Sapphire (Al2O3)

Single crystal sapphire possesses a unique combination of excellent optical, physical and chemical properties. The hardest of the oxide crystals, sapphire retains its high strength at high temperatures, has good thermal properties and excellent transparency.

It is chemically resistant to common acids and alkali at temperatures up to 1000°C as well as to HF below 300°C. These properties encourage its wide use in hostile environments where optical transmission in the range from the visible to the near infrared is required.

Maximum available size for windows, lenses and blanks: 100mm Dia x 10mm Thinkness and 100mm Square x 10mm Thickness.

Sapphire is also available in form of round rod (2-20mm Dia, 150-300mm long), rectangular and square rod and ribbon (10-80mm wide, 1-4mm thick, 150-300mm long), tubing (3-30mm Dia, 1-8mm wall thickness, 150-300 mmlong) and other custom cross-section configurations.

Main properties of sapphire
Transmission Range
0.17 to 5.5μm
Refractive Index 1.75449 (no) 1.74663 (ne) at 1.06μm
Reflection Loss 14% at 1.06μm (2 surfaces)
Absorption Coefficient  0.3 x 10-3 cm-1 at 2.4μm
Restrahlen Peak 13.5μm
dndT 13.7 x 10-6 at 5.4μm
dn/dμ = 0
3.98 g/cm3
Melting Point 2040°C
Thermal Conductivity 27.21 W/(m · K) at 300K
Thermal Expansion (parallel / perpendicular) 5.6 / 5.0 x 10-6/K
Knoop 2000 with 2000g indenter
Specific Heat Capacity
419 J/(kg · K)
Dielectric Constant (parallel / perpendicular)
11.5 / 9.4 at 1MHz
Young's Modulus (E)
335 GPa
Shear Modulus (G) 148.1 GPa
Bulk Modulus (K) 240 GPa
Elastic Coefficients
C11=496MPa C12=164MPa C13=115MPa 
C33=498MPa C44=148MPa
Apparent Elastic Limit
275 MPa (40,000 psi)
Poisson Ratio

The external transmittance of sapphire is shown in the figure below:

External transmittance for 1-mm-thick uncoated sapphire