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 ¹⁸¹Ta Δm=±1 and ±2 absorption lines can be explained as due to quadrupole broadening caused by a random distribution of charged impurities. Unlike hydrogenated Ta, the Δm=±2 line shape and linewidth for the hydrogen-free specimen are independent of magnet angle and temperature between 78 and 300 K. The measured ¹⁸¹Ta Knight shift is (1.14 ±{} 0.02)% relative to ¹⁸¹Ta in KTaO₃. The magnitudes and relative signs of the components of the tensor relating electric field gradient to elastic strain are S₁₁=±26×10¹⁵ statcoulomb cm^-3 and S₄₄=∓29×10¹⁵ statcoulomb cm^-3.