Die Kristallstruktur von Ti3GeC2

Wolfsgruber, H.; Nowotny, H.; Benesovsky, F.

doi:10.1007/bf00902438

Cited by 112 publications

(76 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The A elements are located at the center of trigonal prisms that are larger than the octahedral X sites. [5][6][7][8] Macroscopic properties such as electrical and thermal conductivity and elasticity of ternary carbides and nitrides are known to strongly depend on the valence-electron concentration of the M element. Information about the internal electronic structure and the anisotropic pattern of the chemical bonds is therefore invaluable but generally difficult to obtain experimentally.…”

Section: Introductionmentioning

confidence: 99%

Anisotropy in the electronic structure ofV2GeCinvestigated by soft x-ray emission spectroscopy and first-principles theory

et al. 2008

View full text Add to dashboard Cite

The anisotropy of the electronic structure of ternary nanolaminate V 2 GeC is investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured polarization-dependent emission spectra of V L 2,3 , C K, Ge M 1 , and Ge M 2,3 in V 2 GeC are compared with those from monocarbide VC and pure Ge. The experimental emission spectra are interpreted with calculated spectra using ab initio density-functional theory including dipole transition matrix elements. Different types of covalent chemical bond regions are revealed: V 3d-C 2p bonding at −3.8 eV, Ge 4p-C 2p bonding at −6 eV, and Ge 4p-C 2s interaction mediated via the V 3d orbitals at −11 eV below the Fermi level. We find that the anisotropic effects are high for the 4p valence states and the shallow 3d core levels of Ge, while relatively small anisotropy is detected for the V 3d states. The macroscopic properties of the V 2 GeC nanolaminate result from the chemical bonds with the anisotropic pattern as shown in this work.

show abstract

Section: Introductionmentioning

confidence: 99%

Anisotropy in the electronic structure ofV2GeCinvestigated by soft x-ray emission spectroscopy and first-principles theory

et al. 2008

View full text Add to dashboard Cite

show abstract

“…Ref. [16][17][18][19][20][21], and corresponding structural relatives Ti 3 SiC 2 [22] and Ti 3 GeC 2 [23]. However, it took about 30 years until Barsoum and El-Raghy [24] showed that Ti 3 SiC 2 exhibits unique material properties combining the characteristics of metals and ceramics, a finding which intensified the research on this class of materials.…”

Section: Max Phases and Related Materialsmentioning

confidence: 99%

Materials Design from First Principles : stability and magnetism of nanolaminates

Dahlqvist¹

2014

View full text Add to dashboard Cite

The front cover image is a close up of M (red and blue spheres) and X (grey sphere) in M 2 AX. In the background its nanolaminated structure consisting of ordered, clustered, and disordered atoms or magnetic moments is illustrated.The spine image shows charge redistribution for an interstitial oxygen atom in Cr 2 AlC where blue indicate gain of electrons and red loss of electrons.The back cover image shows charge redistribution when oxygen substitutes for carbon in Ti 2 AlC where blue indicate gain of electrons and red loss of electrons. My daughter described it as "a planet, with water, and trees, and blue leaves". © Martin Dahlqvist, unless otherwise stated. Printed by LiU-Tryck, Linköping, Sweden, 2014 To my JETs ♥ v ABSTRACT In this thesis, first-principles calculations within density functional theory are presented, with a principal goal to investigate the phase stability of so called M n+1 AX n (MAX) phases. MAX phases are a group of nanolaminated materials comprised of a transition metal (M), a group 12-16 element (A), and carbon or nitrogen (X). They combine ceramic and metallic characteristics, and phase stability studies are motivated by a search for new phases with novel properties, such as magnetism, and for the results to be used as guidance in attempted materials synthesis in the lab.To investigate phase stability of a hypothetical material, a theoretical approach has been developed, where the essential part is to identify the set of most competing phases relative to the material of interest. This approach advance beyond more traditional evaluation of stability, where the energy of formation of the material is generally calculated relative to its single elements, or to a set of ad hoc chosen competing phases. For phase stability predictions to be reliable, validation of previous experimental work is a requirement prior to investigations of new, still hypothetical, materials. It is found that the predictions from the developed theoretical approach are consistent with experimental observations for a large set of MAX phases. The predictive power is thereafter demonstrated for the new phases Nb 2 GeC and Mn 2 GaC, which subsequently have been synthesized as thin films. It should be noted that Mn is used for the first time as sole M-element in a MAX phase. Hence, the theory is successfully used to find new candidates, and to guide experimentalists in their work on novel promising materials. Phase stability is also evaluated for MAX phase alloys. Incorporation of oxygen in different M 2 AlC phases are studied, and the results show that oxygen prefer different sites depending on M-element, through the number of available non-bonding M delectrons. The theory also predicts that oxygen substituting for carbon in Ti 2 AlC stabilizes the material, which explains the experimentally observed 12.5 at% oxygen (x = 0.5) inMagnetism is a recently attained property of MAX phase materials, and a direct result of this Thesis work. We have demonstrated the importance of choice of magnetic spin configuration and elec...

