Ordering phenomena in the diphosphate tungsten bronzes with hexagonal tunnels : Ba (P2O4)2 (WO3)2m Bernadette Domengès, Maryvonne Hervieu and Bernard Raveau Microsc. Microanal. Microstruct., 1 1 (1990) 41-53 DOI: 10.1051/mmm:019900010104100