Minor Bands Research Articles

Petrography of the carbonaceous, diamond-bearing stone “Hypatia” from southwest Egypt: A contribution to the debate on its origin

The stone named “Hypatia” found in the Libyan Desert Glass area of southwest Egypt is carbon-dominated and rich in microdiamonds. Previous noble gas and nitrogen isotope studies suggest an extraterrestrial origin. We report on a reconnaissance study of the carbonaceous matrix of this stone and the phases enclosed in it. This focused on areas not affected by numerous transecting fractures mostly filled with secondary minerals. The work employed scanning electron microscopy (SEM) with energy-dispersive (EDS) and wavelength-dispersive (WDS) electron microprobe (EMPA) analysis, Proton Induced X-ray Emission (PIXE) spectrometry and micro-Raman spectroscopy. We found that carbonaceous matrices of two types occur irregularly intermingled on the 50–500 μm scale: Matrix-1, consisting of almost pure carbonaceous matter, and Matrix-2, containing Fe, Ni, P and S at abundances analyzable by microprobe. Matrix-2 contains the following phases as inclusions: (i) (Fe,Ni) sulphide occurring in cloud-like concentrations of sub-μm grains, in domains of the matrix that are enriched in Fe and S. These domains have (Fe + Ni)/S (atomic) = 1.51 ± 0.24 and Ni/Fe = 0.086 ± 0.061 (both 1SD); (ii) grains up to ∼5 μm in size of moissanite (SiC); (iii) Ni-phosphide compound grains up to 60 μm across that appear cryptocrystalline or amorphous and have (Ni + Fe)/P (atomic) = 5.6. ± 1.7 and Ni/Fe = 74 ± 29 (both 1SD), where both these ratios are much higher than any known Ni-phosphide minerals; (iv) rare grains (observed only once) of graphite, metallic Al, Fe and Ag, and a phase consisting of Ag, P and I. In Matrix-2, Raman spectroscopy shows a prominent narrow diamond band at 1340 cm−1. In Matrix-1 the D and G bands of disordered carbon are dominant, but a minor diamond band is ubiquitous, accounting for the uniform hardness of the material. The D and G bands have average full width at half maximum (FWHM) values of 295 ± 19 and 115 ± 19 cm−1, respectively, and the D/G intensity ratio is 0.75 ± 0.09 (both 1SD). These values are similar to those of the most primitive solar system carbonaceous matter. The diamond phase is considered to be a product of shock. The (Fe, Ni) sulphide phase is probably pyrrhotite and a shock origin is likewise proposed for it. Moissanite is frequently associated with the Ni-phosphide phase, and a presolar origin for both is suggested. The lack of recrystallization of the Ni-phosphide phase suggests that the Hypatia stone did not experience long-lasting thermal metamorphism, in accord with the Raman D-G band characteristics.A lack of silicate matter sets the stone apart from interplanetary dust particles and known cometary material. This, along with the dual intermingled matrices internal to it, could indicate a high degree of heterogeneity in the early solar nebula.

Emergence of undulating surface band upon oxygen adsorption of Fe thin film on W(110)

We have performed high-resolution angle-resolved photoemission spectroscopy of oxygen-adsorbed Fe thin films on W(110) to elucidate the evolution of electronic states upon surface oxidation. After oxygen adsorption of 0.25 monolayer onto Fe films, we found a surface state in the vicinity of the Fermi level which exhibits an undulating energy band dispersion. Our first-principles band-structure calculation indicates that this state is attributed to the spin-polarized minority band arising from the hybridization between Fe 3d and O 2p orbitals. The present result suggests that the observed surface state is related to the unusual magnetic properties of oxidized Fe surfaces.

