abstract
Sodium hafnium germanate, Na3Hf1.7Ge3O10(OH)(1.8), with garnet-type of structure was synthesized as a single phase, nanoparticles (100-600 nm) at mild hydrothermal conditions (230 degrees C) and autogenous pressure. The structure was solved ab initio from powder X-ray diffraction data and subsequently refined [R-exp: 6.10, R-wp: 7.26, R-p: 5.39, GOF: 1.19, R-B: 1.50] by the method of Rietveld. The solid crystallizes in cubic space group Ia-3d (230), with a = 12.6819(2) angstrom, V = 2039 .65(1) angstrom(3) and Z = 8. The structure is built up of rare combination of two tetravalent (Ge4+ and Hf4+) and one monovalent (Na+) cation alternating in form corner-sharing GeO4 tetrahedra and HfO6 octahedra whose negative charge is compensated by Na+ residing in dodecahedral coordination. Unlike the typical tetrahedral site disorder in hydrogarnets (hydrogrossular, hibschite, and katoite) we found that the octahedral position of the heavy Hf4+ cation is partly vacant which reveals alternative mechanism of charge unbalance leading to incorporation of hydroxyl group. Furthermore, the synthesized material is the first hafnium germanate with garnet-type of structure and the second known sodium hafnium germanate.
keywords
POWDER PATTERN DECOMPOSITION; ZIRCONIUM GERMANATE; X-RAY; LUMINESCENCE; CHEMISTRY; SPECTRA; PROGRAM; WATER
subject category
Chemistry
authors
Ferdov, S; Lin, Z
our authors
Zhi Lin
Principal Researcheracknowledgements
This work was supported by the Portuguese Foundation for Science and Technology (IF/01516/2013 and UID/CTM/50011/2013).