Octahedral Cations Research Articles

Thermodynamics of Spinel-like Cation Partial Ordering in Ultrahigh Power and Energy Density Li-Ion Batteries for Fast-Charging Electric Vehicles

Recently, a class of new materials exhibiting partial spinel-like cation order, but with excess Li and excess cation content was found to combine very high rate performance with high energy density [1]. Such spinels with a cation to anion ratio higher than 3 are unusual as it requires the face sharing of some tetrahedral and octahedral cations. In this presentation we will report on the ab-initio modeling of the metastable cation arrangements in these lithium manganese oxyfluorides that are responsible for the high-rate performance. The high dimensional configurational space of the materials is described by the cluster-expansion technique and parameterized with multiple hundreds of DFT calculations.Local, atomic-scale features, such as Li-Mn dumbbell formation, antisite defects, and interstitial defects giving rise to face-sharing cations which are challenging to resolve with state-of-the-art diffraction techniques are possible to directly evaluate in our computational approach. We present a computational analysis on how cation excess in spinel-like materials is accommodated and how local cation perturbations ultimately influence short-range order and bulk Li transport. Our understanding of how features in cation-excess spinel-like Li-Mn-O-F materials influence their high rate capabilities may motivate and accelerate design of other high-performance, fast-charging battery materials.[1] Ji, H., Wu, J., Cai, Z. et al. Ultrahigh power and energy density in partially ordered lithium-ion cathode materials. Nat Energy 5, 213–221 (2020).

Bis(diphenylphosphino)methane Dioxide Complexes of Lanthanide Trichlorides: Synthesis, Structures and Spectroscopy

Bis(diphenylphosphino)methane dioxide (dppmO2) forms eight-coordinate cations [M(dppmO2)4]Cl3 (M = La, Ce, Pr, Nd, Sm, Eu, Gd) on reaction in a 4:1 molar ratio with the appropriate LnCl3 in ethanol. Similar reaction in a 3:1 ratio produced seven-coordinate [M(dppmO2)3Cl]Cl2 (M = Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb), whilst LuCl3 alone produced six-coordinate [Lu(dppmO2)2Cl2]Cl. The complexes have been characterised by IR, 1H and 31P{1H}-NMR spectroscopy. X-ray structures show that [M(dppmO2)4]Cl3 (M = Ce, Sm, Gd) contain square antiprismatic cations, whilst [M(dppmO2)3Cl]Cl2 (M = Yb, Dy, Lu) have distorted pentagonal bipyramidal structures with apical Cl. The [Lu(dppmO2)2Cl2]Cl has a cis octahedral cation. The structure of [Yb(dppmO2)3(H2O)]Cl3·dppmO2 is also reported. The change in coordination numbers and geometry along the series is driven by the decreasing lanthanide cation radii, but the chloride counter anions also play a role.

Crystal structure and Raman spectroscopic studies of OH stretching vibrations in Zn-rich fluor-elbaite

Abstract Zinc-rich fluor-elbaite from Piława Górna, Poland, was studied by electron microprobe (EPMA), single-crystal X-ray diffraction (SREF), and Raman spectroscopy (RS) to check the possibility of the application of RS to draw crystal-chemical conclusions for Al-rich and Li-bearing tourmalines on basis of the O–H stretching vibrations in the spectral range 3400–3800 cm–1. This tourmaline, forming a thin metasomatic zone around gahnite, features varying compositions with a ZnO content reaching in the studied fragment of 5.70(12) wt%. The crystal structure of this Zn-rich fluor-elbaite [a = 15.921(1), c = 7.127(1) Å] was refined with a R1 value of 1.67%. Its formula was determined on the basis of electron-microprobe and structure refinement as (Na0.84☐0.14Ca0.01)XΣ1.00(Al1.06Li0.84Zn0.69Fe0.322+Mn0.09)YΣ3.00AlZ6(BO3)3(Si6TO18)(OH)3V(F0.65OH0.26O0.09)W. The deconvolution of the O–H stretching vibration bands, performed by fitting of an input model of component bands with Gaussian function shapes for the empirical spectrum, indicates that each of the three maxima assigned for VOH bonded to YAl3+, Y2+, and YLi+ and with the total integral intensity of at least 75% of the total OH content could be resolved into 1 to 3 bands, depending on the X-site occupation (vacancies, Na+, and Ca2+). The deconvolution indicates further that several low intense bands of WO–H modes above a Raman shift of 3600 cm–1, totally reaching ≤25%, are dependent on the occupation of triplets of YYY cations bonded to the hydroxyl. These WO–H modes are also influenced by the X-site occupation. Due to ordering of all octahedral cations (except Al) at the Y site and a complete occupation of the Z site by Al and the V site by OH, it seems possible to evaluate the Li and OH contents in a Al-rich and Li-bearing tourmaline directly from the Raman spectrum. By using the ratio VOHIYAlZAlZAl/(VOHIYZZ + WOHIYYY) as evaluated from RS, corresponding to the ratio YAl/V+WOH in the crystal, the formula of the Zn-rich fluor-elbaite can be calculated as (Na0.85☐0.14Ca0.01)XΣ1.00(Al1.11Y1.112+Li0.78)YΣ3.00AlZ6(BO3)3(Si6O18)(OH)3(F0.65OH0.13O0.22), where Y 2+ = Zn + Fe + Mn. The formula, determined only on basis of EPMA and deconvolution of RS in the O–H stretching bands, corresponds very well (≤1 SD range of EPMA) to the formula determined on basis of EPMA and SREF. This result implicates that the O–H stretching vibrations, measured by Raman spectroscopy, could be applied for Al-rich and Li-bearing tourmalines as a useful tool for providing additional information for determining the crystal-chemical formula. It is also very helpful when crystal structural data are not available.

