Lattice Parameter A0 Research Articles

Characterization of Co-bearing pyrite from the SEDEX Tuolugou Co(Au) deposit, northern Qinghai-Tibet Plateau, China

The Tuolugou sedimentary-exhalative (SEDEX) Co-Au deposit is located in the eastern Kunlun metallogenic belt of the northern Qinghai-Tibet Plateau in China. Pyrite is the prevalent Co-hosting sulfide mineral that occurs in the Tuolugou deposit. In this study, we investigated mineral characteristics of Co-bearing pyrite and effect of Co on crystal structure of the pyrite to obtain a better understanding of Co mineralization. Three pyrite generations were identified, including Co-barren pyrite (Py-1, formed during the early mineralization stage I, with Co content of 1-3844 ppm), Co-rich pyrite (Py-2, formed during the sedimentary-exhalative stage II, Co content 15–36522 ppm), and Co-rich pyrite (Py-3, formed during metamorphic stage III, with Co contents of 448–10505 ppm in Py-3A, and 1371–14904 ppm in Py-3B). As Co enters the pyrite structure, it is discovered that the octahedrons in pyrite is twisted and tilted, the lattice parameters (a0) rise, and the sulfur atom positions alter. The Co-rich Py-2 shows a similar REE and trace element distribution as those in quartz albitite, which indicates that Co mineralization is related to SEDEX genesis. Subsequent metamorphism resulted in additional Co enrichment. This detailed study of Co-bearing pyrite provides insights on the details of isomorphism Co in pyrite similar to the situation of this deposit as medium–low Co grade.

First-principles investigation of structural, electronic, optical, and magnetic properties of a scintillating double perovskite halides (Cs[formula omitted]LiCeX[formula omitted]) with (X = F, Br, and I)

In this study, several physical properties (structural, electronic, magnetic, and optical) of a scintillating double perovskite halide Cs2LiCeX6 (X = F, Br, and I) are investigated using the density functional theory (DFT) within the Wien2k code. The optimized lattice parameter (a0) of Cs2LiCeBr6 agrees perfectly with the experimental results. The optimized ground state energy appears to confirm the cubic stability. The band structure and densities of states are explored using PBE-GGA coupled with Tb-mBJ approximation. In the spin-up channel, the compound Cs2LiCeX6 (X = F, Br, and I) has a Fermi level occupied, with a band gap of 1.966eV, 1.350eV, and 1.184eV, respectively. While in the spin-down channel, the double perovskite halide Cs2LiCeBr6 and Cs2LiCeI6 behave like a semiconductor, with a band gap of 3.293eV and 2.418eV, respectively. The asymmetric density of states in both spin channels and the optimized energy volume curve in spin-polarized calculation assert to the ferromagnetic nature. The optical properties are calculated, and it is revealed that Cs2LiCeBr6 and Cs2LiCeI6 has a high optical conductivity than Cs2LiCeF6. The absorption in the ultraviolet and gamma frequency range, along with the emittance in the visible light unlocks the door for various applications, like medical imaging, radiation detection and particle detection.

Computational study of structural, thermoelectric, elastic and optoelectronic properties of new halide perovskites CsRbTeX6 (X = I, Br and Cl) for solar cell applications

Recently the lead-free halide perovskites materials have attracted considerable attention due to their nontoxic nature and outstanding performances. In this work, using density-functional theory (DFT), the structural, thermoelectric, elastic and optoelectronic properties of new series perovskites CsRbTeX6 (X= I, Br, and Cl) have been investigated. The Goldschmidt tolerance factor (τ) and octahedral factors (μ) results show a high structural stability. The computed bond length Te-X and lattice parameter a0 decrease progressively when the size of the X Halide atoms increases. The elastic constants and their derived parameters reveal a brittle behavior, high mechanical stability and anisotropy nature of these materials. The low values of the bulk modulus in the three structures indicate that they are relatively soft materials and that they are amenable to being converted into thin films, which is essential for solar cell applications. The computed values of Tm are 582.49K, 579.36 K and 578.71 K for CsRbTeI6, CsRbTeCl6 and CsRbTeBr6, respectively. Because of their high melting temperature, these materials are more appropriate for high temperature applications. The band structure profile exhibits a semiconductor behavior with indirect band gap of about 2.81 eV, 2.2 eV and 1.51 eV for CsRbTeCl6, CsRbTeBr6 and CsRbTel6 respectively. With such tunable band gaps, the optical performance of these materials has been examined. The results show a very high light absorption in the order of 106 cm−1, a high power conversion efficiency (ƞ) and a low reflectivity in the order 20% in the visible and UV region. Finally, the transport properties reveal a sufficient figure of merit and a high Seebeck coefficient. According to these results, we suggest that the studied perovskites exhibit outstanding performance for thermoelectric and optoelectronic applications.

