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

CRT, a Monte Carlo program for the simulation of particle diffusion on a lattice gas ispresented. The particle transition probability is calculated as a function of threeparameters: lattice site energies, inter-particle interactions and neighbour jump-rates.GRT evaluates either the self correlation function, Gs(r,t), or the pair correlationfunction, G(r,t). A method is presented for interpreting these functions in terms ofSjnc(Q,w) and S CO h(Q,co), the incoherent and coherent quasielastic neutron scatteringfunctions. 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-raydiffraction.It is demonstrated that, for diffusion in a lattice gas, the width of S COh(Q,co) isindependent of concentration when there are no inter-particle interactions. Wheninteractions are introduced, it is shown that the quasielastic line-width is reduced atpoints in reciprocal space corresponding to maxima in SdiflGRT is subsequently applied to the intermetallic hydride (deuteride) ZrV 2 H(D) x . Theform of G(r) with repulsive interactions is simulated as a function of concentration.This is compared to G(r), evaluated from neutron diffraction measurements onZrV 2 D x? performed on the GEM diffractometer at ISIS, UK. For ZrV 2 H x, it is shownthat S inc(Q,co), obtained from Monte Carlo simulations from diffusion, can beinterpreted in terms of motion on two time-scales, corresponding to the convolution ofa rapid local motion with a long-range translational diffusion. It is suggested that thegeometry of the diffusion paths causes this behaviour. Incoherent quasielastic neutronscattering measurements on ZrV2 Hi i, measured on the INS time-of- flightspectrometer at the ILL, France, are presented. Again, motion on two time scales canbe inferred from S,nc (Q,co). The characteristic jump-rates from the two types ofmotion are calculated and compared with other AB2 CIS Laves phase hydrides