Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userElectronic band structure and inter-atomic bonding in layered 1111-like Th-based pnictide oxides ThCuPO, ThCuAsO, ThAgPO, and ThAgAsO from first principles calculations
120
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
First-principles FLAPW-GGA band structure calculations were employed to examine the structural, electronic properties and the chemical bonding picture for four ZrCuSiAs-like Th-based quaternary pnictide oxides ThCuPO, ThCuAsO, ThAgPO, and ThAgAsO. These compounds were found to be semimetals and may be viewed as intermediate systems between two main isostructural groups of superconducting and semiconducting 1111 phases. The Th 5f states participate actively in the formation of valence bands and the Th 5f states for ThMPnO phases are itinerant and partially occupied. We found also that the bonding picture in ThMPnO phases can be classified as a high-anisotropic mixture of ionic and covalent contributions: inside [Th2O2] and [M2Pn2] blocks, mixed covalent-ionic bonds take place, whereas between the adjacent [Th2O2]/[M2Pn2] blocks, ionic bonds emerge owing to [Th2O2] to [M2Pn2] charge transfer.
rate research
Read More
By means of the FLAPW-GGA approach, we have systematically studied the structural and electronic properties of tetragonal dichalcogenides KNi2Ch2 (Ch = S, Se, and Te). Our results show that replacements of chalcogens (S -> Se -> Te) lead to anisotropic deformations of the crystals structure, which are related to the strong anisotropic character of the inter-atomic bonds, where inside the [Ni2Ch2] blocks, mixed covalent-ionic-metallic bonds occur, whereas between the adjacent [Ni2Ch2] blocks and K atomic sheets, ionic bonds emerge. We found that in the sequence KNi2S2 -> KNi2Se2 -> KNi2Te2 (i) the overall band structure (where the near-Fermi valence bands are due mainly to the Ni states) is preserved, but the width of the common valence band and the widths of the separate subbands and the gaps decrease; (ii) the total DOSs at the Fermi level also decrease; and (iii) for the Fermi surfaces, the most appreciable changes are demonstrated by the hole-like sheets, when a necklace-like topology is formed for the 2D-like sheets and the volume of the closed pockets decreases. Some trends in structural and electronic parameters for ThCr2Si2-type layered dichalcogenides, KNi2Ch2, KFe2Ch2, KCo2Se2, are discussed.
Very recently (November, 2010, PRB, 82, 180520R) the first 122-like ternary superconductor KxFe2Se2 with enhanced TC ~ 31K has been discovered. This finding has stimulated much activity in search of related materials and triggered the intense studies of their properties. Indeed already in 2010-2011 the superconductivity (TC ~ 27-33K) was also found in the series of new synthesized 122 phases such as CsxFe2Se2, RbxFe2Se2, (TlK)xFeySe2 etc. which have formed today the new family of superconducting iron-based materials without toxic As. Here, using the ab initio FLAPW-GGA method we have predicted for the first time the elastic properties for KFe2Se2 and discussed their interplay with inter-atomic bonding for this system. Our data reveal that the examined phase is relatively soft material. In addition, this system is mechanically stable, adopts considerable elastic anisotropy, and demonstrates brittleness. These conclusions agree with the bonding picture for KFe2Se2, where the inter-atomic bonding is highly anisotropic and includes ionic, covalent and metallic contributions.
The ground state electronic structures of the actinide oxides AO, A2O3 and AO2 (A=U, Np, Pu, Am, Cm, Bk, Cf) are determined from first-principles calculations, using the self-interaction corrected local spin-density (SIC-LSD) approximation. Emphasis is put on the degree of f-electron localization, which for AO2 and A2O3 is found to follow the stoichiometry, namely corresponding to A(4+) ions in the dioxide and A(3+) ions in the sesquioxides. In contrast, the A(2+) ionic configuration is not favorable in the monoxides, which therefore become metallic. The energetics of the oxidation and reduction of the actinide dioxides is discussed, and it is found that the dioxide is the most stable oxide for the actinides from Np onwards. Our study reveals a strong link between preferred oxidation number and degree of localization which is confirmed by comparing to the ground state configurations of the corresponding lanthanide oxides. The ionic nature of the actinide oxides emerges from the fact that only those compounds will form where the calculated ground state valency agrees with the nominal valency expected from a simple charge counting.
We assumed that significant enlargement of the functional properties of the family of quaternary ZrCuSiAs-like pnictide-oxides, often called also as 1111 phases, which are known now first of all as parent phases for new FeAs superconductors, may be achieved by replacement of nonmagnetic ions by magnetic ions in semiconducting ZrCuSiAs-like phases. We checked this assumption by means of first-principles FLAPW-GGA calculations using a wide-band-gap semiconductor YZnAsO doped with Mn, Fe, and Co as an example. Our main finding is that substitution of Mn, Fe, and Co for Zn leads to drastic transformations of electronic and magnetic properties of the parent material: as distinct from the non-magnetic YZnAsO, the examined doped phases YZn0.89Mn0.11AsO, YZn0.89Fe0.11AsO, and YZn0.89Co0.11AsO behave as a magnetic semiconductor, a magnetic half-metal or as a magnetic gapless semi-metal, respectively.
The properties of newly discovered polar ScFeO3 with magnetic ordering are examined using Ab initio calculations and symmetry mode analysis. The GGA+U calculation confirms the stability of polar R3c Phase in ScFeO3 and the pressure induced phase transition to non-polar Pnma phase. Octahedron tilting and structural properties as a function of applied pressure have been analyzed. The origin of polar phase is associated with instability of non-polar R-3c phase and group theory using the symmetry mode analysis has been applied to understand this instability as well as the spontaneous polarization of polar R3c phase. The magnetic phase transition shows G-type AFM ordering of Fe3+ ion within Goodenough-Kanamori theory and the possibility of magnetic spin structure has been analyzed by using energy analysis including spin canting possibility.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
