Ternary system Li 2O–K 2O–Nb 2O 5: Re-examination of the 30 mol% K 2O isopleth and growth of fully stoichiometric potassium lithium niobate single crystals by the micro-pulling down technique

Abstract

Potassium lithium niobate (KLN) single crystals have attractive properties for non-linear optical applications based on frequency conversion of laser diodes in the blue range. Especially, fully stoichiometric K 3Li 2Nb 5O 15 crystals would be capable of doubling a laser light in the near UV range. Using powder X-ray diffraction and DSC experiments, we have re-investigated the 30 mol% K 2O isopleth of the ternary system Li 2O–K 2O–Nb 2O 5 in order to explore the possibility of a limited existence field for this phase. From our results, it was shown that the stoichiometric KLN phase exists between 970 and 1040 °C, temperature at which it undergoes a non-congruent melting. From this conclusion, compositionally homogeneous a-axis oriented single crystals fibers of stoichiometric K 3Li 2Nb 5O 15 were successfully grown by the micro-pulling down technique with pulling rates in the range 0.3–0.7 mm min −1. The crystal length was between 10 and 120 mm for an apparent diameter near 500 μm. The fibers, characterized by optical microscopy, X-ray diffraction and Raman spectroscopy, appeared free of macro-defects and of good quality and their stoichiometric composition was also confirmed.