Validation of Interstitial Iron and Consequences of Nonstoichiometry in Mackinawite (Fe1+xS)

A theoretical investigation of the relationship between chemical composition and electronic structure was performed on the nonstoichiometric iron sulfide, mackinawite (Fe1+xS), which is isostructural and isoelectronic with the superconducting Fe1+xSe and Fe1+x(Te1–ySey) phases. Even though Fe1+xS has not been measured for superconductivity, the effects of stoichiometry on transport properties and electronic structure in all of these iron-excess chalcogenide compounds has been largely overlooked. In mackinawite, the amount of Fe that has been reported ranges from a large excess, Fe1.15S, to nearly stoichiometric, Fe1.00(7)S. Here, we analyze, for the first time, the electronic structure of Fe1+xS to justify these nonstoichiometric phases. First principles electronic structure calculations using supercells of Fe1+xS yield a wide range of energetically favorable compositions (0 \u3c x \u3c 0.30). The incorporation of interstitial Fe atoms originates from a delicate balance between the Madelung energy and the occupation of Fe–S and Fe–Fe antibonding orbitals. A theoretical assessment of various magnetic structures for “FeS” and Fe1.06S indicate that striped magnetic ordering along [110] is the lowest energy structure and the interstitial Fe affects the values of moments in the square planes as a function of distance. Moreover, the formation of the magnetic moment is dependent on the unit cell volume, thus relating it to composition. Finally, changes in the composition cause a modification of the Fermi surface and ultimately the loss of a nested vector

Magnetic Ordering in Tetragonal 3d Metal Arsenides M2As (M = Cr, Mn, Fe): An Ab Initio Investigation

The electronic and magnetic structures of the tetragonal Cu2Sb-type 3d metal arsenides (M2As, M = Cr, Mn, Fe) were examined using density functional theory to identify chemical influences on their respective patterns of magnetic order. Each compound adopts a different antiferromagnetic (AFM) ordering of local moments associated with the 3d metal sites, but every one involves a doubled crystallographic c-axis. These AFM ordering patterns are rationalized by the results of VASP calculations on several magnetically ordered models using a × a × 2c supercell. Effective exchange parameters obtained from SPRKKR calculations indicate that both direct and indirect exchange couplings play essential roles in understanding the different magnetic orderings observed. The nature of nearest-neighbor direct exchange couplings, that is, either ferromagnetic (FM) or AFM, were predicted by analysis of the corresponding crystal orbital Hamilton population (COHP) curves obtained by TB-LMTO calculations. Interestingly, the magnetic structures of Fe2As and Mn2As show tetragonal symmetry, but a magnetostrictive tetragonal-to-orthorhombic distortion could occur in Cr2As through AFM Cr1–Cr2 coupling between symmetry inequivalent Cr atoms along the a-axis, but FM coupling along the b-axis. A LSDA+U approach is required to achieve magnetic moment values for Mn2As in better agreement with experimental values, although computations always predict the moment at the M1 site to be lower than that at the M2 site. Finally, a rigid-band model applied to the calculated DOS curve of Mn2As correctly assesses the magnetic ordering patterns in Cr2As and Fe2As

СЛОВО ПРО ПРОФЕСОРА В. В. КРУТІКОВА

The electronic structures of “Ti9-nFe2+nRu18B8” (n = 0, 0.5, 1, 2, 3), in connection to the recently synthesized Ti9-nFe2+nRu18B8 (n = 1, 2), have been investigated and analyzed using LSDA tight-binding calculations to elucidate the distribution of Fe and Ti, to determine the maximum Fe content, and to explore possible magnetic structures to interpret experimental magnetization results. Through a combination of calculations on specific models and using the rigid band approximation, which is validated by the DOS curves for “Ti9-nFe2+nRu18B8” (n = 0, 0.5, 1, 2, 3), mixing of Fe and Ti is anticipated at both the 2b- and 4h-chain sites. The model “Ti8.5Fe2.5Ru18B8” (n = 0.5) revealed that both Brewer-type Ti−Ru interactions as well as ligand field splitting of the Fe 3d orbitals regulated the observed valence electron counts between 220 and 228 electrons/formula unit. Finally, models of magnetic structures were created using “Ti6Fe5Ru18B8” (n = 3). A rigid band analysis of the LSDA DOS curves concluded preferred ferromagnetic ordering at low Fe content (n ≤ 0.75) and ferrimagnetic ordering at higher Fe content (n \u3e 0.75). Ferrimagnetism arises from antiferromagnetic exchange coupling in the scaffold of Fe1-ladder and 4h-chain sites

