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Melting temperature and binding energy of metal nanoparticles: size dependences, interrelation between them, and some correlations with structural stability of nanoclusters
Journal of Nanoparticle Research ( IF 2.5 ) Pub Date : 2020-08-15 , DOI: 10.1007/s11051-020-04923-6
V. M. Samsonov , S. A. Vasilyev , K. K. Nebyvalova , I. V. Talyzin , N. Yu. Sdobnyakov , D. N. Sokolov , M. I. Alymov

Size dependences of the melting temperature Tm and binding energy E, i.e., their dependences on the particle radius R, have been investigated by employing thermodynamics, a local coordination approximation for E as well as molecular dynamics. We have found that both quantities Tm and E decrease at decreasing the particle size and follow to the linear or close to linear dependence on the reciprocal particle radius R−1. However, Tm(R−1) and E(R−1) dependences are characterized by different values of the slope coefficients : KT > 1 whereas KE < 1. As a result, the binding energy does not take zero value even for the limiting case of smallest nanoclusters down to tetramers, trimer, and dimers. As for the melting temperature Tm, the linear dependence on R−1 should be relevant to mesoscopic metal nanoparticles (NPs) only consisting of at least several hundreds of atoms. A concept is put forward of a characteristic particle radius Rch corresponding to a crossover from region I of mesoscopic NPs (R > Rch) to region II of metal nanoclusters (R < Rch). This characteristic radius cannot be exactly determined. For metal NPs, including Au ones, it is of order of 1 nm, and the characteristic number of atoms Nch varies in a wider range from 100 to 500 atoms as Nch is proportional to \( {R}_{\mathrm{ch}}^3 \). In range II, noticeable fluctuations and non-scalable behavior of Tm are reported. We believe that for nanoclusters (range II), the concepts of the phase transition and of the melting temperature lose their physical meaning. On the structural level, region II relates to statistical distributions of different isomers, their instabilities and corresponding structural transformations depending on temperature and particle size.



中文翻译:

金属纳米颗粒的熔融温度和结合能:尺寸依赖性,它们之间的相互关系以及与纳米团簇的结构稳定性的一些关系

熔融温度T m和结合能E的尺寸依赖性,即它们对颗粒半径R的依赖性,已经通过热力学,E的局部配位近似以及分子动力学进行了研究。我们已经发现,量T mE都随着减小的粒径而减小并且遵循对倒数粒径R -1的线性或接近线性依赖性。但是,T mR -1)和 ER -1)依赖关系的特征在于斜率系数的不同值:K T  > 1而K E  <1。因此,即使对于最小的纳米团簇(至四聚体,三聚体和二聚体)的极限情况,结合能也不为零。 。至于熔化温度T m,对R -1的线性依赖性应该与仅由至少数百个原子组成的介观金属纳米颗粒(NPs)有关。提出了一个特征粒子半径R ch的概念,该半径对应于介观NPs区域I的穿越(R  >  R ch)到金属纳米团簇的区域II(R  <  R ch)。该特征半径不能精确确定。对于金属NP(包括Au),其数量级为1 nm,并且原子的特征数N ch在100至500个原子之间变化,因为N ch\({R} _ {\ mathrm { ch}} ^ 3 \)。在范围II中,T m的明显波动和不可缩放的行为被报道。我们认为,对于纳米团簇(范围II),相变和熔化温度的概念失去了物理意义。在结构水平上,区域II与不同异构体的统计分布,其不稳定性以及取决于温度和粒径的相应结构转变有关。

更新日期:2020-08-15
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