Point defects in lithium triborate (LiB3O5) crystals

Abstract

Electron paramagnetic resonance (EPR), electron-nuclear double resonance, optical absorption, and thermoluminescence have been used to investigate radiation-induced point defects in a single crystal of lithium triborate (LiB3O5). Two prominent defects are observed after irradiation near liquid-nitrogen temperature with 60 kV x rays. A four-line EPR spectrum, with 12.2 G splittings, is assigned to a trapped-hole center, and another four-line EPR spectrum, with 120 G splittings, is assigned to a trapped-electron center. In each case, the nucleus responsible for the observed hyperfine is 11B. The trapped hole is localized on an oxygen ion and has a weak hyperfine interaction with one neighboring boron nucleus, whereas the trapped electron is localized primarily on a boron ion with a correspondingly larger hyperfine interaction. Both defects become thermally unstable near 125 K, and their decay (i.e., recombination) correlates with an intense thermoluminescence peak at this same temperature. An optical absorption peak at 300 nm is produced by the x rays and thermally decays at the same temperatures as the EPR spectra.

Elastic constants and the effect of strain on monovacancy concentration in fcc hard-sphere crystals

“…For both types of strain, the effect on [in Eq. (6)] is observed to be small (not shown), and the change in the vacancy concentration is due largely to the effect of strain on f 1 . This phenomenon can be explained in terms of a cell model, which considers the volume accessible to a sphere in its Wigner-Seitz cell in a distorted lattice with all other atoms constrained to their lattice sites.…”

“…They exist in low concentration in equilibrium crystals, yet they are emphasized in studies of solid state materials because of their disproportionate effect on material properties. [1][2][3][4][5] Known examples can be found in phenomena of photonic materials, stress relaxation, influences on the first-order transition of solid materials (with some exceptions 6 ), and so on. Vacancies are able to increase the electrical conductivity by introducing discrete states in the band gap so that charge carriers (electrons or holes) can easily jump between conduction and valence bands.…”

Kinetics of thermally stimulated recombination processes in lithium borate crystals

“…These crystals have been promising as optical materials for neutron detection using scintillation methods. A sig nificant number of boron atoms per unit cell, large cross sections of thermal neutron capture by the 10 B isotope, and a high energy release per absorbed neu tron (the total energy reaches approximately 2.8 MeV) provide a means for using the reaction 10 B(n, α) 7 Li. The presence of lithium atoms in the crystals makes possible the reaction 6 Li(n, α) 3 H, which has advan tages in detecting low energy neutrons [3].…”

“…The B 2+ electron center was revealed and identified by the EPR method after the X ray irradiation at a temperature of 80 K [6,7,17]. Based on these experi mental data and the results of calculations [19,20], the most adequate model of this paramagnetic center is an interstitial boron atom that has trapped an additional electron.…”

“…X ray irradiation of these crystals at a temperature of 80 K leads to the formation of several types of electron and hole trapping centers. The elec tron paramagnetic resonance (EPR) and nuclear mag netic resonance methods have been used to identify different types of hole centers that are collectively referred to as centers of the O -type [6][7][8][9][10][11][12][13][14][15][16][17][18]. The Ocenter is a hole trapped in the 2p orbitals of the oxygen ion located at the junction of two structures, namely, BO 3 and BO 4 , with a significant delocalization of the electron density toward the p z orbital of the boron atom.…”