Theoretical and experimental electron paramagnetic resonance studies of single crystals (1999)
AuthorsWalsby, Charles Johnshow all
This work presents X-band electron paramagnetic resonance studies of X-irradiated zircon and α-quartz single crystals at 15 K. The first of these is of the Zr3+ (α) electron centre in zircon where a doublet hyperfine splitting has been assigned unequivocally to interaction with a nearby 31P nucleus rather that 89Y as determined in earlier work. The site of the phosphorus ion has also been confidently identified. Three oxygenic-hole centres have been studied. Two of these are thought to be closely related, with one associated with yttrium and the other with an unknown ion. The third hole centre has been precisely determined as containing a boron ion substituting at a silicon lattice position. Three new Ti3+ centres have been identified with two determined as analogues of the well known Zr4+ substituted B(Ti3+) centre and the third as arising from a Ti3+ ion in a silicon lattice position. Studies of the high-spin Nb3+ (I =9/2) and Gd3+ (S = 5/2) centres were conducted in order to establish whether any high-spin Zeeman or mixed-spin terms might be determined but in both case were found to be small at best. Studies of an α -quartz single crystal have identified a previously unreported lithium-"compensated" aluminum oxygenic hole. It has been concluded that the electron vacancy in this centre is localised on one of the long-bonded oxygen atoms of the silicate tetrahedra and that the lithium compensating ion resides in one of the large c-axis cavities. The appropriate algebra for the inclusion of high-spin Zeeman terms of order BJ7 in the spin Hamiltonian has been derived. This has been included in the widely used EPR data fitting programme EPR-NMR and tested on the hyperfine line positions from the 49Ti isotope in the B(Ti3+) centre in zircon. A summary of the various formulations of high-spin terms in the spin Hamiltonian and their interrelations is presented along with a review of the mathematical description of the behaviour of the spin Hamiltonian under coordinate rotation. This serves as background for the inclusion of the appropriate matrix elements of proper rotations of odd-rank tensorial sets into the programme ROTTEN2.