Valence electron concentration- and N vacancy-induced elasticity in cubic early transition metal nitrides

Motivated by frequently reported deviations from stoichiometry in cubic transition metal nitride (TMNx) thin films, the effect of N-vacancy concentration on the elastic properties of cubic TiNx, ZrNx, VNx, NbNx, and MoNx (0.72≤x≤1.00) is systematically studied by density functional theory (DFT) calculations. The predictions are validated experimentally for VNx (0.77≤x≤0.97). The DFT results indicate that the elastic behavior of the TMNx depends on both the N-vacancy concentration and the valence electron concentration (VEC) of the transition metal: While TiNx and ZrNx exhibit vacancy-induced reductions in elastic modulus, VNx and NbNx show an increase. These trends can be rationalized by considering vacancy-induced changes in elastic anisotropy and bonding. While introduction of N-vacancies in TiNx results in a significant reduction of elastic modulus along all directions and a lower average bond strength of Ti–N, the vacancy-induced reduction in [001] direction of VNx is overcompensated by the higher stiffness along [011] and [111] directions, resulting in a higher average bond strength of V–N. To validate the predicted vacancy-induced changes in elasticity experimentally, close-to-single-crystal VNx (0.77≤x≤0.97) are grown on MgO(001) substrates. As the N-content is reduced, the relaxed lattice parameter a0, as probed by X-ray diffraction, decreases from 4.128 Å to 4.096 Å. This reduction in lattice parameter is accompanied by an anomalous 11% increase in elastic modulus, as determined by nanoindentation. As the experimental data agree with the predictions, the elasticity enhancement in VNx upon N-vacancy formation can be understood based on the concomitant changes in elastic anisotropy and bonding.

Energy-dispersive X-ray stress analysis under geometric constraints: exploiting the material's inherent anisotropy.

Two data evaluation concepts for X-ray stress analysis based on energy-dispersive diffraction on polycrystalline materials with cubic crystal structure, almost random crystallographic texture and strong single-crystal elastic anisotropy are subjected to comparative assessment. The aim is the study of the residual stress state in hard-to-reach measurement points, for which the sin2ψ method is not applicable due to beam shadowing at larger sample tilting. This makes the approaches attractive for stress analysis in engineering parts with complex shapes, for example. Both approaches are based on the assumption of a biaxial stress state within the irradiated sample volume. They exploit in different ways the elastic anisotropy of individual crystallites acting at the microscopic scale and the anisotropy imposed on the material by the near-surface stress state at the macroscopic scale. They therefore complement each other, in terms of both their preconditions and their results. The first approach is based on the evaluation of strain differences, which makes it less sensitive to variations in the strain-free lattice parameter a 0. Since it assumes a homogeneous stress state within the irradiated sample volume, it provides an average value of the in-plane stresses. The second approach exploits the sensitivity of the lattice strain to changes in a 0. Consequently, it assumes a homogeneous chemical composition but provides a stress profile within the information depth. Experimental examples from different fields in materials science, namely shot peening of austenitic steel and in situ stress analysis during welding, are presented to demonstrate the suitability of the proposed methods.

Insight into the Structural, Electronic, Elastic, Optical, and Magnetic Properties of Cubic Fluoroperovskites ABF3 (A = Tl, B = Nb, V) Compounds: Probed by DFT.

