Dielectric breakdown strength (DBS) of silicon nitride substrates with thicknesses of 0.25, 0.15, and 0.07 mm was measured by four types of electrodes: 10 mm spherical, 6 mm circular column shape, and 10- and 15-mm gold-coated film. In addition, the DBS was determined by a McKewon electrode in which the gap between the above spherical electrode and substrate was filled with epoxy resin. The DBS increased with decreases in the electrode diameter and the substrate thickness owing to the decreased number of defects within the measurement volume. The DBS measured by the McKewon electrode was the highest because the epoxy resin prevents electrical discharge under high voltages. However, the thickness-independent, intrinsic DBS, which was estimated from the results obtained by the McKewon electrode, was still significantly low compared to the theoretical DBS, indicating that various internal defects such as pores and boundary phases lower the DBS.

Basically, nonconventional aluminate glass is hardly prepared by melt-quenching technique. In this study, we could obtain the 15Li₂O–55SrO–30Al₂O₃ glass through melt-quenching, and suggested the Li₂O–SrO–Al₂O₃ system as new glass-forming system. The studied glass was demonstrated to have a similar structure to binary SrO–Al₂O₃ glasses so far. In addition, we found a restrictive glass-forming region in the Li₂O–SrO–Al₂O₃ system. Furthermore, we observed the photoluminescent (PL) and PL excitation spectra, which were attributed to f–f transitions, in the resulting glass-ceramics (GCs) doped with Eu³⁺, suggesting that the GCs in Li₂O–SrO–Al₂O₃ system have a potential for phosphor host material.