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 (similar to 410 nm). The ferroelectric phase transition was shown to occur between 400 and 500 degrees 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 epsilon(33) provided a phase transition temperature of about 470 degrees 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 degrees 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 degrees C. The appearance of a phase transition in the paraelectric KLN phase (Nb content higher than 55 mol %) was also studied. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.