Defects and hyperfine interactions in Ni–Y intermetallics (Y = Al, Ga, In, Ti) via27Al,47Ti,61Ni,69,71Ga and115In nuclear resonance

Defect structures and nuclear electric hyperfine interactions have been investigated in a series of binary Ni–Al, Ni–Ga, Ni–In intermetallic compounds, and the shape memory compound NiTi using 27 Al, 47,49 Ti, 61 Ni, 71 Ga and 115 In nuclear resonance. Components of the 61 Ni NMR spectrum for a series of cubic Ni 1− x Al x and Ni 1− x Ga x specimens on either side of x = 0.5 have been identified as due to Ni substitutions and Al (or Ga) vacancies. For stoichiometric NiAl, Ni 2 Al 3 and NiAl 3 the 61 Ni lines are narrow and distinguished by well-separated Knight shifts, although the 61 Ni lineshape for the ordered vacancy compound Ni 3 Al 4 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 the 61 Ni Knight shift such that 61 K(Al)< 61 K(Ga)< 61 K(In). This trend is observed not only for cubic NiAl and NiGa, but also for trigonal Ni 2 Al 3 , Ni 2 Ga 3 and Ni 2 In 3 . In NiTi the sharp first-order transition between the (high-temperature) cubic phase and the (low-temperature) monoclinic phase has been observed while monitoring the 61 Ni and 49,47 Ti NMR lineshapes as a function of temperature. In the non-cubic phases of these materials (including hexagonal ε-NiIn) the electric field gradient tensor components V zz and η at the atomic sites have been determined from the nuclear quadrupole perturbed 27 Al, 47 Ti, 61 Ni, 71 Ga NMR lineshapes together with 69 Ga and 115 In NQR transition frequencies, and compared with values derived from ab initio calculation.