MO6 Octahedra Research Articles

Different electrochemical responses of LiFe0.5Mn0.5PO4 prepared by mechanochemical and solvothermal methods

A comparative investigation of the crystal structure, morphology and electrochemistry of LiFe0.5Mn0.5PO4 (LFMP) prepared by the mechanochemically assisted solid-state synthesis (SS) and the solvothermal synthesis (ST) was performed. The as-prepared samples were studied by XRD, FTIR, Raman, Mӧssbauer, SEM, TEM, galvanostatic cycling, GITT, and EIS. The low-temperature carbon-free LFMP-ST displays nanoplatelets with 20–30 nm thickness in the b direction and is characterized by the low concentration of the MLi defects and more distorted MO6 octahedra compared to LFMP-SS. It shows poor conductivity and only one sloping voltage plateau at 3.4 V. Its post-coating with carbon at 750 °C leads to the appearance of two commonly observed plateaus, corresponding to the Fe2+/Fe3+ and Mn2+/Mn3+ redox couples, and improves cyclability and rate capability. Carbon-coated LFMP-SS consists of irregular-shaped submicron particles and demonstrates two two-phase plateaus and an additional one at 3.6–3.7 V upon discharge. According to the GITT study, this plateau increases with cycling rate and is most likely controlled by the slower kinetics of the Mn3+ ions reduction.

New Group 13 MIL‐53 Derivates based on 2,5‐Thiophenedicarboxylic Acid

A new rigid metal‐organic framework (MOF) with MIL‐53 topology built of 2,5‐thiophenedicarboxylate (TDC) and Al, Ga, or In is reported. Its structure contains chains of trans corner sharing MO6 octahedra, connected by the linker molecules to form microporous square shaped 1D channels. A combination of powder X‐ray diffraction (PXRD), density functional theory (DFT) calculations, and 1H, 13C, and 27Al solid‐state NMR spectroscopy (ssNMR) was used to analyse the structures in detail. The synthesis is easily scaled‐up using microwave assisted solvothermal conditions. All materials possess a high thermal stability up to 420 °C in air and permanent porosity towards N2, H2, CO2, and CH4. Al‐MIL‐53‐TDC shows a high specific surface area of as,BET = 1150 m2·g–1 with a micropore volume of Vmic = 0.48 cm3·g–1 as well as water uptake of 5.5H2O molecules per sum formula (469 mg·g–1) with an a sigmoidal shape, advantageous for heat‐transformation processes. Noteworthy, this material adsorbs 2.1 wt % H2 at –196 °C and 1 bar, which surpasses other Al‐MIL‐53 compounds based on linear functionalized terephthalates.

Hermannjahnite, CuZn(SO4)2, a new mineral with chalcocyanite derivative structure from the Naboko scoria cone of the 2012–2013 fissure eruption at Tolbachik volcano, Kamchatka, Russia

A new mineral hermannjahnite, ideally CuZn(SO4)2, was found in the sublimates of Saranchinaitovaya fumarole, Naboko scoria cone, where the recent Fissure Tolbachik Eruption occurred in 2012–2013. The cotype specimen was found in the Arsenatnaya fumarole, on the Second scoria cone of the Great Tolbachik Fissure Eruption (GTFE 1975–1976). The mineral is named in honour of Hermann Arthur Jahn. Jahn-Teller effect is pronounced in the structure of hermannjahnite. The empirical formula of the holotype hermannjahnite, calculated on the basis of 8 O apfu is: Cu1.00(Zn0.43Cu0.31Mg0.25)∑0.99S2.00O8. Hermannjahnite is optically biaxial (+), α = 1.642(2), β = 1.652(2), γ = 1.675(2) (589 nm) with 2 V (calc.) = 67.6°. Hermannjahnite is monoclinic, P21/n, a = 4.8076(2), b = 8.4785(3), c = 6.7648(3) A, β = 93.041(3) °, V = 275.35(2) A3, Z = 2, R 1 = 0.047. The eight strongest lines of the X-ray powder diffraction pattern are (I-d-hkl): 31–4.231-(020), 100–4.177-(110), 72–3.630-(11–1), 25–3.486-(111), 29–2.681-(11–2), 69–2.648-(02–2), 29–2.561-(112), 63–2.428-(130). The structure of hermannjahnite is isotypic to that of dravertite, CuMg(SO4)2, and represents a monoclinically distorted chalcocyanite CuSO4 structure. Crystallographic and structural data on a natural sample of chalcocyanite are provided. Zinc is very close in ionic radii to copper, but the Jahn-Teller effect on Cu2+ causes the segregation of these elements over two symmetrically independent crystallographic sites in hermannjahnite. Bond-length distortion parameters (∆oct) were evaluated for 44 different MO6 (M = Cu, Zn) octahedra in Cu, Zn oxysalt minerals containing Cu- or/and Zn-dominated octahedra. In hermannjahnite CuO6 octahedra exhibit a value of ∆oct × 103 = 14.71, whereas ∆oct × 103 = 0.83 is calculated for ZnO6. In chalcocyanite CuO6 octahedra have a value of ∆oct × 103 = 8.25. Relationships between calculated ∆oct parameters and occupancy of MO6 (M = Cu, Zn) octahedra by Cu2+ and Zn2+ cations in various minerals are evaluated and discussed.

