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Abstract
BaAl2Ge2O8-feldspar (BAGF) undergoes an order/disorder phase transition (C2/m⟷I2/c) with Ttr=1690 K. The kinetic behaviour and equilibrium properties of Al, Ge cation ordering within a tetrahedral framework have been studied by isothermal annealing experiments in the temperature range between 0.5 and 0.9 Ttr., The evolution of the order parameters with time and temperature was followed by X-ray single crystal and powder diffraction methods and by phonon spectroscopy. The kinetic behaviour of the long-range order parameter is contrasted with those of short-range correlations as measured by Hard Mode Infrared Spectroscopy. Possible mechanisms causing the observed kinetic and equilibrium behaviour are discussed.