten-bronze type ferroelectric potassium lithium niobate (KLN) crystals were grown by the Czochralski technique. In order to obtain a crystal with high quality and crack free, crystal growth is performed in two orientations along c and a-axis. We have subjected these crystal to X-ray diffraction studies and found that they are single-crystalline and belong to the tetragonal system with the lattice constants a = b = 1.2500 nm and c = 0.3990nm. The spontaneous polarization, DSC and dielectric constant were measured in the temperature range between 30 degrees C and 700 degrees C. The diffuse dielectric anomaly was observed for these KLN crystals. The phase transition temperature and diffuseness of phase transition are different at several crystals. These behaviors are explained by DPT, it means that the compositional fluctuation and cation distribution has a strong influence on the ferroelectric properties. Diffuse phase transition establishing the influence of composition on structure and dielectric properties are presented and discussed.