Defects and hyperfine interactions in Ni–Y intermetallics(Y = Al, Ga, In,Ti) via 27Al, 47Ti, 61Ni, 69,71Ga and 115In nuclear resonance

Abstract

Defect structures and nuclear electric hyperfine interactions have been investigated in a series ofbinary Ni–Al, Ni–Ga, Ni–In intermetallic compounds, and the shape memory compound NiTi using27Al,47,49Ti,61Ni,71Ga and115In nuclear resonance.Components of the 61Ni NMRspectrum for a series of cubic Ni1−xAlx and Ni1−xGax specimenson either side of x = 0.5 have been identified as due to Ni substitutions and Al (or Ga) vacancies. For stoichiometric NiAl,Ni2Al3 and NiAl3 the 61Ni lines are narrow and distinguished by well-separated Knight shifts, although the61Ni lineshape for the ordered vacancy compoundNi3Al4 indicates a substantial nuclear quadrupole interaction at the Ni site.The substitution for Al of the group III elements Ga and In,which have isoelectronic outer shells, acts to increase the61Ni Knight shiftsuch that 61K(Al)<61K(Ga)<61K(In). This trend is observed not only for cubic NiAl and NiGa, but also for trigonalNi2Al3,Ni2Ga3 and Ni2In3.In NiTi the sharp first-order transition between the (high-temperature) cubic phase andthe (low-temperature) monoclinic phase has been observed while monitoring the61Ni and 49,47Ti NMR lineshapes as a function of temperature.In the non-cubic phases of these materials (including hexagonalε-NiIn) the electric field gradient tensor componentsVzz and η at the atomic sites have been determined from the nuclear quadrupole perturbed27Al,47Ti,61Ni,71Ga NMR lineshapestogether with 69Ga and 115In NQR transition frequencies, and compared with values derived from ab initio calculation.