This work displays the structural, electronic, elastic, optical, and magnetic properties in spin-polarized configurations for cubic fluoroperovskite (A = Tl, B = Nb, V) compounds studied by density functional theory (DFT) by means of the Tran-Blaha-modified Becke-Johnson (TB-mBJ) approach. The ground state characteristics of these compounds, i.e., the lattice parameters , bulk modulus (B), and its pressure derivative are investigated. The structural properties depict that the selected compounds retain a cubic crystalline structure and have stable ground state energy. Electronic-band structures and DOS (density of states) in spin-polarized cases are studied which reports the semiconducting nature of both materials. The TDOS (total density of states) and PDOS (partial density of states) studies in both spin configurations show that the maximum contributions of states to the different bands is due to the B-site (p-states) atoms as well as F (p-states) atoms. Elastic properties including anisotropy factor (A), elastic constants, i.e., C11, C12, and C44, Poisson’s ratio (υ), shear modulus and (G), Young’s modulus (E) are computed. In terms of elastic properties, the higher (bulk modulus) “B” and ratio of “B/G” yield that these materials exhibit a ductile character. Magnetic properties indicate that both the compounds are ferromagnetic. In addition, investigations of the optical spectra including the real () and imaginary () component of the dielectric function, refractive index , optical reflectivity , optical conductivity , absorption coefficient , energy loss function , and electron extinction coefficient are carried out which shows the transparent nature of and . Based on the reported research work on these selected materials, their applications can be predicted in many modern electronic gadgets.

Thermoelectric and optoelectronic properties of novel lead-free halide perovskites CsRbTiX6 (X= I, Br and Cl) for photovoltaic applications

Motivated by the physical properties of halide perovskites. The density functional theory was used to investigate the structural stability, elastic, electronic, optical and thermoelectric properties of new perovskites CsRbTiX6 (X = I, Br and Cl). The obtained results from the ground state show that the calculated lattice parameter a0 and Ti-X bond length decrease progressively when X goes from I to Cl. The elastic constants and their derived parameters like Young's modulus, shear modulus, Poisson's ratio and the anisotropic factor show high mechanical stability, brittle behavior and elastic anisotropy nature. The electronic profile shows a semiconducting nature with an indirect band gap and the values of the band gap decrease when X goes from Cl to Br and then to I. Thermoelectric properties are reported and found to increase with temperature, which also demonstrates the semiconducting nature with electrons as the majority carriers. The optical parameters reveal high light absorption and low reflectivity, particularly in the visible light range. The mechanical stability, strong absorption and low reflectivity in the visible and ultra-violet regions make these materials more suitable for optoelectronic applications.

Effect of alumina content on the crystal structure, lattice thermal expansion and thermal conductivity of aluminium-rich spinel solid solutions

Magnesium alumina spinel solid solutions with different chemical compositions were synthesized and their crystal structures were refined using the Rietveld method based on synchrotron radiation X-ray diffraction (XRD). A linear relationship between the lattice parameters a0 and x in Mg1-xAl2+2/3x□1/3xO4 was established, the thermal stability and lattice thermal expansion of the solid solutions by in-situ high temperature XRD were investigated. Alumina was eliminated from the high-solubility alumina-rich spinel solid solution to form corundum and a lower-solubility alumina-rich spinel solid solution. The relationship between a0 and temperature is expressed by a quadratic polynomial. The thermal conductivity of Mg1-xAl2+2/3x□1/3xO4 decreased almost linearly with an increase in x, which is attributed to the stronger point-defect scattering effect induced by the difference in atomic mass and cation radii and the increase in cation vacancies as alumina dissolves in spinel.

First-principles calculations to investigate structural, electronic, thermoelectric, and optical properties of heavy thallium perovskite TlPbX3 (X = Cl, Br, I)

