Electrical properties and microstructures of hot-pressed silicon nitride

The electrical conductivity of a hot-pressed Si3N4 with additivies of Al2O3 and Y2O3 was measured at temperatures between 580 and 10000C, and at frequencies between 5Hz and 1 MHz. The ac conductivity approached about 3x10-6/Ωcm at 10000C and decreased with decreasing temperature to a minimum in the conductivity. The temperature of the minimum conductivity increased with the frequency. The activation energy of the dc volume conductivity was 101 kJ/mol for the high temperature region above 7500C and 54kJ/mol below 7500C. Although Y and Al in additives were observed to stay at the multiple-grain junction region in an as-received sample, they were distributed in the Si3N4 grain after being heated at 8250C for 3 h. (orig.)