Studies of irradiated cadmium sulfide in a diamond anvil pressure cell

Abstract

Cadmium sulfide (CdS) was irradiated with 7 MeV electrons in the fluence range 1013–1017 cm−2. The samples were subsequently studied in a diamond anvil cell up to a pressure of 100 kbar (1 bar = 105 Pa). Samples irradiated up to 1015 cm−2 underwent the wurtzite (yellow) to rock-salt (black) change of phase at 27 ± 2 kbar. Samples irradiated at 1016, 3 × 1016, and 1017 cm−2 also underwent the wurtzite to rock-salt transformation at 27 ± 2 kbar, but at the critical pressure they changed to an orange form which colour persisted as the pressure was increased. As the pressure was decreased, the orange samples reverted to the rock-salt structure at 30 ± 2 kbar, and then to the orange form, which persisted to atmospheric pressure. Heating the recovered orange CdS to 500 ± 50 °C returned it to its wurtzite form. X-ray diffraction studies of the irradiated but not pressurized samples revealed two peaks that correspond to the distance between planes (d) of 1.40 and 1.26 Å (1 Å = 10−10 m). In the irradiated and pressurized samples, we observed peaks having d = 1.47, 1.40, 1.32, 1.27, 1.19, 1.16, 1.09, and 0.96 Å. We attribute the orange form of CdS to defects. Irradiation of CdS with 7 MeV electrons to a fluence of 1016 cm−2 tends to suppress the wurtzite to rock-salt change of phase.