The formation of kinetic. transient microstructures in structural phase transitions is analysed within the framework of ume-dependent Landau-Ginzburg theories. The mesoscopic rate equation is il#lih = $ -$3 t i12#/;%x2y ;12$/ilx4 i 6 ;lb#/ilx6. A front of a stable state $ = 1 can grow into an unstable region with @ = 0 in an oscillatory manner. It will then leave behind a transient domain structure with quasi-periodic walls. Such domain structures occur for positive and negative values of y with sufficiently large values of IyI The phase diagram in ( y , 8) space is explored using computer simulation. The repetition length does not diverge at the bifurcation between an oscillatory and solitonic regime except at the point y = 1/12. S = 0 studied previously. It is shown that recent computer simulation studies of 'realistic' microstructures used implicit values of y and S close to the bifurcation condition.

The explanation is presented for the temperature dependence of the fourfold intensity peak splitting found recently in diffuse scattering from the disordered Cu3Au alloy. The wavevector and temperature dependence of the self-energy is identified as the origin of the observed behaviour. Two approaches for the calculation of the self-energy, the high-temperature expansion and the αexpansion, are proposed. Applied to the Cu3Au alloy, both methods predict the increase of the splitting with temperature, in agreement with the experimental results. 05.50+q, 64.60.Cn, 61.66.Dk, 71.18+y Recently, in the first in situ experiment to resolve the fine structure of the equilibrium diffuse scattering intensity from the disordered Cu 3 Au alloy, Reichert, Moss and Liang [1] have observed a marked temperature dependence of the fourfold splitting of the (110) short-range order (SRO) diffuse intensity peak. The separation of the split maxima changed reversibly, increasing with temperature. The same behaviour of the splitting was also found in [2] by analysing results of the Monte Carlo (MC) simulations for the Cu 0.856 Al 0.144 alloy [3]. The peak splitting ( Fig.

Kinetics of atomic ordering in a potassium feldspar is simulated using massively parallel computing. The simulation method is based on the Monte Carlo algorithm for the A1-Si redistribution (the Kawasaki dynamics) combined with the lattice relaxation. The Hamiltonian has the symbolic form 1 A H=~u u-uFpwhere u represents displacements of atoms from ideal positions, and p the A1 and Si occupation numbers. The model is purely elastic; there is no direct interaction between A1 and Si atoms. The simulated crystal is a thin film with (010) surfaces and consists of 64 x 64 unit cells; the unit cell defined for the whole film contains slightly more than 4 formula units. The (010) orientation is chosen in order to preserve in the film the main structural feature of feldspars: crankshaft-like sheets formed by four-tetrahedra rings. This makes it possible to observe the Pericline twins only. At the late stage of the kinetic run these twins are clearly seen. The direction for the domain walls is determined by the spontaneous strain and changes with the change of the model parameters; considerable local deviations from this direction are observed.

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An explanation of the anomalous concentration dependence of diffuse scattering from the Pt-V alloy system (splitting of the (100) short-range order intensity peak with increasing Pt content) is proposed. The effect is attributed to the competition between the interaction and self-energy curvatures. A similar temperature behaviour is predicted.