The ferroelectric phase of potassium lithium niobate K 3 Li 2-x Nb 5+x O 15+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 ε 33 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.

The ferroelectric phase of potassium lithium niobate K 3 Li 2-x Nb 5+x O 15 (KLN) is a very promising material for the conversion of infrared light to light in the visible region. However, growing of single crystals is known to be complicated due to the considerable anisotropy of the growth rate and the thermal expansion behaviour. The single crystals of KLN, Mg 2+ -doped KLN, as well as the mixed crystals of potassium lithium tantalate niobate K 3 Li 2 (Nb 1-x Ta x ) 5 O 15 (KLTN) were grown by the Czochralski technique. The chemical analyses of the samples were performed by atomic absorption spectroscopy (AAS) and X-ray fluorescence analysis (XRF). The element concentrations along the single crystals were measured by the electron microprobe analysis (EMPA) to clarify the segregation phenomena in the grown crystals. The elements distribution coefficients were also calculated.