Multifunctional character of revived La-modified lithium titanate electrolyte: solar cell devices at a glance

The multi-functional material Li2LaFeTiO6 belonging to double perovskite family is expected to be non-cubic structure and interaction between La and Fe introduce octahedral B-site cation dis-order or anti-site effect. The material is prepared by conventional solid state reaction technique and its formation has been checked through X-ray diffraction (XRD). It is observed that material is orthorhombic crystal structure with Pbnm space group. Scanning electron microscope (SEM) picture of the surface uncovers distinctive shape and sizes of the grains are consistently appropriated all through the surface leaving not many voids. Energy dispersive spectroscopy (EDX) study indicates there is no impurities are seen in the present material. Fourier transform infrared (FTIR) spectroscopy revels the perovskite phase and different modes of vibration. The room temperature UV–Visible spectroscopic analysis reveals material is a potential candidate photovoltaic/solar cell device. The dielectric and electrical measurement is carried out using computer control LCR analyzer. The room temperature dielectric constant and loss tangent of the material is respectively > 400 and < 0.1 which reflects it can be used for multi-layer capacitor and micro-electronics.

Structural and Crystal-Chemical Features and Rb–Sr Age of Globular Glauconite in the Ust-Il’ya Formation (Lower Riphean, Anabar Uplift)

For the first time, mineralogical, structural, crystal-chemical and isotope-geochronological data were obtained for a glauconite sample from the Lower Riphean Ust-Il’ya Formation on the Magan River (western slope of the Anabar Massif, northern Siberia). It has been established that glauconite from the lenticular layer of friable glauconitite (glauconite grains ≥80%) contains two populations of mixed-layer crystals, in which mica layers (93%) alternate with either smectite-type (7%) or vermiculite-type layers (7%) with the short-range order factor R = 3. The ratio KAl = (VIAl / (VIFe3+ + VIAl) equal to 0.45 allows identifying the micaceous mineral as glauconite with the unit-cell parameter b = 9.065 A and K2O content of 8.29%. Comparison of new data with the previously obtained mineralogical and crystal-chemical characteristics of Ust-Il’ya glauconites from the Kotuikan River section (2.5 km above the Il’ya River mouth), located 65 km south of the Magan River section, showed both similarities and differences. Analysis of the crystal-chemical heterogeneity of Kotuikan glauconite samples from rocks of different lithological types revealed peculiarities in the distribution of individual mica varieties composing the glauconite globules. Isotopic dating of glauconite from the Magan River section was performed in combination with simulation of the distribution of octahedral cations and comparison of the results obtained with Mossbauer and infrared (IR) spectroscopy data. Such an approach combined with the mineralogical and crystal-chemical analyses contributes to correct interpretation of the stratigraphic significance of isotope data. The results obtained provide grounds for the conclusion that isotopic dates of glauconite from the Magan section (1474 ± 21 Ma) coincides within the error limit with the earlier Rb–Sr and K–Ar dating of the Ust-Il’ya Formation (1485 ± 13 and 1459 ± 20 Ma, respectively) based on the glauconite in the Kotuikan section (Zaitseva et al., 2016). The former value marks the stage of early diagenesis of sediments and is suitable for estimating the age of this formation.

