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Mn+1AXn phases in the Ti-Si-C system studied by thin-film synthesis and ab initio calculations
Uppsala University, Department of Materials Chemistry, The Ångström Laboratory, Uppsala, Sweden.
Uppsala University, Department of Physics, The Ångström Laboratory, Uppsala, Sweden.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.ORCID iD: 0000-0001-9140-6724
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
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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, 165401- p.Article in journal (Refereed) Published
Abstract [en]

Thin films of Mn+1AXn layered compounds in the Ti-Si-C system were deposited on MgO(111) and Al2O3(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 Ti3SiC2 (the previously reported MAX phase in the Ti-Si-C system), a previously unknown MAX phase Ti4SiC3 and another type of structure having the stoichiometry of Ti5Si2C3 and Ti7Si2C5. 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 Ti5Si3Cx were deposited and Ti5Si4 is also observed. First-principles calculations, based on density functional theory (DFT) of Tin+1SiCn for n=1,2,3,4 and the observed intergrown Ti5Si2C3 and Ti7Si2C5 structures show that the calculated difference in cohesive energy between the MAX phases reported here and competing phases (TiC, Ti3SiC2, TiSi2, and Ti5Si3) are very small. This suggests that the observed Ti5Si2C3 and Ti7Si2C5 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.

Place, publisher, year, edition, pages
2004. Vol. 70, no 16, 165401- p.
National Category
Natural Sciences
URN: urn:nbn:se:liu:diva-29680DOI: 10.1103/PhysRevB.70.165401Local ID: 15067OAI: diva2:250497
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2016-08-31
In thesis
1. MAX phase thin films: unique multifunctional ceramics with the elements Ti, Si, Ge, Sn, and C
Open this publication in new window or tab >>MAX phase thin films: unique multifunctional ceramics with the elements Ti, Si, Ge, Sn, and C
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Mn+1AXn phases are ternary carbides or nitrides (X) consisting of an early transition metal (M), and (A)- group element (group III-V). They combine ceramic and metallic properties with high oxidation and thermal shock resistance as well as low resistivity. Depending on stoichiometry, they can be classified as 211 (n=1), 312 (n=2), and 413 (n=3) phases. The main purpose of this Thesis is to present the synthesis by epitaxial growth of Tin+1ACn (A: Si, Ge, Sn; n=1-3) thin solid films and to report on the material’s intrinsic mechanical and electrical properties. DC magnetron sputtering of MAX-phase carbides from three individual elemental targets is presented as an original and successful deposition method. The emphasis is on the archetypical Ti3SiC2, but I also demonstrate growth of a wide range of other single-crystal Tin+1ACn thin films, including Ti2GeC, Ti3GeC2, Ti2SnC, previously available only in bulk form, as well as completely new phases of Ti4SiC3, Ti4GeC3, and Ti3SnC2, together with some intergrown 523 (211+312) and 725 (312+413) structures.

A combination of x-ray diffraction (XRD), transmission electron micrcoscopy (TEM) analysis, x-ray photoelectron spectroscopy, elastic recoil detection analysis, and Rutherford backscattering spectrometry of the films reveal single-phase and epitaxial growth of Tin+1SiCn(0001) (n = 2, 3) and Ti2GeC MAX phases at substrate temperatures (TS) above 700 to 1000 °C. For TS = 500 – 700 °C, Si is accommodated at twin boundaries between TiC(111) planes. Depositions at TS = RT – 350 °C yield nc-TiC/SiC nanocomposite films or TiC growth with substitutionally incorporated Si due to kinetic constraints. Vacuum-annealing with in situ XRD measurements of the films between 800 – 1400 °C revealed a thermal stability of up to ~1000 °C. A MAX-phase decomposition model is presented within this Thesis. It starts by Si out-diffusion and evaporation from the surface between ~1000 – 1100 °C and is accompanied by any O uptake and SiO evaporation. Subsequently, the free Ti3C2 slabs relax and undergo detwinning. The decomposition process is ended by TiC0.67 formation by C redistribution and recrystallization with void formation.

The mechanical response to deformation was tested on Ti3SiC2(0001) films using nanoindentation. Small applied normal forces yielding a minimum on plastic deformation reveal hardness values of up to 24 GPa, which decrease with larger indentation depths. Young’s moduli between 320 and 343 GPa were measured. Atomic force microscopy (AFM) surface imaging and Focused Ion Beam cross-sectional TEM studies confirm that mechanical deformation in this ductile ceramic takes place by kink formation and delamination along basal planes, due to edge dislocation pile-ups forming the kink boundaries resulting in local deformation-energy dissipation. Friction measurements yield a friction coefficient (μ) of 0.1 for normal loads of FN = 100-200 μN. μ increases to 0.8 with increased FN up to 0.24 N, as delamination and kinking are introduced accompanied by third-body abrasion as shown by scanning electron microscopy. By comparing electrical resistivity values obtained by four-point probe measurements, it is found that all studied MAX-phase thin film systems exhibit good conduction properties.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi, 2006. 48 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1024
Thin solid films, Single-crystal
National Category
Physical Sciences
urn:nbn:se:liu:diva-7449 (URN)91-85523-64-X (ISBN)
Public defence
2006-06-16, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Available from: 2006-09-27 Created: 2006-09-27 Last updated: 2012-11-19

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Persson, PerEmmerlich, JensHögberg, HansHultman, Lars
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