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2004 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 16, p. 165401-Article in journal (Refereed) Published
Abstract [en]
Thin films of M_{n+1}AX_{n} layered compounds in the Ti-Si-C system were deposited on MgO(111) and Al_{2}O_{3}(0001) substrates held at 900°C using dc magnetron sputtering from elemental targets of Ti, Si, and C. We report on single-crystal and epitaxial deposition of Ti_{3}SiC_{2} (the previously reported MAX phase in the Ti-Si-C system), a previously unknown MAX phase Ti_{4}SiC_{3} and another type of structure having the stoichiometry of Ti_{5}Si_{2}C_{3} and Ti_{7}Si_{2}C_{5}. The latter two structures can be viewed as an intergrowth of 2 and 3 or 3 and 4 M layers between each A layer. In addition, epitaxial films of Ti_{5}Si_{3}C_{x} were deposited and Ti_{5}Si_{4} is also observed. First-principles calculations, based on density functional theory (DFT) of Ti_{n+1}SiC_{n} for n=1,2,3,4 and the observed intergrown Ti_{5}Si_{2}C_{3} and Ti_{7}Si_{2}C_{5} structures show that the calculated difference in cohesive energy between the MAX phases reported here and competing phases (TiC, Ti_{3}SiC_{2}, TiSi_{2}, and Ti_{5}Si_{3}) are very small. This suggests that the observed Ti_{5}Si_{2}C_{3} and Ti_{7}Si_{2}C_{5} structures at least should be considered as metastable phases. The calculations show that the energy required for insertion of a Si layer in the TiC matrix is independent of how close the Si layers are stacked. Hardness and electrical properties can be related to the number of Si layers per Ti layer. This opens up for designed thin film structures the possibility to tune properties.
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-29680 (URN)10.1103/PhysRevB.70.165401 (DOI)15067 (Local ID)15067 (Archive number)15067 (OAI)
2009-10-092009-10-092017-12-13