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Effects of volume mismatch and electronic structure on the decomposition of ScAlN and TiAlN solid solutions
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
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2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 22, 224101- p.Article in journal (Refereed) Published
Abstract [en]

Thin solid films of metastable rocksalt structure (c-) Sc1-xAlxN and Ti1-xAlxN were employed as model systems to investigate the relative influence of volume mismatch and electronic structure driving forces for phase separation. Reactive dual magnetron sputtering was used to deposit stoichiometric Sc0.57Al0.43N(111) and Ti0.51Al0.49N(111) thin films, at 675 °C and 600 °C, respectively, followed by stepwise annealing to a maximum temperature of 1100 °C. Phase transformations during growth and annealing were followed in situ using X-ray scattering. The results show that the as-deposited Sc0.57Al0.43N films phase separate at 1000 °C – 1100 °C into non-isostructural c-ScN and wurtzite-structure (w-) AlN, via nucleation and growth at domain boundaries. Ti0.51Al0.49N, however, exhibits spinodal decomposition into isostructural coherent c-TiN and c-AlN, in the temperature interval of 800 °C – 1000 °C. X-ray pole figures show the coherency between c-ScN and w-AlN, with AlN(0001) || ScN(001) and AlN<01ɸ10> || ScN<1ɸ10>. First principles calculations of mixing energy-lattice spacing curves explain the results on a fundamental physics level and open a route for design of novel metastable pseudobinary phases for hard coatings and electronic materials.

Place, publisher, year, edition, pages
2010. Vol. 81, no 22, 224101- p.
Keyword [en]
TiAlN, ScAlN, spinodal decomposition, nitrides, TiN, ScN, AlN, XRD, TEM, first-principles, phase separation, meta stable
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-56270DOI: 10.1103/PhysRevB.81.224101ISI: 000278300900004OAI: oai:DiVA.org:liu-56270DiVA: diva2:318035
Note
Original Publication: Carina Höglund, Björn Alling, Jens Birch, Manfred Beckers, Per O. Å. Persson, Carsten Baehtz, Zsolt Czigány, Jens Jensen and Lars Hultman, Effects of volume mismatch and electronic structure on the decomposition of ScAlN and TiAlN solid solutions, 2010, Physical Review B. Condensed Matter and Materials Physics, (81), 22, 224101. http://dx.doi.org/10.1103/PhysRevB.81.224101 Copyright: American Physical Society http://www.aps.org/ Available from: 2010-05-06 Created: 2010-05-06 Last updated: 2017-12-12
In thesis
1. Growth and Phase Stability Studies of Epitaxial Sc-Al-N and Ti-Al-N Thin Films
Open this publication in new window or tab >>Growth and Phase Stability Studies of Epitaxial Sc-Al-N and Ti-Al-N Thin Films
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

¨This Thesis treats the growth and characterization of ternary transition metal nitride thin films. The aim is to probe deep into the Ti-Al-N system and to explore novel Sc-Al-N compounds. Thin films were epitaxially grown by reactive dual magnetron sputtering from elemental targets onto single-crystal substrates. Ion beam analyses were used for compositional analysis and depth profiling. Different X-ray diffraction techniques were employed, ex situ using Cu radiation and in situ during deposition using synchrotron radiation, to achieve information about phases, texture, and thickness of films, and to follow roughness evolution of layers during and after growth. Transmission electron microscopy was used for overview and lattice imaging, and to obtain lattice structure information by electron diffraction.

In the Sc-Al-N system, the perovskite Sc3AlN was for the first time synthesized as a thin film and in single phase, with a unit cell of 4.40 Å. The hardness was found to be 14.2 GPa, the elastic modulus 21 GPa, and the room temperature resistivity 41.2 μΩcm. Cubic solid solutions of Sc1-xAlxN can be synthesized with AlN molar fraction up to ~60%. Higher AlN contents yield three different epitaxial relations to ScN(111), namely, #1 Sc1-xAlxN(0001) || ScN(111) with Sc1-xAlxN[11210] || ScN[110], #2 Sc1-xAlxN(1011) || ScN(110) with Sc1-xAlxN[1210] || ScN[110], and #3 Sc1-xAlxN(1011) || ScN(113). An in situ deposition and annealing study of cubic Sc0.57Al0.43N films showed volume induced phase separation into ScN and wurtzite structure AlN, via nucleation and growth at the domain boundaries. The first indications for phase separation are visible at 1000 °C, and the topotaxial relationship between the binaries after phase separation is AlN(0001) || ScN(001) and AlN<01ɸ10> || ScN <1ɸ10>. This is compared with Ti1-xAlxN, for which an electronic structure driving force leads to spinodal decomposition into isostructural TiN and AlN already at 800 °C. First principles calculations explain the results on a fundamental physics level. Up to ~22% ScN can under the employed deposition conditions be dissolved into wurtzite Sc1-xAlxN films, while retaining a single-crystal structure and with lattice parameters matching calculated values.

