Low temperature intrinsic defects in x-irradiated hydroxyapatite synthetic single crystals

Journal Article · Fri May 15 04:00:00 EDT 1981 · J. Chem. Phys.; (United States)

DOI:https://doi.org/10.1063/1.440955· OSTI ID:6581466

Close, D M; Mengeot, M; Gilliam, O R

ESR studies of radiation-induced defects have been conducted on synthetic calcium hydroxyapatite single crystals. For a room temperature x-irradiation a major defect (labeled A) was reported to be an O/sup -/ ion. X irradiation at 6 K shows defect A, trapped atomic hydrogen, and a nonaxial holelike center (labeled I). These new centers are stable at 6 K but anneal near 77 K. Observations at 9 and 35 GHz indicate that the I center is a spin-1/2 defect located in six inequivalent sites. In the ab plane, spectra exhibit an isotropic hyperfine doublet (approx.13 G splitting) and an anisotropic doublet (17--27 G splitting) in three symmetry-related sites. For other orientations additional site splitting and ''forbidden transitions'' make the spectra very complex. The hyperfine coupling tensor for the anisotropic doublet has diagonal elements -29.5, -19.2, and +3.11 G. The g tensor for this defect has diagonal elements 2.0068, 2.0032, and 2.0148. The sets of directional cosines associated with the minimum g value and the intermediate A value each indicate a direction corresponding approximately to that of the vector from an OH oxygen to a neighboring PO/sub 4//sup 3 -/ oxygen. The model proposed for the I center is a hole trapped by both an OH/sup -/ and a neighboring PO/sub 4//sup 3 -/. The anisotropic doublet is accounted for with 65% of the spin density on OH/sup -/. The remaining spin density is on a phosphate oxygen. This creates a PO/sup 2 -//sub 4/ defect with the isotropic coupling arising from hyperfine interaction with the /sup 31/P nucleus.

• Research Organization: East Tennessee State University, Physics Department, Johnson City, Tennessee 37614
• OSTI ID: 6581466
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 74:10; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
400600* -- Radiation Chemistry
ALKALINE EARTH METAL COMPOUNDS
APATITES
CALCIUM COMPOUNDS
CHEMICAL RADIATION EFFECTS
CHEMICAL REACTIONS
CHEMISTRY
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
CRYSTALS
DECOMPOSITION
ELECTROMAGNETIC RADIATION
ELECTRON SPIN RESONANCE
HYDROXY COMPOUNDS
HYPERFINE STRUCTURE
IONIZING RADIATIONS
LOW TEMPERATURE
MAGNETIC RESONANCE
MINERALS
MONOCRYSTALS
ORGANIC COMPOUNDS
RADIATION CHEMISTRY
RADIATION EFFECTS
RADIATIONS
RADIOLYSIS
RESONANCE
X RADIATION