Electron Spin Resonance of Boron in Single—Crystal BeO

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Abstract
Single crystals of synthetic BeO which have been irradiated with 6-MeV electrons show an ESR spectrum at room temperature identified as being due to boron ions substituting for beryllium at normal lattice sites. The hyperfine tensor A is cylindrically symmetric with its principal axis pointing towards one of the near oxygen bonds. Six equivalent directions are observed corresponding to the positions of the nonaxial nearest-neighbor oxygen atoms. The constants of the spin Hamiltonian are: g∥ = 2.0035±0.0005, g⊥ = 2.0044±0.0005, A∥ = 122 Oe, A⊥ = 76.5 Oe. The spectrum is analyzed in terms of the paramagnetic electron occupying an antibonding orbital located along the direction of a B–O bond. Comparison of the observed hyperfine interaction with those expected for the free atom suggests deviations of the orbital from tetrahedral sp3 configuration to one in which the ratio of the p to s contribution increases from √3 to 2.64, implying that the B–O bond is lengthened along the direction in which the paramagnetic electron is stabilized, the bond angle decreasing from 109 to 105 deg.