show abstract

“…Equation (4.9) can also be written as 10) where is the phonon wave vector, and is the band index; the first term on the righthand side is the zero point energy, which, even though it is actually present at 0 K, is typically neglected in 0 K calculations; it is often quite small, however. The allowed phonon frequencies , can be calculated using, e.g., the linear response method, also known as density functional perturbation theory (DFPT) [37,38].…”

Section: Vibrational Free Energymentioning

confidence: 99%

“…phases Ti3SiC2 and Ti3GeC2 [9,10]. However, interest in further research on these phases was relatively low for almost 30 years following this work [11].…”

Section: Historymentioning

confidence: 99%

See 1 more Smart Citation

Phase stability and physical properties of nanolaminated materials from first principles

Thore¹

2016

View full text Add to dashboard Cite

The cover shows an exponential curve. It is a visual representation of Moore's lawGordon Moore's observation that the number of components, such as transistors, per integrated circuit doubles roughly every two years. The exponential increase in computational power that this has entailed has made computational materials science possible. Curiously enough, computational materials science is now an important driver of this increase, and, consequently, a driver of its own capabilities. Printed by LiU-tryck, Linköping 2016 AbstractThe MAX phase family is a set of nanolaminated, hexagonal materials typically comprised of three elements: a transition metal (M), an A-group element (A), and carbon and/or nitrogen (X). In this thesis, first-principles based methods have been used to investigate the phase stability and physical properties of a number of MAX and MAX-like phases.Most theoretical work on MAX phase stability use the constraint of 0 K conditions, due to the very high computational cost of including temperature dependent effects such as lattice vibrations and electronic excitations for all relevant competing phases in the ternary or multinary chemical space. Despite this, previous predictions of the existence of new MAX phases have to a large extent been experimentally verified. In an attempt to provide a possible explanation for this consistency, and thus help strengthen the confidence in future predictions, we have calculated the temperature dependent phase stability of Tin+1AlCn, to date the most studied MAX phases. We show that both the electronic and vibrational contribution to the Gibbs free energies of the MAX phases are cancelled by the corresponding contributions to the Gibbs free energies of the competing phases. We further show that this is the case even when thermal expansion is considered.We have also investigated the stability of two hypothetical MAX-like phases, V2Ga2C and (Mo1-xVx)2Ga2C, motivated by a search for ways to attain new two-dimensional MAX phase derivatives, so-called MXenes. We predict that it is possible to synthesize both phases. For x≤0.25, stability of (Mo1-xVx)2Ga2C is indicated for both ordered and disordered solid solutions on the M sublattice. For x=0.5 and x≥0.75, stability is only indicated for disordered solutions. The ordered solutions are stable at temperatures below 1000 K, whereas stabilization of the disordered solutions requires temperatures of up to 2100 K, depending on the V concentration.Finally, we have investigated the electronic, vibrational, and magnetic properties of the recently synthesized MAX phase Mn2GaC. We show that the electronic band structure is anisotropic, and determine the bulk, shear, and Young's modulus to be 157, 93, and 233 GPa, respectively, and Poisson's ratio to be 0.25. We further predict the magnetic critical order-disorder temperature of Mn2GaC to be 660 K. We base the predictions on Monte Carlo simulations of a bilinear Heisenberg Hamiltonian constructed from magnetic exchange interaction parameters derived using two different supe...

show abstract

Die Kristallstruktur von Ti3GeC2

Cited by 112 publications

References 0 publications

Anisotropy in the electronic structure ofV2GeCinvestigated by soft x-ray emission spectroscopy and first-principles theory

Anisotropy in the electronic structure ofV2GeCinvestigated by soft x-ray emission spectroscopy and first-principles theory

Materials Design from First Principles : stability and magnetism of nanolaminates

Phase stability and physical properties of nanolaminated materials from first principles

Contact Info

Product

Resources

About