Abstract
An intense electron paramagnetic resonance (EPR) spectrum has been unexpectedly observed at room temperature in polycrystalline samples of NaYGeO4 with olivine crystal structure. Signals were registered in a wide range of fields up to 6000 G. Along with strongly broadened unresolved resonance lines, the relatively narrow spectral components were found. It is shown that the spectrum profile depends on synthesis conditions and mechanical treatment of samples, all suggesting a partial orientational order of microcrystallites in the powders. The spectra are interpreted under the assumption of strong superhyperfine interaction between the oxygen-deficient centers like [GeO3]3- and the nuclei of Na+ cations. In addition, a sharp anisotropic resonance at g-values exceeding free-electron value is attributed to oxygenic-hole centers. The density functional theory (DFT) calculations are employed for the estimation of the thermodynamic stability of various intrinsic defects.
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