PARAMAGNETIC DEFECTS IN AUGELITE

The electron paramagnetic resonance spectra of augelite single crystal s, Al-2(PO4)(OH)(3) have been studied at room temperature in the X-ban d frequency range. The monoclinic structure of augelite has two distin ct Al3+ sites in the unit cell, Al(1) and Al(2) in sixfold and fivefol d coordination, respectively. Paramagnetic signals from Fe3+, Cr3+, an d V4+ have been detected, and the spectra have been described by the s pin Hamiltonian H = beta HgS + D[(S-z(2) - S(S + 1)/3 + E(S-x(2) - S-y (2))]. The spin resonance reveals that the Fe ions occupy both Al(1) a nd Al(2) sites, with preference for the larger sixfold coordinated sit e, while the Cr ions are only located at the octahedrally coordinated positions. A mosaic angle of the crystal has been estimated from the a nisotropic broadening of the +1/2 --> -1/2 transition of Fe3+. (C) 199 4 Academic Press, Inc.