(PO2)4(WO3)14Single Crystals of the MPTBpFamily: A HREM Study

Domengès, B.; Roussel, Pascal; Labbé, Ph.; Groult, D.

doi:10.1006/jssc.1996.0387

Cited by 5 publications

(2 citation statements)

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“…The above results are discussed in relation to candidate mechanisms for the reduction of MoO 3 to MoO 2 . Clearly, any successful description must account for the presence of the intermediate Mo 4 O 11 which has been widely studied over the last two decades as part of an extensive literature − ,− surrounding the reduction of MoO 3 . Four candidate mechanisms are given.…”

Section: Discussionmentioning

confidence: 99%

Mechanisms of Reduction of MoO₃to MoO₂Reconciled?

et al. 2001

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The topotactic mechanism for the reduction of MoO 3 to MoO 2 has been well-supported by experiments, though the detection of Mo 4 O 11 during the process has been a challenge to the notion of direct conversion. In this study, high quality in-situ Neutron Powder Diffraction (NPD) has been used to monitor phase composition during the reduction of MoO 3 in a flow of hydrogen at 550 °C. Three phases have been detected: MoO 3 , MoO 2 , and Mo 4 O 11 . Multiphase Rietveld refinement has been used to obtain concentration profiles for all three oxides throughout the reduction process. Examination of these profiles reveals the following: (1) a higher content, initially, of MoO 2 than Mo 4 O 11 ; (2) a period of constant MoO 2 content; (3) an induction period of Mo 4 O 11 formation; and (4) a resumption in growth of MoO 2 but with different unit cell dimensions.

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Section: Discussionmentioning

confidence: 99%

Mechanisms of Reduction of MoO₃to MoO₂Reconciled?

et al. 2001

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“…41 In relationship with the study of the 4/6 member it is tempting to suggest that the intergrowth defects could lead to local charge transfers between adjacent layers of different m val-ues. It would result a smeared FS exhibiting a distribution of 2k F values, the broadening of which will smoothen its nesting properties and thus the divergence of the associated electron-hole response function.…”

Section: Discussionmentioning

confidence: 99%

Sliding charge density wave in the monophosphate tungsten bronze(PO2)4(WO
Foury-Leylekian
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Ravy³
et al. 2002
Phys. Rev. B
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The monophosphate tungsten bronzes (PO 2 ) 4 (WO 3 ) 2m form family of two-dimensional metals which exhibit charge density wave ͑CDW͒ instabilities. These materials are generally built by the regular stacking of (a,b) layers in which chains made of segments of m WO 6 octahedra directed along the a and aϮb directions are delimited. Their electronic structure thus originates from quasi-one-dimensional ͑1D͒ bands located on these chains. As a consequence their Fermi surface ͑FS͒ exhibits large flat portions whose nesting gives rise to successive CDW instabilities. Here we present a structural study of the CDW instability of the (PO 2 ) 4 (WO 3 ) 10 member formed by the alternate stacking of layers built with segments of mϭ4 and mϭ6 WO 6 octahedra. Its ab initio electronic structure calculation shows that the FS of this member exhibits large flat portions which can be extremely well nested. Its best nesting wave vector accounts for the modulation wave vector stabilized by the CDW transition which occurs at 156 K. Because of the regular stacking of layers of different m values the FS is slightly split. The unusual thermal dependence of the x-ray satellite intensity provides evidence that the two types of layers become modulated at different temperature. This also leads to a slight thermal sliding of the CDW-nesting modulation wave vector, which can be accounted for within the framework of a Landau-Ginzburg theory. In addition, the observation of a global hysteresis in the thermal cycling of the satellite intensity, as well as the degradation of the interlayer order upon cooling, suggest the formation of a disordered lattice of dilute solitons. Such solitons allow to accomodate the charge transferred between the two types of layer. Finally the relevance of local charge transfers, at intergrowth defects, for example, to create pinned discommensurations that break the CDW coherence is emphasized in this whole family of bronzes.

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