Melting and freezing temperatures of confined Bi nanoparticles over a wide size range

The size dependences of the melting and freezing temperatures, Tm and Tf, respectively, of spherical Bi nanoparticles embedded in a sodium borate glass were determined by applying a new experimental procedure based on the combined and simultaneous use of small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). This experimental procedure is particularly useful for materials in which a widely polydisperse set of nanoparticles are embedded. The results provide additional and stronger evidence supporting the main previous conclusions: (i) the melting and freezing temperatures both decrease linearly for increasing reciprocal radius (1/R); and (ii) the effect of undercooling is suppressed for Bi nanoparticles with radii smaller than a critical value equal to 1.8   nm. These results confirm a previously proposed low-resolution structural model for Bi nanocrystals below their melting temperature and with radius R> 1.8   nm, which consists of a crystalline core surrounded by a disordered shell. In the present work, a number of samples with different and partially overlapping radius distributions were studied, allowing the determination of Tm(R) and Tf(R) functions over a wide range of radii (1
Source: Journal of Applied Crystallography - Category: Physics Authors: Tags: small-angle X-ray scattering nanocrystals wide-angle X-ray scattering melting crystallization nanoparticles research papers Source Type: research