Superatom representation of high-TC superconductivity
A “super-atom” conceptual interface between chemistry and physics is proposed in order to assist in the search for higher TC superconductors. The plaquettes generating the checkerboard superstructure in the cuprates, the C60 molecules in K3C60, and the Mo6 clusters in Chevrel phase materials offer such candidate super-atoms. Thus, in the present study high-TC superconductivity HTSC is articulated as the entanglement of two disjoint electronic manifolds in the vicinity of a common Fermi energy. The resulting HTSC ground state couples near-degenerate protected local super-atom states to virtual magnons in an antiferromagnetic AFM embedding. The composite Cooper pairs emerge as the interaction particles for virtual magnons mediated “self-coherent entanglement” of super-atom states. A Hückel type resonating valence bond RVB formalism is employed in order to illustrate the real-space Cooper pairs as well as their delocalization and Bose Einstein condensation BEC on a ring of super-atoms. The chemical potential μBECfor Cooper pairs joining the condensate is formulated in terms of the super-exchange interaction, and consequently the TC in terms of the Neél temperature. A rationale for the robustness of the HTSC ground state is proposed: achieving local maximum “electron correlation entropy” at the expense of non-local phase rigidity.
Hydrogen Storage in Perovskite-Type Oxides ABO3 for Ni/MH Battery Applications: A Density Functional Investigation
Perovskite oxides were typically considered as the electronic and ionic conductors for application in the electrolytes for solid oxides fuel cells (SOFCs). Recently, LaFeO3-based systems were mainly focused on the electrochemical property for the anode of Ni/MH batteries in our previous work, and the exciting results of their electrochemistry capacity and cycle life examination exhibited much scientific values for further investigation. In the present work, the effects of A (La)-site or B (Fe)-site metal ions doped and substituted on the fundamental properties of these materials were calculated by a first-principle approach. In conjunction with the experimental results, the microscopic mechanisms of the doped or substituted effect were discussed and elucidated. On the other hand, the hydrides of LaFe(Cr)O3 were established and computed to explore the nature of electrochemical behaviors of these perovskite oxides.
Decohesion of Ti3SiC2induced by He impurities
Using the first principle method, we investigated the effect of He impurities on the properties of layered Ti3SiC2. Helium usually segregates near Si planes. The evolution of He weakens the cohesion between Si–Ti layers, and intensifies delamination in a way of cleaving between Ti and Si layers. As a consequence, the effect of He impurities on weakening the mechanical properties of Ti3SiC2 has to be considered when such Ti3SiC2 materials are chosen as high temperature structural materials.
Reinterpretation of the monohydrate of clarithromycin from X-ray powder diffraction data as a trihydrate
Noguchi, Fujiki, Iwao, Miura & Itai [Acta Cryst. (2012), E68, o667–o668] recently reported the crystal structure of clarithromycin monohydrate from synchrotron X-ray powder diffraction data. Voids in the crystal structure suggested the possible presence of two more water molecules. After successful location of the two additional water molecules, the Rietveld refinement still showed minor problems. These were resolved by noticing that one of the chiral centres in the molecule had been inverted. The corrected crystal structure of clarithromycin trihydrate, refined against the original data, is now reported. Dispersion-corrected density functional theory calculations were used to check the final crystal structure and to position the H atoms.
Haloplumbate hybrids with organically coordinated halometal complexes as templates and mixed halo atoms: Solvothermal syntheses, crystal structures, and optical properties
Inorganic–organic hybrids with mixed halo atoms or organically coordinated halometal-complex cations are rare. A series` of haloplumbate hybrids with these structural features, [Cu(phen)2Cl]n(PbCl3)n (phen = 1,10-phenanthroline) (1), [Cu(phen)2Cl]n[PbClI(Cl0.5I0.5)]n (2), and [Cu(phen)2I]n(PbI3)n (3), have been solvothermally synthesized using phen coordinated halocopper(II) complexes as templates and balance cations. Their haloplumbate ions all show 1-D chain structures. Compounds 1–3 feature the hybridization of inorganic–organic hybrids: 1) their absorption edges fall in the range of those of semiconductors, which is typical for bulk lead(II) halides, but show a red shift compared with those of the latter; 2) bulk lead(II) halides are nonluminous upon UV irradiation, but introduction of the phen coordinated halocopper(II) complexes as templates enable the hybrids to emit blue light. Their luminescent intensities gradually decrease with the increase of I content, which indicates the potential to design and syntheses of new luminescent halide materials by means of variation of halo atoms and that iodoplumbates are not good candidates for luminescent materials.
Pressure-dependent properties of a multifunctional material: Lithium platinum boride (LiPt3B)
This paper presents our study on pressure-dependent structural, mechanical, dynamical, electronic, and optical properties of lithium platinum boride (LiPt3B) by using a first-principles plane-wave pseudopotential method. In order to determine pressure-dependent mechanical properties of the material and to check its mechanical stability, single-crystal elastic constants are calculated in the pressure range of 0–80 GPa. It is shown that LiPt3B is mechanically stable throughout the pressure range. From the calculated electronic structure, LiPt3B has a metallic character. The hardness of the material is calculated as a function of pressure, and it is observed that Pt-B bonds play an important role in the hardness. The optical properties of LiPt3B are calculated by including the Drude term. There are significant changes in the degree and the character of electronic and optical properties of LiPt3B at high pressure. Our pressure-dependent results revealed that LiPt3B is a ductile, hard, and also good reflective material, thus, we can say that it is very promising multifunctional material for a wide range of electronic and electro-optical technologies.
