Olivine-type Structure Research Articles

Effect of Various Organic Precursors on the Performance of LiFePO4 ∕ C Composite Cathode by Coprecipitation Method

The goal of this research was to study the effect of organic precursors with functionalized aromatic anhydrides or aromatic diketones on the performance of the composite. A coprecipitation method was applied to prepare a series of materials by calcinating amorphous with organic precursors at . The materials were characterized by X-ray diffraction, scanning electron microscopy, particle size analysis, thermal analysis, Brunauer-Emmett-Teller specific surface area and electrochemical methods. The obtained composites showed a well-ordered olivine-type structure with a minor impurity. The occurrence of the phase can be attributed to the relatively high temperature of . The composites produced by pyrolysis of an aromatic diketone with a longer alkoxy branch exhibited a better capacity compared to other types of organic compounds. The longer alkoxy aromatic diketone showed a better performance because its decomposition temperature was close to the temperature of the phase transformation resulting in a fine particle size and uniform carbon distribution on the composite surface. The performance of different organic precursors showed a strong relationship with its decomposition temperature, but was not in correlation with its weight loss. According to Raman spectral analysis, longer alkoxy aromatic diketones have a larger peak ratio indicating higher uniform and carbon content coating on particles.

Synthetic LiFePO 4/C without using inert gas

LiFePO 4/C was synthesized by high temperature solid-state method with cheap Fe 2O 3, LiH 2PO 4 and glucose as raw materials in absence of inert gas. The sample had ordered olivine-type structure other impurities characterized by the test of X-ray diffraction (XRD). The charge-discharge test showed the sample could demonstrate 120.5 mAh/g at 0.2C rate with good cyclic capability. The powder microelectrode cyclic voltammetry test indicated that the redox process of the sample had good reversibility.

Electronic absorption spectra of phosphate minerals with olivine-type structures: I. Members of the triphylite-lithiophilite series, M1[6]LiM2[6](Fex2+Mn1-x2+)[PO4

Electronic absorption spectra of the orthorhombic olivine-type phosphate minerals of the triphylite-lithiophilite series, M1[6]LiM2[6](Fex2+Mn1-x2+)[PO4], were obtained on members with XFe 0.195 (p, rs), 0.326 (sc, ps), 0.500 (p, rs), 0.564 (sc, ps), 0.708 (sc, ps), 0.750 (p, rs). Polarized spectra, ps, were measured on properly oriented single crystal slabs, sc, while powder remission spectra, rs, were scanned on unoriented fine grained powders, p. In all cases, microscope-spectrometric methods were used. All triphylite-lithiophilite spectra show the following features: (i) a nearly unpolarized absorption edge at around 30000 cm−1, which shifts slightly towards higher energies on increasing XFe, (ii) very weak and sharp bands at 24200 and 23800 cm−1 ( c > b > a ) typical of spin-forbidden dd -bands in Mn2+, and a series of very weak, differently polarized bands in the range 19000-15000 cm−1, (iii) an intense band system in the NIR typical of spin-allowed dd -transitions in octahedral Fe2+, consisting of two strongly polarized bands, I. at around 9100-9400 cm−1 ( c > > a > b ) and II. at around 7400-7200 cm−1 ( c > > a ≈ b ) attached as a strong shoulder to I. Energies and polarization behavior of band I. correspond closely to those of the strong Fe2+ -band in M2-octahedra of silicate olivines when the permutation of axes in Pmnb (ortho-phosphates) compared to Pbnm (orthosilicates) are taken into account. Band no. II. originates also from Fe2+ in M2, as no other transition metal ions are present eventually giving rise to absorptions in the NIR. Both bands, I. and II. are assigned to the 5 A 1(5 T 2g)→5 A 1(5 E g), →5 B 1(5 E g) transitions of Fe2+ in M2 under pseudosymmetry mm 2, which is usually adopted for M2 in silicate olivines. The energy difference, δe, between I. and II. represents the low-symmetry splitting of the excited state 5 E g of octahedral Fe2+ under m3m. Polarization-averaged energies of the above transition I. and of δe increase with iron contents XFe as \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[{\bar{{\nu}}}\_{I.} = 8906.5 {+} 669.7 {\cdot} X\_{Fe} (r = 0.949)\] \end{document} \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[{\bar{{\delta}}}\_{e} = 1749.2 {+} 525.7 {\cdot} X\_{Fe} (r = 0.923)\] \end{document} In contrast to silicate olivines, where energies of the spin-allowed bands of both Fe2+(M1) and Fe2+(M2) decrease with Fe-content, the energy of the barycenter \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(({\bar{{\nu}}}\_{I.}{+}{\bar{{\nu}}}\_{II.})/2\) \end{document} increases with XFe in the phosphates studied. This is evidently caused by the fact that Fe2+ substitutes the larger ion, Mn2+, in triphylite-lithiophilite, but the smaller one, Mg2+, in forsterite-fayalite. Adopting the energies of the 5 T 2g ground-state splitting, δg, in Fe2+ (M2) of silicate olivines also for the phosphates, then the crystal-field parameter, 10 Dq , of Fe2+(M2), is obtained as 10 Dq \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \({\bar{{\nu}}}\_{I.} - {\bar{{\delta}}}\_{e}/2 - 2{\bar{{\delta}}}_{g}/3\) \end{document} with values increasing on XFe as \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[10\mathit{Dq}\_{Fe2{+}} = 7031.9 {+} 406.7{\cdot}X\_{Fe}(r = 0.948).\] \end{document} Using this 10 Dq f (XFe) relation, local mean octahedral (Fe2+-O) distances in the phosphate olivines are calculated as \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[{\bar{R}}\_{(Fe-O)}^{local} = 2.175{\mbox{--}}0.024{\cdot}X\_{Fe}(r = 0.972)\] \end{document} From this, we obtain the local relaxation parameter ϵ −0.40. The splitting δe ≈ 2000 cm−1 found here for Fe2+(M2) in phosphate olivines is much higher than δe ≈ 400 cm−1 published for silicate olivines, although the geometry of the M2-octahedra in these phosphate olivines and in (Mg, Fe)-silicate olivines are very similar, especially the (Fe-O) distances. This discrepancy needs further study.

