51V NMR of the layered δ-LiV 2O 5

Abstract

Magnetic susceptibility indicates an apparent similarity in the electronic structure of δ- and γ-LiV 2O 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 51V 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 2O 5, as in Pb x V 2O 5 ( x = 0.44).