Preparation and electrical properties of Li–Si–Al–O–N ceramics

Ceramic samples were synthesized by hot pressing mixtures of Li3N, Si3N4, AlN, Al2O3, and Li2CO3 with nominal compositions of LiSi2−xAlxOxN3−x (x = 0–0.75) at 20 MPa and 1773–2073 K in a N2 atmosphere of 0.10 MPa. The samples prepared with nominal compositions, x = 0.25 and 0.50, showed electronic conductivities of 2.2 and 4.2 S m−1 at room temperature with activation energies of 3.8 and 3.9 kJ mol−1, respectively. Electronic conductive parts were detected in the sample of x = 0.50 by conductive atomic force microscopy (AFM). In this sample, a glassy thin layer, having a Si/Al atomic ratio of 3.8, was observed between the grains of LiSi2−xAlxOxN3−x solid solution by high-resolution transmission electron microscopy (HRTEM). It was expected that the glassy phase of grain boundaries is an electronic conductive pathway besides the conductive parts observed by AFM.