TEMPERATURE-DEPENDENT NUCLEAR-MAGNETIC-RESONANCE STUDY OF BE-9 IN AN ALEXANDRITE SINGLE-CRYSTAL

Nuclear magnetic resonance (NMR) spectra of the Be-9 nucleus in an ale xandrite (BeAl2-xCrxO4, x = 0.02) single crystal, grown by the Czochra lski method, have been investigated employing a Bruker FT NMR spectrom eter. Two sets of NMR spectra for Be-9 (I = 3/2) were observed in the crystallographic planes. The principal X axis of the electric held gra dient tensors for both is found to be along the crystallographic a axi s. The principal Y and Z axes are located in the b-c plane at about 9 degrees from the crystallographic c and b axes, respectively. These re sults indicate that there are two magnetically inequivalent Be sites, but they are chemically equivalent. The temperature dependence of Be-9 NMR spectra has been measured in the temperature range 120-440 K. e(2 )qQ/h for Be-9 is found to increase linearly whereas eta decreases wit h increasing temperature.