two-phase state of crystallite and grain boundary in nanocrystalline gold stabilized by vacancy-type defects with compositional concentration

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We found that nanocrystalline gold (ultrafine polycrystalline with the mean grain size below a few tens nm, n-Au, hereafter) shows characteristic behaviors. We have proposed that a two-phase state with crystallite phase and surrounding grain boundary phase are in quasi-equilibrium. From the anelastic measurement, an increase in grain boundary anelasticity was found at around 200 K. The x-ray diffraction measurement showed that the lattice constant at room temperature was smaller by about 0.05% from that of the conventional polycrystalline gold (poly-Au) and the temperature change of the lattice constant became slightly moderate at around 200 K. These propertie s were recovered to those of poly-Au after grain growth by annealing. It is indicated that the state of the grain boundaries of n-Au is different from that of poly-Au and the lattice contraction play an important role on the quasi-equilibrium of two-phase state.