Upadhyayula V Varadaraju

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Upadhyayula V Varadaraju
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Upadhyayula V Varadaraju
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Varadaraju, Upadhyayula V.
Varadaraju, Upadhyayula
Varadaraju, U. V.
Varadaraju, Upadhyayula Venkata
Varadaraju, Upadhayayula V.
Varadaraju, U.
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2003 - 20073
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    Solid state studies on Bi1.7-xHgxV8O 16 (x≤0.4) and magnetic properties of alkali metal inserted A xBi1.7V8O16 (A=Li and Na) hollandite type phases
    (10-03-2006)
    Marimuthu, K. N.
    ;
    Upadhyayula V Varadaraju 
    The effect of substitution of 'Hg' at the Bi-site in Bi1.7V 8O16 on the phase formation and electrical properties has been studied. In Bi1.7-xHgxV8O16, single phase formation is achieved only for x ≤ 0.4 and all the phases crystallize in tetragonal structure. The dc electrical resistivity studies indicate that all the mercury substituted single phase compounds Bi 1.7-xHgxV8O16 are electrically semiconducting and the room temperature resistivity values increase with increasing mercury content. Alkali metals like lithium and sodium have been inserted successfully into the tunnels of Bi1.7V8O 16. The lithium intercalated phase Li2.7Bi 1.7V8O16 shows antiferromagnetic ordering, whereas the sodium intercalated phase NaBi1.7V8O 16 exhibits Pauli paramagnetic like behavior down to 4.5 K.
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    Solid state studies on K2Ti6-xNbxFe 2O16 (x = 0 and 1) and lithium insertion into K 2Ti6M2O16 (M = Cr, Fe and Ga) and K2Ti5NbFe2O16 hollandite type phases
    (20-12-2003)
    Marimuthu, K. N.
    ;
    Smart, L. E.
    ;
    Berry, F. J.
    ;
    Upadhyayula V Varadaraju 
    A new niobium-substituted hollandite K2Ti5NbFe 2O16 has been synthesised for the first time. The compound is crystallised in tetragonal structure. A two to three orders change in electrical resistivity is observed with temperature as compared to the parent phase K2Ti6Fe2O16. The niobium-substituted phase shows antiferromagnetic ordering with TN = 37K at a field of 0.1T and the antiferromagnetic ordering disappears at higher field (0.2T) indicating field induced magnetic behaviour. The Mössbauer spectrum of K2Ti5NbFe2O16 shows majority of the Fe ions are 3+ oxidation state (96%). For the first time, we have intercalated lithium into K2Ti6M2O 16 (M = Cr, Fe and Ga) and K2Ti5NbFe 2O16 hollandite type phases using n-butyllithium in hexane. The estimated lithium content for all the phases are in the range 1.7-2.7mol per formula unit. © 2003 Elsevier B.V. All rights reserved.
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    Publication
    Stabilization of γ-La2S3 by alkali metal ion doping
    (15-02-2007)
    Biswas, Krishnendu
    ;
    Upadhyayula V Varadaraju 
    La3S4 is known to crystallize in a defect cubic Th3P4 structure. The effect of alkali metal ion doping in the lacunar La3-xS4 structure has been studied. Compounds with molecular formula La3-xAxS4 (A = Li, Na and K) with varying A/La ratios (0.1, 0.15, 0.2, 0.25 and 0.3) have been synthesized by gas-solid reaction method. The band gap increases with increase in dopant concentration. The optical properties show an increase in yellowness of the doped compositions when compared to the parent phase. © 2006 Elsevier Ltd. All rights reserved.