Abstrakt
The MonoPhosphate Tungsten Bronzes (MPTB) family, (P02)4(W03)2m, can be described by a regular intergrowth of (P04) tetrahedral layers and of slabs constituted by cor- ner-sharing-(W06) octahedra, with a thickness depending on the m parameter. These low-dimensional oxides are known to exhibit successive transitions toward Charge Den- sity Wave (CDW) states.
These transitions are associated to lattice distortions leading to the appearance of incommen- surate or commensurate structural modulations [1].In this family, the electronic anisotropy and the density of carriers of the system can be tuned by modifying the thickness of the W03 slabs, i.e.changing m. MPTB family is thus a rel- evant system to analyse the effect of the dimensionality on the CDW electronic instabilities.
Temperature-dependant X-Ray Diffraction (XRD) [1] and transport measurements reported in the literature, for different terms of the family, reveal a significant change of behaviour between the terms with a low and high value of m, m 7 respectively. Classical CDW transitions are reported for the low terms, characterized by a smooth resistivity jump and by the for- mation of clusters of tungsten in the centre of the W03 slabs [2].
For the high terms [3], a structural transition is observed in XRD but the electronic transport studies do not show the usual signature attributed to a CDW. Moreover, the only structural study performed on a high term in the modulat- ed state (m=10) [3] evidences anti-ferroelectric-type (AFE) atomic displacements for the tungsten atoms without report- ing of the formation of clusters of tungsten.