Manifestation of intra-atomic 5d6s-4f exchange coupling in photoexcited gadolinium

Intra-atomic exchange couplings (IECs) between 5d6s and 4f electrons are ubiquitous in rare-earth metals and play a critical role in spin dynamics. However, detecting them in real time domain has been difficult. Here we show the direct evidence of IEC between 5d6s and 4f electrons in gadolinium. Upon femtosecond laser excitation, 5d6s electrons are directly excited; their majority bands shift toward the Fermi level while their minority bands do the opposite. For the first time, our first-principles minority shift now agrees with the experiment quantitatively. Excited 5d6s electrons lower the exchange potential barrier for 4f electrons, so the 4f states are also shifted in energy, a prediction that can be tested experimentally. Although a significant number of 5d6s electrons, some several eV below the Fermi level, are excited out of the Fermi sea, there is no change in the 4f states, a clear manifestation of intra-atomic exchange coupling.

Surface-Enhanced Resonance Raman Scattering of Rhodamine 6G in Dispersions and on Films of Confeito-Like Au Nanoparticles.

Surface-enhanced resonance Raman scattering (SERRS) of rhodamine 6G was measured on confeito-like Au nanoparticles (CAuNPs). The large CAuNPs (100 nm in diameter) in aqueous dispersion systems showed stronger enhancing effect (analytical enhancement factor: over 105) of SERRS than the small CAuNPs (50 nm in diameter), while the spherical Au nanoparticles (20 nm in diameter) displayed rather weak intensities. Especially, minor bands in 1400–1600 cm−1 were uniquely enhanced by the resonance effect of CAuNPs. The enhancement factors revealed a concentration dependence of the enhancing effect at low concentration of rhodamine 6G. This dependency was due to a large capacity of hot-spots on CAuNPs, which were formed without agglomeration. The surface-enhancing behaviour in the film systems was similar to that in the dispersions, although the large CAuNPs had lower enhancing effect in the films, and the small CAuNPs and the spherical Au nanoparticles were more effective in their films. These results suggest that the CAuNPs have an advantage in ultrasensitive devices both in dispersions and films, compared to the agglomerate of spherical Au nanoparticles.

Optimal Charge-to-Spin Conversion in Graphene on Transition-Metal Dichalcogenides.

When graphene is placed on a monolayer of semiconducting transition metal dichalcogenide (TMD) its band structure develops rich spin textures due to proximity spin-orbital effects with interfacial breaking of inversion symmetry. In this work, we show that the characteristic spin winding of low-energy states in graphene on a TMD monolayer enables current-driven spin polarization, a phenomenon known as the inverse spin galvanic effect (ISGE). By introducing a proper figure of merit, we quantify the efficiency of charge-to-spin conversion and show it is close to unity when the Fermi level approaches the spin minority band. Remarkably, at high electronic density, even though subbands with opposite spin helicities are occupied, the efficiency decays only algebraically. The giant ISGE predicted for graphene on TMD monolayers is robust against disorder and remains large at room temperature.

Effect of erythropoietin administration on proteins participating in iron homeostasis in Tmprss6-mutated mask mice.

Tmprss6-mutated mask mice display iron deficiency anemia and high expression of hepcidin. The aim of the study was to determine the effect of erythropoietin administration on proteins participating in the control of iron homeostasis in the liver and spleen in C57BL/6 and mask mice. Administration of erythropoietin for four days at 50 IU/mouse/day increased hemoglobin and hematocrit in C57BL/6 mice, no such increase was seen in mask mice. Erythropoietin administration decreased hepcidin expression in C57BL/6 mice, but not in mask mice. Erythropoietin treatment significantly increased the spleen size in both C57BL/6 and mask mice. Furthermore, erythropoietin administration increased splenic Fam132b, Fam132a and Tfr2 mRNA content. At the protein level, erythropoietin increased the amount of splenic erythroferrone and transferrin receptor 2 both in C57BL/6 and mask mice. Splenic ferroportin content was decreased in erythropoietin-treated mask mice in comparison with erythropoietin-treated C57BL/6 mice. In mask mice, the amount of liver hemojuvelin was decreased in comparison with C57BL/6 mice. The pattern of hemojuvelin cleavage was different between C57BL/6 and mask mice: In both groups, a main hemojuvelin band was detected at approximately 52 kDa; in C57BL/6 mice, a minor cleaved band was seen at 47 kDa. In mask mice, the 47 kDa band was absent, but additional minor bands were detected at approximately 45 kDa and 48 kDa. The results provide support for the interaction between TMPRSS6 and hemojuvelin in vivo; they also suggest that hemojuvelin could be cleaved by another as yet unknown protease in the absence of functional TMPRSS6. The lack of effect of erythropoietin on hepcidin expression in mask mice can not be explained by changes in erythroferrone synthesis, as splenic erythroferrone content increased after erythropoietin administration in both C57BL/6 and mask mice.