The evolution of saponite: An experimental study based on crystal chemistry and crystal growth

AbstractElement incorporation and partitioning during the evolution of clay minerals have significant implications for element cycling in geochemical processes. The main aim of this experimental study is to further our understanding of element redistribution and crystal growth during smectite evolution under different physicochemical conditions. The precursors (i.e., pure Mg- and Ni-saponite) were separately prepared by hydrothermal syntheses at the same set of temperatures (i.e., RT, 50, 150, 180, 200, and 220 °C) for one day. Then the starting materials were obtained from the mechanical mixtures of the identical molar weight of Mg- and Ni-smectite precursors prepared at the same temperature. Subsequently, Series I samples were obtained by hydrothermally treating different starting materials at 220 °C for two weeks while Series II samples were hydrothermally synthesized under various temperatures (220, 300, 400, and 500 °C) for one week using the starting materials prepared at 220 °C. Both the precursors and resultant saponites were characterized by XRD, FTIR, TEM, and STEM. The FTIR spectra of the precursors only exhibit the vMg3OH and vNi3OH bands, corresponding to Mg-saponite and Ni-saponite, respectively. However, the occurrence of vMg2NiOH and vNi2MgOH bands in the resultant saponite indicates the dissolution of the corresponding Mg- and Ni-saponite precursors and recrystallization of Mg-Ni mixed saponite. The dissolution extents of Mg- and Ni-saponite precursors, which affect the degrees of random distribution of octahedral Ni and Mg in resultant Mg, Nisaponite, are significantly controlled by the temperature gap (ΔT) between the precursors prepared and the resultant Mg, Ni-saponite obtained. In general, a larger ΔT leads to a higher dissolution extent of saponite precursors and a higher degree of random distribution of octahedral Ni and Mg cations in the resultant Mg, Ni-saponite structures. Thus, the distribution mode of octahedral cations in saponite, which is not only relevant to a given hydrothermal temperature but also dependent on ΔT for final products, cannot be used as a geothermometer. TEM and STEM observations provide visual evidence that the particles of saponite coarsen when ΔT is higher than zero. Both the crystal-chemical and morphological features during saponite evolution suggest that saponite particles coarsen mainly via partial/complete dissolution of precursors followed by recrystallization and growth of Mg, Ni-saponite in which crystal growth by layer attachment cannot be excluded. This study presents an experimental approach to evaluate the evolution of clay minerals in terms of crystal chemistry and crystal growth and offers a better understanding of the contributions of clay mineral evolution to element cycling.

Monteneroite, Cu2+Mn2+2(AsO4)2⋅8H2O, a new vivianite-structure mineral with ordered cations from the Monte Nero mine, Liguria, Italy

AbstractMonteneroite (IMA2020-028), Cu2+Mn2+2(AsO4)2⋅8H2O, is a new vivianite-structure mineral from the Monte Nero mine, Rocchetta di Vara, La Spezia, Liguria, Italy. It is a secondary mineral that crystallised from As-, Cu- and Mn-rich fluids and it is associated with braunite, copper, cuprite, rhodochrosite and strashimirite. Monteneroite occurs as light green, thick blades up to ~2.5 mm long. The streak is white. Crystals are transparent with vitreous lustre. The mineral has Mohs hardness of 2, is somewhat sectile, exhibits two cleavages ({010} perfect and {001} fair) and has irregular stepped fracture. The measured density is 2.97(2) g cm–3. Monteneroite is optically biaxial (+), with α = 1.604(2), β = 1.637(2) and γ = 1.688(2), determined in white light; 2V = 80(1)°; slight dispersion is r &lt; v, orientation: X = b; Z ^ c = 52° in obtuse β. Electron microprobe analyses provided the empirical formula (Cu2+0.88Mn2+0.11)Σ0.99Mn2+2.00(As1.00O4)2⋅8H2O. Monteneroite is monoclinic, C2/m, a = 10.3673(14), b = 13.713(2), c = 4.8420(8) Å, β = 105.992(8)°, V = 661.72(18) Å3 and Z = 2. Monteneroite has a vivianite-type structure (R1 = 0.0535 for 534 I &gt; 2σI reflections). It is the first mineral with this structure type to be defined with ordered octahedral cation sites.

