Solubility of lanthanum oxide was measured by thermal analysis. The solubility in alkali cryolites is rather high, because of chemical reactions between lanthanum oxide and cryolites. In Li3AlF6-La2O3, alumina precipitates, in the other systems the mixed oxide LaAlO3 is formed. In La2O3-Li3AlF6 the eutectic point is at 9.5 mol% La2O3 and 755 degrees C. The eutectic points in La2O3-Na3AlF6 and La2O3-K3AlF6 are at 11.5 mol% La2O3, and at 937 and 934 degrees C, respectively. (c) 2006 Elsevier B.V. All rights reserved.