Evidence of High Critical Temperature Charge Density Wave lhansitions in the ( P 02 ) 4 ( W 03 ) 2 m Family of Low Dimensional Conductors for m > 8

Trie monophosphate tungsten bronzes with pentagonal tunnels (MPTBp) of general formula (P02)4(W03)2m form a family of layered conductors where trie average number of conduction electrons per tungsten atom 2/m can be changed while keeping trie same structural array. Previous investigation of trie low m = 4, 6 and 7 members of this family bave shown that this serres is subject to several successive mcommensurate charge density wave (CDW) long range orders below room temperature (RT). Here we present an X-ray scattering study of trie m = 8, 9,10,11,12,13 and 14 members of this family. A very ricin and diverse structural phase diagram is observed. Trie m = 8 member shows only short range order below RT at two different incommensurate wave vectors while commensurate and/or incommensurate long rpnge order is observed above RT for m > 9. Incommensurate modulations are observed for trie m = 11 and 13 members and commensurate ones for trie other members. In most of trie 7 > m > 13 members trie observation of several harmomcs suggests that trie CDW modulation is non-sinusoïdal, which could be trie fingerprint of electron localization phenomena due either to strong electron-phonon or electron-electron interactions. These CDW instabilities bave been tentatively attributed to chains a and a ~ b of W06 octahedra into which trie Re03 type layers of (P02)4(W03)2m can be decomposed. In addition, trie observation for m > 9 of a commensurate (1/2,0,0) or (1/2, 0, 1/2) modulation or (1/2, 0, ii diffuse scattering suggests trie occurrence of an mcipient W03 type antiferroelectric mstability which interacts with the CDW for m < 13. We further discuss trie division between high m value and low m value members m relation to trie x dependence of trie physical properties of some M~W03 tungsten bronzes famines and finally propose a dielectric to magnetic duality between CDW tungsten oxides and superconducting copper oxides.