Revisiting polyanionic LiFePO4 battery material for electric vehicles

Although oxide cathodes have been widely used in these Li-ion batteries, these cathodes suffer from instability of the oxygen close-packed structure. In contrast, polyanionic phosphates such as LiFePO4 have incredible lattice stability and safety features owing to the strong covalent bond of P-O, which constrains the oxygen atoms and minimizes the defects of the oxygen site, resulting in stable frameworks. In addition, the presence of the strong P-O covalent bond stabilizes the anti-bonding transitional metal redox couple through an M-O-P inductive effect to generate a relatively high potential. Hence, polyanionic LiFePO4 has been an ideal choice of cathode materials for batteries deployed in electric vehicles. In this review, we revisit the basic features and development of LiFePO4, as an attempt to speeding its future deployment in massive electric vehicles.

Analysis of magnetic properties of A3B6 type of semiconductor crystals with metalic impurities due to their military applications

The Earth's magnetic field is affected by the presence of heavy military armored vehicles which creates an additional magnetic moment. This distortion of the magnetic field, can be detected using magnetoresistive structures. This article touches base on the possibility of using semiconductor material such as InSe for high precision measurement of the magnetic field. The properties of InSe structures with regard to electrical, magnetic and optical characteristics are discussed. The effect of sharp anisotropy of InSe layered structure which consists in the strong covalent bond within the layers and a weak van-der-Waals bond in the interlayer space is discussed with regard to the explanation of how electrical, magnetic and optical properties are altered. The peculiarity of the spatial orientation of the material with regard to the direction of the magnetic field is considered. The impact of intercalation of InSe, GaSe by various concentrations of metal impurities such as nickel and other elements of 3d iron group is studied. Bode diagrams for pure InSe system are compared with the ones of NixInSe (for various x values). Also the effect of different temperatures ranging from room temperature to liquid nitrogen on the pattern of Bode diagrams is analyzed. The extent of how the magnetic properties of semiconductor crystals of the A3B6 type are altered by the presence of the metal impurities and their concentration is analyzed. Theoretic background for this paper is based on a well-known statement that layer structures such InSe or other A3B6 structures can be viewed as quasi two-dimensional. So, layers with strong covalent bond are formed by In-Se atoms, whereas interlayer space is filled with a weak Van der Waals bond. Within this model the processes across the layers can be described as a perturbation to the ones along the layers. This causes a strong anisotropy of the properties of these structures. Military implication of InSe structures mentioned throughout this paper is that these structures possess magnetoresistive properties and they were proved to be useful for the components of the magnetic sensors of civil and military use. This paper also touches base on how the InSe semiconductor crystals intercalated by 3d-elements can extend the functionality of magnetic sensors designed for heavy armor detection.

Оценки констант электрон-фононной связи графена с металлическими и неметаллическими подложками

Two modes of graphene–substrate interaction have been considered: a weak van der Waals bond and a strong covalent bond. The Lennard–Jones potential and Harrison bond-orbital method are used in the former and latter cases, respectively. Analytical expressions for the electron–phonon interaction constants, which contain only two parameters (binding energy E _ B for graphene and a substrate and distance d between them) have been obtained. The constants have been calculated for metallic, semiconductor, and dielectric substrates.

Internal Geometric and Electronic Structures of Natural Bornite Crystal

The geometric and electronic structures of bornite (Cu5FeS4) were studied using the first-principle calculation based on density function theory. By analyzing the results, a mixed bonding state is found in bornite, which is a strong covalent bond with much weaker ionic bonds. The interaction between S and Fe is stronger than that between S and Cu. The main bonding orbitals are as follows: Cu: 3d104s1, S: 3s23p4, and Fe: 3d64s2. Fe center is to be reduced receiving electrons in its 3dorbitals and the S center is mostly to be oxidized.

Study of High Temperature Microwave Annealing on the Performance of 4H-SiC MOS Capacitors

The strong covalent bond of SiC imposes harsh post implantation annealing condition requirement for SiC MOS devices. As a consequence the effect of the annealing conditions on the channel region of the MOS devices becomes critical. High temperature microwave annealing has been shown to be an attractive alternative to conventional thermal annealing techniques. The effect of high temperature rapid microwave annealing on the performance of 4H-SiC MOS capacitors has been studied in this paper. Annealing temperatures ranging from 1600°C up to 2000°C for 30secs is used and the effect of annealing conditions is studied via C-V measurements on MOS capacitors.

Theoretical Studies of the Atomic and Electronic Structure of Mercury/Aluminium Oxide Interface

Density-functional theory (DFT) theory is conducted for the structural and electronic features at the Hg/Al2O3 interface by the analysis of optimal structural geometry, partial density of states (PDOS) and difference charge density. The two adsorption sites of on-top and hollow locations according to the symmetry is adopted to construct the associated interfacial models between Hg atom and free surface. The calculated studies show that the oxygen atoms near Hg atom in the Al2O3 surface, for both on-top and hollow sites, have the gathering effect by shifting toward Hg atom. But their interacting electrons at the interface exhibit different statues in terms of the PDOS analysis that there have no evolution tendency to form the bond between associated O and Hg atoms at the on-top site; and the occurrence of Hg-5d and O-2p overlapping orbitals reveals the strong covalent bond existed at the interface. The PDOS curves show that Al atom in the surface is not liable to contribute to the formation of corresponding bonds by mixing its electrons with Hg atom. Meanwhile, the calculated results derived from difference charge density are in good agreement with the PDOS analysis. The calculated results support some advanced atomic investigation on design a new sorbent refined from fly gas, especially improving the mercury removal from the flue gas.

Thermoelectric properties of icosahedral cluster solids – Metallic-Covalent Bonding Conversion and Weakly Bonded Rigid Heavy Clusters

ABSTRACTBoron- or Aluminum-rich icosahedral cluster solids (ICS) consist mainly of B12 or Al12 icosahedral clusters. In the ICS, a slight change of the structure or environment of icosahedral cluster can cause metallic-covalent bonding conversion, which can cause that the electrical conductivity σ and the Seebeck coefficient S can be as high as those of metals and semiconductors, respectively. Five-fold symmetry of the icosahedral cluster does not match with the translational symmetry of a crystal, consequently makes lower thermal conductivity with complex structure. For these reasons, ICS are promising candidates for thermoelectric materials.Using MEM/Rietvelt method, we successfully obtained the clear image of the electron density distribution for alpha-AlReSi approximant crystal. The bond strength distributes widely from weak metallic to strong covalent bond, and the intra-cluster bonds are stronger than the inter-cluster ones. This means that alpha-AlReSi is located at the intermediate state of molecular, metallic- and covalent-bonded solids. Composition dependences of atomic density and quasi-lattice constant for AlPdRe icosahedral quasicrystals show the above situation is the same in the quasicrystals. The thermoelectric figure of merit Z and the effective mass m* of AlPdRe quasicrystals can be increased by strengthening the intra- and weakening the inter-cluster bonds. According to this scenario, Z was improved by a factor of 1.5 by substitution of Ru for Re.In β-rhombohedral boron, several interstitial sites, which have space large enough to accommodate foreign atoms, are known. For the V doped sample, in which V atoms mainly occupy A1 site, the metallic-covalent bonding conversion may occur, σ is increased very much, S is decreased even to negative value and kappa is decreased. The maximum and n-type ZT value is obtained and is approaching to that of B4C, which is considered to have the largest and p-type ZT value in boron-rich ICS.