Study of Growing Ni Nanoparticles Loaded on Layered Inorganic-Imidazoline Covalently Bonded Hybrids Under a Transmission Electron Microscope

This study investigates nanoclusters loaded on layered inorganic-imidazoline covalently bonded hybrids. To reveal the existence of nanoclusters, transmission electron microscopy (TEM) and selected-area diffraction (SAD) analyses were performed. An imidazolyl group bonded covalently with an inorganic layer, which contained Ni2+ (and not Mg2+) as an octahedral cation, in the layered hybrids. In this study, the layered hybrids synthesized at 170 and 150 °C are referred to as Ni-Im170 and Ni-Im150, respectively. The TEM observations confirmed the presence of nanoclusters of 1–2 nm in diameter on thin sheets of Ni-Im170 and Ni-Im150. The nanoclusters appeared as dark dots in the bright-field images and were brighter than the thin sheets in dark-field images. The SAD analyses exhibited halo patterns similar to those of phyllosilicates at the beginning of the TEM observations. The TEM analyses further revealed that the nanoclusters in both Ni-Im170 and Ni-Im150 grew into Ni nanoparticles (3–5 nm diameter) under TEM. The SAD analyses demonstrated diffraction patterns with a weak ring with a d-value of 0.20 nm and/or diffraction patterns attributed to Ni exhibiting rings with d-values of 0.20, 0.18, 0.12, and 0.11 nm after the nanocluster growth. Furthermore, in the case of Ni-Im150, drastic growth was observed under TEM, i.e., the diameters increased to approximately 30 nm.

Hydrothermal Precipitation of Sanidine (Adularia) Having Full Al,Si Structural Disorder and Specular Hematite at Maunakea Volcano (Hawai'i) and at Gale Crater (Mars)

AbstractHydrothermal high sanidine and specular hematite are found within ferric‐rich and gray‐colored cemented basaltic breccia occurring within horizontal, weathering‐resistant strata exposed in an erosional gully of the Pu'u Poliahu cinder cone in the summit region of Maunakea volcano (Hawai'i). The cone was extensively altered by hydrothermal, acid‐sulfate fluids at temperatures up to ~400 °C, and, within strata, plagioclase was removed by dissolution from progenitor Hawaiitic basalt, and sanidine and hematite were precipitated. Fe2O3T concentration and Fe3+/∑Fe redox state are ~12 wt.% and ~0.4 for progenitor basalt and 46–60 wt.% and ~1.0 for cemented breccias, respectively, implying open‐system alteration and oxic precipitation. Hydrothermal high sanidine (adularia) is characterized by full Al,Si structural disorder and monoclinic unit‐cell (Rietveld refinement): a = 8.563(19) Å, b = 13.040(6) Å, c = 7.169(4) Å, β = 116.02(10)°, and V = 719.4(19) Å3. Hematite (structure confirmed by Rietveld refinement) is the predominant Fe‐bearing phase detected. Coarse size fractions of powdered hematite‐rich breccia (500–1000 μm) are dark and spectrally neutral at visible wavelengths, confirming specular hematite, and SEM images show platy to polyhedral hematite morphologies with longest dimensions &gt;10 μm. Smectite and 10‐Å phyllosilicate, both chemically dominated by Mg as octahedral cation, are additional diagenetic hydrothermal alteration products. By analogy and as a working hypothesis, high sanidine (Kimberly formation) and specular hematite (Mt. Sharp group at Hartmann's Valley and Vera Rubin ridge) at Gale crater are interpreted as diagenetic alteration products of Martian basaltic material by hydrothermal processes.

