Papers by Dr. Litty Sebastian BMC
Dalton Trans., 2014
Single crystals of Li3BP2O8 were prepared by heating a mixture of starting materials with a Li : ... more Single crystals of Li3BP2O8 were prepared by heating a mixture of starting materials with a Li : B : P molar ratio of 22 : 11 : 13 at 933 K in air and by cooling at a rate of -10 K h(-1). The X-ray diffraction (XRD) reflections of a single crystal were indexed with triclinic cell parameters: a = 5.1888(5) Å, b = 7.4118(7) Å, c = 7.6735(7) Å, α = 101.18(1)°, β = 105.07(1)°, γ = 90.34(1)° (space group P1 (no. 2)). In the crystal structure of Li3BP2O8, BO4 and PO4 tetrahedra share O atoms and form one-dimensional 1(∞)[BP2O8](3-) chains along the c-axis direction. A polycrystalline Li3BP2O8 bulk sample was synthesized by the solid state reaction of Li4P2O7 and LiPO3 prepared from the starting materials in advance with H3BO3 at 923 K. The lithium ion conductivities measured for the polycrystalline sample by the AC impedance and DC methods were 1.5 × 10(-5) S cm(-1) at 583 K and 6.0 × 10(-8) S cm(-1) at 423 K, respectively.
Perovskite oxides of the general formula, La0·9Sr0·1Ga0·8M0·2O3-δ for M = Mn, Co, Ni, Cu and Zn, ... more Perovskite oxides of the general formula, La0·9Sr0·1Ga0·8M0·2O3-δ for M = Mn, Co, Ni, Cu and Zn, have been prepared and investigated. All the oxides exhibit high electrical conductivities ( σ
We investigated Li/H exchange in the lithium ion conductors (LISICONS) [Li212xZn12xGeO4; x ~ 0.5 ... more We investigated Li/H exchange in the lithium ion conductors (LISICONS) [Li212xZn12xGeO4; x ~ 0.5 (I) and x ~ 0.75 (II)] and their parent, c-Li2ZnGeO4. Facile exchange of approximately 2x lithium ions per formula unit occurs with both the LISICONS in dilute acetic acid, while the parent material does not exhibit an obvious Li/H exchange under the same conditions. The results can be understood in terms of lithium ion distribution in the crystal structures: the parent Li2ZnGeO4, where all the lithium ions form part of the tetrahedral framework structure, does not exhibit a ready Li/H exchange; LISICONS, where lithium ions are distributed between framework (tetrahedral) and nonframework sites, undergo a facile Li/H exchange of the nonframework site lithium ions. Accordingly, Li/H exchange in dilute aqueous acetic acid provides a convenient probe to distinguish between the mobile and the immobile lithium ions in lithium ion conductors.
Materials Science and Engineering: B, 2003
Based on a consideration of the crystal structures of well-known negative thermal expansion (NTE)... more Based on a consideration of the crystal structures of well-known negative thermal expansion (NTE) materials, ZrV 2 O 7 and ZrW 2 O 8 , we have identified a new series of tetramolybdates, Ln 2 Mo 4 O 15 (Ln = Y, Dy, Ho, Tm), that exhibit an anomalous thermal expansion behaviour. Unlike ZrW 2 O 8 and ZrV 2 O 7 which are cubic, the tetramolybdates are monoclinic (space group P2 1 /c). Nevertheless, the framework is similar to ZrV 2 O 7 /ZrW 2 O 8 consisting of MoO 4 tetrahedra that are weakly connected to Mo 2 O 7 anions, which bind the Ln in a seven-fold anion coordination. An exploratory investigation of these materials using dilatometry, differential scanning calorimetry (DSC) and high-temperature powder X-ray diffraction (XRD) (Dy 2 Mo 4 O 15) reveals a negative or low thermal expansion in the 30-200 • C temperature range. Since there are no major structural changes in the high-temperature XRD and there is no first-order phase transition in DSC in the 30-500 • C range, we believe the mechanism of anomalous thermal expansion in these molybdates likely involves second-order structural changes of the molybdate oxygens, in a manner similar to the second-order changes found in ZrW 2 O 8. Further detailed structural studies are essential to unravel the mechanism of anomalous thermal expansion behaviour of these molybdates.