By dint of the Full potential linearized augmented plane wave (FP-LAPW) method employed in density functional theory (DFT) technique, the mechanical stability, electronic behaviour, optical response, and thermoelectric behaviour of Thallium based halide perovskites TlPbX3 (X = Cl, Br, I) have been theoretically investigated for the first time. The energy volume optimization curves, formation energy, and cohesive energy also confirm these perovskites' structural stability. The calculated value of lattice parameter a0 agrees well with available results. The electronic band structure plots, as well as density of states plots of these compounds, reveal their semiconducting nature using Tran Blaha modified Becke Johnson approximation- generalized gradient approximations (TB-mBJ-GGA) and (PBE-GGA) Perdew–Burke-Ernzerhof- generalized gradient approximation with wide band gaps for TlPbCl3 and TlPbBr3. The nature of chemical bonding in these compounds is discussed by the electron density plots. The optical constants such as the dielectric functions, refractive index, extinction coefficient, optical reflectivity, absorption coefficient, and transmittance are also calculated and discussed in detail. Furthermore, we examined the elastic and mechanical properties which ensure the mechanical stability of TlPbX3 (Cl, Br, I) respectively. The chemical potential, carrier concentration and, the temperature dependence of Seebeck coefficient, electrical conductivity, electrical, thermal conductivity, power factor, and figure of merit are investigated in detail using BoltzTrap code. Together these results lead an outlook on the future progress of thermoelectric halide perovskites to accentuate the augmentation of electronic performance, such as changing carrier concentration chemical potential optoelectronic devices and renewable energy harvesting technologies.

Understanding Stability of FeTiVNi and CoFeVNi High Entropy Alloys Using Density Functional Theory

The research based on High Entropy Alloys (HEAs) has increased significantly due to the fact that HEAs contain numerous primary elements, allowing for a much greater variety of their compositions than conventional alloys. We have investigated two HEAs namely, FeTiVNi and CoFeVNi for their structural and electronic properties that include total energy minimization, equilibrium lattice parameter a0, Density of States (DOS), partial Density of States (pDOS) and band structure of the systems. To predict the stable phase of the alloys, we have calculated atomic size difference (δ) and Valence Electron Concentration (VEC) parameters empirically. The results from empirically calculated parameters and the total energy minimization agrees that stable phase for FeTiVNi HEA is body centered cubic (bcc) and for CoFeVNi is face centered cubic (fcc). The findings show that these HEAs have metallic phases with overlapping bands near fermi region.

The Rigidity of the (BH4)-Anion Dispersed in Halides AX, A = Na, K; X = Cl, Br, I, and in MBH4 with M = Na, K, Rb, Cs

The B–H bond length of the borohydride anion (BH4−) in alkali metal borohydrides MBH4 with M = Na, K, Rb, Cs, and diluted in different alkali halide matrices, was investigated experimentally by infrared spectroscopy (FTIR) and theoretically using first principles calculations. The peak positions in IR absorption spectra of NaBH4 pressed at 754 MPa in halides NaX and KX with X = Cl, Br, I show significant variations indicating ion exchange effects between the halide and NaBH4. For NaBH4 in NaBr, NaI, KBr and KI pellets, the peak positions indicate that BH4− could be highly diluted in the AX matrix, which renders an isolation of BH4− in AX (i-BH4−). For NaBH4 in NaCl and KCl pellets, a solution of BH4− in AX occurred only after a further thermal treatment up to 450 °C. The observed peak positions are discussed with respect to the lattice parameter (a0), anion to cation ratio (R = rA/rX), standard enthalpy of formation (ΔfH) and ionic character (Ic) of the halides. A linear relation is obtained between ν3(i-BH4−) and the short-range lattice energies of AX. Density functional theory (DFT) calculations at generalized gradient approximation (GGA) level were used to calculate the IR vibrational frequencies ν4, ν3 and ν2 + ν4 for series of compositions Na(BH4)0.25X0.75 with X = Cl, Br, I, and MBH4. The theoretical and experimental results show the same trends, indicating the rigidity of the B–H bond length and the failure of Badger’s rule.

Structural and optoelectronic properties of CsSnBr3 metal halide perovskite as promising materials toward novel-generation optoelectronics