Identification by Raman spectroscopy of pararealgar as a starting material in the synthesis of amorphous arsenic sulfide pigments

In this study, a combination of elemental analytical techniques (MA-XRF and SEM-EDX) were used to localize arsenic sulfide pigments within a 17th-century Dutch painting and in the stratigraphy of an 18th-century Flemish polychrome sculpture. Once located, Raman spectroscopy was used to obtain the vibrational signature of the arsenic sulfide pigments employed. By means of the latter analytical technique and due to the very distinctive Raman scattering signal of the various arsenic sulfide compounds, it was possible to identify the arsenic-based pigments as natural orpiment and amorphous arsenic sulfide. In the latter case, based on the minor bands observed and the good condition of the paint layers, it was possible to identify pararealgar, the orangey-yellow to yellow degradation product of realgar, as the initial arsenic sulfide material used for the synthesis of the amorphous pigment. To the best of our knowledge, this is the first time that combined pararealgar/amorphous arsenic sulfide Raman spectra are reported in historical samples. Therefore, this would be the first identification of pararealgar as the starting material to produce amorphous arsenic sulfide pigments used in artworks.

First-Principles Study in New Hf2CoZ (Z = B, C, Al, Si, Ga, Ge, In, Sn, Tl, and Pb) Heusler Alloys

The full-potential linearized augmented plane wave method within density functional theory was used to investigate the electronic structures, magnetic properties, and half-metallicity in Hf2CoZ (Z = B,C, Al, Si, Ga, Ge, In, Sn, Tl, and Pb) alloys with AlCu2Mn- and CuHg2Ti-type structures. The AlCu2Mn-type structure is energetically favorable than the CuHg2Ti-type structure for all compounds. Hf2CoGa, Hf2CoAl, Hf2CoIn, Hf2CoTl, and Hf2CoSn compounds in the CuHg2Ti-type structure were half-metallic ferromagnets. The d-d and covalent hybridizations between transition metals Hf and Co were effective in the formation of minority band gap. The total magnetic moments of half-metallic Hf2CoZ (Z = Al, Ga, In, Sn, and Tl) compounds in the CuHg2Ti-type structure obeyed the Slater–Pauling rule (M tot = Z tot − 18). Hf2CoIn and Hf2CoTl compounds were half-metals in relatively wide ranges of lattice constants which indicates that they can be promising and interesting candidates for spintronic devices.

Tight binding calculation of tunneling conductance of a metal/ferromagnetic junction

A tight binding approximation was used to describe the electronic properties of a metal/ ferromagnetic junction in a one-dimensional system. The appropriate boundary conditions were calculated to describe the quality of the interface, the non-spin-flip and spin-flip scattering potential. The BTK model was used to compute the reflection and transmission probabilities, and the Landauer formulation was used to calculate the conductance spectrum. It was found that the conductance spectrum changes slope at the bias voltage that reached the bottom of the minority band and the top of the majority band of the ferromagnetic. The conductance spectrum was suppressed for all energies when either the non-spin-flip or spin-flip scattering at the interface increased. However, the conductance spectrum can be enhanced when the interface was taken into account for the appropriate value of the spin-flip and non-spin-flip scattering. In addition, the conductance can be increased by increasing the next-nearest neighbor hopping energy in the ferromagnetic material.

