Electron paramagnetic resonance of photochromic Fe2+-O-in SrTIO3

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Abstract
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+or-0.0005, g2=2.0180+or-0.0005 and g3=2.0515+or-0.0005, the magnetic main axes being along the (110), (110) 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 mod A1 mod =19.6+or-0.5 MHz, mod A2 mod =16.9+or-0.5 MHz and mod A3 mod =11.5+or-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*10-4e AA 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*10-24 cm3 could be determined.