In this study, first-principles density functional theory (DFT) calculations of the structural and optoelectronic properties of Sn-based inorganic metal halide perovskite CsSnBr3 are carried out and discussed in details. The Wu-Cohen (WC)-Generalized Gradient Approximation (GGA) based on the full-potential linearized augmented plane-wave (FPLAPW) method is used to optimize the geometry structure of unit cell and then find the accurate optoelectronic properties of CsSnBr3. Analysis of structural optimization results revealed that the lattice parameters (𝑎0 = 5.776 Å) and unit cell volume of CsSnBr3 are exactly consistent with the experiments reports. Based on the results of band structures and density of states, CsSnBr3 is found to be nonmagnetic semiconductor with suitable direct band gap of (Eg = 0.610 eV) along the R symmetry point. In addition, the calculations of optical properties of CsSnBr3, such as the real 𝜀1 (𝜔) and imaginary 𝜀2 (𝜔) parts of the dielectric function, 𝜀(𝜔), absorption coefficient 𝛼(𝜔), reflectivity 𝑅(𝜔) and refractive index 𝑛(𝜔), have been performed in the photonic energy range of (0.0 – 15.0 eV). Finally, the results attained in the present study, which include the stable crystal structure and the high accurate optoelectronic properties such as appropriate direct band gap and high absorption of visible radiation, confirm the possible utilization of CsSnBr3 materials in novel optoelectronics applications as photovoltaic solar cells, photosensors, photodetectors, photodiodes and other related optoelectronics devices

Sample preparation induced phase transitions in solution deposited copper selenide thin films.

Thin films of CuSe were deposited onto GaAs substrate. XRD showed that the as-deposited films were of the Klockmannite (CuSe – P63/mmc 194) phase with lattice parameters a0 = b0 = 0.3939 nm, c0 = 1.7250 nm; however, electron diffraction in the TEM surprisingly indicated the β-Cu2−xSe phase (Cu1.95Se – R3̄m 166) with lattice parameters a0 = b0 = 0.412 nm, c0 = 2.045 nm. The discrepancy originated from the specimen preparation method, where the energy of the focused ion beam resulted in loss of selenium which drives a phase transition to β-Cu2−xSe in this system. The same phase transition was observed also upon thermal treatment in vacuum, as well as when the 200 keV electron beam was focused on a powder sample in the TEM. The initial phase can be controlled to some extent by changing the composition of the reactants in solution, resulting in thin films of the cubic α-Cu2−xSe (Cu1.95Se – Fm3̄m) phase co-existing together with the β-Cu2−xSe phase.

The crystal structure of mineral magadiite, Na2Si14O28(OH)2∙8H2O

Abstract Magadiite from Lake Magadi was structurally analyzed based on X-ray powder diffraction data. The idealized chemical composition of magadiite is Na16[Si112O224(OH)16]∙64H2O per unit cell. The XRD powder diffraction pattern was indexed in orthorhombic symmetry with lattice parameters a0 = 10.5035(9) Å, b0 = 10.0262(9) Å, and c0 = 61.9608(46) Å. The crystal structure was solved from a synthetic magadiite sample in a complex process using 3D electron diffraction combined with model building as presented in an additional paper. A Rietveld refinement of this structure model performed on a magadiite mineral sample in space group F2dd (No. 43) converged to residual values of RBragg = 0.031 and RF = 0.026 confirming the structure model. Physico-chemical characterization using solid-state NMR spectroscopy, SEM, TG-DTA, and DRIFT spectroscopy further confirmed the structure. The structure of magadiite contains two enantiomorphic silicate layers of, so far, unknown topology. The dense layers exhibit no porosity or micro-channels and have a thickness of 11.5 Å (disregarding the van der Waals radii of the terminal O atoms) and possess a silicon Q4 to Q3 ratio of 2.5. 16 out of 32 terminal silanol groups are protonated, and the remaining groups compensate for the charge of the hydrated sodium cations. Bands of edge-sharing [Na(H2O)6/1.5] octahedra are intercalated between the silicate layers extending along (110) and (110). The water molecules are hydrogen bonded to terminal silanol groups with O···O distances of 2.54–2.91 Å. The structure of magadiite is slightly disordered, typical for hydrous layer silicates (HLS), which possess only weak interactions between neighboring layers. In this respect, the result of the structure refinement represents a somewhat idealized structure. Nevertheless, the natural magadiite possesses a higher degree of structural order than any synthetic magadiite sample. The structure analysis also revealed the presence of strong intra-layer hydrogen bonds between the terminal O atoms (silanol/siloxy groups), confirmed by 1H MAS NMR and DRIFT spectroscopy. The surface zone of the silicate layers, as well as the interlayer region containing the [Na(H2O)6/1.5] octahedra, are closely related to the structure of Na-RUB-18.

