Spin-singlet clusters in the ladder compound NaV2O5
The space group of alpha(')-NaV2O5 turns below T(c) = 34 K from Pmmn with all V sites equivalent, into Fmm2 with three independent vanadium sites per layer. This is incompatible with models of charge ordering into V4+ and V5+. Our structure determination indicates that the phase transition consists of a charge ordering with three distinct valence states, formally V4+, V4.5+, and V5+. The singlet formation is not associated with dimerization on the spin ladder, but with the formation of spin clusters. Finally, we ascribe the quadrupling of the c axis to the large polarizability of the V2O5 skeleton.
de Boer JL
Solid State Chemistry Laboratory, Materials Science Center, University of Groningen, 9747 AG Groningen, The Netherlands.
Meetsma
A
Baas
J
Palstra
TT