In the Ti-Al-N system, the Ti2AlN phase was synthesized epitaxially by solid state reaction during interdiffusion between sequentially deposited layers of AlN(0001) and Ti(0001). When annealing the sample, N and Al diffused into the Ti layer, forming Ti3AlN(111) at 400 ºC and Ti2AlN(0001) at 500 ºC. The Ti2AlN formation temperature is 175 ºC lower than earlier reported results. Another way of forming Ti2AlN phase is by depositing understoichiometric TiNx at 800 °C onto Al2O3(0001). An epitaxial Ti2Al(O,N) (0001) oxynitride forms close to the interface between film and substrate through a solid state reaction. Ti4AlN3 was, however, not possible to synthesize when depositing films with a Ti:Al:N ratio of 4:1:3 due to competing reactions. A substrate temperature of 600 ºC yielded an irregularly stacked Tin+1AlNn layered structure because of the low mobility of Al ad-atoms. An increased temperature led to Al deficiency due to outdiffusion of Al atoms, and formation of the Ti2AlN phase and a Ti1-xAlxN cubic solid solution.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2010. 98 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1314
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-56274 (URN)978-91-7393-391-9 (ISBN)
Public defence
2010-05-28, Visionen, Hus B, ingång 27, Campus Valla, Linköpings universitet, Linköping, 09:15 (English)
Opponent
Supervisors
Available from: 2010-05-06 Created: 2010-05-06 Last updated: 2016-08-31Bibliographically approved
2. Configurational and Magnetic Interactions in Multicomponent Systems
Open this publication in new window or tab >>Configurational and Magnetic Interactions in Multicomponent Systems
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is a theoretical study of configurational and magnetic interactions in multicomponent solids. These interactions are the projections onto the configurational and magnetic degrees of freedom of the underlying electronic quantum mechanical system, and can be used to model, explain and predict the properties of materials. For example, the interactions govern temperature induced configurational and magnetic order-disorder transitions in Heusler alloys and ternary nitrides.

In particular three perspectives are studied. The first is how the interactions can be derived from first-principles calculations at relevant physical conditions. The second is their consequences, like the critical temperatures for disordering, obtained with e.g. Monte Carlo simulations. The third is their origin in terms of the underlying electronic structure of the materials.

Intrinsic defects in the half-Heusler system NiMnSb are studied and it is found that low-energy defects do not destroy the important half-metallic property at low concentrations. Deliberate doping of NiMnSb with 3d-metals is considered and it is found that replacing some Ni with extra Mn or Cr creates new strong magnetic interactions which could be beneficial for applications at elevated temperature. A self-consistent scheme to include the effects of thermal expansion and one-electron excitations in the calculation of the magnetic critical temperature is introduced and applied to a study of Ni1−xCuxMnSb.

A supercell implementation of the disordered local moments approach is suggested and benchmarked for the treatment of paramagnetic CrN as a disordered magnetic phase. It is found that the orthorhombic-to-cubic phase transition in this nitride can be understood as a first-order magnetic order-disorder transition. The ferromagnetism in Ti1−xCrxN solid solutions, an unusual property in nitrides, is explained in terms of a charge transfer induced change in the Cr-Cr magnetic interactions.

Cubic Ti1−xAlxN solid solutions displays a complex and concentration dependent phase separation tendency. A unified cluster expansion method is presented that can be used to simulate the configurational thermodynamics of this system. It is shown that short range clustering do influence the free energy of mixing but only slightly change the isostructural phase diagram as compared to mean-field estimates.

Place, publisher, year, edition, pages
Linköping: Linköpings Universitet, 2010. 98 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1334
Keyword
Magnetic interactions, Configurational thermodynamics, Curie temperature, theoretical physics, magnetism, TiAlN, TiN, AlN, CrN, TiCrN, nitrides, NiMnSb, NiCuMnSb, Heusler alloys, spintronics, half-metallic, spinodal decomposition, first-principles, ab-initio
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-60446 (URN)978-91-7393-330-8 (ISBN)
Public defence
2010-09-09, Planck, Fysikhuset, Campus Valla, Linköping University, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2010-11-17 Created: 2010-10-13 Last updated: 2016-08-31Bibliographically approved

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Höglund, CarinaAlling, BjörnBirch, JensBeckers, ManfredPersson, Per O. Å.Jensen, JensHultman, Lars

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