Sapphire is a single crystal aluminum oxide (Al2O3). Its Mohs hardness is 9, it is one of the hardest materials. Sapphire has good mechanical strength, and it is also transparent from visible to IR spectrum. So, it is always used as window material where scratch resistance is required.

Lattice Constant: a =4.75 A; c =12.97A

 Transparent Range: 180nm ~ 4500nm

Density: 3.98g/cm³

Mohs Hardness: 9

Melting Point: 2030℃

Thermal Conductivity: 0.04W/m/K

Expansion Coefficient: 8.4x10^-6/K

Refractive Index: 1.755@1um

Specifications:
Material: Sapphire
Diameter Tolerance: +0.0, -0.1mm
Thickness Tolerance: ±0.2mm 
Clear Aperture: >80% 
Parallelism: 1 arc minute 
Wavefront Distortion:λ per 25mm@633nm
Surface Quality: 80/50 scratch and dig 
Protective Bevel: <0.25x45deg
Coating: Uncoated 

Custom designs for other sizes and coatings are also available upon request.