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Spin-Singlet Clusters in the Ladder Compound NaV 2 O 5

2000; American Physical Society; Volume: 84; Issue: 17 Linguagem: Inglês

10.1103/physrevlett.84.3962

1092-0145

J. L. de Boer, Auke Meetsma, Jacob Baas, T. T. M. Palstra,

Physics of Superconductivity and Magnetism

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.