Interplay of phase sequence and electronic structure in the modulated martensites of Mn2NiGa from first-principles calculations

We investigate relative stability, structural properties and electronic structure of various modulated martensites of the magnetic shape memory alloy Mn$_{2}$NiGa by means of density functional theory. We observe that the instability in the high-temperature cubic structure first drives the system to a structure where modulation shuffles with a period of six atomic planes are taken into account. The driving mechanism for this instability is found to be the nesting of the minority band Fermi surface, in a similar way as established for the prototype system Ni$_{2}$MnGa. In agreement with experiments, we find 14M modulated structures with orthorhombic and monoclinic symmetries having energies lower than other modulated phases with same symmetry. In addition, we also find energetically favourable 10M modulated structures which have not been observed experimentally for this system yet. The relative stability of various martensites is explained in terms of changes in the electronic structures near the Fermi level, affected mostly by the hybridisation of Ni and Mn states. Our results indicate that the maximum achievable magnetic field-induced strain in Mn$_{2}$NiGa would be larger than in Ni$_{2}$MnGa. However, the energy costs for creating nanoscale adaptive twin boundaries are found to be one order of magnitude higher than that in Ni$_{2}$MnGa.

Combustion synthesis and characterization of blue long lasting phosphor CaAl2O4: Eu2+, Dy3+ and its novel application in latent fingerprint and lip mark detection

This work investigates the structural, optical and photometric characterization of a Eu2+/Dy3+ doped calcium aluminates phosphor (CaAl2O4: Eu2+/Dy3+) for finger and lip print detections. Synthesis of CaAl2O4: Eu2+/Dy3+ (CAED) phosphors were carried out via a combustion synthesis method with urea as a fuel. Eu2+/Dy3+ doped CaAl2O4 phosphors have been studied with X-ray diffraction (XRD, Energy Dispersive X-Ray Spectroscopy Selected Area Diffraction (SAED) and High resolution Transmission Electron Microscope (HR-TEM). The XRD pattern shows that the synthesized Eu2+/Dy3+ doped CaAl2O4 phosphor have a single monoclinic structure and show that the addition of the dopant/co-dopants didn’t change the crystal structure. The formation of monoclinic phase was confirmed by the selected area diffraction pattern. The TEM micrograph displays the morphology of the synthesized Eu2+/Dy3+ doped CaAl2O4 phosphors as spherical particles with an average particle size of 33nm. The optical band gap was calculated using the diffuse reflectance for the synthesized nanophosphor powders. The photoluminescence emission spectra was recorded for the synthesized powder, with an excitation wavelength of 326nm and the major bands was recorded at 447nm corresponding to the blue color and two minor bands were recorded at 577nm and 616nm. To the best of our knowledge, this work is the first to show the use of CaAl2O4: Eu2+/Dy3+ nanophosphor in developing latent fingerprint and lip print effectively.

An Alternative Pathway of Light-Induced Transmembrane Electron Transfer in Photosynthetic Reaction Centers of Rhodobacter sphaeroides.

In the absorption spectrum of Rhodobacter sphaeroides reaction centers, a minor absorption band was found with a maximum at 1053nm. The amplitude of this band is ~10,000 times less and its half-width is comparable to that of the long-wavelength absorption band of the primary electron donor P870. When the primary electron donor is excited by femtosecond light pulses at 870nm, the absorption band at 1053nm is increased manifold during the earliest stages of charge separation. The growth of this absorption band in difference absorption spectra precedes the appearance of stimulated emission at 935nm and the appearance of the absorption band of anion-radical BA- at 1020nm, reported earlier by several researchers. When reaction centers are illuminated with 1064nm light, the absorption spectrum undergoes changes indicating reduction of the primary electron acceptor QA, with the primary electron donor P870 remaining neutral. These photoinduced absorption changes reflect the formation of the long-lived radical state PBAHAQA-.