Syntheses, Structures, and Characterization of Quaternary Tellurites, Li3MTe4O11 (M = Al, Ga, and Fe).

Three new quaternary lithium metal tellurites, Li3MTe4O11 (M = Al, Ga, and Fe), have been synthesized through hydrothermal and solid-state reactions by heating a mixture of LiOH·H2O, TeO2, and M2O3. The structures of the title compounds have been determined by single-crystal and powder X-ray diffraction. Li3MTe4O11 reveal three-dimensional (3D) frameworks that consist of MO6 octahedra, TeO3 trigonal pyramids, and TeO4 polyhedra. The variable coordination mode of Te4+ within the framework leads to the formation of 1D channels that host Li+ cations on both tetrahedral and octahedral sites. The bulk and grain boundary Li+ ion conductivities for a Li3FeTe4O11 pellet in open air are estimated to be 1.0 × 10-4 and 2.7 × 10-6 S cm-1, respectively, at room temperature from the impedance profile analysis. A lower activation energy of 19.9 kJ mol-1 is obtained for the system, which is similar to that of Li10GeP2S12 (24 kJ mol-1). Detailed characterizations such as thermal, spectroscopic, and magnetic properties for the reported materials are also reported.

Change of local structures for 0.5Li2MnO3–0.5LiMn1/3Ni1/3Co1/3O2 in first charge process of different rates

An investigation was carried out into the charging rate dependence of local structural changes in a layered 0.5Li2MnO3–0.5LiMn1/3Ni1/3Co1/3O2 solid solution during the initial charging cycle. To clarify the mechanism involved in local atomic rearrangement, a pair distribution function (PDF) analysis was performed using the results of powder neutron diffraction and synchrotron X-ray total scattering measurements. First-principles calculations (VASP code) were used to determine the initial structure when performing the PDF analysis. The bond-length strain (λ) and the bond-angle strain (σ 2) for the optimized model were calculated following the PDF analysis in order to clarify the effect of the charging rate on the crystal structure distortion. Before charging, the distortion was small for MnO6 octahedra compared to that for NiO6 and CoO6 octahedra. During charging at a rate of 1C, the MnO6 octahedra experienced increasing distortion, whereas at 3C the CoO6 octahedra became more distorted. In addition, when charging at 3C, the values of λ and σ 2 increased for NiO6 octahedra that had entered the Li layer as a result of cation mixing. This appeared to be related to whether the localized atom was Mn or Co within the average structure during charge process. It is thought that distortion occurs in MO6 octahedra containing whichever element becomes localized, and this depends on the charging rate. This leads to the possibility that decreasing the fractional composition of the element that becomes localized may lead to reduced distortion and improved the cyclability.

