Sapphire is a single crystal of aluminum oxide Al2O3. Sapphire has exceptional physical (optical, mechanical, dielectric and thermal) and chemical properties compared to other optical materials
Sapphire is the second hardest material in nature after diamond. It has high hardness, resistance to abrasion and corrosion, durability under extreme pressure and temperature conditions, biocompatibility and chemical inertness
Sapphire is a material that is an ideal dielectric substrate material for making electronic devices. Its ability to be fabricated in various shapes and sizes and its unique crystalline and physical properties make it the preferred material for many scientific, industrial and military applications. Sapphire is transparent from 180 nm to over 5500 nm. This wide transparency window makes sapphire one of the best materials in optics
| Chemical formula | Al2O3 |
| Type of crystal structure, symmetry class | hexagonal, 3m |
| Lattice parameters, Å | a=4,758 c=12,991 |
| Density, g/cm3 | 3,98 |
| Moss hardness | 9 |
| Melting point, K | 2303 |
| Specific heat, J/(kg x K) | 105 at 91К, 761 at 291К |
| Temperature coefficient of linear expansion (at T = 323K), К | 6.66 x 10-6 parallel to the C-axis, 5 x 10-6 perpendicular to the C-axis |
| Thermal conductivity (at T = 300K), W/(m x K) | 23.1 parallel to the C-axis, 25.2 perpendicular to the C-axis |
| Electrical resistance, Ohm x cm (in the range of 200-500 °С) | 1011 – 1016 |
| Dielectric constant | 10.0 |
| Dielectric strength, V/cm | 4 x 105 |
| Loss tangent (dielectric) | 1 x 10-4 |
Transmission spectrum of a polished plate in the range of 10-20 mm thickness
Transmission spectrum of a polished plate 5 mm thick in the range of 200-1100nm
