Nuclear acoustic resonance in single-crystal hydrogen-free tantalum

Nuclear-acoustic-resonance studies have been made of single-crystal 99.99% pure tantalum metal from which all hydrogen has been removed (hydrogen concentration much less than 7 at. ppm or 0.04 wt ppm). The shapes and widths of the ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$ $\Delta m=\pm 1 \mathrm{and} \pm 2$ absorption lines can be explained as due to quadrupole broadening caused by a random distribution of charged impurities. Unlike hydrogenated Ta, the $\Delta m=\pm 2$ line shape and linewidth for the hydrogen-free specimen are independent of magnet angle and temperature between 78 and 300 K. The measured ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$ Knight shift is (1.14 ± 0.02)% relative to ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$ in KTa${\mathrm{O}}_3$. The magnitudes and relative signs of the components of the tensor relating electric field gradient to elastic strain are $S_{11}=\pm 26\times {10}^{15}$ statcoulomb ${\mathrm{cm}}^{-3\mathrm{}}$ and $S_{44}=\mp 29\times {10}^{15}$ statcoulomb ${\mathrm{cm}}^{-3\mathrm{}}$.