Atomic-Scale Investigation of Defects, Dopants, and Lithium Transport in the LiFePO4 Olivine-Type Battery Material

Key issues relating to intrinsic defects, dopant incorporation, and lithium ion migration in the LiFePO4 electrode material have been investigated using well-established atomistic modeling techniques. Our simulation model shows good reproduction of the observed olivine-type structure of LiFePO4. The most favorable intrinsic defect is the Li−Fe “anti-site” pair in which a Li ion (on the M1 site) and an Fe ion (on the M2 site) are interchanged. This type of anti-site defect or “intersite exchange” has been observed in olivine silicates. The lowest Li migration energy is found for the pathway along the [010] channel, with a nonlinear, curved trajectory between adjacent Li sites. Trends in dopant substitution energetics of a range of cations with charges varying from +2 to +5 are also examined. Low favorable energies are found only for divalent dopants on the Fe site (such as Mn), which is in accord with experimental work. Our results suggest that, on energetic grounds, LiFePO4 is not tolerant to aliovalent d...

Electronic limitations of lithium diffusibility. From layered and spinel toward novel olivine type cathode materials

The ability and efficiency of lithium intercalation into transition metal compounds have been found to depend strongly on their electronic structure. This work is a brief review of physicochemical properties of intercalated transition metal compounds with layered, spinel or olivine type structure in order to correlate their microscopic electronic properties, i.e. the nature of electronic states with the efficiency of lithium intercalation process that is controlled by the chemical diffusion coefficient of lithium. The data concerning cell voltages and character of discharge curves for various materials are correlated with the nature of chemical bonding and electronic structure following it. The nature of the metallic type conductivity of doped phospho-olivine is discussed and some fundamental arguments against the bulk nature of the observed high electronic conductivity are presented.

