Study on the ferroelectric phase transition in potassium lithium niobate (KLN)

The ferroelectric phase of potassium lithium niobate K3Li2-xNb5+xO15+2x (KLN) in the range of 0.15<x<0.5 is a very promising material for the second harmonic generation (SHG) in the blue visible region (∝410 nm). The ferroelectric phase transition was shown to occur between 400 and 500 C depending on the composition of the KLN phase. In this study several analysis techniques were used to investigate the phase transition on ferroelectric (x=0.3) KLN samples. The temperature-dependent measurements of the relative dielectric constant ε33 provided a phase transition temperature of about 470 C. In our DTA experiments, a small but reproducible thermal effect at the phase transition in KLN was indicated. The temperature-dependent birefringence measurement technique, applied the first time on KLN, shows a second order behaviour at a temperature of 467 C. However, this phase transition is accompanied by a small thermal effect. The DSC analysis for the other KLN composition (x=0.5) provided a phase transition temperature of 514 C. The appearance of a phase transition in the paraelectric KLN phase (Nb content higher than 55 mol%) was also studied. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)