(Invited) P2-Nax(Mn,Fe,Co,Ni) Layered Oxides in Na-Batteries

In the perspective of the development of electrical vehicles and also of very large scale renewable energy systems the prevailing parameters are the lifetime, the price and the material availability. From these points of view, sodium based batteries have to be investigated. Our research group studied layered oxides as positive electrode for 30 years. Recently, a general investigation was undertaken with a focus on P2-type layered phases.One of the main interests of this structure is the existence of an ion conduction plane made of face sharing trigonal prims which exhibits a high ionic diffusivity thanks to the existence of a large bottleneck (oxygen rectangle) for sodium diffusion. This structure is able to accommodate a lot of transition metal cations, allowing the optimization of the properties by cationic substitution. The study will be focused on the P2-Nax(Mn,Fe)O2, P2-Nax(Mn,Co)O2 Nax(Mn,Fe,Co)O2 and Nax(Mn,Fe,Ni)O2 systems with various amounts of transition metal ions. All materials crystallize in the hexagonal system (P63/mmc space group). The structure is made of MO2 slabs built of corner sharing MO6 octahedra. The sodium ions are in trigonal prismatic sites. Half of them share edges (Nae) with the MO6 octahedra while the other one share faces (Naf). As the two types of prisms share a common faces, they cannot be occupied simultaneously. The sodium distribution depends of the cationic charge distribution and of the sodium amount is order to minimize the Na+-Na+ and Na+-Mn+ electrostatic repulsions.In all systems, the P2 type packing is preserved in the 0.3 < x < 1 range. The fully intercalated phase is difficult to be obtained due to the very low ionic conductivity when the amount of vacancies is very small. For these compositions, only the Naf prisms are occupied. The specific capacity is in the 130-170 mAh.g-1 depending on the voltage range.In the case of materials with a single transition metal ion like NaxCoO2 and NaxVO2 the shape of the electrochemical curves present a lot of plateau resulting from ordering Na+/Vacancies in the sodium layer. For multi-cations systems, the transition metal disordering is the MO2 slabs prevents from most of the ordering except for the Na.050MO2 composition.A general overview of the electrochemical behavior of these materials will be presented with a special focus on the relation between the oxidation process and the shape of the electrochemical curve.

High-temperature behaviour of astrophyllite, K2NaFe7 2+Ti2(Si4O12)2O2(OH)4F: a combined X-ray diffraction and Mössbauer spectroscopic study

High-temperature X-ray powder-diffraction study of astrophyllite, K2NaFe7 2+Ti2(Si4O12)2O2(OH)4F, and investigation of the samples annealed at 600 and 700 °C, reveal the occurrence of a phase transformation due to the thermal iron oxidation coupled with (1) deprotonation according to the scheme Fe2+ + OH− → Fe3+ + O2− + ½H2 ↑, and (2) defluorination according to the scheme Fe2+ + F− → Fe3+ + O2−. The phase transformation occurs at 500 °C, it is irreversible and without symmetry changes. The mineral decomposes at 775 °C. Both astrophyllite and its high-temperature dehydroxylated (HT) modification are triclinic, P-1. The unit-cell parameters are a = 5.3752(1), b = 11.8956(3), c = 11.6554(3) A, α = 113.157(3), β = 94.531(2), γ = 103.112(2)o, V = 655.47(3) A3 for unheated astrophyllite, and a = 5.3287(4), b = 11.790(1), c = 11.4332(9) A, α = 112.530(8), β = 94.539(6), γ = 103.683(7)o, V = 633.01(9) A3 for the HT (annealed) modification of astrophyllite. The oxidation of iron is confirmed: (1) by the presence of an exothermic effect at 584 °C in the DTA/TG curves in an Ar–O atmosphere and its absence in an Ar–Ar atmosphere and (2) by ex situ Mossbauer spectroscopy that showed the oxidation of Fe2+ to Fe3+ in the samples heated to 700 °C. Deprotonation was detected by the evolution of IR spectra in the region 3600–3000 cm−1 for astrophyllite and its HT modification. Defluorination was detected by the presence of F in the electron microprobe analysis of unheated astrophyllite and the absence of F in the analysis of unpolished heated astrophyllite. The significant difference between astrophyllite and its HT modification is in the reduction of the M–O interatomic distances after heating to 500 °C and the distortion indices of the MO6 and Dφ6 octahedra. Thermal behaviour of astrophyllite in the 25–475 °C temperature range can be described as a volume thermal expansion with maximal coefficient of thermal expansion in the direction perpendicular to the plane of the HOH layers. In contrast, the HT phase experiences a strong contraction in the 600–775 °C temperature range, again in the direction perpendicular to the plane of the HOH layers.

