Determination of the melting and freezing temperatures of Pb nanoparticles embedded in a PbO-B2O3-SnO2 glass by using only the SAXS method

摘要

Melting and freezing of metallic nanoparticles embedded in glass matrices usually occur at temperatures lower than for the same metal in the bulk state. In situ small-angle X-ray scattering (SAXS) measurements using a synchrotron beamline and a specially designed high-temperature chamber allowed the determination of the temperature dependence of the SAXS intensity produced by a dilute and nearly monodisperse set of spherical Pb nanoparticles, with an average radius R = 16.1nm, embedded in a homogeneous lead-borate oxide glass. The temperature dependences of the nanoparticle volume V(T) and nanoparticle radius of gyration R-g(T) derived from SAXS results exhibit clear discontinuities during the cooling and during the heating processes, thus allowing for precise determinations of the melting and freezing temperatures of the studied Pb nanoparticles. Additional features observed in both V(T) and R-g(T) curves showed that during the heating cycle the frozen Pb nanoparticles suffer a transition to a more compact phase at 433K before melting at 580K. The results of this work demonstrate that the melting and freezing temperatures of nanoparticles in a very diluted state - for which the X-ray diffraction technique is not sensitive enough - can be precisely determined by applying only the SAXS method.