Growth of KY(WO4)2 single-crystal:: Investigation of the rich WO3 region in the K2O-Y2O3-WO3 ternary system.: 1.: The K2O-WO3 binary system

KY(WO4)(2) is known as the most popular third order optically non linear tungstate. Although it is said to be stoichiometric and to melt congruently, single-crystals couldn't be obtained by the Laser Heated Pedestal Growth method. In order to determine the best conditions of crystallization of this compound, the study of its stability domain was undertaken in the ternary system K2O-Y2O3-WO3. This paper reports the first results concerning the K2(O)-WO3 binary system in the composition range between 50 and 100 mol % WO3. Three compounds, K2W3O10, K2W4O13 and K2W6O19 have been underscored and their stability domains have been precised.