Batisite, Na2BaTi2(Si4O12)O2, from Inagli massif, Aldan, Russia: crystal-structure refinement and high-temperature X-ray diffraction study

The crystal structure of batisite, Na2BaTi2 (Si4O12)O2, from the Inagli massif (Aldan, Yakutia, Russia) was refined to R 1 = 0.032 for 1449 unique observed reflections. The mineral is orthorhombic, Imma, a = 8.0921(5), b = 10.4751(7), c = 13.9054(9) A, V = 1178.70(13) A3. The mineral is based upon three-dimensional titanosilicate framework consisting of chains of corner-sharing MO6 octahedra (M = Ti, Nb, Fe and Zr) and vierer chains of corner-sharing SiO4 tetrahedra. Both chains are parallel to the a axis and are linked by sharing peripheral O atoms. The octahedral chains display disorder of M atoms and bridging O sites related to the out-of-center distortion of octahedral geometry around Ti4+ cations. Electron microprobe analysis gives SiO2 39.46, TiO2 24.66, BaO 21.64, Na2O 7.56, K2O 4.38, Fe2O3 0.90, ZrO2 0.66, Nb2O5 0.36, (H2O)calc 0.58, sum 99.76 wt%. The seven strongest X-ray powder-diffraction lines [listed as d in A (I) hkl] are: 8.39 (94) 011, 3.386 (56) 031, 3.191 (36) 123, 2.910 (46) 222, 2.896 (100) 024, 2.175 (45) 035, 1.673 (57) 055. The thermal behaviour of batisite in the temperature range from 25 to 950 °C was studied using high-temperature powder X-ray diffraction. The thermal expansion coefficients along the principal crystallographic axes are: α a = 14.4 × 10−6, α b = 8.7 × 10−6, α c = 8.4 × 10−6, α V = 31.5 °C−1 for the temperature range 25–500 °C and α a = 19.6 × 10−6, α b = 9.1 × 10−6, α c = 8.8 × 10−6, α V = 37.6 °C−1 for the temperature range 500–900 °C. The direction of maximal thermal expansion is parallel to the chains of both MO6 octahedra and SiO4 tetrahedra, which can be explained by the stretching of silicate chains due to the increasing thermal vibrations of the Ba2+ cations. At 1000 °C, the titanosilicate framework in batisite collapses with the formation of fresnoite, Ba2TiSi2O7O.

Magnetic Structures of Orthorhombic Li2M(SO4)2 (M = Co, Fe) and LixFe(SO4)2 (x = 1, 1.5) Phases.

We report herein on the magnetic properties and structures of orthorhombic Li2M(SO4)2 (M = Co, Fe) and their oxidized phases LixFe(SO4)2 (x = 1, 1.5), which were previously studied as potential cathode materials for Li-ion batteries. The particular structure of these orthorhombic compounds (space group Pbca) consists of a three-dimensional network of isolated MO6 octahedra enabling solely super-super-exchange interactions between transition metals. We studied the magnetic properties of these phases via temperature-dependent susceptibility measurements and applied neutron powder diffraction experiments to solve their magnetic structures. All compounds present an antiferromagnetic long-range ordering of the magnetic spins below their Néel temperature. Their magnetic structures are collinear and follow a spin sequence (+ + - - - - + +), with the time reversal associated with the inversion center, a characteristic necessary for a linear magneto-electric effect. We found that the orientation of the magnetic moments varies with the nature of M. While Li2Co(SO4)2 and Li1Fe(SO4)2 adopt the magnetic space group Pb'c'a', the magnetic space group for Li2Fe(SO4)2 and Li1.5Fe(SO4)2 is P1121'/a, which might hint for a possible monoclinic distortion of their nuclear structure. Moreover we compared the orthorhombic phases to their monoclinic counterparts as well as to the isostructural orthorhombic Li2Ni(SO4)2 compound. Finally, we show that this possible magneto-electric feature is driven by the topology of the magnetic interactions.

Benzothiophene hydrodesulfurization over NiMo/alumina catalysts modified by citric acid. Effect of addition stage of organic modifier

