Observation of positional disorder in LiNaSO4 crystals by the electron spin resonance of the SO4- free radicals

Jiang-Tsu Yu, Jin Fa Sheu

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Abstract

Paramagnetic SO4- free radicals produced in pure LiNaSO4 crystals and in LiNaSO4 crystals doped with CrO42-, Cd2+, and Mg2+ were detected by electron spin resonance (ESR) at room temperature and at low temperatures. Both the SO4- centers of axial symmetry and of orthorhombic symmetry are observed. It is established through the ESR of the orthorhombic SO4- centers that a small fraction of the sulfate oxygens is positionally disordered, and the ESR spectra can be fitted by assuming that the disordered sulfate group is related to the main group by reflections about the {112̄0} planes or by two-fold rotations about the 112̄0 axes. Observations by polarized light and by chemical etching does not reveal any twin-domain structure in the LiNaSO4 sample crystals. Consequently, the disorder is randomly and uniformly distributed at equivalent positions in the crystal lattice. It is also established by ESR that the SO4- free radicals of orthorhombic symmetry are most likely to be associated with local Na+ vacancies produced mainly by radiation damage, and that the lowering of the molecular symmetry from axial to orthorhombic is not intrinsic.

Original languageEnglish
Pages (from-to)5663-5669
Number of pages7
JournalPhysical Review B
Volume37
Issue number10
DOIs
Publication statusPublished - 1988 Jan 1

ASJC Scopus subject areas

  • Condensed Matter Physics

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