ELECTRON-PARAMAGNETIC RESONANCE OF PHOTOCHROMIC FE2+-O- IN SRTIO3

A new photochromic hole centre in SrTiO3, trapped at an oxygen anion site near an iron impurity and thermally stable below 35 K, is reported. The hole is characterized by S = 1/2 and has been studied by means of EPR. The hole is of orthorhombic local symmetry and its spin-Hamiltonian parameters are given as: g1 = 2.0071 +/- 0.0005, g2 = 2.0180 +/- 0.0005 and g3 = 2.0515 +/- 0.0005, the magnetic main axes being along the [110], [110BAR] and [001] crystallographic directions. Hyperfine interaction with a nuclear spin of I = 1/2 in a 2.21% natural abundance was also resolved. The hyperfine splittings are given by \A1\ = 19.6 +/- 0.5 MHz, \A2\ = 16.9 +/- 0.5 MHz and \A3\ = 11.5 +/- 0.5 MHz. The hole is identified as the Fe2+-O- centre. Under the influence of applied static electric fields the hole centre main axes undergo a reorientation. From the measurements, an electric dipole moment of mu = 5.07 x 10(-4) e angstrom at 20 K was determined. Upon the application of uniaxial stress the hole centre main axes are also reoriented. From the measurements at 30 K, a differential stress coupling coefficient of beta[001] = 3.48 x 10(-24) cm3 could be determined.