Impact of Early Sport Specialization on Interscholastic Athletes and Programs

Early sport specialization (ESS) is a popular pathway for athletic development with implications for enhanced skill acquisition but also adverse mental and physical outcomes (LaPrade et al., 2016). As such, adolescent athletes may face a dilemma regarding whether to play multiple sports or immediately narrow the focus to one. Coaches are positioned to influence motivational climates and sport-specific skill development (Amorose & Anderson-Butcher, 2007), making it important to understand their perceptions of ESS. Interviews were conducted with thirteen coaches of girls’ volleyball and basketball teams to gain an understanding of ESS as it pertains to athletes and programs at the interscholastic level. Participants identified influences and impacts of ESS, specifically how it can affect participation and competitiveness of interscholastic sports.        &nbsp

Identifying a Structural Preference in Reduced Rare-Earth Metal Halides by Combining Experimental and Computational Techniques

The structures of two new cubic {TnLa3}Br3 (Tn = Ru, Ir; I4132, Z = 8; Tn = Ru: a = 12.1247(16) Å, V = 1782.4(4) Å3; Tn = Ir: a = 12.1738(19) Å, V = 1804.2(5) Å3) compounds belonging to a family of reduced rare-earth metal halides were determined by single-crystal X-ray diffraction. Interestingly, the isoelectronic compound {RuLa3}I3 crystallizes in the monoclinic modification of the {TnR3}X3 family, while {IrLa3}I3 was found to be isomorphous with cubic {PtPr3}I3. Using electronic structure calculations, a pseudogap was identified at the Fermi level of {IrLa3}Br3 in the new cubic structure. Additionally, the structure attempts to optimize (chemical) bonding as determined through the crystal orbital Hamilton populations (COHP) curves. The Fermi level of the isostructural {RuLa3}Br3 falls below the pseudogap, yet the cubic structure is still formed. In this context, a close inspection of the distinct bond frequencies reveals the subtleness of the structure determining factors

Impact of Early Sport Specialization on Interscholastic Athletes and Programs

Early sport specialization (ESS) is a popular pathway for athletic development with implications for enhanced skill acquisition but also adverse mental and physical outcomes (LaPrade et al., 2016). As such, adolescent athletes may face a dilemma regarding whether to play multiple sports or immediately narrow the focus to one. Coaches are positioned to influence motivational climates and sport-specific skill development (Amorose & Anderson-Butcher, 2007), making it important to understand their perceptions of ESS. Interviews were conducted with thirteen coaches of girls’ volleyball and basketball teams to gain an understanding of ESS as it pertains to athletes and programs at the interscholastic level. Participants identified influences and impacts of ESS, specifically how it can affect participation and competitiveness of interscholastic sports.        &nbsp

Strong Coupling of Self-Trapped Excitons to Acoustic Phonons in Bismuth Perovskite Cs3Bi2I9\textrm{Cs}_{3}\textrm{Bi}_{2}\textrm{I}_{9}

To assess the potential optoelectronic applications of metal-halide perovskites, it is critical to have a detailed understanding of the nature, strength, and dynamics of the interactions between carriers and the polar lattices. Here, we report the electronic and structural dynamics of bismuth-based perovskite $\textrm{Cs}_{3}\textrm{Bi}_{2}\textrm{I}_{9}$ revealed by transient reflectivity and ultrafast electron diffraction. A cross-examination of these experimental results combined with theoretical analyses allows the identification of the major carrier-phonon coupling mechanism and the associated time scales. It is found that carriers photoinjected into $\textrm{Cs}_{3}\textrm{Bi}_{2}\textrm{I}_{9}$ form self-trapped excitons on an ultrafast time scale. However, they retain most of their energy and their coupling to Fr\"ohlich-type optical phonons is limited at early times. Instead, the long-lived excitons exert an electronic stress via deformation potential and develop a prominent, sustaining strain field as coherent acoustic phonons in 10 ps. From sub-ps to ns and beyond, a similar extent of the atomic displacements is found throughout the different stages of structural distortions, from limited local modulations to a coherent strain field to the Debye-Waller random atomic motions on longer times. The current results suggest the potential use of bismuth-based perovskites for applications other than photovoltaics to take advantage of carriers' stronger self-trapping and long lifetime.Comment: 21 pages, 4 figures for the main tex