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Cesium Iodide (CsI) Optical Material

Cesium iodide is a non-glass, inorganic optical material. It has a fairly low heat capacity among non-glass optical ceramics. In addition, it has a fairly low thermal conductivity and a moderately low melting temperature. The graph bars on the material properties cards below compare cesium iodide to other non-glass optical ceramics (top) and the entire database (bottom). A full bar means this is the highest value in the relevant set. A half-full bar means it's 50% of the highest, and so on.

Mechanical Properties

Elastic (Young's, Tensile) Modulus

4.0 GPa 0.58 x 106 psi

Knoop Hardness


Poisson's Ratio


Shear Modulus

6.2 GPa 0.9 x 106 psi

Thermal Properties

Melting Onset (Solidus)

620 °C 1150 °F

Specific Heat Capacity

200 J/kg-K 0.048 BTU/lb-°F

Thermal Conductivity

1.1 W/m-K 0.64 BTU/h-ft-°F

Thermal Expansion

48 µm/m-K

Otherwise Unclassified Properties


4.5 g/cm3 280 lb/ft3

Light Transmission Range

0.25 to 55 µm

Refractive Index


Common Calculations

Stiffness to Weight: Axial

0.49 points

Stiffness to Weight: Bending

12 points

Thermal Diffusivity

1.2 mm2/s

Followup Questions

Further Reading

Handbook of Optical Materials, Marvin J. Weber, 2003

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