NiMo/Al2O3 catalysts were obtained by one-pot simultaneous impregnation of Mo, Ni and P (at 12, 3 and 1.6 wt%, respectively) over alumina. Citric acid (CA) was added (Ni/CA=1 mol ratio) to determine its influence over molybdenum species, as nickel precursor used was complexated Ni acetate. Three different preparation methodologies were used: (a) modification of calcined (400 °C) NiMo/Al2O3 by CA impregnation, (b) CA deposition directly onto Al2O3 carrier, prior to Ni-Mo-P impregnation, (c) simultaneous Ni-Mo-P-CA deposition on alumina support. Materials were characterized by N2 physisorption, infrared and UV-vis spectroscopies, temperature-programmed reduction and thermal analysis (TG-DTG), and tested in liquid-phase benzothiophene (BT) conversion in batch reactor. CA deposition over calcined NiMo/Al2O3 resulted in diminished proportion of refractory Mo6+(t) tetrahedral species but also in octahedral Mo6+(o) reducible at higher temperature, as to those over non-modified NiMo/alumina. That was reflected in lower hydrodesulfurizating (HDS) ability. The highest BT HDS activity (70% increase, as to the conventional calcined formulation with no organic additive) was found when CA was impregnated over bare alumina prior to Ni-Mo-P deposition. In that case, decreased interaction between deposited molybdenum and nickel species and the support was evidenced, that due to surface “passivation” from citric adsorption/decomposition on alumina surface. On the other hand, simultaneous Ni-Mo-P-CA deposition, where low pH of impregnating solution (pH~1.4) devoided citric acid ionization, (then, no Mo-citrate complex formation) was ineffective in providing catalyst of enhanced HDS activity.

Change of Average and Local Structures for 0.5Li2MnO3-0.5LiMn1/3Ni1/3Co1/3O2 in First Charge Process of Different Rate

In recent years, there is an increasing demand for lithium ion batteries. It was used in small devices such as mobile phones. Recently, the expansion of the intended use of electric vehicles and power storage equipment has been expected. However, it is necessary to improve high energy density. The solid solution material Li2MnO3 –Li（Mn,Ni,Co）O2 have attracted attention because they deliver high discharge capacity. On the other hand, it was reported such a problem that this material shows large irreversible capacity in the first cycle and discharge capacity greatly decreased at the high rate. It has been considered that irreversible capacity is due to oxygen removal to take place during the initial charge process above 4.5 V. But the mechanism of the discharge capacity fade is not clear. To commercialize the solid solution materials, it is necessary to solve the problem. We focused on the above problem. Our previous report described a transition metal rearrangement that occurs between 4.6 and 3.3 V during the initial discharge process at low rate [1]. In this study, we focused on the change of average and local structures of 0.5Li2MnO3 -0.5LiMn1/3Ni1/3Co1/3O2, layered solid solution material, during the initial charge process to clarify the arrangements of formation at the different rates. First, the change of average structures of 0.5Li2MnO3 -0.5LiMn1/3Ni1/3Co1/3O2, layered solid solution material during the initial charge process was clarified the arrangements of formation at different rates using Synchrotron X-ray [BL02B2, SPring-8, Japan] and neutron diffractions [iMATERIA, J-PARC, Japan}. The refined site occupancy in the charging process showed different results from before charge. The Mn occupancy localized to 4g site after charge at 1C rate whearas that moved from 4g site to 2b site at 3C rate. Although the both 4g and 2b sites were occupied by Co in the charging process at 1C rate, the only 4g site was occupied by Co in the charge at 3C rate. It was revealed that the differentiation of charge rate induced the atomic arrangement in the transition metal layer. Second, to clarify the mechanism local atomic arrangement change, we carried out PDF analysis using powder neutron diffraction measurements and synchrotron X-ray total scattering measurement [BL04B2, SPring-8, Japan]. In addition, first-principle calculation (VASP-code) used to determine the initial structure when performing PDF analysis. The λ and σ2 of optimal model was calculated after PDF analysis, in order to investigate the distortion of the crystal structure of the charging process of different rates.In the pristine, distortion of MnO6 octahedra is small compared to NiO6 and CoO6 octahedra. Comparing MnO6 and CoO6 octahedra distortion in the initial charging process at 1C rate, MnO6 octahedra showed an increasing trend. At 3C rate, CoO6 octahedra showed an increasing trend. In λ and σ2 of NiO6 octahedra entered the Li layer by cation mixing in the charging process at 3C rate increased . This was related to the trend of localization of Mn and Co of average structure. Perhaps, MO6 octahedra to localize tend to distorted in the charging process and localized element is different by the charging rate. Acknowledgement This work was supported in part by JSPS KAKENHI Grant Number 25420718. [1] Y. Idemoto et al, Electrochimica Acta, , 153, 399(2015).

