Quadrupole effects on Ge-73 NMR spectra in isotopically controlled Ge single crystals

NMR spectra of Ge-73 (nuclear spin I=9/2) in perfect single crystals of ger manium with different isotopic content were measured at 80, 300, and 450 K. The observed specific line shapes gave evidence of the isotopic disorder, in particular, abnormal broadening of the spectrum was found for the magnet ic field directed along the [111] axis. Local lattice deformations in the g ermanium crystal lattice due to "isotopic disorder" were calculated in the framework of the adiabatic bond charge model. The results were applied to s tudy random non-cubic crystal field interactions with the nuclear quadrupol e moments and corresponding effects on NMR spectra. The simulated second mo ment of the resonance frequency distributions caused by the magnetic dipole -dipole and electric quadrupole interactions are used to analyze the linesh apes, theoretical predictions being in a qualitative agreement with the exp erimental data.