Thermal Stability of Ni, Pd, and Ag Core-Shell Clusters with Bergman Geometry

Abstract

This study investigates the thermal behavior of nanoalloys with a 13-atom icosahedral core surrounded by a 32-atom Bergman shell using molecular dynamics simulations. Both monometallic (Ni₁₃@Ni₃₂, Pd₁₃@Pd₃₂, Ag₁₃@Ag₃₂) and bimetallic (Ni₁₃@Ag₃₂, Ni₁₃@Pd₃₂) clusters were analyzed to evaluate the effects of atomic size mismatch and cohesive energy on melting behavior. Simulations were performed from 1 K to 1300 K under constant-temperature conditions. Caloric curves and Lindemann indices were used to identify structural transitions. Among all systems, only the Ni₁₃@Ag₃₂ cluster maintained its quasi-spherical shell integrity during heating and showed clear surface-driven melting. Other systems, including those with ideal size matching, experienced structural instabilities or rearrangements before melting. These results demonstrate that the Bergman shell offers thermal and structural stability specifically for the Ni-Ag combination, despite its moderate (~16%) size mismatch. The findings highlight the importance of both geometric compatibility and energetic favorability in the design of stable core-shell nanoalloys.

Keywords

• Bergman shell
• core-shell nanoalloy
• molecular dynamics .

Bergman Geometrisine Sahip Ni, Pd ve Ag İç-Kabuk Topak Yapılarının Termal Kararlılığı

Abstract

Bu çalışmada, 13 atomlu bir ikosahedral çekirdek üzerine yerleştirilmiş 32 atomlu Bergman kabuğa sahip nanoalaşımların termal davranışı moleküler dinamik simülasyonları ile incelenmiştir. Atomik boyut uyumsuzluğu ve kohezyon enerjisinin erime davranışı üzerindeki etkilerini değerlendirmek amacıyla, tek elementli (Ni₁₃@Ni₃₂, Pd₁₃@Pd₃₂, Ag₁₃@Ag₃₂) ve iki elementli (Ni₁₃@Ag₃₂, Ni₁₃@Pd₃₂) kümeler analiz edilmiştir. Simülasyonlar sabit sıcaklık koşullarında 1 K ile 1300 K arasında gerçekleştirilmiştir. Yapısal geçişleri belirlemek için kalorik eğriler ve Lindemann indisleri kullanılmıştır. Tüm sistemler arasında yalnızca Ni₁₃@Ag₃₂ kümesi ısıtma süresince küreselimsi kabuk yapısını korumuş ve belirgin bir yüzey kaynaklı erime davranışı sergilemiştir. İdeal boyut uyumu gösteren sistemler de dahil olmak üzere diğer yapılar, erime öncesinde yapısal kararsızlık veya yeniden düzenlenme göstermiştir. Bu sonuçlar, yaklaşık %16’lık bir boyut uyumsuzluğuna rağmen Bergman kabuğunun yalnızca Ni-Ag kombinasyonu için termal ve yapısal açıdan kararlı olduğunu ortaya koymaktadır. Bulgular, kararlı iç-kabuk nanoalaşımlar tasarımında geometrik uyumun ve enerjik uygunluğun birlikte önem taşıdığını göstermektedir.

Keywords

• Bergman kabuğu
• iç-kabuk nanoalaşımı
• moleküler dinamik .

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