Role of Potassium Substitution in the Magnetic Properties and Magnetocaloric Effect in La0.8−xKxBa0.05Sr0.15MnO3 (0 ≤ x ≤ 0.20)

The magnetic and magnetocaloric effects of potassium-substituted La0.8−xKxBa0.05Sr0.15MnO3 (0 ≤ x ≤ 0.20) manganite were explored. The samples in polycrystalline form were synthesized by the sol–gel method, with a final sintering temperature of 1100 °C. Powder X-ray diffraction (XRD) patterns refined by Rietveld refinement show that all samples crystallized in rhombohedral structure with R-3c space group. The unit cell volume of the samples decreases with increasing potassium concentration. In addition, small changes in average bond length and bond angle are also observed in the samples. Scanning electron microscope (SEM) images reveal that the largest average grain size was observed for x = 0.10. Field-cooled (FC) magnetization measurements show that the Curie temperature ( T C ) of the samples increases from 320 K for x = 0 to 360 K for x = 0.2. The largest magnetocaloric (MCE) effect, which is represented by maximum magnetic entropy change (− Δ S M , M A X ), reaches its greatest value for the x = 0.10 sample. The monotonous increase in T C suggests that TC is mainly governed by the ferromagnetic coupling between Mn ions induced by the changes on average bond length and bond angle. The obtained − Δ S M , M A X value suggests that MCE property is more sensitive to Zener theory of double exchange, which is strongly related to the Mn3+/Mn4+ ratio of the samples.

Lithium and sodium diffusion in solid electrolyte materials of AM2(PO4)3(A = Li, Na, M = Ti, Sn and Zr)

Electrolytes with a high ionic conductivity are the prerequisite for the success of solid state rechargeable ion batteries. In this paper, density functional theory (DFT) calculations are applied in combination with a climbing-image nudged elastic band (CI-NEB) method to obtain the diffusion barriers of the lithium (Li) and sodium (Na) in stoichiometric AM 2( PO 4)3 (A = Li, Na, M = Ti, Sn and Zr) compounds. In the AM 2( PO 4)3, Li and Na ions occupy the interstitial sites, M1, which is coordinated by a trigonal antiprism of oxygen, and M2, which has a distorted eight-fold coordination. Results show that the diffusion barriers are closely related with the average bond length of A–O bond when the atom A occupies the M2 site in the AM 2( PO 4)3 compounds, and the diffusion barriers decrease with increasing the average bond length. Among the various types of the AM 2( PO 4)3 compounds, the AM 2( PO 4)3 has a good potential for solid electrolytes due to its low diffusion barriers for the Li and Na.

1,2,3,4,5,6,7,8,13,13,14,14-Dodecachloro-1,4,4a,4b,5,8,8a,12b-octahydro-1,4:5,8-dimethanotriphenylene at 90 K

The previously reported room-temperature crystal structure [Jaud Baldy, Negrel, Poite & Chanon (1993).Z. Kristallogr.204, 289–291] of the title compound, C20H8Cl12, is monoclinic withZ′ = 1, whereas the 90 K structure reported herein is triclinic withZ′ = 2 and shows a 2% volume contraction. The crystallographically independent unit chosen consists of both enantiomers (Λ and Δ) of this propeller-like molecule. Both enantiomers display quasi-twofold symmetry, with average bond-length/bond-angle deviations of 0.0018 (4) Å and 0.41 (2)° for Λ, and 0.0026 (4) Å and 0.50 (2)° for Δ.

Die Kristallstruktur von Bis-[methylammonium]-hexafluorosilikat, (MeNH3)2SiF6 / The Crystal Structure of Bis-[methylammonium]-hexafluorosilicate, (MeNH3)2SiF6

The results of a single crystal X-ray structure determination of monoclinic (MeNH3)2SiF6 are reported: a = 962.3(5), b = 964.4(1), c = 966.4(5) pm, " = 100.03(3)°; V = 883.2(7) Å3, Z = 4, space group C2/c; wR2 = 0.0999 based on F02 of 1291 independent reflections (including H refinement without restrictions). The structure is related to that of (NH4)2SiF6, but contains the dumb-bells of the cations well oriented along the greater cell diagonals and fixed by one nearly linear and two bi-furcated hydrogen bonds (N...F: 281 and 293 - 305 pm, resp.). The [SiF6]2- octahedron is nearly undistorted with average bond length Si-F: 167.7 pm (169.9 pm corrected for thermal motion)

A contribution to the structure of coals from x-ray diffraction studies

Detailed X-ray diffraction studies have been carried out on a series of vitrains, anthracites, lignites, durains, fusains and certain coal extracts, of varying rank. The results are interpreted in terms of a basic structural model in which the carbon atoms are arranged in small aromatic layers linked to each other by aliphatic or alicyclic material or by five-membered rings to form large buckled sheets. Data have been obtained on the layer size distributions, the average layer diameters, the average bond length, the proportion of amorphous material and on the nature of the packing. The significance of the various structural parameters deduced from X-ray data is discussed critically. All the results are considered together in an attempt to develop as detailed a structural model as possible. The nature of the coalification process and the structural differences between various macerals are discussed and the results are compared with those deduced from other studies.