Micro‐Raman study of crichtonite group minerals enclosed into mantle garnet

AbstractWe report the first comprehensive micro‐Raman study of crichtonite group minerals (CGM) as inclusions in pyropic garnet grains from peridotite and pyroxenite mantle xenoliths of the Yakutian kimberlites as well as in garnet xenocrysts from the Aldan shield lamprophyres (Russia). The CGM form (i) morphologically oriented needles, lamellae, and short prisms and (ii) optically unoriented subhedral to euhedral grains, either single or intergrown with other minerals. We considered common mantle‐derived CGM species (like loveringite, lindsleyite, and their analogues), with Ca, Ba, or Sr dominating in the dodecahedral A site and Zr or Fe in the octahedral B site. The Raman bands at the region of 600–830 cm−1 are indicative of CGM and their crystal‐chemical distinction, although the intensity and shape of the bands appear to be dependent on laser beam power and wavelength. The factor‐group analysis based on the loveringite crystal structure showed the octahedral and tetrahedral cation groups with 18f and 6c Wyckoff positions, namely, dominantly TiO6 and to a lower extent CrO6, MgO4, and FeO4 groups, to be the major contributors to the Raman spectral features. The ionic groups with dodecahedral (M0) and octahedral (M1) coordination are inactive for Raman scattering while active in infrared absorption. A number of observed Raman modes in the CGM spectra are several times lower than that predicted by the factor group analysis. The noticed broadening of modes in the CGM Raman spectra may result from a combining of bands at the narrow frequency shift regions. Solid solution behavior, luminescence, and partial metamictization of the CGM may exert additional influence on the Raman band shape. The Raman spectral features showed CGM to be accurately identified and distinguished from other Ti‐, Fe‐, Cr‐, and Zr‐containing oxides (e.g., ilmenite or those of spinel and magnetoplumbite groups) occurring as accessory mantle minerals.

Biotite reactivity in nitric and oxalic acid at low temperature and acid pH from surface and bulk dissolution measurements

The dissolution of biotite, a trioctahedral mica, was investigated for a temperature range of 25–70 °C and a pH range of 1–3 in the presence of HNO3 (nitric acid) and H2C2O4 (oxalic acid) solutions. Single millimetric, cleaved flakes of biotite were reacted in batch and flow-through experiments to obtain kinetic information and elucidate the mechanisms that control the overall dissolution reaction under these conditions. The reacting basal surface was explored using in-situ laser confocal microscopy (LCM-DIM) and ex-situ scanning and phase shifting interferometry (VSI-PSI), while the release of tetrahedral (Al and Si), octahedral (Mg and Fe) and exchange (K) cations in solution was monitored over time. This experimental approach allowed us to calculate far-from-equilibrium dissolution rates associated with changes in topography of the (001) surface (horizontal retreat (Rstep) and vertical retreat (Rvertical)), etch pit formation and growth (Rpit) and the release of Si in solution, i.e., bulk dissolution (Rbulk,Si). In HNO3 solutions, a proton promoted reaction mechanism (PPRM), through proton adsorption on the biotite surface, was dominant. The variation of Rstep, Rvertical and Rbulk,Si accounting for the dissolution of (hk0) surfaces at different temperature and pH was used to calculate the apparent activation energy (Ea) and the proton reaction order (nH+). The respective values decreased from 63 kJ mol−1 at pH 1 to 31 kJ mol−1 at pH 3 and increased from 0.46 at 25 °C to 0.77 at 70 °C. This variability was related to the variation of proton consumption with temperature. In H2C2O4 solutions, formation and growth of etch pits on the (001) surface occurred, yielding an increase in surface roughening. Rpit accounted for the rate of etch pit development which was observed to increase, as temperature increased. Based on Rpit, relatively high Ea values (121 kJ mol−1 and 162 kJ mol−1) were associated with an early evolution of the basal etch pits, whereas lower values (36 kJ mol−1 and 56 kJ mol−1) were calculated using Rbulk,Si. The present study contributes to the interpretation of the mechanisms involved in the biotite dissolution process at highly acidic pH, in the presence of inorganic and organic acid, and low temperature (T ≤ 80 °C). Furthermore, our results highlight the importance of combining surface and bulk analyses to assess the balance between the different reactions involving proton consumption during the dissolution and its dependency on temperature, pH and organic acids concentration.

Four Lead-free Layered Double Perovskites with the n = 1 Ruddlesden-Popper Structure.

