Static and dynamic correlation in lattice gas systems : an application to the intermetallic hydride ZrV2Hx

Bull, DJ

Abstract

CRT, a Monte Carlo program for the simulation of particle diffusion on a lattice gas is
presented. The particle transition probability is calculated as a function of three
parameters: lattice site energies, inter-particle interactions and neighbour jump-rates.
GRT evaluates either the self correlation function, Gs(r,t), or the pair correlation
function, G(r,t). A method is presented for interpreting these functions in terms of
Sjnc(Q,w) and S CO h(Q,co), the incoherent and coherent quasielastic neutron scattering
functions. GRT can also be used to calculate the static pair correlation function, G(r).
which is related to SdifKQ), the diffuse structure factor from neutron and X-ray
diffraction.
It is demonstrated that, for diffusion in a lattice gas, the width of S COh(Q,co) is
independent of concentration when there are no inter-particle interactions. When
interactions are introduced, it is shown that the quasielastic line-width is reduced at
points in reciprocal space corresponding to maxima in Sdifl
GRT is subsequently applied to the intermetallic hydride (deuteride) ZrV 2 H(D) x . The
form of G(r) with repulsive interactions is simulated as a function of concentration.
This is compared to G(r), evaluated from neutron diffraction measurements on
ZrV 2 D x? performed on the GEM diffractometer at ISIS, UK. For ZrV 2 H x, it is shown
that S inc(Q,co), obtained from Monte Carlo simulations from diffusion, can be
interpreted in terms of motion on two time-scales, corresponding to the convolution of
a rapid local motion with a long-range translational diffusion. It is suggested that the
geometry of the diffusion paths causes this behaviour. Incoherent quasielastic neutron
scattering measurements on ZrV2 Hi i, measured on the INS time-of- flight
spectrometer at the ILL, France, are presented. Again, motion on two time scales can
be inferred from S,nc (Q,co). The characteristic jump-rates from the two types of
motion are calculated and compared with other AB2 CIS Laves phase hydrides.

• Thesis Type: Thesis
• Deposit Date: Jun 24, 2021
• Additional Information: Funders : Engineering and Physical Sciences Research Council (EPSRC)
• Award Date: Sep 1, 2001