Materials Research Bulletin, 2004
Investigation of the interaction of hydrogen with alkaline earth manganites (IV) AMnO 3 (A = Ca, ... more Investigation of the interaction of hydrogen with alkaline earth manganites (IV) AMnO 3 (A = Ca, Sr, Ba), dispersed with 1 atom % Pt, has revealed an unprecedented uptake of hydrogen by BaMnO 3 /Pt to the extent of ~ 1.25 mass % at moderate temperatures (190 − 260 °C) and ambient pressure. Gravimetric sorption isotherms and mass spectrometric analysis of the desorption products indicate that approximately three hydrogen atoms per mole of BaMnO 3 /Pt is inserted reversibly. The nature of hydrogen in the insertion product, BaMnO 3 H 3 , is discussed. The work suggests the possibility of developing new hydrogen storage materials based on electropositive metal-transition metal-oxide systems.
Journal of Solid State Chemistry, 2003
We describe the synthesis and characterization of a new series of oxides, Li 2 MTiO 4 (M=Mn, Fe, ... more We describe the synthesis and characterization of a new series of oxides, Li 2 MTiO 4 (M=Mn, Fe, Co, Ni) that crystallize in the rocksalt structure. For M=Ni, we have also obtained a low-temperature modification that adopts a Li 2 SnO 3-type structure. All the phases, excepting M=Ni, undergo oxidative deinsertion of lithium in air/O 2 at elevated temperatures (41501C), yielding LiMTiO 4 (M=Mn, Fe) spinels and a spinel-like Li 1+x CoTiO 4 as final products.
Journal of Materials Chemistry, 2003
Nominal Pb 2 FeReO 6 adopts a defect pyrochlore structure at ambient pressure unlike the other A ... more Nominal Pb 2 FeReO 6 adopts a defect pyrochlore structure at ambient pressure unlike the other A 2 FeReO 6 (A~Ca, Sr, Ba). Rietveld refinement of the crystal structure of one of the compositions Pb 2 FeReO 6.1 from powder XRD data shows that the structure is cubic pyrochlore (a~10.382 Å ; space group: Fd3m) where oxygen vacancies occur at O2 (8b) sites. The divergence between the ZFC and FC magnetic susceptibility data and the non-Arrhenius resistivity behaviour of Pb 2 FeReO 6 compositions are characteristic of the underlying geometrically frustrated Fe/Re cation sublattice in the pyrochlore structure.
Journal of Materials Chemistry, 2003
Metal oxides containing mobile lithium ions are technologically important materials in the contex... more Metal oxides containing mobile lithium ions are technologically important materials in the context of design and development of electrolytes and electrodes for solid-state lithium batteries. Mobility of lithium in a solid manifests itself in the following measureable ways: ionic conductivity/diffusion, redox insertion/deinsertion and ion exchange. While ionic conductivity and redox insertion/deinsertion determine the practical use of a material as an electrolyte and electrodes, respectively, ion exchange involving lithium in aqueous/molten salt media under mild conditions not only provides a convenient probe for the investigation of lithium mobility in solids, but also enables synthesis of new metastable phases. In this article, we present a chemical (rather than electrochemical) perspective of lithium ion mobility in inorganic oxide materials, in an attempt to bring out the relationships between structure and properties associated with lithium ion mobility. The survey shows that considerable lithium ion mobility occurs both in closepacked (rocksalt and its relatives, spinel, LiNbO 3 , rutile and perovskite) as well as open-framework (e.g. NASICON) oxide structures. LiCoO 2 (a-NaFeO 2), LiMn 2 O 4 (spinel), LiNbO 3 /LiTaO 3 (structure based on HCP array of anions), LiNbWO 6 (trirutile) and (Li,La)TiO 3 (perovskite) are some of the oxide materials (structure type indicated in parentheses) where high lithium mobility has been well established by various experimental studies. An investigation of the factors that control lithium ion conductivity in the (Li,La)TiO 3 perovskite has enabled us to design new perovskite oxides in the Li-Sr-B-B'-O (B~Ti, Zr; B'~Nb, Ta) systems that exhibit high lithium ion mobility/conductivity. Among the framework materials, NASICON (e.g. Na 3 Zr 2 PSi 2 O 12) turns out to be a versatile structure that supports high lithium mobility under ion-exchange, ionic conductivity and redox insertion/deinsertion conditions.
