Thermal expansion measurements on four optical materials from room temperature to 10 k.

In a continuing study of the physical properties of optical materials, measurements are reported of the linear thermal expansion coefficients for four ir-transmitting materials in the temperature range 10-300 K. A new glass and three polycrystalline materials were investigated by use of a three-terminal capacitance- type dilatometer incorporated into a cryostat. The glass, designated No. 20 by Texas Instruments, Inc., is a nonoxide chalcogenide glass with the composition Ge(33)Se(55)As(l2). One of the po]ycrystalline materials studied, T-12 (Harshaw Chemical Co.), is an optically integral two-phase material composed of equal molar proportions of CaF(2) and BaF(2). The other two materials are microcrystalline, hot-pressed forms of CdS and CdTe (Irtran 6), manufactured by the Eastman Kodak Co.