The V(III) monophosphate series AV(2)O(PO4)(2) with A=Cd, Ca, Sr: Structure and magnetism

The strontium vanadophosphate, belonging to the series AV(2)O(PO4)(2) with A = Cd, Ca, Sr has been synthesized. Its single-crystal X-Ray study shows its isotypism with the cadmium and calcium phases. It crystallizes in the space group Pnma with a = 14.220(1) Angstrom, b = 6.5138(6) Angstrom, and c = 7.5166(8) Angstrom, Z = 4, and R = 0.039. In its structure, built up from [(VO2)-O-III](infinity) rutile chains connected through VO6 octahedra and PO4 tetrahedra, the geometry of the polyhedra is very close to that obtained for the Cd and Ca phases. The main difference deals with the V(2)-V(2) intrachains distances that increase significantly with the size of the A cation. The study of the magnetic susceptibility of the three monophosphates (A = Cd, Ca, Sr) evidences a narrow transition of 20 K from a paramagnetic to antiferromagnetic state. This behavior is in contrast with that of the (VPO4)-P-III phase that also exhibits isolated rutile chains but shows a broad transition spreading over 100 K. This difference is explained by the presence of additional VO6 octahedra that may weaken the unidimensional character of these phosphates compared to VPO4. (C) 1996 Academic Press.