Fabrication of transparent polycrystalline cubic silicon nitride and its physical properties

Reference	Presenter	Authors (Institution)	Abstract
09-093	Norimasa Nishiyama	Nishiyama, N.(Tokyo Institute of Technology); Wakai, F.(Tokyo Institute of Technology);	Transparent polycrystalline cubic silicon nitride was fabricated at 15.6 GPa and 1800 degrees Celsius a Kawai-type multi anvil apparatus. The dimensions of the synthesized disks are 2 mm in diameter and 0.5 mm in thickness. Real in-line transmission (RIT) was measured at wavelength between 200 and 1600 nm. The RIT value of visible light reaches 38%. Observations by atomic resolution scanning transmission electron microscopy were performed for the grain boundaries. We observed the presence of disordered/amorphous intergranular films (IGFs) with thickness less than 1 nm including multi-grain junctions. The thin IGFs produce no triple junction pocket, which can be one of the main reasons of the optical transparency. In order to show a potential of this material as a structural material, we measured hardness and estimated fracture toughness by Vickers indentation tests. The Vickers hardness determined at 9.8 N is 34.9 GPa. This material is categorized as one of the third hardest materials next to diamond and cubic boron nitride. The fracture toughness is determined to be 3.5 MPa m0.5. This material is tougher than other transparent spinel ceramics such as MgAl2O4 and ganma-AlON. In addition, we observed that cubic silicon nitride survives metastably at least up to 1460 degrees Celsius in air. The transparent polycrystalline cubic silicon nitride can be a potential window material that can be used under very severe conditions.
<< Back