Structure and dynamics of liquid ${\text{Ni}}_{36}{\text{Zr}}_{64}$ studied by neutron scattering

We report on investigations on the atomic dynamics and the static structure factors of binary ${\text{Ni}}_{36}{\text{Zr}}_{64}$ alloy melts. In order to undercool the melts deeply below the melting temperature and to avoid reactions with crucible materials, the liquids are containerlessly processed by the application of the electromagnetic levitation technique. This technique is combined with quasielastic neutron scattering at the time-of-flight spectrometer TOFTOF of the Munich research reactor (FRM II) and neutron diffraction at the diffractometer D20 of the Institut Laue-Langevin. Partial static structure factors of liquid ${\text{Ni}}_{36}{\text{Zr}}_{64}$ have been derived via isotopic substitution. The quasielastic neutron-scattering experiments indicate a large activation energy for Ni self-diffusion in liquid ${\text{Ni}}_{36}{\text{Zr}}_{64}$ of 0.64 eV. This may result from a peculiar short-range order of the Ni-Zr melts that differs from the icosahedral short-range order that was previously found to prevail in most melts of pure metals and of metallic alloys with a small difference of the atomic radii of the components and that is characterized by a high nearest-neighbor coordination number of $⟨Z⟩\approx 13.9$, as found by elastic neutron scattering.

Figure 1

Temperature dependence of the Ni self-diffusivity in molten ${\text{Ni}}_{36}{\text{Zr}}_{64}$, ${\text{Al}}_{80}{\text{Ni}}_{20}$ (Ref. 4), ${\text{Ni}}_{80}{\text{P}}_{20}$ (Ref. 5), ${\text{Pd}}_{40}{\text{Ni}}_{40}{\text{P}}_{20}$ (Ref. 5), ${\text{Pd}}_{43}{\text{Cu}}_{27}{\text{Ni}}_{10}{\text{P}}_{20}$ (Ref. 5), and Ni (Ref. 6) as well as of the mean Ni and Ti self-diffusivities in liquid ${\text{Zr}}_{41.2}{\text{Ti}}_{13.8}{\text{Cu}}_{12.5}{\text{Ni}}_{10}{\text{Be}}_{22.5}$ (Ref. 7).

Figure 2

Scattering law for liquid ${\text{Ni}}_{36}{\text{Zr}}_{64}$ at $T=1210\text{K}$ for two different wave vectors $Q=0.8{\text{Å}}^{-1}$ and $Q=1.8{\text{Å}}^{-1}$ (upper part) and at $Q=0.9{\text{Å}}^{-1}$ for two different temperatures $T=1290\text{K}$ and $T=1650\text{K}$ (lower part).

Figure 3

Full width at half maximum $\Gamma$ of the Lorentzian curves as a function of $Q^2$ for liquid ${\text{Ni}}_{36}{\text{Zr}}_{64}$ at three different temperatures. The errors are smaller than the symbol size.

Figure 4

Total structure factors measured by neutron scattering for ${{}^{58}\text{N}\text{i}}_{36}{\text{Zr}}_{64}$, ${{}^{60}\text{N}\text{i}}_{36}{\text{Zr}}_{64}$, and ${{}^{\text{nat}}\text{N}\text{i}}_{36}{\text{Zr}}_{64}$ at $T=1375\text{K}$. The curves are shifted by multiples of 0.5 along the vertical axis.

Figure 5

Static partial Bhatia-Thornton (upper part) and Faber-Ziman (lower part) structure factors of liquid ${\text{Ni}}_{36}{\text{Zr}}_{64}$ at $T=1375\text{K}$. The curves for $S_{\text{ZrZr}}$ and $S_{CC}$ are shifted by two and $S_{NC}$ and $S_{\text{NiZr}}$ are shifted by four along the vertical axis.

Figure 6

Partial Bhatia-Thornton (upper part) and Faber-Ziman (lower part) pair-correlation functions of liquid ${\text{Ni}}_{36}{\text{Zr}}_{64}$ at $T=1375\text{K}$. The curves for $g_{\text{ZrZr}}$ and $g_{CC}$ are shifted by two, $g_{NC}$ is shifted by three, and $g_{\text{NiZr}}$ is shifted by four along the vertical axis.

Figure 7

Measured (gray symbols) and simulated (solid line) $S_{NN}$ of liquid ${\text{Ni}}_{36}{\text{Zr}}_{64}$ at large momentum transfer. For the simulation, an icosahedral short-range order is assumed to prevail in the melt.