Optical phonons, OH vibrations, and structural modifications of phlogopite at high temperatures: An in-situ infrared spectroscopic study

The thermal behavior of optical phonons and OH vibrations of phlogopite (a trioctahedral mica) was examined at temperatures up to 1000 K using in situ infrared spectroscopy. The results showed that with increasing temperature, O–K bands in phlogopite exhibited a relatively strong variation in frequency in a manner similar to those in muscovite. The work revealed that different types of OH bands (fundamentals and combinations) have very different thermal behavior or temperature dependence, and their absorption coefficients are commonly not constant on heating. OH combination bands that are associated with summation processes of multi-phonon interactions commonly show a decrease in their intensities on heating, but in contrast combination bands due to difference processes generally exhibit an increase. This means that temperature dependencies of their absorption coefficients need to be considered when using the Beer-Lambert law to determine or estimate OH contents or hydrogen concentrations at high temperatures. The results showed a structural anomaly associated with a discontinuity in the temperature derivative of the wavenumber of Al–O and Si–O vibrations and O–H stretching near 600 K. However, framework-related phonon modes in the FIR and MIR regions do not suggest a break of the original monoclinic structural symmetry in the investigated temperature region. The complex changes are attributed to temperature-induced alteration of local configuration involving TO4 tetrahedra and a possible change of the orientation of OH dipoles, in addition to a previously reported distortion of MO6 octahedra. Increasing temperature to 1000 K also causes partial dehydroxylation, as evidenced by the disappearance of the OH band near 3623 cm−1 and the decrease in OH band height and area of other OH bands. The study did not record the formation of H2O inside phlogopite as a result of partial dehydroxylation. The work offers new data and findings that have important implications in understanding the complex structural modifications and the behavior of phonon modes and the thermal stability of hydroxyls on approaching the dehydroxylation, as well as the way hydrogen is released from micas at high temperatures. Our data also show that phologpite becomes less transparent with increasing temperature suggesting a change of radiative properties and ability to transmit heat, which could be of interest for modeling thermal-transmission in crustal rocks.

Unique Domain Structure of Two-Dimensional α-Mo2C Superconducting Crystals.

The properties of two-dimensional (2D) materials such as graphene and monolayer transition metal dichalcogenides are strongly influenced by domain boundaries. Ultrathin transition metal carbides are a class of newly emerging 2D materials that are superconducting and have many potential applications such as in electrochemical energy storage, catalysis, and thermoelectric energy conversion. However, little is known about their domain structure and the influence of domain boundaries on their properties. Here we use atomic-resolution scanning transmission electron microscopy combined with large-scale diffraction-filtered imaging to study the microstructure of chemical vapor deposited high-quality 2D α-Mo2C superconducting crystals of different regular shapes including triangles, rectangles, hexagons, octagons, nonagons, and dodecagons. The Mo atom sublattice in all these crystals has a uniform hexagonal closely packed arrangement without any boundaries. However, except for rectangular and octagonal crystals, the C atom sublattices are composed of three or six domains with rotational-symmetry and well-defined line-shaped domain boundaries because of the presence of three equivalent off-center directions of interstitial carbon atoms in Mo octahedra. We found that there is very small lattice shear strain across the domain boundary. In contrast to the single sharp transition observed in single-domain crystals, transport studies across domain boundaries show a broad resistive superconducting transition with two distinct transition processes due to the formation of localized phase slip events within the boundaries, indicating a significant influence of the boundary on 2D superconductivity. These findings provide new understandings on not only the microstructure of 2D transition metal carbides but also the intrinsic influence of domain boundaries on 2D superconductivity.

New Facile Microwave-Assisted Technique for Chemical Intercalation of Multivalent Cations, Mg2+ and Zn2+, into Cathode Materials for Multivalent-Ion Batteries

