• J Gopalakrishnan

      Articles written in Journal of Chemical Sciences

    • Co3-xZnxO4 (0 ≤x ≤ 1) spinel oxides

      J Gopalakrishnan N K Appandairajan B Viswanathan

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      A series of solid solutions of composition ZnxCo3-xO4 with 0 ≤x ≤ 1, crystallising in spinel structure have been characterised by measurements of unit cell parameter, electrical conductivity and magnetic susceptibility. The results have been rationalised on the basis of cation distribution. A comparison with the solid solutions of composition NixCo3-xO4 is also made.

    • Preparative solid state chemistry. Recent developments

      J Gopalakrishnan

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      A survey of recent developments in preparative solid state chemistry shows that, with a knowledge of structural chemistry and reactivity patterns of solids, it is possible to synthesize a variety of new solids possessing novel structures. A distinction is made between synthesis ofnew solids and synthesis of solids bynew methods. Three new routes to solid state synthesis are recognized: the precursor method, and topochemical methods involving redox and ion-exchange reactions. The low-temperature topochemical methods enable synthesis of metastable phases that are inaccessible by the high temperature route. Several illustrative examples of solid state synthesis from the recent literature are presented.

    • Magnetic properties of Ca2F2-xMnxO5

      A K Ganguli J Gopalakrishnan

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      Magnetic susceptibility of Ca2F2-xMnxO5 members crystallizing in two different structures, one having octahedral (O), tetrahedral (T) and square-pyramidal (SP) coordination of transition metal atoms (OTSP structure) and the other having octahedral and tetrahedral coordination (OT structure), has been investigated. Susceptibility behaviour of the oxides with OTSP structure is different from that of the oxides with OT structure. Ca2Fe1-33Mn0-67O5 with OTSP structure shows an antiferromagnetic ordering while the corresponding oxide with OT structure shows weak ferromagnetism.

    • Soft-chemical routes to synthesis of solid oxide materials

      J Gopalakrishnan S Uma K Kasthuri Rangan N S P Bhuvanesh

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      We describe three different families of metal oxides, viz., (i) protonated layered perovskites, (ii) framework phosphates of NASICON and KTiOPO4 (KTP) structures and (iii) layered and three-dimensional oxides in the H-V-W-O system, synthesized by ‘soft-chemical’ routes involving respectively ion-exchange, redox deintercalation and acid-leaching from appropriate parent oxides. Oxides of the first family, HyA2B3O10(A = La/Ca; B = Ti/Nb), exhibit variable Bronsted acidity and intercalation behaviour that depend on the interlayer structure. V2(PO4)3 prepared by oxidative deintercalation from Na3 V2(PO4)3 is a new host material exhibiting reductive insertion of lithium/hydrogen, while K0.5Nb0.5 M0.5OPO4 (M = Ti, V) are novel KTP-like materials exhibiting second harmonic generation of 1064nm radiation. HxVxW1-xO3 for x = 0–125 and 0.33 possessing α-MoO3 and hexagonal WO3 structures, prepared by acid-leaching of LiVWO6, represent functionalized oxide materials exhibiting redox and acid-base intercalation reactivity.

    • Foreword

      J Gopalakrishnan Ram Seshadri

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    • New lithium-ion conducting perovskite oxides related to (Li, La)TiO3

      Litty Sebastian A K Shukla J Gopalakrishnan

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      We describe the synthesis and lithium-ion conductivity of new perovskite-related oxides of the formulas, LiCa1.650.35Ti1.3B1.7O9 (B =Nb,Ta)(I,II), LiSr2Ti2.5W0.5O9 (III) and LiSr1.650.35Ti2.15W0.85O9(IV). OxidesI andII crystallize in orthorhombic (GdFeO3-type) structure, while oxidesIII andIV possess cubic symmetry. All of them exhibit significant lithium-ion conduction at high temperatures, the highest conductivity of ∼ 10−2S/cm at 800°C among the oxides is exhibited by the composition IV. The results are discussed in the light of previous work on lithium-ion conducting perovskite oxides containingd0 cations.

    • Emerging directions in chemical sciences - Foreword

      G U Kulkarni B Bagchi J Gopalakrishnan

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    • Quest for new materials: Inorganic chemistry plays a crucial role

      J Gopalakrishnan Rohini Mani

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      There is an endless quest for new materials to meet the demands of advancing technology. Thus, we need new magnetic and metallic/semiconducting materials for spintronics, new low-loss dielectrics for telecommunication, new multi-ferroic materials that combine both ferroelectricity and ferromagnetism for memory devices, new piezoelectrics that do not contain lead, new lithium containing solids for application as cathode/anode/electrolyte in lithium batteries, hydrogen storage materials for mobile/transport applications and catalyst materials that can convert, for example, methane to higher hydrocarbons, and the list is endless! Fortunately for us, chemistry - inorganic chemistry in particular - plays a crucial role in this quest. Most of the functional materials mentioned above are inorganic non-molecular solids, while much of the conventional inorganic chemistry deals with isolated molecules or molecular solids. Even so, the basic concepts that we learn in inorganic chemistry, for example, acidity/basicity, oxidation/reduction (potentials), crystal field theory, low spin-high spin/inner sphere-outer sphere complexes, role of 𝑑-electrons in transition metal chemistry, electron-transfer reactions, coordination geometries around metal atoms, Jahn-Teller distortion, metal-metal bonds, cation-anion (metal-nonmetal) redox competition in the stabilization of oxidation states - all find crucial application in the design and synthesis of inorganic solids possessing technologically important properties. An attempt has been made here to illustrate the role of inorganic chemistry in this endeavour, drawing examples from the literature as well as from the research work of my group.

    • Manganese-mediated ferromagnetism in La2Fe$_{1-x}$Mn$_{2x}$Cr$_{1-x}$O6 perovskite oxides

      R M Tiwari Mrudul Gadhvi Abanti Nag N Y Vasanthacharya J Gopalakrishnan

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      We have investigated the structure and magnetic properties of the perovskite oxides of the formula La2Fe$_{1-x}$Mn$_{2x}$Cr$_{1-x}$O6 ($0 < x < 1.0$). For $0 < x ≤ 0.5$, the members adopt the orthorhombic (Pbnm) structure, where the transition metal atoms are disordered at the 4b sites and the MO6 (M = Fe, Mn, Cr) octahedra become increasingly distorted with increasing 𝑥. For $0.65 ≤ x < 1.0$, the members adopt the rhombohedral (R-3c) structure that is similar to LaMnO$_{3+\delta}$ ($\delta ≥ 0.1$) where the MO6 octahedra are undistorted. While the magnetic properties of the latter series are largely similar to the parent LaMnO$_{3+\delta}$ arising from the double-exchange (DE) between mixed valent MnIII/MnIV, the magnetic properties of the orthorhombic members show a distinct (albeit weak) ferromagnetism ($T_C \sim 200$ K) that seems to arise from a MnIII-mediated superexchange (SE) between FeIII/CrIII in the disordered perovskite structure containing FeIII, MnIII and CrIII.

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