Abstract
Electron-spin-resonance studies have been conducted at 9.2 and 23.1 GHz on synthetic calcium hydroxyapatite single crystals after exposure to ionizing radiation. The major paramagnetic defect is a spin-1/2 holelike center which is observable at 92 K but not at room temperature. It exhibits hyperfine interaction with a hydrogen nucleus as proved by deuterium substitution. The center is believed to be an ion which results from removal of hydrogen from an O ion. The hyperfine interaction is with the hydrogen of an adjacent O ion. In first approximation the defect is axially symmetric with respect to the pseudohexagonal axis; the spin-Hamiltonian parameters are , , G, and G. "Forbidden" transitions cause complex unresolved spectra for orientations intermediate between and . To fit computer-simulated spectra to the experimental spectra, it was necessary to postulate that the hyperfine interaction is with an O ion tilted 6° or 7° relative to in six geometrically inequivalent directions. The isotropic hyperfine interaction was calculated using an approximate wave function constructed by a linear combination of orbitals from the and O ions. This establishes that the hole is strongly localized on the and gives the absolute signs of the hyperfine components.
- Received 20 January 1975
DOI:https://doi.org/10.1103/PhysRevB.11.4110
©1975 American Physical Society