Ab initio study of the phase stability of modulated structures in Co-doped Ni-Mn-In (Sn) Heusler alloys

Using ab initio calculations, the phase stability of modulated and tetragonal martensitic structures in Ni43.75Co6.25Mn43.75(In, Sn)6.25 Heusler alloys with different magnetic order is investigated. The stability against the segregation is considered by a method for generating all possible decay reactions assuming the calculated ground state energies of each composition. It is shown that the highest probable stability under equilibrium conditions is demonstrated by alloys with tetragonal martensitic structure in accordance with reactions: Ni35Co5Mn35In5 → 25Mn + 35Ni + 5Mn2InCo and Ni35Co5Mn35Sn5 → 5CoSn + 35Mn + 35Ni.

Mössbauer investigation of Co-doped Bismuth Ferrite prepared by the solution method

In this work, [Formula: see text] ([Formula: see text] = 0, 0.08) nanoparticles were synthesized by the solution method and their structural differences were studied. X-ray diffraction results show that the rhombohedral R3c space group and perovskite structures are detected in both samples, accompanied by an impurity phase. The (104) and (110) peaks merge when cobalt ions are doped. The decrease in lattice parameters indicates that the microstructure of the nanoparticles becomes gradually distorted. Mössbauer spectroscopy analysis at room temperature reveals an additional doublet due to the oxygen vacancies in [Formula: see text]. Hyperfine interactions, spatial spin-modulated structures and oxygen deficiencies around iron ions are also reflected in the observed spectra and variations in hyperfine parameters.

Electron-Acoustic (Un)Modulated Structures in a Plasma Having (r, q)-Distributed Electrons: Solitons, Super Rogue Waves, and Breathers

The propagation of electron-acoustic waves (EAWs) in an unmagnetized plasma, comprising (r,q)-distributed hot electrons, cold inertial electrons, and stationary positive ions, is investigated. Both the unmodulated and modulated EAWs, such as solitary waves, rogue waves (RWs), and breathers are discussed. The Sagdeev potential approach is employed to determine the existence domain of electron acoustic solitary structures and study the perfectly symmetric planar nonlinear unmodulated structures. Moreover, the nonlinear Schrödinger equation (NLSE) is derived and its modulated solutions, including first order RWs (Peregrine soliton), higher-order RWs (super RWs), and breathers (Akhmediev breathers and Kuznetsov–Ma soliton) are presented. The effects of plasma parameters and, in particular, the effects of spectral indices r and q, of distribution functions on the characteristics of both unmodulated and modulated EAWs, are examined in detail. In a limited cases, the (r,q) distribution is compared with Maxwellian and kappa distributions. The present investigation may be beneficial to comprehend and predict the modulated and unmodulated electron acoustic structures in laboratory and space plasmas.

Are the St John's wort Hyp-1 superstructures different?

Two commensurately modulated structures (PDB entries 4n3e and 6sjj) were solved using translational noncrystallographic symmetry (tNCS). The data required the use of large supercells, sevenfold and ninefold, respectively, to properly index the reflections. Commensurately modulated structures can be challenging to solve. Molecular-replacement software such as Phaser can detect tNCS and either handle it automatically or, for more challenging situations, allow the user to enter a tNCS vector, which the software then uses to place the components. Although this approach has been successful in solving these types of challenging structures, it does not make it easy to understand the underlying modulation in the structure or how these two structures are related. An alternate view of this problem is that the atoms and associated parameters are following periodic atomic modulation functions (AMFs) in higher dimensional space, and what is being observed in these supercells are the points where these higher dimensional AMFs intersect physical 3D space. In this case, the two 3D structures, with a sevenfold and a ninefold superstructure, seem to be quite different. However, describing those structures within the higher dimensional superspace approach makes a strong case that they are closely related, as they show very similar AMFs and can be described with one unique (3+1)D structure, i.e. they are two different 3D intersections of the same (3+1)D structure.

Modulated Structures, Microstructures and Subsolidus Phase Relations of Labradorite Feldspars

The coupled substitution between Na+Si and Ca+Al, in the plagioclase solid solution, results in a continuous variation in the Al/Si ratio of the composition, which is the reason for the complicated ordering patterns in the intermediate plagioclase feldspars such as labradorite. Both fast-cooled and slow-cooled labradorite feldspars display the incommensurately modulated structures. The ordering pattern in the incommensurately modulated structures of e-plagioclase (characterized by the satellite diffraction peak called e-reflections) is the most complicated and intriguing. The modulated structure has a super-space group symmetry of X(αβγ)0, with a special centering condition of (½ ½ ½ 0), (0 0 ½ ½), (½ ½ 0 ½), and the q-vector has components (i.e., δh, δk, δl) along all three axes in reciprocal space. Displacive modulation, occupational modulation, and density modulation are observed in slowly cooled labradorite feldspars. No density modulation was observed in fast cooled (volcanic) labradorite feldspars. The amplitudes of the modulation waves are new parameters for quantifying the ordering state of labradorite. Iridescent labradorite feldspars display exsolution lamellae with an average periodicity ranging from ~150 nm to ~350 nm. Compositional difference between the lamellae is about 12 mole % in anorthite components. Areas or zones with red (or yellow) iridescent color (i.e., long lamellae periodicity) always contain more Ca (~1 to 3 mole %) than the areas with blue (or green) iridescent color within the same labradorite crystal. We proposed that the solvus for Bøggild intergrowth has a loop-like shape, ranging from ~An44 to ~An63. The Ca-rich side / zone has higher exsolution temperature than the Na-rich side / zone. The shapes of satellite peaks, the distances between e-reflections (modulation periods), and even the intensity of e-reflections may also be used to evaluate the ordering state or cooling rate of the plagioclase feldspar. Both modulated structure and the exsolution lamellae can be used as proxies for quantifying cooling rate of a labradorite and it’s host rock.