New series of triple molybdates AgA sub(3)R(MoO sub(4)) sub(5) (A=Mg, R=Cr, Fe; A=Mn, R=Al, Cr, Fe, Sc, In) with framework structures and mobile silver ion sublattices

Triple molybdates AgA sub(3)R(MoO sub(4)) sub(5) (A=Mg, R=Cr, Fe; A=Mn, R=Al, Cr, Fe, Sc, In) of the NaMg sub(3)In(MoO sub(4)) sub(5) type were synthesized and single crystals of AgMg sub(3)R(MoO sub(4)) sub(5) (R=Cr, Fe) were grown. In their structures, the MoO sub(4) tetrahedra, pairs and trimers of edge-shared (Mg, R)O sub(6) octahedra are connected by common vertices to form a 3D framework. Large framework cavities involve Ag super(+) cations disordered on three nearby positions with CN=3+1 or 4+1. Alternating (Mg, R)O sub(6) octahedra and MoO sub(4) tetrahedra in the framework form quadrangular windows penetrable for Ag super(+) at elevated temperatures. Above 653-673 K, the newly obtained molybdates demonstrate abrupt reduction of the activation energy to 0.4-0.6 eV. At 773 K, AgMg sub(3)Al(MoO sub(4)) sub(5) shows electric conductivity 2.5.10 super(-2) S/cm and E sub(a)=0.39 eV compatible with characteristics of the best ionic conductors of the NASICON type.