Phosphate tungsten and molybenum bronzes represent an outstanding class of materials displaying textbook examples of charge-density-wave (CDW) physics among other fundamental properties. Here we report on the existence of a novel structural branch with the general formula [Ba(PO4 )2 ][Wm O3m-3 ] (m=3, 4 and 5) denominated 'layered monophosphate tungsten bronzes' (L-MPTB). It results from thick [Ba(PO4 )2 ]4- spacer layers disrupting the cationic metal-oxide 2D units and enforcing an overall trigonal structure. Their symmetries are preserved down to 1.8 K and the compounds show metallic behaviour with no clear anomaly as a function of temperature. However, their electronic structure displays the characteristic Fermi surface of previous bronzes derived from 5d W states with hidden nesting properties. By analogy with previous bronzes, such a Fermi surface should result into CDW order. Evidence of CDW order was only indirectly observed in the low-temperature specific heat, giving an exotic context at the crossover between stable 2D metals and CDW order.
Keywords: 2D Metals; Charge-Density Waves; Fermi Surfaces; Mixed-Valence Oxides; Transition-Metal Oxides.
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