Synthesis, structure, and physical studies of the new beta-LiVOAsO4 compound

Two new compounds of the A(x)MOXO(4) family, beta-LiVOAsO4 and beta-VOAsO4, have been synthesized by solid state reaction and electrochemical lithium deintercalation from beta-LiVOAsO4, respectively. Both compounds are isostr uctural and are built like other beta-VOXO4 (X = S, P) by (VO5)infinity cha ins of distorted VO6 octahedra connected via corner-shared AsO4 tetrahedra. For beta-LiVOAsO4 the additional Li+ ions occupy chains of edge-shared oct ahedra running perpendicularly to the (VO5)infinity chains. The one-dimensi onal antiferromagnetic behavior suggested by the structure has been experim entaly confirmed. It is shown that lithium deintercalation occurs through a first-order transition at 4.02 V vs Li+/Li-0. From chemical bond considera tions it is shown why the redox potential of a given transition element M i n a six-fold coordination involving (M = O)(m+) units lies between those ob served in oxides and in M-2(XO4)(3) compounds with (XO4)(n-) oxo anions (X = S, P, As). (C) 2000 Academic Press.