The invention concerns novel compounds derived from La₂Mo₂O₉ and their use as ion conductors. The compounds of the invention have formula (1):

A_2-xA_xB_2-yB_yO_9-z+X_z

in which A is at least one trivalent element selected from trivalent rare earths, trivalent bismuth, trivalent antimony and trivalent arsenic; A is at least one monovalent element selected from alkalis; or a divalent element selected from alkaline-earths, tin, lead, samarium, europium, erbium, thulium and ytterbium; or a quadrivalent element selected from thorium, uranium, group IVA elements, cerium, praseodymium and terbium; B is at least one hexavalent element from groups VIA, VIIA, VIII and group VIB with the exception of oxygen; B is at least one element selected from lithium, sodium, magnesium, calcium, scandium, yttrium, rare earths with atomic numbers 63 to 71, elements from groups IVA to IIB with an oxidation number of less than 6, aluminium III, silicon IV, gallium III, germanium IV, indium III, tin IV, phosphorus V, antimony V and bismuth V; X is selected from sulphur, fluorine and chlorine; where 0x2; 0y2; 0z3; and with the condition that when A is lanthanum and B is tungsten or molybdenum, at least one of x, y or z is different from 0; the compounds having a cationic cubic or pseudo-cubic -SnWO₄ type lattice.