J. Mater. Chem., 2003
Lithium magnesium molybdates of the general formula Li 222x Mg 21x (MoO 4) 3 , for 0 ¡ x ¡ 0.3, h... more Lithium magnesium molybdates of the general formula Li 222x Mg 21x (MoO 4) 3 , for 0 ¡ x ¡ 0.3, have been synthesized and their structure and lithium ion conductivity investigated. Determination of crystal structure of one of the members, Li 2 Mg 2 (MoO 4) 3 , has revealed a three-dimensional framework consisting of metal-oxygen octahedra and trigonal prisms (where Li and Mg reside) which are interconnected by MoO 4 tetrahedra. Although the framework is three-dimensional, lithium-ion conductivity appears to be restricted to the onedimensional channels formed by interconnected trigonal prisms. Isotypic molybdates, Li 3 M(MoO 4) 3 (M~Cr, Fe), where lithium ions occupy exclusively the trigonal prismatic channels, exhibit a higher lithium ion conductivity than Li 222x Mg 21x (MoO 4) 3 , lending support to the idea that the conductivity is one-dimensional in these materials. 7 Li NMR spectral data are consistent with this interpretation.
J. Mater. Chem., 2003
ABSTRACT
Applied Physics Letters, 2000
We report microwave absorption measurements as a function of temperature ͑from 290 to 125 K͒ and ... more We report microwave absorption measurements as a function of temperature ͑from 290 to 125 K͒ and magnetic field ͑from 0 to 0.3 T͒ in mm-thick parallelepipeds of sintered V 2 O 3 and V 2 O 3 containing micron-size Fe precipitates. As before, it turns out that near the metal-insulator ͑MI͒ transition, the loss exhibits a sharp peak as a function of temperature. On application of a magnetic field, the peak temperature for (V 2 O 3 ϩFe) changes by a few kelvin, causing a giant magnetoimpedance ͑Ϸ 200% in 0.1 T field͒ in the neighborhood of the MI transition.
Bulletin of Materials Science, 2000
Perovskite oxides of the general formula, La 0⋅ ⋅9 Sr 0⋅ ⋅1 Ga 0⋅ ⋅8 M 0⋅ ⋅2 O 3-δ δ for M = Mn, ... more Perovskite oxides of the general formula, La 0⋅ ⋅9 Sr 0⋅ ⋅1 Ga 0⋅ ⋅8 M 0⋅ ⋅2 O 3-δ δ for M = Mn, Co, Ni, Cu and Zn, have been prepared and investigated. All the oxides exhibit high electrical conductivities (σ σ ~ 10-2 S/cm at 800°C) comparable to that of the best perovskite oxide ion conductor, La 0⋅ ⋅9 Sr 0⋅ ⋅1 Ga 0⋅ ⋅8 Mg 0⋅ ⋅2 O 2⋅ ⋅85 (LSGM) (σ σ ~ 8 × × 10-2 S/cm at 800°C). While M = Mn, Co, Ni, Cu members appear to be mixed conductors with a variable electronic contribution to the conductivity, especially at high oxygen partial pressures (pO 2 ≥ ≥ 1 atm), arising from mixed-valency of the transition metals, the M = Zn(II) phase is a pure oxide ion conductor exhibiting a conductivity (σ σ ~ 1⋅ ⋅5 × × 10-2 S/cm at 800°C) that is slightly lower than that of LSGM. The lower conductivity of the M = Zn(II) derivative could be due to the preference of Zn(II) for a tetrahedral oxygen coordination.
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Papers by Dr. Litty Sebastian BMC