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Minerals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1409
Author(s):  
Gerson A. C. Lopes ◽  
Daniel Atencio ◽  
Javier Ellena ◽  
Marcelo B. Andrade

The roméite-group is part of the pyrochlore-supergroup and comprises cubic oxides of A2B2X6Y formula in which Sb5+ predominates in the B-site. The A and Y main occupants determine different minerals in the group and are important for the discovery of new mineral species. Two different roméite-group mineral samples were analysed by electron microprobe analysis (EMPA), Raman spectroscopy and single-crystal X-ray diffraction (XRD). The first sample is from Prabornaz Mine (locality of the original roméite), Saint Marcel, Valle d’Aosta, Italy, whereas the other one occurs in Kalugeri Hill, Babuna Valley, Jakupica Mountains, Nezilovo, Veles, Macedonia. Sample 1 was identified as fluorcalcioroméite, and sample 2 as hydroxycalcioroméite. Both samples belong to the cubic crystal system, space group Fd3¯m, Z = 8, where a = 10.2881(13) Å, V = 1088.9(4) Å3 for sample 1, and a = 10.2970(13) Å, V = 1091.8(4) Å3 for sample 2. The crystal structure refinements converged to (1) R1 = 0.016, wR2 = 0.042; and (2) R1 = 0.023, wR2 = 0.049. Bond-valence calculations validated the crystal structure refinements determining the correct valences at each crystallographic site. Discrepancies observed in the Sb5+ bond-valence calculations were solved with the use of the proper bond valence parameters. The resulting structural formulas are (Ca1.29Na0.55□0.11Pb0.05)Σ=2.00(Sb1.71Ti0.29)Σ=2.00[O5.73(OH)0.27]Σ=6.00[F0.77O0.21(OH)0.02]Σ=1.00 for sample 1, and (Ca1.30Ce0.51□0.19)Σ=2.00(Sb1.08Ti0.92)Σ=2.00O6.00[(OH)0.61O0.21F0.18]Σ=1.00 for sample 2. The Raman spectra of the samples exhibited the characteristic bands of roméite-group minerals, the most evident corresponding to the Sb-O stretching at around 510 cm−1.


Author(s):  
Sumaya Altamimi ◽  
Dong-Wook Lee ◽  
Imad Barsoum ◽  
Reza Rowshan ◽  
Iwona M. Jasiuk ◽  
...  

2021 ◽  
Vol 2114 (1) ◽  
pp. 012047
Author(s):  
Maryam M. Hassen ◽  
Isam MJbrahim

Abstract In this paper nanocomposites materials of Polyaniline (PAni) nano-fiber (NFs) and Cerium oxide (CeO2) nanoparticles (NPs) were prepared by two method; hydrothermal and chemical method respectively. The spin coating method was used to prepare PAni and Pani/CeO2 on Si and glass substrates and then screened with XRD, FE-SEM, UV-Vis and as-prepared thin-film photodetectors. The X-ray diffraction pattern of all the prepared films showed the presence of crystalline nature. It was found that the PAni/CeO2 films have a cubic crystal structure.. FESEM results proved that the PAni film prepared have nanofiber like structure, while the PAni/CeO2 films proved that CeO2 NPs fully caped with PAni nanofiber. The UV-Vis spectra showed peaks of PAni 340nm, 651nm and PAni/CeO2 320nm, 620 nm and in the energy gap it is noticed that the band gap value decreases as the CeO2 ratios increases where the maximum values of energy gap of B-band and Q-band (1.65 – 2.74) eV. The maximum sensitivity values of the photoconductive detectors were observed at PAni/CeO2 (2 vol.%) nanoparticles deposited on n-Si substrate which were approximately (2696.5%, 946.15%, 1402.2%, 1613.9%3837.9%, and 2700%) for wavelengths 360, 465, 510, 595,660 and 965 nm respectively.


2021 ◽  
Author(s):  
Zizhen Liang ◽  
Wai Tsun Yeung ◽  
Keith Ka Ki Mai ◽  
Juncai Ma ◽  
Zhongyuan Liu ◽  
...  

AbstractThe crystalline structure of prolamellar bodies (PLBs) and light-induced etioplasts-to-chloroplasts transformation have been investigated with electron microscopy methods. However, these studies suffer from chemical fixation artifacts and limited volumes of tomographic reconstruction. We have examined Arabidopsis thaliana cotyledon samples preserved by high-pressure freezing with scanning transmission electron tomography to visualize larger volumes in etioplasts and their conversion into chloroplasts. PLB tubules were arranged in a zinc blende-type lattice like carbon atoms in diamonds. Within 2 hours after illumination, the lattice collapsed from the PLB exterior and the disorganized tubules merged to form fenestrated sheets that eventually matured into lamellar thylakoids. These planar thylakoids emerging from PLBs overlapped or folded into grana stacks in PLBs’ vicinity. Since the nascent lamellae had curved membrane at their tips, we examined the localization of CURT1 proteins. CURT1A transcript was most abundant in de-etiolating cotyledon samples, and CURT1A concentrated at the peripheral PLB. In curt1a mutant etioplasts, thylakoid sheets were swollen and failed to develop stacks. In curt1c mutant, however, PLBs had cracks in their lattices, indicating that CURT1C contributes to cubic crystal growth under darkness. Our data provide evidence that CURT1A and CURT1C play distinct roles in the etioplast and chloroplast biogenesis.


