NEUTRON-DIFFRACTION STUDY OF THE NUCLEAR AND MAGNETIC-STRUCTURE OF THE CRVO4 TYPE PHOSPHATES TIPO4 AND VPO4

The nuclear structures of TiPO4 and VPO4 have been refined from neutro n powder data using the Rietveld technique. For both compounds, the Cr VO4 type nuclear structure (Cmcm, Z = 4) was confirmed at 2 K with res iduals of R(N) = 0.033 (TiPO4) and R(N) 0.022 (VPO4). In this structur e the magnetic ions form chains running along the c-axis. For VPO4, ma gnetic ordering with a propagation vector k = (1/2 0 0) was found betw een 2 and 10.3(5) K. This magnetic structure shows antiferromagnetic i ntra-chain as well as inter-chain ordering. The magnetic moments are a ligned parallel to the b-axis and reach the value (mu(exp) = 0.8(1) mu (B). In the temperature range from 10.3(5) K up to the Neel point T-N 25.5(5) K an incommensurate magnetic structure with increasing k(x) co mponent of the propagation vector (0.5 less than or equal to k(x) less than or equal to 0.561) was found. In contrast to the vanadium compou nd no magnetic ordering was detected for TiPO4 down to 2 K. (C) 1996 A cademic Press, Inc.