Solid Solution in the System Si_3N_4-Ga_2O_3-Al_2O_3

概要

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The solid solution of Si_3N_4 containing Ga_2O_3 and Al_2O_3 denoted as Si_3N_4s.s.(Ga_2O_3, Al_2O_3) has been found to be formed through sintering by hot- pressing at 1730-1800℃ and 250 kg/cm^2 for 20-180 min. The solubility limits of Ga_2O_3 and Al_2O_3 in Si_3N_4s.s.(Ga_2O_3, Al_2O_3) have been determined. From the observation of the specific gravity of Si_3N_4s.s.(Ga_2O_3, Al_2O_3), the solid solution is thought to be mainly of substitutional type, and most a1uminium and gallium atoms are substituted for silicon atoms, and most oxygen atoms for nitrogen atoms. Small amounts of solute atoms are located in interstitial spaces. A close correlation exists between the oxygen and gallium or aluminium atoms in the solid solution. A new compound, m(Al_2O_3, Ga_2O_3)・nSi_3N_4 (m≒3, n≒2), has also been found. The nature of the bond changes from covalent to ionic with an increase in Al_2O_3 concentration. The thermal expansion coefficient of the solid solution Si_3N_4s.s.(Al_2O_3) is decreased and then increased with the addition of Al_2O_3. This increase may be attributed to an increase of (Si, Al) N_2O_2 tetrahedron. The liquid phase has been observed in the region of high concentration of Al_2O_3. Its appearance is explained on the basis of the increased ionicity (electrostatic interaction) in the bond.
社団法人応用物理学会の論文
1973-04-05