Sa Li

Structure and bulk modulus of M2AlC (M=Ti, V, and Cr)

We have performed theoretical studies of the bulk modulus of M2AlC, where M=Ti, V, Cr by means of ab initio total energy calculations using the projector augmented wave methods. Our estimated equilibrium volume and the lattice parameters (c/a) agree well (within ±2% and ±0.06%, respectively) with experimental data. The bulk modulus of M2AlC increases as Ti is substituted with V and Cr by 19% and 36%, respectively. This can be understood since the substitution of Ti by V and Cr is associated with an extensive increase in the M–Al and M–C bond energy.

Theory of the ternary layered system Ti-Al-N

We present calculations on the physical properties of Ti4AlN3 obtained from first principles, as well as some general observations concerning this group of materials. We further report mechanical data obtained through numerical simulations for some representative phases, and elaborate on the issue of high pressure stability. By examining the density of states of Ti4AlN3, we conclude that it is a semimetal, and we predict an opening up of the band gap around the Fermi level with increasing pressure.

Electronic structure and chemical bonding in Ti2AlC investigated by soft x-ray emission spectroscopy

The electronic structure of the nanolaminated transition metal carbide Ti2AlC has been investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured Ti L, C K, and Al L emission spe ...

Electronic structure investigation ofTi3AlC2,Ti3SiC2, andTi3GeC2by soft x-ray emission spectroscopy

The electronic structures of epitaxially grown films of Ti3AlC2 , Ti3SiC2 , and Ti3GeC2 have been investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured high-resolution Ti L ...

Electronic structure investigation of Ti3AlC2, Ti3SiC2, and Ti3GeC2 by soft x-ray emission spectroscopy

The electronic structures of epitaxially grown films of Ti3AlC2 , Ti3SiC2 , and Ti3GeC2 have been investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured high-resolution Ti L ...

Synthesis and characterization of highly porous borazine-linked polymers and their performance in hydrogen storage application

A new class of highly porous borazine-linked polymers (BLPs) has been synthesized utilizing arylamines and boron trihalides. BLPs exhibit Brunauer–Emmett–Teller (BET) surface areas in the range of 503 to 1364 m2 g−1 and store up to 1.3 wt% of hydrogen with 7.1 kJ mol−1 isosteric heat of adsorption.

Electronic structure and chemical bonding in Ti4SiC3 investigated by soft x-ray emission spectroscopy and first-principles theory

Theelectronic structure in the new transition-metal carbide Ti4SiC3 has beeninvestigated by bulk-sensitive soft x-ray emission spectroscopy and compared tothe well-studied Ti3SiC2 and TiC systems. The measured high-resolution TiL, C K, and Si L x-ray emission spectra arediscussed with ab initio calculations based on density-functional theory includingcore-to-valence dipole matrix elements. The detailed investigations of the Ti-Cand Ti-Si chemical bonds provide increased understanding of the physicalproperties of these nanolaminates. A strongly modified spectral shape isdetected for the intercalated Si monolayers due to Si 3phybridization with the Ti 3d orbitals. As a result ofrelaxation of the crystal structure and the charge-transfer from Ti(and Si) to C, the strength of the Ti-C covalentbond is increased. The differences between the electronic and crystalstructures of Ti4SiC3 and Ti3SiC2 are discussed in relation tothe number of Si layers per Ti layer in thetwo systems and the corresponding change of materials properties.

Layered compound Nb3SiC2 predicted from first-principles theory

A previously unobserved ternary carbide, Nb3SiC2, belonging to the family of the so-called Mn+1AXn or MAX phases is predicted from first-principles calculations. It has a theoretical bulk modulus of 269Gpa, which is much higher than that of Ti3SiC2. The new phase is metastable with a formation energy of +0.02eV∕atom. We suggest that the phase may possibly be synthesized using thin film technology. The chemical binding of Nb3SiC2 is investigated using the balanced crystal orbital overlap population indicator and it is found to be dominated by the formation of Nb 4d–C2p covalent bonds.

Theoretical study of C60 as catalyst for dehydrogenation in LiBH4.

Complex light metal hydrides possess many properties which make them attractive as a storage medium for hydrogen, but typically catalysts are required to lower the hydrogen desorption temperature and to facilitate hydrogen uptake in the form of a reversible reaction. The overwhelming focus in the search for catalysing agents has been on compounds containing titanium, but the precise mechanism of their actions remains somewhat obscure. A recent experiment has now shown that fullerenes (C(60)) can also act as catalysts for both hydrogen uptake and release in lithium borohydride (LiBH(4)). In an effort to understand the involved mechanism, we have employed density functional theory to carry out a detailed study of the interaction between this complex metal hydride and the carbon nanomaterial. Considering a stepwise reduction of the hydrogen content in LiBH(4), we find that the presence of C(60) can lead to a substantial reduction of the involved H-removal energies. This effect is explained as a consequence of the interaction between the BH(x)( - ) complex and the C(60) entity.

High pressure theoretical studies of actinide dioxides

Actinide dioxides (ThO 2 , UO 2 , Pu 2 etc.) compounds have the CaF 2 -type structure at ambient pressure and temperature. Under high pressure, they exist in the PbCl 2 -type structure, belonging to space group Pnma [1]. We have studied crystal structures under high pressure in actinide dioxides by means of first-principles self-consistent total-energy calculations with the non-local Perdew, Burke and Ernzerhof (PBE) exchange correlation using the full-potential linear-muffin-tin-orbital (FPLMTO) method. The atomic equilibrium volume, bulk modulus and transition pressure for actinide dioxides were calculated, covering the full pressure range for which the mentioned experiments have been done [2].