Alloyed silver–gold nanoparticles (spherical,
8 nm) were
wet-chemically prepared by reduction with sodium citrate/tannic acid
and colloidally stabilized by poly(N-vinylpyrrolidone)
(PVP), in steps of 10 atom %, including pure silver nanoparticles
(35 nm) and pure gold nanoparticles (7 nm). The nanoparticles were
subjected to in situ X-ray powder diffraction up to 850 °C to
induce internal stress relaxation and recrystallization. The stress-induced
negative deviation from Vegard’s rule that was present in the
original alloyed nanoparticles vanished between 150 and 250 °C,
indicating the internal healing of defects. Simultaneously, a discontinuous
increase in the crystallite size and a drop in the microstrain were
observed. After heating to 850 °C, the original gradient structure
(silver-rich shell, gold-rich core) had changed to a homogeneous elemental
distribution as shown by high-angle annular dark-field scanning transmission
electron microscopy/energy-dispersive X-ray spectroscopy (STEM/EDX).
Thus, there is a considerable mobility of the metal atoms inside the
nanoparticles that starts as low as 150 °C.