Herein we report the synthesis, structure, and band gaps of four layered halide double perovskites, i.e., BA2Cu0.5In0.5Cl4, BA2Ag0.5In0.5Cl4, BA2Ag0.5Sb0.5Cl4, and BA2Ag0.5Sb0.5Br4 [BA = butylammonium = CH3(CH2)3NH3+], each of which has the n = 1 Ruddlesden-Popper structure. In addition, the crystal structure of BA2Ag0.5Bi0.5Br4 is revisited and that of BA2PbCl4 is reported for the first time. Only BA2Ag0.5Sb0.5Cl4 has the tetragonal I4/mmm symmetry of the undistorted Ruddlesden-Popper structure. The other five compounds have orthorhombic structures due to tilts of the octahedra and orientational ordering of the butylammonium groups. As the lateral dimensions of the inorganic layer decrease, the c/a ratio increases due to decreased interdigitation of the alkyl ends of the butylammonium cations. This structural feature may help to explain the increased stability of the bromide phases with respect to the chloride phases. There are features in the diffraction patterns of BA2Ag0.5Bi0.5Br4 and BA2Cu0.5In0.5Cl4 that suggest ordering of octahedral cations within the layers, but in those compounds there appears to be a high concentration of stacking faults between layers that limits long-range, three-dimensional ordering of cations. In the other cases the scattering powers of the cations (Ag/Sb and Ag/In) are too similar to say anything definitive about cation ordering. The band gaps of these compounds range from 2.65 to 4.27 eV, with the bromide compositions possessing smaller band gaps than the chlorides. The band gaps of layered BA2M0.5M'0.5X4 compositions studied here are roughly 0.5-0.8 eV larger than analogous Cs2MM'X6 cubic double perovskites due to a combination of dimensional reduction (3D → 2D), distortions of the octahedral environment around the M/M' ions, and octahedral tilting distortions.

Trivalent iron rich CoFe layered oxyhydroxides for electrochemical water oxidation

Layered double hydroxides (LDHs) are presently among the best-performing oxygen evolution reaction (OER) electrocatalysts in alkaline media. The high activity of LDHs is due to synergistic effects between two transition metals as well as the layered structure which facilitates electron transfer. Because of a perfect match with the size of interlayer carbonate a ratio of 2:1 for the di- and tri-valent octahedral cations is energetically preferred. Here we present a strategy, where first mixed valent (Co2+1-zFe2+z)4 Fe3+2 - LDHs, with z values between 0 and 0.75 are synthesized, which are subsequently oxidized to Co2+Fe3+ LDH-type layered (oxy)hydroxides with an unusual high trivalent Fe content. Characterization of the chemically oxidized materials using bulk and surface techniques demonstrated the successful synthesis of LDH-like trivalent iron rich (Co2+)4-4z (Fe3+)2+4z (oxy)hydroxides with a final Fe content ranging from 33.3 to 83.3%. Current densities of up to 200 mA cm−2 were obtained at potentials lower than 1.7 V vs. RHE for (Co2+)4-4z (Fe3+)2+4z (oxy)hydroxides containing a maximum of 80% Fe.

Structural Characterization of Octahedral Sheet in Dioctahedral Smectites by Thermal Analysis

The structures of octahedral sheets of dioctahedral phyllosilicates show cis-vacant (cv) and trans-vacant (tv) configurations due to the different distributions of the octahedral cations over cis- and trans-sites. On the basis of the different dehydroxylation temperatures, a thermal analysis is an effective method used to identify the cv and tv configurations of an octahedral sheet in dioctahedral smectites. The proportions of cv and tv configurations were determined by fitting the derivative thermogravimetry (DTG) curves. A wide range of cv and tv proportions were detected in the samples. The dehydroxylation temperatures of samples consisting of cv configuration are about 150 to 200 °C higher than those consisting of tv configurations. The samples were classified as tv varieties when octahedral Fe3+ &gt; 0.46 mol/FU, and the pure tv dioctahedral smectites were found when Fe3+ &gt; 1.8 mol/FU. A clear linear relationship was found between the content of octahedral Fe3+ and Al3+ and the proportion of cv and tv configurations. The substitution of Al3+ by Fe3+ in the octahedral sheets is the main factor for the formation of tv varieties. There was no relationship detected between the layer charge density, octahedral Mg2+ content, and the proportion of tv and cv. The present results indicate that the iron content has a significant effect on the structure of the octahedral sheet.

Al27 NMR chemical shift of Al(OH)4 - calculated from first principles: Assessment of error cancellation in chemically distinct reference and target systems.

