Synthesis and structural characterization of two new reduced barium vanadium (III) phosphates: Beta-barium vanadium(2)(phosphorus(2)oxygen(7))(2) and barium(3)vanadium(6)(phosphorus oxygen(4))(8)
Carroll, Richard Irwin
Master of Arts
Investigation into the synthesis of reduced transition metal phosphates has led to the formation of two novel pseudo-ternary vanadium (III) phosphate compounds, each of which exhibits empty channels within the lattice. $\beta$-BaV$\sb2$(P$\sb2$O$\sb7)\sb2$ crystallizes in the P-1 (No. 2) space group with a = 6.269(1)A, b = 7.864(3)A, c = 6.1592(9)A, $\alpha$ = 101.34(2)$\sp\circ$, $\beta$ = 105.84(1)$\sp\circ$, and $\gamma$ = 96.51(2)$\sp\circ$ and exhibits three channels, two empty (one two-dimensional and one one-dimensional) and one occupied by the barium cation (three-dimensional). This compound is believed to be a high temperature phase. Ba$\sb3$V$\sb6$(PO$\sb4)\sb8$ crystallizes in the P2/c (No. 14) space group with a = 8.969(6)A, b = 9.907(5)A, c = 14.470(4)A, and $\beta$ = 104.26(3)$\sp\circ$. This structure also exhibits an empty, pentagonal-shaped channel visible along the a axis. In addition, the two barium sites form unusual corner sharing polyhedra through oxygen 16. Edge sharing of V(2)O$\sb6$ and P(2)O$\sb4$ polyhedra results in a structure distortion to avoid a short V-P distance. These structures appear stable through a wide temperature range.