Phase relations in the system Fe2O3B2O3 and its application in single crystal growth of FeBO3

Abstract

A study of the phase relations in the system Fe2O3B2O3 to aid in finding the optimum conditions to grow single crystals of iron borate was made. The compositions of the system Fe2O3B2O3 studied were with 20, 30, 40, 50, 60, 70 and 80 mole% of Fe2O3, at temperatures of 670, 800, 860 and 900°C. At all compositions and at low temperatures (670−800°C), FeBO3 is the prevalent stable phase. FeBO3 is stable up to 800°C for 0.25 ≤ Fe2O3/B2O3 ≤ 2.6. At 750°C and for 1 ≤ Fe2O3/B2O3 ≤ 2.6, two phases are present, FeBO3 and Fe3BO6. When Fe2O3/B2O3 > 2.6, FeBO3 disappears and Fe3BO6 and α-Fe2O3 are found. Thus, FeBO3 is obtained at low temperatures and with an excess of B2O3. Single crystals of borate FeBO3 with maximum dimensions of up to 8 mm are obtained from the flux with a mixture containing 1 Fe2O35 B2O31 Bi2O3. To avoid the formation of α-Fe2O3 and Fe3BO6, the mixture was cooled rapidly between 1135 and 860°C.