Oxygen-vacancy donor-electron center in Y3Al5O12 garnet crystals: Electron paramagnetic resonance and dielectric spectroscopy study

V. Laguta, M. Buryi, P. Arhipov, O. Sidletskiy, O. Laguta, M. G. Brik, and M. Nikl
Phys. Rev. B 101, 024106 – Published 15 January 2020

Abstract

The F+ center consisting of an electron trapped at an oxygen vacancy (VO) was investigated in oxygen deficient Y3Al5O12 (YAG) garnet crystals by electron paramagnetic resonance (EPR) techniques. The measurements were performed in the wide temperature interval 5–450 K and the frequency range 9.4–350 GHz using both the conventional continuous-wave and pulse EPR experiments. Pulse electron-nuclear double resonance was applied to resolve the hyperfine interaction of the trapped electron with surrounding nuclei. The measurements show that at low temperatures, T<50 K, the EPR spectrum of the F+ center is anisotropic with g factors in the range 1.999–1.988 and originates from three magnetically inequivalent positions of the center in a garnet lattice. As the temperature increases, the EPR spectrum becomes isotropic suggesting a motional averaging of the anisotropy due to motion of the F+-center electron between neighboring oxygen vacancies. With further increase of temperature up to T > 200 K, we observed delocalization of the F+-center electron into the conduction band with the activation energy about 0.4–0.5 eV that resulted in substantial narrowing of the EPR spectral line with simultaneous change of its shape from Gaussian to Lorentzian due to disappearance of the Fermi contact hyperfine field at Al27 and Y89 nuclei. Such temperature behavior of the F+-center electron in YAG is completely similar to behavior of a donor electron in a semiconductor. Our findings are further supported by measurements of the conductivity and dielectric properties. In particular, these data show that the electrons in the conduction band are not homogeneously distributed in the crystal: There are highly conductive regions separated by poorly conductive dielectric layers. This leads to the so-called Maxwell-Wagner dielectric relaxation with huge apparent dielectric constant at low frequencies. This paper reports an observation of a donorlike behavior of an F+ center in wide band-gap insulating crystals.

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  • Received 24 October 2019
  • Revised 27 December 2019

DOI:https://doi.org/10.1103/PhysRevB.101.024106

©2020 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

V. Laguta1, M. Buryi1, P. Arhipov2, O. Sidletskiy2, O. Laguta3, M. G. Brik4,5,6, and M. Nikl1

  • 1Institute of Physics Academy of Science of Czech Republic, Cukrovarnická 10, 162 00 Prague 6, Czech Republic
  • 2Institute for Scintillation Materials, National Academy of Sciences of Ukraine, Nauky Avenue 60, 61072 Kharkiv, Ukraine
  • 3Brno University of Technology, Central European Institute of Technology, Purkyňova 656/123, 612 00 Brno, Czech Republic
  • 4CQUPT-BUL Innovation Institute & College of Sciences, Chongqing University of Posts and Telecommunications, Chongqing 400065, People's Republic of China
  • 5Institute of Physics, University of Tartu, W. Oswaldi 1, Tartu 50411, Estonia
  • 6Institute of Physics, Jan Długosz University, Armii Krajowej 13/15, PL-42200 Częstochowa, Poland

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Issue

Vol. 101, Iss. 2 — 1 January 2020

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