Weak ferromagnetism of LiMnPO 4

Structural and magnetic properties of the novel materials for lithium batteries LiFePO 4 and LiMnPO 4 were studied by X-ray diffraction, SQUID magnetometry and EPR spectroscopy. LiMnPO 4 has an olivine-type structure with a Mn-ion square lattice in the b– c plane. The occupation factors for Li and those oxygen atoms, which bridge Mn ions in the b– c plane showed noticeable deviation from the stoichiometry. In addition, the oxygen atoms, which are in the same layer as Li ions, exhibit a remarkable mean-square displacement in LiMnPO 4 but not in LiFePO 4. The olivine structure suggests quasi-two-dimensional (quasi-2D) antiferromagnetic structure of Mn(II) ions ( S=5/2) with sizable interlayer exchange interactions. Magnetization measurements clearly revealed a transition to a weak ferromagnetic state below T N=45 K. On the other hand we find that LiFePO 4 orders antiferromagnetically below 50 K. The difference in the magnetic properties of LiMnPO 4 and LiFePO 4 reflect the differences in the electronic states between these two compounds and may be very important for the electrochemical inactivity of LiMnPO 4. EPR measurements also suggest that at temperatures above T N the low-energy magnetic excitations in LiMnPO 4 are characteristic for the quasi-2D magnetic structure with the soliton excitation energy E S=139 K.

Determination of the chemical diffusion coefficient of lithium in LiFePO 4

The lithium insertion in the ordered olivine-type structure of LiFePO 4 was analyzed as an insertion process with a Frumkin-type sorption isotherm. A minimum in the chemical diffusion coefficient of lithium ( D Li) was predicted by the model for strong attractive interactions between the intercalation species and the host matrix. The D Li in the material was measured as a function of the lithium content by using the galvanostatic intermittent titration technique (GITT). The diffusion coefficient was found 1.8×10 −14 and 2.2×10 −16 cm 2 s −1 for LiFePO 4 and FePO 4, respectively, with a minimum in correspondence of the peak of the differential capacity. The D Li has also been measured by AC impedance method for various lithium contents. The calculated values are in very good agreement with the previous calculated ones.

Raadeite, Mg7(PO4)2(OH)8: a new dense-packed phosphate from Modum (Norway)

The new mineral raadeite, Mg 7(PO4)2(OH)8, was found in nodules of apatite + Mg-phosphates within the Tingelstadtjern serpentinite body, Modum district, Norway. It occurs as veinlets, a few tens of µ m wide, crosscutting althausite crystals; also as rare, up to 150 µ m large anhedral inclusions in holtedahlite; and with apatite, althausite and magnesite in fibrous coronae replacing heneuite. It is colourless, transparent, biaxial (- ); for l = 589 nm, n x 1.5945(5), n y 1.6069(5), n z 1.6088(5), 2V meas 45.6(1)° , 2V calc 43° ; strong dispersion r > v, n y // b. The infrared spec- trum shows prominent OH stretching bands at 3375, 3475, 3540 and 3580 cm -1. Electron-microprobe analyses indi- cate near-end-member composition, with minor As, Fe and Mn. Raadeite could be synthesized from 3 to 15 kbar, 500 to 700° C. It is monoclinic, space group P21/n, a = 5.250(1), b = 11.647(2), c = 9.655(2) A , b = 95.94(1)° , Z = 2. Single-crystal structure study ( R = 0.021) shows raadeite to be isostructural with the Mn-arsenate allactite and could localize the four protons. The structure consists of brucite-derived layers with 2/7 octahedral vacancies, which are linked by sharing a face and corners with interlayer Mg polyhedra (5+1 coordination) and corners with the PO 4 tetra- hedra. Raadeite and similar hydrous Mg-phosphates on the join brucite- Mg 3(PO4)2 (olivine-type structure) can be formally compared with the polysomatic humite series and other dense hydrous Mg silicates on the brucite- forsterite join. However, the structural variety of the relevant phosphates cannot be accounted for by a polysomatic series, nor are they all high-pressure phases.The new mineral honours Gunnar Raade, for his contribution to the mineralogy of Mg-phosphates.

Oxidative dehydrogenation of ethane and propane over magnesium–cobalt phosphates CoxMg3−x(PO4)2