Epitaxial growth of rhombohedral β- and cubic γ-CuI

Isolated small crystals and closed epitaxial layers of CuI could be deposited on various substrates by close distance sublimation (CDS). X-ray diffraction measurements and detailed TEM studies revealed phase pure cubic γ-CuI (zincblende structure) layers and a combination of a CuI multilayer structure with γ-CuI. The multilayer structure, a 12R polytype with the space group R3m, the lattice parameters a0 = 0.4279 nm, c0 = 4.25 nm, and a twelve layers array consisting of wurtzite-like and zincblende layer sequences in combination with γ-CuI could be detected. The presence of the polytype phase was detected always together with γ-CuI. The epitaxial relationships between the CuI phases and various substrates are discussed. Low temperature (2 K) photoluminescence spectra of phase-pure γ-CuI layers show typical excitonic emission spectra in the range between 3.0 and 3.1 eV. Samples containing both, the 12R polytype and γ-CuI, additionally reveal a predominant series of intense emission lines around 3.25 eV attributed to excitonic emission from the rhombohedral phase.

The crystal structure of synthetic kenyaite, Na2Si20O40(OH)2·8H2O

A synthetic kenyaite sample possessing the chemical composition Na16[Si160O320(OH)16]·64H2O per unit cell was structurally analysed using X-ray powder data. The powder pattern was indexed based on space group symmetry Fdd2 (No. 43) with lattice parameters a0 ​= ​10.080(1) Å, b0 ​= ​79.383(8) Å, c0 ​= ​10.604(1) Å. The crystal structure was solved by model building based on the unit cell parameters, the results of a general characterisation of the material and the comparison with the closely related structures of RUB-6, Na-RUB-18 and magadiite. A Rietveld refinement of this structure model converged to residual values of χ2 ​= ​3.1, RF ​= ​0.020 and RBragg ​= ​0.025, confirming the structure model. Physico-chemical characterisation using solid-state NMR spectroscopy, SEM, TG-DTA, and DRIFT spectroscopy further confirmed the structure. The structure of kenyaite contains thick silicate layers with a thickness of 15.9 ​Å (ignoring the van der Waals radii of the terminal oxygen atoms). The dense layers possess the same topology as the layers of RUB-6, exhibit no porosity and have a silicon Q4 to Q3 ratio of 4.0. 16 out of 32 terminal silanol groups are protonated while 16 siloxy groups (≡Si–O–) compensate the charge of the sodium cations. RUB-6 and kenyaite differ, however, with respect to the cation intercalated and to the stacking arrangement of layers. Bands of edge-sharing [Na(H2O)6/1.5] octahedra are intercalated between the silicate layers extending along [110] and [1¯10]. The equatorial water molecules of the octahedra are hydrogen bonded to terminal silanol groups with O⋯O distances of 2.5 ​Å to 2.6 ​Å. The structure of kenyaite is slightly disordered typical for hydrous layer silicates which possess only weak interactions between neighbouring silicate layers. In this respect, the result of the structure refinement represents a somewhat idealised structure. The structure analysis also revealed the presence of strong intra-layer hydrogen bonds (d(O⋯O) ≈ 2.5 ​Å) between the terminal O atoms (silanol/siloxy groups) confirmed by 1H MAS NMR spectroscopy. The surface zone of the silicate layers as well as the inter-layer region containing the edge-sharing [Na(H2O)6/1.5] octahedra are closely related to the structures of Na-RUB-18 and magadiite.

Synthesis of sulfated zirconium supported MCM-41 composite with high-rate adsorption of methylene blue and excellent heterogeneous catalyst

Zirconia-based mesoporous MCM-41 was successfully prepared then loaded with different content of sulfate (5, 10, 15, 25, 40 and 50 wt.%) through the wet impregnation method. The prepared samples were characterized by numerous methods like N2 adsorption (T= - 196 °C), FT-IR, XRD and TEM images. FTIR spectra of chemically adsorbed pyridine and non-aqueous potentiometric titration were applied to measure the acidity of SO42−/ZrO2@MCM-41 (SZ/MCM-41) catalysts. XRD results showed that the lattice cell parameter (a0) is increased from 37.8 to 39.5 Ǻ with increasing the sulfate content. TEM images of SZ/MCM-41 samples exhibit ordered arrays of mesoporous structure with light and dark contrast and also the formation of nanorods with a diameter of 50 nm. The resulting materials showed a large surface area with a uniform pore diameter distribution. All samples displayed both Lewis and Brønsted acid sites. The catalytic activity of SZ/MCM-41 samples was examined for the preparation of 7-hydroxy-4-methyl coumarin which dramatically enhanced when compared with MCM-41 and Z/MCM-41 and the reaction continued efficiently with a yield of 99.3–89.8 % after reused four times. Furthermore, the adsorption behavior of as-synthesized samples was examined over methylene blue (MB) in the aqueous solution with varying parameters such as dye concentration, pH of the solution and contact time. The prepared samples have a good ability to eliminate the methylene blue from aqueous solution with adsorption capacity equal to 186 mg/g and the equilibrium time of 60 min.