X-ray Photoelectron Spectroscopic and Raman microscopic investigation of the variscite group minerals: Variscite, strengite, scorodite and mansfieldite

Several structurally related AsO4 and PO4 minerals, were studied with Raman microscopy and X-ray Photoelectron Spectroscopy (XPS). XPS revealed only Fe, As and O for scorodite. The Fe 2p, As 3d, and O 1s indicated one position for Fe2+, while 2 different environments for O and As were observed. The O 1s at 530.3eV and the As 3d 5/2 at 43.7eV belonged to AsO4, while minor bands for O 1s at 531.3eV and As 3d 5/2 at 44.8eV were due to AsO4 groups exposed on the surface possibly forming OH-groups. Mansfieldite showed, besides Al, As and O, a trace of Co. The PO4 equivalent of mansfieldite is variscite. The change in crystal structure replacing As with P resulted in an increase in the binding energy (BE) of the Al 2p by 2.9eV. The substitution of Fe3+ for Al3+ in the structure of strengite resulted in a Fe 2p at 710.8eV. An increase in the Fe 2p BE of 4.8eV was found between mansfieldite and strengite. The scorodite Raman OH-stretching region showed a sharp band at 3513cm−1 and a broad band around 3082cm−1. The spectrum of mansfieldite was like that of scorodite with a sharp band at 3536cm−1 and broader maxima at 3100cm−1 and 2888cm−1. Substituting Al in the arsenate structure instead of Fe resulted in a shift of the metal-OH-stretching mode by 23cm−1 towards higher wavenumbers due to a slightly longer H-bonding in mansfieldite compared to scorodite. The intense band for scorodite at 805cm−1 was ascribed to the symmetric stretching mode of the AsO4. The medium intensity bands at 890, 869, and 830cm−1 were ascribed to the internal modes. A significant shift towards higher wavenumbers was observed for mansfieldite. The strengite Raman spectrum in the 900–1150cm−1 shows a strong band at 981cm−1 accompanied by a series of less intense bands. The 981cm−1 band was assigned to the PO4 symmetric stretching mode, while the weak band at 1116cm−1 was the corresponding antisymmetric stretching mode. The remaining bands at 1009, 1023 and 1035cm−1 were assigned to υ1(A1) internal modes in analogy to the interpretation of the AsO4 bands for scorodite and mansfieldite. The variscite spectrum showed a shift towards higher wavenumbers in comparison to the strengite spectrum with the strongest band observed at 1030cm−1 and was assigned to the symmetric stretching mode of the PO4, while the corresponding antisymmetric stretching mode was observed at 1080cm−1. Due to the band splitting component bands were observed at 1059, 1046, 1013 and 940cm−1. The AsO4 symmetric bending modes for scorodite were observed at 381 and 337cm−1, while corresponding antisymmetric bending modes occurred at 424, 449 and 484cm−1. Comparison with other arsenate and phosphate minerals showed that both XPS and Raman spectroscopy are fast and non-destructive techniques to identify these minerals based on their differences in chemistry and the arsenate/phosphate vibrational modes due to changes in the symmetry and the unique fingerprint region of the lattice modes.

