Received 24 May 2011; revised 24 July 2011; Accepted 26 July 2011. Available online 3 August 2011.
The synthesis of orthorhombic Mn3(VO4)2 via a simple solid state route as well as the description of a new tetragonal high temperature phase are reported in this paper. Additionally, the system LiMnVO4–Mn3(VO4)2 (=Mn1.5VO4), described by the formula LixMn1.5−x/2VO4, is investigated in detail, showing that substitution of one Mn2+ in Mn1.5VO4 by two Li+ ions favors the formation of the tetragonal high temperature phase for x≤0.22. This substitution is facilitated by the statistical half occupancy of the 4b site by Mn2+ in tetragonal Mn1.5VO4, whereas additional crystallographic sites would have to be occupied in the orthorhombic phase. The inverse substitution of Li by Mn in orthorhombic LiMnVO4 is also shown to be possible in the range 0.72≤x≤1. For 0.22≤x≤0.72, there is a large miscibility gap with a two phase mixture of the tetragonal Mn1.5VO4 type and orthorhombic LiMnVO4 type phases.
The unusual coordination of Mn in the form of a stella quadrangula with the surrounding vanadate groups.