Pressure dependence of the electric-field gradient in semimetallic arsenicand antimony: NQR measurements and full-potential linearized augmented-plane-wave calculations

The pressure variation of the electric-field gradient (efg) at nuclear site s in powder samples of semimetallic arsenic and antimony has been investiga ted up to 2.0 Cpa at 293 K using pulsed nuclear quadrupole resonance to mea sure the nuclear resonance frequency. Theoretical calculations of both the total efg and the ionic contributions have been carried out. Full-potential linearized augmented plane wave (FLAPW) calculations of the total efg give values that are approximately 70% of the measured efg. The comparison betw een experimental and theoretical magnitudes of the efg is, however, to some extent limited by the accuracy of the values used for the quadrupole momen ts of As-75 and Sb-121. Additional uncertainties arise from the pressure de pendence of the lattice parameters. FLAPW calculations of the dependence of the internal z parameter on the cia ratio suggest an inconsistency in avai lable data for the pressure dependence of the lattice parameters. This inco nsistency is particularly marked in the arsenic case, where very little hig h-pressure data are available. In the antimony case, our FLAPW estimate of the relative pressure variation of the efg at the nuclear sites, using expe rimentally determined lattice parameters, shows good agreement with the nuc lear quadrupole resonance measurements. The pressure variation of the efg i n arsenic is well reproduced by the FLAPW calculation when the experimental c/a ratio and theoretically estimated z parameter are used. [S0163-1829(98 )03043-4].