Predicting accurate nuclear magnetic resonance chemical shieldings relies upon cancellation of different types of errors between the theoretically calculated shielding constant of the analyte of interest and the reference. Often, the intrinsic error in computed shieldings due to basis sets, approximations in the Hamiltonian, description of the wave function, and dynamic effects is nearly identical between the analyte and reference, yet if the electronic structure or sensitivity to local environment differs dramatically, this cannot be taken for granted. Detailed prior work has examined the octahedral trivalent cation Al(H2O)6 3+, accounting for ab initio intrinsic errors. However, the use of this species as a reference for the chemically distinct tetrahedral anion Al(OH)4 - requires an understanding of how these errors cancel in order to define the limits of accurately predicting Al27 chemical shielding in Al(OH)4 -. In this work, we estimate the absolute shielding of the Al27 nucleus in Al(OH)4 - at the coupled cluster level (515.1 ± 5.3 ppm). Shielding sensitivity to the choice of method approximation and atomic basis sets used has been evaluated. Solvent and thermal effects are assessed through ensemble averaging techniques using ab initio molecular dynamics. The contribution of each type of intrinsic error is assessed for the Al(H2O)6 3+ and Al(OH)4 - ions, revealing significant differences that fundamentally hamper the ability to accurately calculate the Al27 chemical shift of Al(OH)4 - from first principles.

Solution combustion synthesis, characterization, magnetic, and dielectric properties of CoFe2O4 and Co0.5M0.5Fe2O4 (M = Mn, Ni, and Zn).

Nanocrystalline CoFe2O4 and Co0.5M0.5Fe2O4 (M = Mn, Ni, and Zn) ferrites were prepared by the solution combustion method using oxalyl dihydrazide as a fuel. These materials were characterized by several physicochemical techniques. X-ray diffraction (XRD) patterns indicate the cubic spinel structure of these ferrites. Field emission scanning electron microscopy (FESEM) images demonstrate the microporous nature of the materials because of the large amount of gas production during their synthesis. High resolution transmission electron microscopy (HRTEM) images show lattice fringes corresponding to the {220} and {311} planes of the spinel structure. Fourier transform infrared (FTIR) spectra exhibit absorption bands around the 500-600 cm-1 wavenumber region which are related to metal-oxygen bonds with tetrahedral coordination. Symmetric and asymmetric stretching and symmetric bending modes associated with tetrahedral and octahedral cations present in the spinel structures have been assessed by Raman spectroscopy. X-ray photoelectron spectroscopy (XPS) studies demonstrate the presence of Co2+, Mn2+, Ni2+, Zn2+, and Fe3+ in tetrahedral and octahedral coordinations in these ferrites. Co0.5Zn0.5Fe2O4 is observed to show the highest saturation magnetization among all these materials. The dielectric measurements reveal that the dielectric constant and loss values decrease with an increase in frequency and the ac conductivity increases at higher frequencies due to mobilization of the charge carriers.

Molecular dynamics study on the Li diffusion mechanism and delithiation process of Li2MnO3

Li2MnO3 is critical component in the well-studied Li-excess cathode materials xLi2MnO3·(1- x)LiMO2 for achieving high lithium storage capacity. In this article, the diffusion of Li ions in Li2MnO3 is studied using molecular dynamics (MD) simulation with well-behaved empirical force fields obtained by fitting against the crystal structure from experiment and phonons calculated using Density Function Theory (DFT). We have found two possible tetrahedral hopping channels, 0-TM and 1-TM(Mn4+) channel, which are differentiated by the face sharing octahedral cations. Simulation results show that the 0-TM channel is active for Li hopping, while 1-TM(Mn4+) channel is inactive. During the delithiation process, the Li ions in the transition metal (TM) layer are firstly removed, then those in the Li layer. However, the Li ions will be trapped in the tetrahedral 0-TM channels as long as the four face sharing octahedral sites are cleared. Up to x = 1.0 for Li2-xMnO3, almost all the Li ions are located at the tetrahedral sites, forming a regular array along a axis. The de-intercalation of tetrahedral Li ions requires a high voltage (>5.2 V vs. Li/Li+), limiting the practical capacities measured in lab. The diffusion of Mn ions into the Li layer is observed in a deeper delithiated structure (x = 1.2 for Li2-xMnO3), indicating an initial phase transformation to a spinel-like structure. However, the Mn ions are mainly trapped in the tetrahedral sites in the Li layer, instead of the octahedral sites in spinel-like structure. A few of Mn ions diffusing into the octahedral sites in Li layers have no face sharing tetrahedral Li ions, revealing a further Li de-intercalation is imperative for the complete phase transformation. During the delithation process, the oxygen sublattice shows a strong stability. In the deeply dilithiated structure Li0.8MnO3, the local distortion of the oxygen sublattice is observed, which may indicate the oxygen release at this high delithation stage. Our model is not stable for x ≥ 1.4 in Li2-xMnO3. Other charge compensation mechanism should be considered in this high delithiation stage, eg. oxygen release.

