Composition-induced phase transition in Ca14Zn6−xGa10+xO35+x/2 (x=0.0 and 0.5)

Novel complex oxides Ca14Zn6Ga10O35 and Ca14Zn5.5Ga10.5O35.25 were prepared in air at 1200 °C, 72 h. Refinements of their crystal structures using X-ray powder diffraction data showed that Ca14Zn6Ga10O35 is ordered (S.G. F  23, RF2=0.0458, Rp=0.0485, Rwp=0.0659, χ2=1.88) and Ca14Zn5.5Ga10.5O35.25 disordered (S.G. F  432, RF2=0.0346, Rp=0.0601, Rwp=0.0794, χ2=2.82) variants of the crystal structure of Ca14Zn6Al10O35. In the crystal structure of Ca14Zn6Ga10O35, there are large empty voids, which could be partially occupied by additional oxygen atoms upon substitution of Zn2+ by Ga3+ as in Ca14Zn5.5Ga10.5O35.25. These oxygen atoms are introduced into the crystal structure of Ca14Zn5.5Ga10.5O35.25 only as a part of four tetrahedra (Zn, Ga)O4 groups sharing common vertex. This creates a situation where even a minor change in the chemical composition leads to considerable anion and cation disordering resulting in a change of space group from F23 (no. 196) to F432 (no. 209).

In the crystal structure of Ca14Zn6Ga10O35, only four positions marked by dark circles are occupied by group of four tetrahedra, while four positions marked by light circles are empty. In the crystal structure of Ca14Zn5.5Ga10.5O35.25, all eight positions marked by both dark and light circles are randomly occupied by group of four tetrahedra.Figure optionsDownload as PowerPoint slide