Optical absorption, Mössbauer, and FTIR spectroscopic studies of two blue bazzites

Two samples of bazzite, a very rare Sc analog of beryl, from Tordal, Telemark, Norway and Kent, Central Kazakhstan were studied by electron microprobe, optical absorption, and Mossbauer spectroscopies; the latter sample was also studied by FTIR. Electron microprobe results show that the Norway bazzite is composed of two bazzites with slightly different FeO contents, viz. 5.66 and 5.43 wt%. The Kazakhstan sample consists of several varieties of bazzite displaying strong differences in iron, manganese, magnesium, and aluminum contents (in wt%): FeO from 2.02 to 6.73, MnO from 0.89 to 2.98, MgO from 0.37 to 1.86, and Al2O3 from 0.30 to 1.30. Mossbauer spectroscopy shows different degrees of iron oxidation. The Norway bazzite is completely Fe2+, while the Kazakhstan sample contains roughly equivalent Fe3+ and Fe2+ accommodated in the octahedral site. The difference in iron oxidation causes strong variations in the intensity of the broad optical absorption band around 13,850 cm−1, which is assigned to Fe2+ → Fe3+ IVCT; as a result, there are strong differences in the intensity of blue color. Dichroism (E||c ≫ E⊥c) is much stronger in the Kazakhstan sample than in the Norway one. Intensities of the electronic spin-allowed bands of [6]Fe2+ at ~8900 and ~10,400 cm−1 are somewhat higher in the latter than in the former. FTIR spectra of the sample from Kent show the presence of only water type II molecules with the H–H vector perpendicular to the c-axis, in contrast to more typical beryls that always show at least weak minor bands of H2O I. This result shows that trapped water molecules in structural channels of studied bazzite occupy only sites next to or between six-membered rings centered by Na atoms. Definite structure can be observed in the vicinities of ν2 and ν3 peaks. Peaks at 1621 and 3663 cm−1 are assigned to “doubly coordinated” H2O (IId), whereas maximums at 1633 and 3643 cm−1 likely represent “singly coordinated” H2O (IIs). Interpretation of the third components in complex ν2 and ν3 bands needs further investigations.

GENETIC VARIATION OF MAIZE GENOTYPES (ZEA MAYS L.) DETECTED USING SDS-PAGE

The assessment of genetic diversity among the members of a species is of vital importance for successful breeding and adaptability. In the present study 20 old genotypes of maize from Hungary, Union of Soviet Socialist Republics, Poland, Czechoslovakia and Slovak Republic were evaluated for the total seed storage proteins using sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) through vertical slab unit. The number of total scorable protein bands was twentythree as a result of SDS-PAGE technique but those that were not cosistent in reproducibility and showed occasional variation in sharpness and density were not considered. Out of twentythree polypeptide bands, 6 (31%) were commonly present in all accessions and considered as monomorphic, while 17 (65%) showed variations and considered as polymorphic. On the basis of banding profiles of proteins of different kDa, gel was divided into zones A, B and C. The major protein bands were lied in zones A and B, while minor bands were present in zones C. In zone A out of 10 protein bands, 1 were monomorphic and 9 were polymorphic. In zone B out of 8 protein bands, 3 was monomorphic and 5 was polymorphic and in zone C out of 5 protein bands, 2 were monomorphic whereas 3 polymorphic. The dendrogram tree demonstrated the relationship among the forty registered old maize genotypes according to the similarity index, using UPGMA cluster analysis. The dendrogram was divided into three main clusters. The first cluster contained Czechoslovakia genotype Mikulická and the second cluster contained Czechoslovakia genotypes Celchovicka ADQ. Cluster 3 was divided into 3 subclasters. Similarly the present study of genetic variability in the seed storage polypeptide determined by SDS-PAGE technique proved that it is fruitful to identify genetic diversity among accessions of maize.