Due to a significantly increasing demand for large-scale energy storage units especially for the power grid and sustainable vehicles, systems that are beyond lithium chemistry have gained much attention in recent years. New secondary battery chemistries based on multivalent cation charge carriers, such as Mg2+ and Zn2+, which involve more than one electron transfer, may lead to higher specific capacity and energy density. They are also relatively abundant, inexpensive, and offer superior safety compared to lithium when exposed to air. Despite the advantages of these systems over lithium chemistry, the development of multivalent-ion rechargeable batteries has been hampered by a variety of intrinsic problems related to the design and synthesis of multivalent intercalation cathodes. An approach to developing electrode materials that can reversibly insert multivalent cations is to chemically intercalate ions such as Mg2+ and Zn2+ into a host structure with a highly open framework or large interlayer distance, thus allowing facile multivalent-ion transport. As a result, the inserted Mg2+ or Zn2+cations inside the host structure can serve as charge carriers in energy storage systems. Traditionally, chemical intercalation is done by using organometallic reagents in heptane or hexane, such as di-n-butylmagnesium for Mg2+ and dimethylzinc or diethylzinc for Zn2+ by constant stirring the solution for 1‒2 weeks. These organometallic compounds are, however, known to be moisture-sensitive and react violently with water, thus raising safety concerns. We present here a new microwave-assisted chemical insertion technique, using the corresponding metal acetate as a metal ion source and diethylene glycol (DEG) as a reducing agent. This approach has been successfully demonstrated in microporous Mo2.5+yVO9+z host framework with large open channels. Mo2.5+yVO9+z with tunnels constructed by three-, six-, and seven-membered ring units of MO6 octahedra (M = Mo5+/6+ or V4+/5+) belongs to the family of isostructural MoVNbTeO compounds, which are very active oxidation catalysts for light alkanes due to the redox activities of Mo and V. With this microwave-assisted technique, divalent-ion-inserted compounds AxMo2.5+yVO9+z (A = Mg, Zn, 0 < x ≤ 3) can be prepared in as little as 30 min at 160‒200 ºC. The Mg-inserted compounds MgxMo2.5+yVO9+z (0 < x ≤ 3) thus obtained have been investigated as cathode materials in Mg-ion batteries. Our preliminary results suggest that the inserted Mg2+ ions can be removed electrochemically from the framework and reinserted for many cycles.This novel process offers a fast, inexpensive, easily scalable method to insert multivalent metal ions using relatively much safer chemicals which can be carried out in ambient atmosphere.

Crystal structure of CsNbMoO6

Single crystals of CsNbMoO6 were grown from solution in melt, and their crystal structure was solved by X-ray diffraction (R[I > 2σ(I)]1 = 0.0386). Crystals were cubic, а = 10.41039(8) A, Z = 8, space group \(F\bar 43m\). The synthesized crystals were shown to exhibit the second harmonic generation effect, which confirmed the absence of an inversion center in the structure. The structure was built of MO6 (M = Nb, Mo) octahedra, which share all vertices to form a three-dimensional framework where niobium and molybdenum atoms are randomly distributed. Framework interstices accommodate cesium ions. Crystals of CsNbMoO6 can be considered as pseudo-symmetric with respect to space group \(Fd\bar 3m\) due to a small shift of some oxygen atoms relative to the regular system of points in this group.

Hydrothermal synthesis of W–Ta–O complex metal oxides by assembling MO6 (M = W or Ta) octahedra and creation of solid acid

Layered-type tungsten and tantalum oxides (W–Ta–O) were synthesized by the hydrothermal method. The synthesized W–Ta–O showed characteristic peaks at 2θ=22.7° and 46.2° in an X-ray diffraction pattern (Cu Kα), indicating linear corner sharing of MO6 (M=W, Ta) octahedra in the c-direction. The same layered-type materials were obtained with a wide range of W and Ta composition ratios using soluble Lindqvist-type tantalum polyoxometalate (Na8(Ta6O19)·24.5H2O). Na+ cations of as-synthesized W–Ta–O were replaced with NH4+ and then calcined at 500°C to form Brønsted acid sites. The catalytic activity of W–Ta–O increased with increasing W ratio, suggesting that strong acid sites were generated. From Raman and adsorption measurements of W–Ta–O with various crystalline structures, it was revealed that the crystalline motif of W–Ta–O in the a–b plane was an interconnection of MO6 (M=W, Ta) octahedra and {M6O21} pentagonal units and micropore channels, but without long-range order.

First-Principles Investigations of the Structure, Electronic, and Optical Properties of Mullite-Type Orthorhombic Bi2M4O9 (M = Al(3+), Ga(3+)).

The structure, electronic band structure, density of state, projected wave function, and optical properties of mullite-type orthorhombic Bi2M4O9 (M = Al(3+), Ga(3+)) crystals have been studied by applying density functional theory based on the Vanderbilt ultrasoft pseudopotential in the frame of the generalized gradient approximation as an exchange-correlation function. Satisfactory agreement between experimental and theoretical results indicates that the used method and conditions are suitable. M-O bonds in tetrahedral MO4 environments are stronger and more covalent with respect to octahedral MO6; also Bi-O bonds in both studied structures are almost ionic in nature. The photocatalytic activity of Bi2Al4O9 and Bi2Ga4O9 is enhanced due to unequal values of Mulliken charges on the O atoms in MO4, MO6, and BiO6E groups. Bi2Al4O9 and Bi2Ga4O9 are direct and indirect band gap semiconductors with band gaps of 2.71 and 2.86 eV, respectively. Higher photocatalytic activity of Bi2Al4O9 is inferable from the lower effective masses of photogenerated carriers around the conduction band minimum and valence band maximum, in comparison with Bi2Ga4O9. The presence of M and O orbitals in the valence and conduction bands reveals that symmetry breaking in the MO4 and MO6 units has an important role in separating charges and increasing photocatalytic activity. Photocatalytic activities of Bi2Al4O9 and Bi2Ga4O9 for decomposition of organic pollutants and generation of hydrogen from water splitting are confirmed from band edge potentials.

