Anjali Basu

51V NMR of the layered δ-LiV2O5

Abstract Magnetic susceptibility indicates an apparent similarity in the electronic structure of δ- and γ-LiV 2 O 5 . However, 51 V (I = 7 2 ) NMR clearly demonstrates a significant difference between the two: While at room temperature, γ has a broad asymmetric line, which narrows and splits up as the temperature is lowered; δ at room temperature exhibits three lines, a central split line from 1 2 → − 1 2 transition (17.318 MHz) flanked on both sides by broad lines from spin paired singlets (17.489 MHz) and hyperfine shifted isolated V 4+ spins (17.237 MHz). At 100 K, the 51 V NMR line of δ is unshifted, though considerably broadened and intensified. NMR indicates that γ undergoes a structural distortion around 150 K, whereas the already highly distorted δ undergoes no further distortion. Finally NMR and susceptibility studies point to the possibility of bipolaron formation (even at room temperature) in δ-LiV 2 O 5 , as in Pb x V 2 O 5 ( x = 0.44).

Solid solutions of Li3VO4Li4GeO4 as solid electrolytes: NMR and related studies

Abstract It has been shown from NMR and conductivity studies of Li 3 VO 4 Li 4 GeO 4 solid solution that the activation energy is insensitive to change of composition over a wide range while it is highly sensitive to moisture. This effect has been significantly brought out in NMR studies as revealed in the ultimate disappearance of the NMR line due to penetration of the moisture within the grains.

NMR studies of the mixed conductor LixV2O5

Abstract A systematic NMR study of 51 V and 7 Li in the mixed conductor Li x V 2 O 5 is presented. The paramagnetic effect in the β bronze with the highest σ is very much evident, whereas it is much subdued in the intercalates. LiV 2 O 5 interecalate shows a second order quadrupolar effect in contrast to first order effects in both intercalates and bronzes with x ∼0.4.

59Co NMR studies of the spin-state equilibria in rare-earth cobaltites

Abstract Hyperfine interaction parameters reveal differences in the nature of spin-state equilibria in the lighter and heavier rare-earth cobaltites; the crystal-field parameter is lower in the lighter cobaltites. Temperature variation of the quadrupolar coupling constant is also more marked in the lighter rare-earth cobaltites, with NdCoO 3 showing evidence for a structural phase transition.

Dynamics of the Lisicon system from 7Li NMR

Abstract T 1 measurements in the Lisicon system conform to BPP mechanism due to Li + diffusion at higher temperatures. Quadrupolar satellites are observed in FT spectra of both Lisicon and ZRA at 500K. At 666K, e 2 qQ vanishes for Lisicon but exists for the ZRA (e 2 qQ/h ∼ 40.5 KHz). Finally FID indicates that T 2 involves two different processes, one arising from mobile Li ions and the other from the frame-work Li.

A comparative study of V6O13.27 and V6O13

Abstract A comparative study of the oxygen-enriched V 6 O 13.27 and stoichiometric V 6 O 13 is made from susceptibility and 51 V NMR. Instead of a susceptibility peak at 150 K as in V 6 O 13 , a plateau was observed in this region. A single broad 51 V NMR line was observed in V 6 O 13.27 at room temperature, which narrowed on lowering of temperature. Close to 150 K, three different lines, corresponding to the three inequivalent sites as in V 6 O 13 , were observed. Though occurrence of spin-pairing at 150 K has been recognized for some time, a bipolaronic mechanism for this pairing in V 6 O 13 itself is proposed for the first time. Interestingly, though susceptibilitywise V 6 O 13.27 and V 6 O 13 show very different behavior, bipolaronic spin-pairing possibly occurs in V 6 O 13.27 also. However, at 50 K, antiferromagnetic ordering as in V 6 O 13 does not occur in V 6 O 13.27 as the latter has fewer V 4+ spins than required, due to the presence of excess oxygen.

Hyperfine interaction in the mixed conductor γ LiV2O5

Transferred hyperfine interaction effects as studied from51v NMR in γ LiV2O5 (bronze) between the non-magnetic V5+ and paramagnetic V4+ lead to differing non-integral valences (neither 5+ nor 4+) on these sites at room temperature and below. However, at high temperatures exchange between two sites leads to a single mixed-valence state. d-d (V4+ −V4+) pairing along with relaxation effects show up in the low temperature spectra. Though susceptibility remains almost constant from 300–100K, there is considerable narrowing as well as intensification of the lines.