A Simple Method to Study Host-Pathogen Interaction in Sesamum Indicum

Differential activation of early defense responses like increased activity of phenylalanine ammonia-lyase (PAL), peroxidases (PO), and pathogenesis proteins (PR proteins) predisposes the host plant resistance against pathogens. Therefore, in the present study interaction between this defenses related compounds and pathogen (Macrophomina phaseolina) was used as new strategy to enhance sesamum defense responses against root rot disease. There was a marked increase in these biochemical compounds in pathogen treated sesamum plants after pathogen attack. The investigation was carried after infection, which shows increase in activities of all defense related proteins to varying degrees of infection. Interestingly, there are significant changes in cytoplasmic proteins under pathogen inoculation. In the control plants, 8 major bands and 3 minor bands are obtained. In contrast, in the inoculated plants 8 major and 4 minor bands are obtained, which however, are of different Rf- values than the control plants. The differences in the protein are more pronounced in the molecular mass range of 15 to 36 kda and 40 to 59 kda. Individual protein bands obtained through SDS-PAGE were further quantified by scion image programme. This programme gives the peak area values of the corresponding band. The peak area denotes the densities of protein bands on the gel. A comparison of the densities of the protein bands in control and inoculated plants amply demonstrated that exposure to pathogen not only results in higher protein amounts but synthesis of a few new proteins, possibly PR-proteins. The biochemical approach described in this paper should provide the basis for further efforts concentrating on genetic regulation of sesamum in the form of transcript accumulation for expression of disease resistance proteins.

Deprotonation of Fe-dominant amphiboles: Single-crystal HT-FTIR spectroscopic studies of synthetic potassic-ferro-richterite

High-temperature Fourier transform infrared (HT-FTIR) spectroscopy was used to characterize the deprotonation process of synthetic potassic-ferro-richterite of composition A ( K 0 . 90 Na 0 . 07 ) B ( Ca 0 . 54 Na 1 . 46 ) C ( Fe 4 . 22 2 + Fe 0 . 78 3 + ) T Si 8 O 22 W ( OH 1 . 70 O 0 . 30 2 − ) . Unpolarized single-crystal spectra were collected both in situ and on quenched samples, and heating experiments were conducted in air, at a rate of 10 °C/min. The room- T spectrum measured before annealing shows a main band at 3678 cm −1 and a minor band at 3622 cm −1 ; these are assigned to local configurations involving Fe 2+ at M (1) M (1) M (3) and facing a filled and an empty alkali-site, respectively. At 400 °C, a new band grows at 3656 cm −1 ; this is the most intense feature in the pattern at 450 °C. At T ≥ 500 °C, all peaks decrease drastically in intensity, and finally disappear at T > 600 °C. The total absorbance measured in situ increases significantly in the 25 T T range. This feature is consistent with an increase of the absorption coefficient (e) with T , the reason for which is still unclear. However, this feature has significant implications for the quantitative use of FTIR data in HT experiments. Examination of the relevant OH-stretching bands shows that iron oxidation occurs preferentially at the M (1,3) sites associated with occupied A sites. The deprotonation temperature indicated by FTIR for single-crystals is around 100 °C higher that that obtained by HT-X-ray diffraction (XRD) on single crystal by Oberti et al. (2016), whereas that obtained by HT-XRD on powders is intermediate. This unexpected observation can be explained by considering that: (1) the iron oxidation process, which is coupled to deprotonation and is probed by XRD, occurs preferentially at the crystal surface where it is triggered by the availability of atmospheric oxygen; (2) the proton diffusion, probed by FTIR, is slower that the electron diffusion probed by XRD; thus, the temperature shift may be explained by a much longer escape path for H in single-crystals than in powders. These results suggest that possible effects due to crystals size should be carefully considered in HT experiments done on Fe-rich silicates.

Influence of Species, Geographic Location, Seasonal Variation and Extraction Method on the Fucoidan Yield of the Brown Seaweeds of Gulf of Mannar, India

