Lithium Fluoride (LiF)

Lithium Fluoride is used for windows, prisms, and lenses in the visible and infrared where desired transmission is in the 0.104μm - 7μm range. Modest precautions should be taken against moisture and high energy radiation damage. LiF is attacked by atmospheric moisture at 400 °C and softens at 600 °C. LiF is sensitive to thermal shock. Irradiation produces color centers. The material can be cleaved. Lithium fluoride is grown by vacuum Stockbarger technique in diameters of 115mm. Although the optical characteristics are good the structure is not perfect and cleavage is difficult. For good structure LiF is less commonly grown by the Kyropoulos method (air-grown) specifically for monochromator plates. Cleavage is (100) and less commonly (110). LiF is slightly plastic and can be bent into radius plates.

Specifications of LiF
Transmission Range 0.12 to 8.5μm
Refractive Index 1.3943 at 0. 5μm
Reflection Loss 5.3% at 0.5μm (2 surfaces)
Restrahlen Peak 25μm
dn/dT -12.7 x 10-6/ °C at 0.6μm
Density 2.63905 g/cm3
Melting Point 870 °C
Thermal Conductivity 4. 01 W/(m K) at 41 °C
Thermal Expansion 37 x 10-6/ °C
Hardness Knoop 102 to 113 kg/mm2 with 600g indenter
Specific Heat Capacity 1562 J/(kg K) at 10 °C
Dielectric Constant 9.1 at 25 °C
Young's Modulus (E) 64.79 GPa
Shear Modulus (G) 55.14 GPa
Bulk Modulus (K) 62.03 GPa
Elastic Coefficients C11=97.4MPa C12=40.4Mpa C44=55.4MPa
Apparent Elastic Limit 11.2MPa
Poisson Ratio 0.326