Mechanical properties of YM3B phases: The effect of 4d shell population on the elastic properties of YM3B thin films ( M = Zr, Mo, Rh, and Ag)
Zusammenfassung der Projektergebnisse
2.1. Allgemeinverständliche Darstellung der wesentlichen Ergebnisse und der erzielten Fortschritte gegenüber dem Stand des Wissens zum Zeitpunkt der Antragstellung, (major results) RM{B phases (space group Pm3m, prototype CaTiO3), where A is a rare earth element and M designates a transition metal, can be described as nanolaminates with M - R layers stacked on M - B layers. Alternating covalent-ionic and metallic bonding in these compounds may give rise to similar properties as observed for the so-called MAX phases (space group PG^/mmc), known to exhibit a combination of metallic and ceramic attributes. We have synthesized YPdsB thin films for the first time and examined the correlation between the chemical composition and the film constitution. Further studies will include the determination of elastic properties and a comparison with other nanolaminated phases. Simultaneously with these experimental efforts, we have carried out theoretical work using ab initio calculations and ab initio molecular dynamics to determine: (i) the correlation between valence electron concentration and elastic properties of ARh3B (R = Y, Zr, and Nb), (ii) if CaPdsB is superconductive, (iii) the elastic properties of isostructural Srn+iTinO3n+i phases, (iv) general design principle for nanolaminates, and (v) the correlation between chemical composition, structure, chemical bonding, and elastic properties for amorphous boron rich solids. One of the highlights of the theoretical investigations is the compilation of a general design principle for nanolaminates. Based on the similarity in electron density distribution between the many investigated layered compounds, such as perovskite nitrides or Srn+iTinO3n+l phases, and the MAX phases, it is suggested that alternating covalent-ionic and metallic bonding may give rise to similar properties as observed for MAX phases. These results are relevant for the fundamental understanding of electronic structure-elasticity relationships for nanolaminates. Another important result is the correlation between chemical composition, structure, chemical bonding, and elastic properties for amorphous icosahedra based boron rich solids. This is relevant for this project since many borides are commonly amorphous when grown by magnetron sputtering at lower temperatures. These boron rich solids investigated are of different chemical compositions, but the elasticity data appear to be a function of density. The icosahedral bonding is the dominating bonding type in these structures, where C and N promote crosslinking of icosahedra, while H hinders the crosslinking by forming OH groups. The presence of icosahedral bonding was found to be independent of density. 2.2. Ausblick auf künftige Arbeiten und Beschreibung möglicher Anwendungen, (future work and possible applications) From the standpoint of materials engineering and applications, the major impediment of ceramics is their often unsatisfactory damage tolerance. Traditionally, composite materials have been developed to address this limitation, often imitating naturally occurring highly damage tolerant structures like sea shells. A drastically scaled down version of this "ceramic plywood" composite approach within a single unit cell, referred to as nanolaminates, is considered in this project. A general contribution to knowledge of this project is a possible design criterion for novel nanolaminates. We have synthesized one of these novel phases, namely YPdsB, and examined the correlation between the chemical composition and the constitution. Future studies will include the determination of elastic properties and a comparison with various nanolaminated phases. Other perovskite borides will be grown in the near future. Another important result of this DFG project is the correlation between chemical composition, structure, chemical bonding, and elastic properties for amorphous boron rich solids, obtained by ab initio molecular dynamics. This may allow for quantum chemical design of other amorphous phases, such as glasses, where major research and developments steps were carried out based on the "trial and error" approach and were not necessarily knowledge based.
Projektbezogene Publikationen (Auswahl)
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D. Music and J. M. Schneider, Elastic properties of amorphous boron suboxide based solids studied by ab initio molecular dynamics, J. Phys.: Condens. Matter 20, 195203(2008)
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D. Music and J. M. Schneider, Elastic properties of Srn+iTinO3n+i phases (n = 1 - 3, oo), J. Phys.: Condens. Matter 20, 055224 (2008)
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D. Music and J. M. Schneider, Influence of valence electron concentration on elastic properties of ARh3B (R = Y, Zr, and Nb), Appl. Phys. Lett. 89, 121914 (2006)
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D. Music and J. M. Schneider, invited review: The correlation between the electronic structure and elastic properties of nanolaminates, JOM 59, 60 (2007) 10
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D. Music and J. M. Schneider, invited talk: Elastic properties of amorphous boron suboxide based solids studied by ab initio molecular dynamics, International Conference on Metallurgical Coatings and Thin Films, April 23-27, 2007, San Diego, USA
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D. Music, Electronic structure and elastic properties of nanolaminates, Habilitation thesis, RWTH Aachen University, 2008
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D. Music, R. Ahuja, and J. M. Schneider, Electronic structure and lattice dynamics of CaPdjB studied by first-principles methods, Phys. Lett. A 356, 251 (2006)
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J. M. Schneider, invited talk: Synthesis, elastic properties, and chemical stabiliability of MAX phases, The 9th International Symposium on Ceramic Materials and Components for Energy and Environmental Applications, November 10-14, 2008, Shanghai, China
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J. M. Schneider, invited talk: Synthesis, elastic properties, and chemical stabiliability of MAX phases, TMS 2009 Annual Meeting, February 15-19, 2009, San Francisco, USA
