2-DIMENSIONAL NUTATION ECHO AS-75 NQR SPECTROSCOPY IN ANTIFERROELECTRIC NH4H2ASO4 USING THE MAXIMUM-ENTROPY METHOD

With a view to developing efficient methodologies for the evaluation o f the asymmetry parameter of the electric field gradient (EFG) tenser from polycrystalline specimens, an alternative approach which involves two-dimensional spin-echo NQR data processing by the maximum entropy method (MEM) is presented. The superiority of MEM over the traditional fast Fourier transform (FFT) method is demonstrated by the analysis o f two-dimensional NQR data obtained using the modified pulse sequence. The method has been successfully applied to the determination of the EFG tenser at the As-75 site in the antiferroelectric phase of polycry stalline ammonium dihydrogenarsenate (ADA), where conventional nutatio n spectroscopy fails owing to the large NQR linewidth.