Coatings ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1325
Author(s):  
Igor Bychkov ◽  
Sergey Belim ◽  
Ivan Maltsev ◽  
Vladimir Shavrov

In this paper, we investigate the behavior of 2D ferromagnetic (FM) films on a ferroelectric (FE) substrate with a periodic structure. The two-dimensional Frenkel–Kontorova (FK) potential simulates the substrate effect on the film. The substrate potential corresponds to a cubic crystal lattice. The Ising model and the Wolf cluster algorithm are used to describe the magnetic behavior of a FM film. The effect of an electric field on a FE substrate leads to its deformation, which is uniform and manifests itself in a period change of the substrate potential. Computer simulation shows that substrate deformations lead to a decrease in the FM film Curie temperature. If the substrate deformations exceed 5%, the film deformations become inhomogeneous. In addition, we derive the dependence of film magnetization on the external electric field.


AIP Advances ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 105111
Author(s):  
K. A. Pestka ◽  
A. M. Crews ◽  
R. C. Highley ◽  
L. K. Deale

Symmetry ◽  
2021 ◽  
Vol 13 (10) ◽  
pp. 1837
Author(s):  
Degang Zhang

The three-dimensional Ising model in a zero external field is exactly solved by operator algebras, similar to the Onsager’s approach in two dimensions. The partition function of the simple cubic crystal imposed by the periodic boundary condition along two directions and the screw boundary condition along the third direction is calculated rigorously. In the thermodynamic limit an integral replaces a sum in the formula of the partition function. The critical temperatures, at which order–disorder transitions in the infinite crystal occur along three axis directions, are determined. The analytical expressions for the internal energy and the specific heat are also presented.


2021 ◽  
Vol 9 ◽  
Author(s):  
Daniel Atencio

The general formula of the pyrochlore-supergroup minerals is A2B2X6Y. The mineral names are composed of two prefixes and one root name (identical to the name of the group). The first prefix refers to the dominant anion (or cation or H2O or vacancy) of the dominant valence at the Y-site. The second prefix refers to the dominant cation of the dominant valence [or H2O or vacancy] at the A-site. Thirty-one pyrochlore-supergroup mineral species are currently distributed into four groups [pyrochlore (B = Nb, X = O), microlite (B = Ta, X = O), roméite (B = Sb5+, X = O), and elsmoreite (B = W, X = O)] and two unassigned members [hydrokenoralstonite (B = Al, X = F) and fluornatrocoulsellite (B = Mg, X = F)]. However, when the new nomenclature system of this supergroup was introduced (2010) only seven mineral species, namely, oxycalciopyrochlore, hydropyrochlore, hydroxykenomicrolite, oxystannomicrolite, oxystibiomicrolite, hydroxycalcioroméite, and hydrokenoelsmoreite, were valid. The seven species belong to the cubic crystal system and space group Fd3¯m and O is predominant in the X structural site. The 24 new mineral species described between 2010 and 2021 are cesiokenopyrochlore, fluorcalciopyrochlore, fluornatropyrochlore, hydrokenopyrochlore, hydroxycalciopyrochlore, hydroxynatropyrochlore, hydroxykenopyrochlore, hydroxymanganopyrochlore, hydroxyplumbopyrochlore, fluorcalciomicrolite, fluornatromicrolite, hydrokenomicrolite, hydroxycalciomicrolite, kenoplumbomicrolite, oxynatromicrolite, oxycalciomicrolite, oxybismutomicrolite, fluorcalcioroméite, hydroxyferroroméite, oxycalcioroméite, oxyplumboroméite, fluornatrocoulsellite, hydrokenoralstonite, and hydroxykenoelsmoreite. Among the new species, hydroxycalciomicrolite belongs to a different space group of the cubic system, i.e., P4232. There are also some mineral species that crystallize in the trigonal system. Hydrokenoelsmoreite occurs as 3C (Fd3¯m) and 6R (R3¯) polytypes. Hydrokenomicrolite occurs as 3C (Fd3¯m) and 3R (R3¯m) polytypes, of which the latter corresponds to the discredited “parabariomicrolite.” Fluornatrocoulsellite crystallizes as 3R (R3¯m) polytype. Surely there are several new pyrochlore-supergroup minerals to be described.


2021 ◽  
Vol 1 (1) ◽  
pp. 71-82
Author(s):  
V. Kavitha ◽  
V. Ragavendran ◽  
N. Sethupathi ◽  
Suresh Sagadevan ◽  
V. Sasirekha ◽  
...  

Gadolinium (Gd) doped barium strontium titanate (BST) was prepared using the microwave-assisted solid-state reaction method for dye sensitized solar cell (DSSC) applications. The optical properties and the structural analysis of the prepared samples reveal the optical band gap and the morphology. The XRD pattern of the annealed samples confirms the polycrystalline nature with the cubic crystal structure. When the dopant is added, the bandgap increases slightly from 3.11 to 3.27 eV. The J-V characteristics of DSSCs prepared with pure and doped BST were investigated. The efficiency of the DSSCs remained constant and there is a slight increase in the Jsc for highly doped samples under 1-sun illumination. Gadolinium doped barium strontium titanate shows variation in the J-V characteristics and could be a potential candidate for the solar photovoltaic applications.


2021 ◽  
pp. 2100566
Author(s):  
Yong Zhao ◽  
Mohammed Al‐Fahdi ◽  
Ming Hu ◽  
Edirisuriya M. D. Siriwardane ◽  
Yuqi Song ◽  
...  

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