Defect compensation in LaAlO3 perovskite-based high dielectric constant oxides
We show that the gap states of the oxygen vacancy in LaAlO3 and related high dielectric constant (high K) perovskite oxides can be passivated by fluorine, or by substitutional nitrogen or by substitutional alkaline earth metal atoms at adjacent sites. The mechanism works by the substitutions completing an electronic closed shell, plus a repulsion of the now empty vacancy gap state into the conduction band by a relaxation of the adjacent Al and La ions away from the vacancy because it is locally +2 charged.
Structure and ferromagnetism in vanadium-doped LiNbO3
Doping into LiNbO3 (LN) and studying its magnetism might provide an alternative way for fabricating diluted magnetic compounds with potential application in the field of spintronics. Room-temperature ferromagnetic V-doped LN with V contents of 1–3 at. % was prepared by ion-beam implantation. The samples exhibit a maximum atomic magnetic moment of 3.82 μB/V at a V doping concentration of 2 at. %. Structural characterization and first principle calculation suggest that the magnetism most likely arises from the oxygen vacancy around the V dopant. X-ray absorption near-edge spectroscopy reveals that the V atom principally substituted for the Nb atom in the LN lattice and that the V is octahedrally coordinated but with a large distortion. It also showed that oxygen vacancies are present in the third shell of the doped V atoms. With the aid of first-principle calculations, we constructed the electronic structure of this system and demonstrated that the O vacancies play an important role in modulating the magnetism. These O vacancies can release the magnetic moment of the V dopant and enhance spin coupling over a long range. Two O vacancies are estimated to have an atomic magnetic moment of 4 μB, which is consistent with the results of magnetic measurements.
Synthesis, structure, physical properties, and electronic structure of KGaSe2
The ternary gallium selenide KGaSe2 has been synthesized by solid-state reactions and good quality crystal has been obtained. KGaSe2 crystallizes in the monoclinic space group C2/c with cell dimensions of a = 10.878(2) Å, b = 10.872(2) Å,c = 15.380(3) Å, and β = 100.18(3)°. In the structure, adamantane like [Ga4Se10]8− units are connected by common corners forming two-dimensional [GaSe2]− layers which are separated by K+ cations. KGaSe2 exhibits congruent-melting behavior at around 965 °C. It is transparent in the range of 0.47–20.0 μm and has a band gap of 2.60(2) eV. From a band structure calculation, KGaSe2 is a direct-gap semiconductor. The band gap is mainly determined by the [GaSe2]−layer.
First-principles investigation of the ternary scandium based inverse-perovskite carbides Sc3AC (A = Al, Ga, In and Tl)
Based on first-principles approach, we present a comparative study of structural, electronic, elastic and thermo-dynamical properties of the series of inverse-perovskites Sc3AC, with A = Al, Ga, In and Tl. The calculated equilibrium lattice constants are in excellent agreement with the experimental and available theoretical data. The electronic band structures and densities of states profiles show that the studied compounds are conductors. Analysis of atomic site projected local density of states and charge densities reveals that a mixture of covalent–ionic–metallic characterizes the chemical bonding of the considered inverse-perovskites. Pressure dependence up to 40 GPa of the single-crystal and polycrystalline elastic constants has been investigated in details. The computed B/Gratios show that all Sc3AC compounds are brittle. We have estimated the sound velocities in the principal directions. Through the quasi-harmonic Debye model, in which the phononic effects are taken into account, the temperature and pressure effects on the lattice constant, bulk modulus, heat capacity and Debye temperature are performed.
Synthesis, crystal structure and characterization of a new compound, Li3NaBaB6O12
Li3NaBaB6O12 was synthesized by high temperature solution method. It crystallizes in trigonal space group (No. 148) with lattice constantsa = 9.462(9) Å, c = 18.71(3) Å, Z = 6. The crystal structure of Li3NaBaB6O12 is a three-dimensional (3D) network composed of the isolated twelve-membered cyclic B12O24 groups interconnected by NaO6, LiO4 and BaO9 polyhedra. Functional groups in the sample were identified by IR spectrum. Li3NaBaB6O12 exhibits a short UV cutoff edge below 190 nm. Band structures and density of states were calculated.
Effects of atmospheric species and vacancy defect on electron transfer between diamond (0 0 1) surface and adlayer
The electron transfer between diamond (0 0 1) surface without and with various vacancy defects and adlayer with various adsorbed atmospheric species is examined based on first-principles calculations, which plays an important role for the conductivity of diamond (0 0 1) surface. The results show that the electron transfer from the perfect diamond surface (without defect in diamond surface or subsurface layer) to the adlayer varies with the adlayer adsorbed on the surface. The largest electron transfer is about 1.08e from the perfect surface to the adlayer (10) (O2, H3O+) among the possible adlayers, such as (1) (H2O, H2O), (2) (H2O, H3O+), (3) (H2O, CO2) … (20) (N2, O2), (21) (N2, N2) layers. It is found that the vacancy defect in surface or subsurface layer also affects the diamond (0 0 1) surface conductivity by increasing or reducing the electron transfer from the surface to the adlayer. It is also noted that the electron transfer increases largely in the case that the (10) (O2, H3O+) system is adsorbed on the diamond (0 0 1) surface with vacancy defect in the surface or subsurface layer, in which the electron transfer is largest with 1.27e when the monovacancy defect forms in the subsurface layer. Our study is useful to understand the conductivity of diamond surface.