EPR AND MAGNETIC-SUSCEPTIBILITY STUDIES ON A6V6P6O31 (A=K, RB, TL) SYSTEMS IN THE TEMPERATURE-RANGE 4.2-300-K

EPR measurements of the A6V6P6O31 (A = K, Rb, Tl) systems at 300, 77 a nd 4.2 K have been carried out. Negative g-shift is observed in all ca ses. The g(iso) values in the systems do not change significantly in t he temperature range 4.2-300 K. Unresolved EPR lineshapes are observed in all cases owing to the delocalization of the vanadium 3d1 electron in the host lattice. Because of the similar effective ionic radii of the Rb+ and Tl+ ions, which are bigger than that of the K+ ion, these ions compress the octahedral VO6 units and the pyramidal VO5 units hav ing the V4+ sites to the same extent. Thus in the case of the Rb+ and Tl+ ions, the observed g(iso) values are similar. The magnetic suscept ibility plots show that these systems exhibit antiferromagnetic behavi our, with the Neel temperature around 50 K in all cases.