High-temperature ionic and electronic resistivity of MgO- and Ta2O5- doped aluminum nitride

In this work, using high-temperature impedance spectroscopy and microstructure analysis, we investigated the ionic and the electronic transport properties of aluminum nitride materials doped with MgO and Ta 2 O 5 at temperatures up to 773 K. The electronic conductivity, due to the electron carrier, was greatly inhibited by addition of MgO, which might be due to the decreased electron carrier concentration via electronic compensation of MgO in the AlN matrix. The ionic conductivity due to grains of MgO-doped AlN increased by several orders of magnitude due to ionic defects generated by MgO substitution, whereas the ionic conductivity of the grain boundary of MgO-doped AlN decreased by one order of magnitude as a result of the formation of Mg′ Al defects in the grain boundary, which elevated the Schottky barrier. The microstructural analysis showed that MgO addition promoted formation of an amorphous liquid phase including Mg, which is evidence of the selective precipitation of Mg in the grain boundary. Ta 2 O 5 -doped AlN also exhibited a decreased ionic conductivity of the grain boundary, which might have been due to the formation of an ionic pair of (O N · −V‴ Al ) caused by the dissolution of Ta in the AlN matrix.