The magnesium–cobalt phosphates CoxMg3−x(PO4)2 belonging to the olivine-type structure were synthesized by coprecipitation and then investigated in the oxidative dehydrogenation (ODH) of ethane and propane. The best yields, with the exception of Co0.5Mg2.5(PO4)2, were achieved with the compositions ranging between 1≤x≤2.5. Magnesium phosphate Mg3(PO4)2 displayed no activity and pure cobalt phosphate Co3(PO4)2 was found to be the less active component of the solid solution. Comparison of the catalysts performances showed that they all have similar activity in ethane and propane ODH, albeit, they are more selective in propylene than in ethylene production. The CoxMg3−x(PO4)2 solid solution was also studied, for characterization purposes, in butan-2-ol conversion. The samples presented acid–base properties due essentially to the (PO–H) groups but they do not bear conventional redox centers. All the catalysts were active at low temperatures in the alcohol dehydration. The dehydrogenation activity versus the phosphates composition displayed two maxima around x=1 and 2, respectively. Similar striking behavior was also observed in ethane and propane ODH. UV-visible investigations of CoxMg3−x(PO4)2 showed, in agreement with the XRD data, that the Co2+ ions are distributed in the phosphate framework between six- and five-coordinated sites. The cobalt atoms in the five-coordinated sites Co(5) and their Co(5)–Co(5) interatomic distances were assumed to play the main role in the C–H bond activation and the appearance of maxima in the activity. Magnesium cations presumably intervene in acid–base properties of the samples and O2 activation. Characterization of the samples showed that they do not undergo any noticeable transformation after the catalytic tests.

Electron Energy-Loss Spectroscopy (EELS) of Fe-Bearing Olivine and Laihunite (an Oxidized Olivine)

Abstract Laihunite that has distorted olivine-type structure with ferric and ferrous irons and ordered distribution of vacancies was first discovered in a high-grade metamorphosed banded iron formation (BIF) [1, 2]. The laihunite coexisting with fayalite (Fe-olivine), magnetite, quartz, ferrosilite, garnet and hedenbergite, formed in the process of oxidation of fayalite [2, 3]. The structure refinement of 1-layer laihunite shows P21/b symmetry and ordered distribution of vacancies in half M1 sites of olivine structure [2, 3]. Early high-resolution transmission electron microscopy (HRTEM) study and HRTEM image simulation of the 1-layer laihunite verified the structure refinement [4]. Specimens of weakly oxidized fayalite and laihunite containing fayalite islands collected from Xiaolaihe and Menjiagou of Liaoning Province, NE China, have been studied using selected area electron diffraction (SAED), high-resolution transmission electron microscopy (HRTEM), electron energy-loss spectroscopy (EELS), and X-ray energy-dispersive spectroscopy.

Neutron powder diffraction study of the crystal and magnetic structures of Fe 2SiS 4

The orthorhombic Fe 2SiS 4 (space group no. 62, Pnma) showing olivine-type structure has been studied. Measurements using neutron powder diffraction experiments were performed at 295, 140, 120, 40, 20 and 10 K in order to determine the crystal and magnetic structures of Fe 2SiS 4 at low temperatures. No crystallographic phase transition was observed between 295 and 10 K while two magnetic transitions were found. One transition around 127 K denotes a change from the paramagnetic (P) to an antiferromagnetic (AF) state while at 30 K the appearance of a ferrimagnetic (Fi) state is observed. Different magnetic models are presented. Relations are found between indirect magnetic interactions, on the one hand, and the Fe(4a), Fe(4c) and sulfur positions, on the other hand, and relations between the crystal structure and the magnetic models are given. The neutron powder diffraction results are compared with results, already reported, of Mössbauer and magnetization measurements.

Crystal structure of dilithium zinc tetrachloride, Li2ZnCl4 with spinel- and olivine-type structure

Article Crystal structure of dilithium zinc tetrachloride, Li2ZnCl4 with spinel- and olivine-type structure was published on November 1, 1996 in the journal Zeitschrift für Kristallographie - Crystalline Materials (volume 211, issue 11).

Hochdruckreaktionen quaternärer Chalkogenide mit Schichtstruktur / High-Pressure Reactions of Quaternary Layered Chalcogenides

Abstract The layered chalcogenides CoGa1.7Ti0.3S4, CoGa1.7V0.3, CoGa1.6Cr0.4S4, CoGaInS4, MnGa1.5Cr0.5S4, MnGa1.4Sc0.6S4, MnGa0.8In1.2S4, MnIn2S1.6Se2.4 and CdIn2S2.1 Se1.9 have been investigated under high-pressure - high-temperature conditions (p ≤ 60 kbar, T ≤ 1600°C). MnIn2S1.6Se2.4 and CdIn2S2.1,S1.9 show a phase transition to spinel-type compounds (a = 11.022(2) and a = 11.059(1) Å, respectively). MnGa0.8In1.2S4 forms a high-pressure polymorph with an olivine-type structure (a = 12. 856(3), b = 7.500(3), c = 6.128(2)Å. All other compounds decompose under the conditions applied. The results of a Rietveld structure refinement for the two high-pressure spinels are presented

Structure refinement and magnetic behaviour of the only selenide in the olivine group family: Mn 2SiSe 4

Mn 2SiSe 4 has been synthesized at 800°C. This compound cristallizes in the olivine-type structure with the cell parameters a = 13.3066(8)A˚, b = 7.7780(5)A˚andc = 6.2451(3)A˚ in the Pnma space group. To date this structure type had been only reserved for oxides and sulfides. We report here the crystal structure determination of the first selenide with olivine structure. The magnetic measurements from 5 K to room temperature suggest the existence of preponderant antiferromagnetic interactions.