Brown seaweeds such as Sargassum wightii, S. oligocystum, Padina tetrastromatica and Turbinaria ornata were collected from two locations, Valinokkam and Hare Island in Gulf of Mannar, South East coast of India, to extract fucoidan and to analyze its variation in the yield for a period from July 2012 to January 2013. Water and acid extraction methods were followed to extract fucoidan. Water extraction yielded much higher fucoidan (9.46±0.18) than acid method (1.63±0.05). The yield of fucoidan also varied between the species, season and also geographic location. The highest yield was obtained from P. tetrastromatica (9.46±0.18%) followed by T. ornata (5.83±0.07%) and S. wightii (3.90±0.05%). The yield was higher during maturation stage of the algae, which was September for T. ornata and S. wightii and January for P. tetrastromatica. Seaweeds found in shallow region gave higher yield (Hare Island) than those collected from more than 1 m depth in Valinokkam region. Compositional analysis of fucoidan revealed that sulphate content was higher in T. ornata (24.27±0.85%) than P. tetrastromatica (22.70±0.53%) and S. wightii (18.73±0.82%). The fucose content was higher in P. tetrastromatica (54.51±1.08) and lower in S. oligocystum(43.16±3.21). Fourier transform infrared spectroscopy carried out for the two dominant species viz. P. tetrastromatica and S. oligocystum, showed a major broad band centered around 3448 cm-1 assigned to be due to hydrogen bonded O-H stretching vibration. Another two bands appeared at 723 cm-1 and 601 cm-1 seem to be the characteristic of C-O-S stretching of sulfate group and C=C-H stretching vibration, respectively in both the species. However, the major differences among the species were the presence of a minor band at 2103.73 cm-1 in P. tetrastromatica and slight shifts noticed in sulphate group band.

Half-metallicity and magnetism of the full-Heusler compounds KYX 2 (Y=Ti, V, and Cr; X=C, N, and O)

Abstract The electronic structure and half-metallic (HM) properties of new alloys KYX2 (Y=Ti, V, and Cr; X=C, N, and O) containing transition metals and sp elements were investigated within the density functional theory (DFT) using the self-consistent full-potential linearized augmented plane wave (FPLAPW) method. It was found that these new compounds can be experimentally synthesized because of their negative formation energies. The total energy calculations showed that in all compounds, the stable state structure was a ferromagnetic AlCu2Mn-type structure except for KTiC2 and KTiN2 which were stable in a nonmagnetic (NM) AlCu2Mn-type structure. The KTiO2 in both structures, KCrO2 in AlCu2Mn-type structure, and KVO2 in CuHg2Ti-type structure were half-metallic ferromagnets. KVO2 in AlCu2Mn-type structure was a special case with a ferromagnetic semiconducting behavior. The origin of minority band gaps for KTiO2 in both structures was also studied using the band structure calculations. The total magnetic moments of HM compounds were integer values which were in agreement with Slater-Pauling rule (Mtot=Ztot−12). Furthermore, the regions of half-metallictiy in HM compounds were considerably wider than those of Heusler compounds including transition metals, indicating the high robustness of half-metallicity with variation of lattice constants.

The effect of pressure and alloying on half-metallicity of quaternary Heusler compounds CoMnYZ (Z = Al, Ga, and In)

AbstractIn this work, first-principles calculations of the structural, electronic and magnetic properties of Heusler alloys CoMnYAl, CoMnYGa and CoMnYIn are presented. The full potential linearized augmented plane waves (FP-LAPW) method based on the density functional theory (DFT) has been applied. The structural results showed that CoMnYZ (Z = Al, Ga, In) compounds in the stable structure of type 1+FM were true half-metallic (HM) ferromagnets. The minority (half-metallic) band gaps were found to be 0.51 (0.158), 0.59 (0.294), and 0.54 (0.195) eV for Z = Al, Ga, and In, respectively. The characteristics of energy bands and origin of minority band gaps were also studied. In addition, the effect of volumetric and tetragonal strain on HM character was studied. We also investigated the structural, electronic and magnetic properties of the doped Heusler alloys CoMnYGa1−xAlx, CoMnYAl1−xInxand CoMnYGa1−xInx(x = 0, 0.25, 0.5, 0.75, 1). The composition dependence of the lattice parameters obeys Vegard’s law. All alloy compositions exhibit HM ferromagnetic behavior with a high Curie temperature (TC).