Scientists have synthesised the first transparent sample of a popular industrial ceramic at DESY. The result is a super-hard window made of cubic silicon nitride that can potentially be used under extreme conditions like engines, as the Japanese-German team writes in the journal Scientific Reports. Cubic silicon nitride (c-Si3N4) forms under high pressure and is the second hardest transparent nanoceramic after diamond but can withstand substantially higher temperatures.

“Silicon nitride is a very popular ceramic in industry,” explains lead author Dr. Norimasa Nishiyama from DESY who now is an associate professor at Tokyo Institute of Technology. “It is mainly used for ball bearings, cutting tools and engine parts in automotive and aircraft industry.” The ceramic is extremely stable, because the silicon nitrogen bond is very strong. At ambient pressures, silicon nitride has a hexagonal crystal structure and sintered ceramic of this phase is opaque. Sintering is the process of forming macroscopic structures from grain material using heat and pressure. The technique is widely used in industry for a broad range of products from ceramic bearings to artificial teeth.