Structural Determination and Thin Film Preparation of LiYSiO4 by Sol-Gel Method

Abstract LiYSiO4 was synthesized by sol-gel method and its crystal structure was determined by the Rietveld analysis. The structure was found to be an olivine-type structure with orthorhombic Pnma space group. The thin film deposited on an quartz substrate could be prepared by a dip-coating method using sol solutions consisting of lithium i-propoxides, silicon tetraethoxide and yttrium acetate.

High-pressure phase transformation of BeGa2O4

High-pressure phase transformation of beryllium gallium oxide (BeGa2O4) has been studied. Applying high pressure at elevated temperatures to the original hexagonal BeGa2O4 (β–Si3N4-type structure), a high-pressure modification with orthorhombic structure (olivine-type structure) was obtained, i.e., o-BeGa2O4. Lattice parameters of the new phase were determined to be a = 0.5698, b = 0.9759, and c = 0.4551 nm. The pressure and temperature ranges where the high-pressure phase was observed are 3.5 to 7.5 GPa and 800 to 1600 °C, respectively. A tentative pressure-temperature phase diagram for BeGa2O4 was proposed. Transformation is not straightforward; decomposition of the original phase into single oxides and their recombination to form o-BeGa2O4 are necessary. This process seems to apply in both ways, formation and decomposition of the high-pressure phase. The stability of the high-pressure phase is explained in terms of the total molar volume for the phase, the result of summing up molar volumes of constituent compounds. This is the first known report on transformation of β–Si3N4-type structure into a denser structure.

ChemInform Abstract: Synthesis and Characterization of Two New Quaternary Chalcogenides, CaYbInQ4 (Q: S and Se), with an Olivine‐Type Structure.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Structural and magnetic properties of LiCrGeO4

The crystal structure of LiCrGeO4 has been refined using powder neutron diffraction data at 300 and 1.2 K. This compound has a spine) structure with tetrahedral sites mainly occupied by Li+ ions: IVLi1–x-yIVGexIVCryVILix+yVIGe1–xVICr1–yO4 with x+y– <0.05.Above 130 K, the magnetic susceptibility of LiCrGeO4 obeys the Curie–Weiss law with a negative paramagnetic Curie temperature θp=–284 K (antiferromagnetic interactions between Cr3+ ions in octahedral coordination). No long-range magnetic order is observed at lower temperatures, a result which can be explained by a Cr/Ge disorder in octahedral sites and frustration effects. Crystallochemical considerations about IVGeVILiVIInO4, of olivine-type structure, and IVLiVICrVIGeO4 of spine)-type structure, were made considering the cationic radii; the olivine-type structure is stabilized by big cations (ca. 0.8 A) in octahedral sites and small cations (ca. 0.4 A) in tetrahedral sites. Cations with intermediate size (ca. 0.6 A) in tetrahedral and octahedral sites stabilize the spine)-type structure.

Synthesis and characterization of two new quaternary chalcogenides, CaYbInQ4 (Q = S and Se), with an olivine-type structure

Synthesis and characterization of two new quaternary chalcogenides, CaYbInQ4 (Q = S and Se), with an olivine-type structure

Li 2ZnI 4: A neutron powder study

The crystal structure of Li 2ZnI 4 was determined by means of neutron powder diffraction studies at 298 K. The olivine-type structure (space group Pnma, Z = 4, a = 1480.3(9), b = 856.0(2), c = 701.2(1) pm) was refined by the Rietveld method to a final R I = 5.48%. In a nearly ideal hexagonal close-packed iodide ion arrangement, Li is located in octahedral, and Zn, in tetrahedral voids, respectively. Apart from the ZnI distances, which are significantly shortened, the bond lengths obtained are as expected from the crystal radii.