Size-Dependent Phase Stability of Silver Nanocrystals

Abstract

Size dependences of three structural phase transitions, melting, evaporation, and solid-solid transition for silver (Ag) nanocrystals, were investigated with nanothermodynamics. The size-dependent melting temperature T m (r) and evaporation temperature T ev (r) of Ag nanocrystals were determined based on a root-mean-squaredisplacement (rmsd) model. It is found that both T m (r) and T ev (r) decrease with crystal size decreasing for the isolated Ag nanoparticles while T m (r) increases for the Ag nanoparticles embedded in the Ni matrix. A nanothermodynamic model was also established to reveal the origin of size effect on the polymorphism (facecentered-cubic and 4H structures) behavior of Ag nanocrystals with the contributions of surface energy and surface stress to the total Gibbs free energy. It shows that the lower surface energy and surface stress coupled with a higher volume Gibbs free energy predominates the thermal stability of 4H-structured Ag in nanometer scale. The results may provide new insight into the fundamental understanding of high-performance nanostructural metals for their applications in nanodevices.

Size, Dimensionality, and Constituent Stoichiometry Dependence of Physicochemical Properties in Nanosized Binary Alloys

“…This is caused by the enhanced atomic vibrational amplitude with decreasing r associated with the increase of surface/volume ratio. 23,26,38 As shown in Figure 2, our model predictions agree quite well with the simulation results of T m (x, r, d) for Cu x Ni 1−x nanoparticles. In Figure 3, although the simulation results of T m (x, r, d) for Pd 0.5 Pt 0.5 nanowires do not match perfectly our predicted curve, they show the same trend within measurement errors.…”

“…Thus, the T m (x, r, d)/T m (∞) and T eu (x, r, d)/T eu (∞) functions in eq 1 can be rewritten as obeys the thermodynamic law of low dimensional materials, in which the variation of a size-dependent quantity is related to the surface (interface)/volume ratio, or 1/r. [23][24][25][26][27][28][29]38,43 This indicates that surface or interface engineering plays an important role in developing high-performance nanoalloys. Moreover, eq 4 can also be roughly used to compare (a) sizedependent melting temperatures of solid solutions or eutectic alloys in different systems or (b) size-dependent melting temperatures of nanoalloys and those of their constituent metal nanocrystals.…”

Influence of Size on Melting Thermodynamics of Nanoparticles: Mechanism, Factors, Range, and Degree

“…For all the spherical nano‐Au studied, the initial melting temperatures are lower than that of bulk Au (1337.34 K), decreasing from 1331.28 K for 37.4 nm particles to 889.91 K for 0.9 nm particles. This downward result also was observed in other substances . This is caused by nanoeffects.…”

“…A large number of research results show that there is a significant effect of size on melting behaviors of nanoparticles . Neyts and Bogaerts researched the melting of nano‐Ni with different particle sizes and found that the melting temperature decreases with the particle size decreasing.…”

Bimetallic Ag–Au/SiO2 catalysts: Formation, structure and synergistic activity in glucose oxidation

“…Size-dependent phase stability of silver nanocrystals governing the formation of different Ag polytypes was reported in references [38,44]. Chakraborty et al [39] underlined the importance of the control of growth kinetics prior to the size effect and concluded that the former is enough to obtain any of the three polytypes of Ag.…”