Comparison of structural characteristics and electrochemical properties of LiMPO4 (M=Fe, Mn, and Co) olivine compounds

Olivine-type compounds of structural formula LiMPO4 (M=Fe, Mn, and Co) were prepared by sol-gel method. In the entire composite, no secondary phase was detected, and the sponge-like particle morphology was found to be suitable for use as a cathode material. Rietveld refinement shows that all materials have the same orthorhombic olivine structure in the Pnma space group, with lithium occupying octahedra into 4c sites and Mn2+ and Co2+ replacing Fe2+ at the octahedral sites. The a, b, and c cell parameters and cell volume increase with Mn substitution. Local geometric changes in MO6 octahedra occur with substitution of different transition metals. Distortion of the PO4 tetrahedra occurs in LiMnPO4 composite. LiFePO4 shows good electrochemical properties, whereas LiCoPO4 displays poor reversible capacity and unstable cycle performance.

Synthesis and Characterization of Three New Layered Vanadium Tellurites, MVTe2O8 (M = Al, Ga, and Mn): Three-Dimensional (3-D) Antiferromagnetic Behavior of MnVTe2O8 with a Zigzag S = 2 Spin Chain.

Three new metal vanadium tellurites, MVTe2O8 (M = Al, Ga, and Mn) have been synthesized through standard solid-state and hydrothermal reactions. Crystal structure analyses using X-ray diffraction reveal that the isostructural materials exhibit layered structures consisting of MO6, TeO4, and VO4 polyhedra. The corner-sharing of MO6 octahedra results in one-dimensional (1-D) zigzag chains that are further interconnected by tetrameric Te4O12 units and the VO4 tetrahedra to complete a layered structure. Detailed structural analysis suggests that the unit-cell volumes and the very long Te(2)-O(2) bond distances in MVTe2O8 are closely related to the ionic radii of M(3+) cations. Additional characterizations such as ultraviolet-visible light (UV-vis) and infrared spectroscopies, thermogravimetric analyses, and electron paramagnetic resonance measurements were performed. The temperature-dependent magnetic susceptibility measurements on MnVTe2O8 suggest that the material behaves like a three-dimensional (3-D) antiferromagnet with T(N) = 30 K, although the structure consists of a zigzag S = 2 spin chain.

NiMo/alumina hydrodesulphurization catalyst modified by saccharose: Effect of addition stage of organic modifier

NiMo/Al2O3 catalysts, obtained by one‐pot simultaneous impregnation, were modified by saccharose (SA, at Ni/SA = 1 mol ratio) addition. To address the influence of stage of saccharide impregnation on the hydrodesulphurization activity of sulphided catalysts, three different preparation methodologies were followed: (a) modification of already calcined (400 °C) NiMo/Al2O3 by SA impregnation; (b) SA deposition directly onto the alumina support, prior to Ni + Mo impregnation; (c) simultaneous Ni + Mo + SA deposition. Materials were characterized by N2 physisorption, X‐ray diffraction, infrared (IR) spectroscopy, UV‐vis spectroscopy, and temperature‐programmed reduction (TPR), and tested on liquid‐phase dibenzothiophene (DBT) conversion (batch reactor, T = 320 °C, P = 7.2 MPa, n‐hexadecane as solvent). The last methodology resulted in the catalyst with the highest DBT hydrodesulphurization (HDS) activity, on a pseudo‐first order kinetic constant basis. A decreased proportion of tetrahedral Mo6+ species due to diminished interaction with the carrier, increased reducibility of octahedral Mo6+, and Ni complexation as well seemed to play determining roles in the trends of the activity observed. Simultaneous saccharose addition during NiMo phase impregnation required no additional preparation steps to efficiently integrate the organic modifier.