Phase diagram studies in the systems La 2O 3–SrO–MgO–Ga 2O 3 at 1350–1400°C in air with emphasis on Sr and Mg substituted LaGaO 3

Abstract

The ternary systems La 2O 3–SrO–Ga 2O 3, La 2O 3–MgO–Ga 2O 3, and the quaternary system La 2O 3–SrO–Ga 2O 3–MgO were studied at 1350–1400°C in air with emphasis on the solid solubility of Sr and Mg in LaGaO 3. In both ternary systems the solid solubility of Sr substituting for La and that of Mg substituting for Ga, respectively, is rather small. However, when Sr and Mg are present simultaneously, the solid solubility of Sr and Mg in LaGaO 3 increases significantly. In addition, several phases of the quaternary system exhibit a pronounced variation of their La:Sr ratio and a high solid solubility of Mg, as for example LaSrGa 3O 7 and LaSrGaO 4. The structure LaGaO 3 containing Sr and Mg has been determined to be orthorhombic, space group Pbnm, a=5.53443 Å, b=5.49523 Å, and c=7.78320 Å. In the quaternary system, extended four phase regions exist between LaGaO 3, MgO and the La–Sr–Ga–O compounds. Quaternary phases were not observed.