Two-Dimensional Nutation NQR Broad-Line Spectra in Oriented Samples

Abstract

The NQR nutation method to determine the electric field gradient asymmetry parameter η in systems, where the resonance line is so broad that the radio frequency field can excite only a portion of the nuclear spins, is presented. In this situation, the recently developed spectroscopic methods are not applicable. Two-dimensional nutation NQR spectra of oriented powders are calculated and used to determine η at particular frequencies along a broad NQR line. The proposed method is useful for single crystals, oriented powders, glasses, and disordered systems even for small values of the asymmetry parameter. Therefore it can be used to evaluate fluctuations in η and the quadrupole coupling constant e2qQ due to inhomogeneities. We demonstrate the application of this method to oriented chalcogenide semiconducting glasses.

Determination of the electric field gradient asymmetry from 2D nutation NQR spectra of 75As nuclei in oriented samples of As2Se3 semiconductor

“…To find a solution in recent theoretical work [10] we have proposed the NQR nutation method to determine the EFG asymmetry parameter Z in systems, where the resonance line is so broad that the radio frequency field can excite only a portion of the nuclear spins. The first, most interesting predicted feature we employed is, that for ordered powders the nutation singularities should have the form of sharp peaks as opposed to ordinary isotropic powders, where the nutation spectra show continuum-like powder pattern with broad shoulders only, thus giving rise to difficulties in accurate spectral analysis and precise determination of nutation singularities.…”

“…Secondly, to detect any NQR signals in a glassy solid sample like As 2 Se 3 spinecho method is obviously required so the effects of adding a second refocusing pulse on the resultant nutation NQR spectrum had to be considered in Ref. [10]. To some extent these effects have been discussed in [5,6]; however, contrary to Refs.…”

“…[5,6], in Ref. [10], the length of the refocusing pulse was taken into account. The essential results obtained in Ref.…”

“…The essential results obtained in Ref. [10] may be summarized as follows. The refocusing pulse affects the amplitudes of the singularities in the nutation spectrum, however, the positions of the singularities remain unchanged.…”

NQR study of chalcogenide glasses Ge‐As‐Se

“…As has been shown by many authors, NQR has become an important tool for investigation of chalcogenide-based materials. [3,4] In contrast to the magnetic resonance, the quadrupolar one is based on electric interactions and permits direct investigation of electric field on the atoms' nuclei. High sensitivity of NQR to small changes in the electric field makes it a valuable tool for investigation of local surrounding of the nuclei studied.…”