Metal-organic frameworks derived porous Co3O4 dodecahedeons with abundant active Co3+ for ppb-level CO gas sensing

Co3O4 dodecahedeons with abundant trivalent cobalt cation (Co3+) and surface absorbed oxygen species were prepared via regulating calcination temperature and heating rate of Co-based metal-organic framework (ZIF-67) templates. The influence of the calcination temperature and heating rate on the relative content of trivalent cobalt cation has been discussed in detail. The gas-sensing experiment demonstrates that the Co3O4 dodecahedeons with abundant active Co3+ exhibit significantly enhanced response to CO and a low detection limit (≤500 ppb). The response value is 20 times higher than that of Co3O4 nanoparticles to CO at the relatively low temperature of 150 °C and exhibits rapid response-recovery, good stability, reproducibility and selectivity. Such superior sensing performance to CO is mainly due to the accessible octahedral trivalent cobalt cation active sites and abundant absorbed-oxygen species as well as the large specific surface area which is beneficial to CO absorption, diffusion and the surface redox reaction. This facile method sheds light on the reasonable design of Co3O4 with different relative content of trivalent cobalt ion. The results afford decisive insights to realize the influence of Co3+ on the gas-sensing performance to CO, which allows new choices to design highly sensitive gas sensors.

Unified View of the Local Cation-Ordered State in Inverse Spinel Oxides.

Cation ordering/disordering in spinel oxides plays an essential role in the rich physical and chemical properties which are hallmarks of the structural archetype. A variety of cation-ordering motifs have been reported for spinel oxides with multiple cations residing on the octahedral site (or B-site). This has attracted tremendous attention from both experimental and theoretical communities in the last few decades. However, no unified view has been reached, presumably due to the richness of cation species and corresponding complex arrangements emergent in this large family of compounds. In this report, local cation-ordered ground states of (inverse) spinel oxides with two different cations on the octahedral site have been thoroughly investigated using neutron and X-ray total scattering, and a comprehensive theory has been proposed to explain the commonly observed cation-ordered polymorphs. It is found that a cation-zigzag-ordered structure (space group P4122) is the ground state for inverse spinel oxides with a pure or strong ionic lattice, while a cation-linear-ordered arrangement (space group Imma) emerges when one of the B-site cations forms very strong directional covalent bonds with lattice oxygen. The degree and length scale of cation ordering is strongly correlated with the charge and ionic radius difference between the two octahedral site cations. More complicated cation ordering schemes can be formed when there is a concomitant charge and orbital ordering which fall on a similar energy scale. This can lead to the formation of orbital-driven cation clusters or the broad concept of "molecules" in solid- state compounds. It is expected these findings will help to better understand the observed physical properties of spinel oxides and thus facilitate design strategies for improved functional materials.

Improvement of palm oil biodiesel filterability by treatment with reactivated spent bleaching earths

Reactivation and reuse of Spent Bleaching Earth (SBE) to improve Palm Oil Biodiesel (POB) filterability were examined in this study. The SBE was reactivated by washing with hexane, heating treatment at 500 °C and a combination of heating and acid treatment with 0.1 M HCl solution. The resulting adsorbents, denominated as extracted bleaching earth, calcinated bleaching earth (CBE) and regenerated bleaching earth (RBE), respectively, were characterized by several techniques. Virgin Bleaching Earth (VBE) was also characterized. As a result, solvent extraction of residual oil alone was found not to be an effective method for reactivation of SBE. In contrast, the other two methods tested resulted in an adsorbent capable of achieving the needed filterability. Reactivation was found to have a negligible effect on the crystal structure of the parent clay. It was also found not to alter the layered structure of the clay. SBET of CBE (98.94 m2/g) was smaller than that of VBE (160.11 m2/g), but the amount of N2 adsorbed was not significantly different to each other, evidencing that SBE recovered its initial adsorptive properties after being reactivated. Acid treatment led to a rise in SBET of RBE compared to CBE (121.70 m2/g), but it did not significantly increase its adsorption capacity. This was consistent with EDS analyses, where the content of Al+3, Mg+2, and Fe+3, the octahedral cations susceptible of being dissolved during acid treatment, was not statistically different between RBE and CBE.