Germanium, Germanium windows, Germanium lenses, Germanium Transmission, Ge

Germanium is most widely used for lenses and windows in IR systems operating in the 2 µm - 12 µm range. Its transmission is very temperature sensitive, becoming opaque near 100°C. Environment does not cause problems because Germanium is inert, mechanically rugged, and fairly hard. Maximum available size: 100 mm Dia x 50 mm Thk.

Chemical Formula	Ge
Crystal Form	Poly or Single Crystal
Crystal Class	Cubic
Lattice Constant, Å	5.66
Molecular Weight	72.60
Density, g/cm³ at 300 K	5.33
Dielectric Constant for 9.37 x 10⁹ Hz at 300 K	16.6
Melting Temperature, K	1210
Thermal Conductivity, W/(m K) at 293 K	59
Thermal Expansion, 1/K at 298 K	6.1 x 10^-6
Specific Heat, cal/(g K) at 273-373 K	0.074
Debye Temperature, K	370
Bandgap, eV	0.67
Solubility in water	None
Knoop Hardness, kg/mm²	800
Mohs Hardness	6.3
Young's Modulus, GPa	102.66
Shear Modulus, GPa	67.04
Bulk Modulus, GPa	77.86
Poisson's Ratio	0.278

Wavelength, µm	2.06	2.15	2.44	2.58	3.00	3.42	4.36	6.24	8.66	9.72	11.04	13.02
Refractive Index	4.10	4.09	4.07	4.06	4.05	4.03	4.02	4.01	4.00	4.00	4.00	4.00