Charge-Order Pattern of the Low-Temperature Phase from a Monoclinic Single Domain ofNaV2O5Uniquely Determined by Resonant X-Ray Scattering

Abstract

The present resonant x-ray scattering has been performed on a monoclinically split single domain of NaV(2)O(5). The observation of a critically enhanced contrast between V(4+) and V(5+) ions has led us to the unequivocal conclusion of the charge-order pattern of the low-temperature phase of NaV(2)O(5) below T(c) = 35 K. In spite of the possible four types of configuration of the zigzag-type charge-order patterns in the ab plane (A,A',B and B'), the stacking sequence along the c axis is determined as the AAA'A' type by comparison with model calculations.

Theoretical Aspects of Charge Ordering in Molecular Conductors

“…A MF study 110 predicted a CO state with a "zigzag" pattern, which is now confirmed experimentally. 171 As discussed in § 3, such a 2D model is difficult to study in a controlled way, and some authors studied the quarter-filled EHM on a two-leg ladder system. 168,172 In fact, ladders are also found to be realized in molecular systems, 173 which is an interesting target for future studies.…”

Rich Behaviors of Vanadium Oxides under High Pressure

“…3) along the c-axis under ambient pressure, where A-and A'-type are different each other in the phase of the in-plane zigzag-type charge order, namely, V 5+ (V 4+ ) ions have the nearest V 4+ (V 5+ ) ions along the c-axis in the AA'-stacking. 8,12) High-pressure brings a surprisingly complex P-T phase diagram ( Fig. 3) with various stacking sequences of zigzag-type charge ordered planes, which resembles the global phase diagram theoretically predicted by the ANNNI model.…”

Effect of electron doping on the magnetic properties of spin-Peierls like material α′-NaV2O5

“…There is only one crystallographic site of vanadium ion with formal valence of +4.5. At 35 K, ␣ -NaV 2 O 5 undergoes a phase transition associated with charge disproportionation as 2 V 4.5+ → V 4+ (S = 1/2) + V 5+ (S = 0) [6]. So the dimerazation of V 4+ ions should be responsible for the formation of spin-gap through spin arrangement antiferromagnetically [5].…”

“…Seven crystallographic sites of vanadium ion are suggested in -Na 1.3 V 2 O 5 : V(1), V(2), V(3) and V(6) in V 4+ O 5 square pyramids; V(5) in V 4.5+ O 5 square pyramid; and V(4) and V(7) in V 5+ O 4 tetrahedron. -Na 1.3 V 2 O 5 is a new type of low-dimensional system showing spin-Peierls transition at a high temperature of 100 K which may arise from the formation of spin-singlet of V(1), V(2), V(3) and V (6) in the zigzag chain [20]. Although -Na 1.3 V 2 O 5 and ␣ -Na 1+x V 2 O 5 (x = 0.04 and 0.10) are both electron-doped materials, the crystal structure of two materials are definitely different, which results in the different mechanism of spin-singlet formation and different magnetic ground state.…”

“…␣ -NaV 2 O 5 is well described by the orthorhombic structure with quarter-filled two-leg spin ladders running along the b axis and all vanadium ions have a nominal valence state of +4.5 at room temperature [3,4]. At T C , ␣ -NaV 2 O 5 undergoes a cooperative phase transition associated with charge ordering of 2 V 4.5+ → V 4+ (S = 1/2) + V 5+ (S = 0), lattice dimerization and formation of spin-singlet [5,6]. Recently, the nature of insulator and formation of spin-singlet in ␣ -NaV 2 O 5 have been further studied experimentally [7] and theoretically [8,9], where the coupling of orbit, charge and lattice [10][11][12][13][14][15] play an important role.…”