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Thallium Bromoiodide (KRS-5) Optical Material

Thallium bromoiodide is a non-glass, inorganic optical material. It has the highest density among non-glass optical ceramics. In addition, it has the lowest melting temperature and the lowest heat capacity. The graph bars on the material properties cards below compare thallium bromoiodide to other non-glass optical ceramics (top) and the entire database (bottom).

Mechanical Properties

Elastic (Young's, Tensile) Modulus

31 GPa 4.5 x 106 psi

Poisson's Ratio


Shear Modulus

12 GPa 1.7 x 106 psi

Thermal Properties

Melting Onset (Solidus)

420 °C 780 °F

Specific Heat Capacity

150 J/kg-K 0.036 BTU/lb-°F

Thermal Conductivity

0.55 W/m-K 0.32 BTU/h-ft-°F

Thermal Expansion

6.0 µm/m-K

Otherwise Unclassified Properties


7.4 g/cm3 460 lb/ft3

Light Transmission Range

0.6 to 40 µm

Refractive Index


Common Calculations

Stiffness to Weight: Axial

2.3 points

Stiffness to Weight: Bending

14 points

Thermal Diffusivity

0.5 m2/s

Followup Questions

Further Reading

Handbook of Optical Materials, Marvin J. Weber, 2003

Handbook of Optical Constants of Solids, Edward D. Palik (editor), 1998