OPTICAL, MECHANICAL AND WATER DROP IMPACT CHARACTERISTICS OF POLYCRYSTALLINE GAP

A polycrystalline form of GaP has been synthesized and its optical and mechanical properties determined. The optical transmission is found t o be intrinsic at long wavelengths in the infrared, being limited only by Fresnel reflection and multiphonon absorptions, beginning at appro ximately 1100 cm(-1). The optical cut-off at short wavelengths is in a greement with earlier measurements on single crystal material. The fra cture toughness of the polycrystalline material is found to be greater than that previously reported for single-crystal material. The single impact water drop damage velocity threshold (2 mm drop diameter) was estimated to be 250-280 m s(-1), which is consistent with the measured polycrystalline fracture toughness.