The solubility of Ga2O3 or In2O3 in liquid B2O3 which is used as a flu
x for pulling single crystal of III-V compounds has been measured by t
he sampling method in the temperature range of 973 to 1573 K. The gall
ium or indium contents in the samples were analyzed by ICP atomic emis
sion spectroscopy. The phase equilibrium in the Ga2O3-B2O3 or In2O3-B2
O3, binary system has been determined by X-ray diffraction and differe
ntial thermal analysis for the precipitates in liquid phase or the bin
ary compounds which were synthesized from pure oxides. The solid phase
equilibrated with liquid phase was clarified. The phase diagrams of t
he Ga2O3-B2O3 and In2O3-B2O3 binary systems were constructed.