Concepts for nondestructive and depth-resolved X-ray residual stress analysis in the near-surface region of nearly single crystalline materials with mosaic structure.

Two evaluation concepts for nondestructive depth-resolved X-ray residual stress analysis in the near-surface region of materials with cubic symmetry and nearly single crystalline structure are introduced by simulated examples. Both concepts are based on the same data acquisition strategy, which consists in the determination of lattice-spacing depth profiles along the 〈hkl〉 poles by stepwise sample rotation around the scattering vector. Segmentation of these profiles parallel to the sample surface provides the lattice strain state as a function of depth. The first evaluation concept extends the crystallite group method developed for materials with pronounced crystallographic texture by the feature of depth resolution and can be applied to samples with arbitrary orientation. The second evaluation concept, which adapts the linear regression approach of the sin2ψ method for the case of single crystalline materials, is restricted to samples with (001) orientation. The influence of the strain-free lattice parameter a 0 on residual stress analysis using both evaluation concepts is discussed on the basis of explicitly derived relations.

Origin, properties, and structure of breyite: The second most abundant mineral inclusion in super-deep diamonds

AbstractEarth's lower mantle most likely mainly consists of ferropericlase, bridgmanite, and a CaSiO3- phase in the perovskite structure. If separately trapped in diamonds, these phases can be transported to Earth's surface without reacting with the surrounding mantle. Although all inclusions will remain chemically pristine, only ferropericlase will stay in its original crystal structure, whereas in almost all cases bridgmanite and CaSiO3-perovskite will transform to their lower-pressure polymorphs. In the case of perovskite structured CaSiO3, the new structure that is formed is closely related to that of walstromite. This mineral is now approved by the IMA commission on new minerals and named breyite. The crystal structure is triclinic (space group: P1) with lattice parameters a0 = 6.6970(4) Å, b0 = 9.2986(7) Å, c0 = 6.6501(4) Å, α = 83.458(6)°, β = 76.226(6)°, γ = 69.581(7)°, and V = 376.72(4) Å. The major element composition found for the studied breyite is Ca3.01(2)Si2.98(2)O9. Breyite is the second most abundant mineral inclusion after ferropericlase in diamonds of super-deep origin. The occurrence of breyite has been widely presumed to be a strong indication of lower mantle (=670 km depth) or at least lower transition zone (=520 km depth) origin of both the host diamond and the inclusion suite.In this work, we demonstrate through different formation scenarios that the finding of breyite alone in a diamond is not a reliable indicator of the formation depth in the transition zone or in the lower mantle and that accompanying paragenetic phases such as ferropericlase together with MgSiO3 are needed.

Magneto-structural correlations in a systematically disordered B2 lattice

Ferromagnetism in certain B2 ordered alloys such as Fe60Al40 can be switched on, and tuned, via antisite disordering of the atomic arrangement. The disordering is accompanied by a ∼1 % increase in the lattice parameter. Here we performed a systematic disordering of B2 Fe60Al40 thin films, and obtained correlations between the order parameter (S), lattice parameter (a0), and the induced saturation magnetization (Ms). As the lattice is gradually disordered, a critical point occurs at 1 − S = 0.6 and a0 = 2.91 Å, where a sharp increase of the Ms is observed. DFT calculations suggest that below the critical point the system magnetically behaves as it would still be fully ordered, whereas above, it is largely the increase of a0 in the disordered state that determines the Ms. The insights obtained here can be useful for achieving tailored magnetic properties in alloys through disordering.