Speaker
Mr
Mashikoane Mogodi
(University of the Witwatersrand)
Description
In this work we present the synthesis and structure-property investigation of anhydrous non-porous borophsophates BPO4 and hydrated porous (NH4)0.5Co1.25(H2O)2(BP2O8)(H2O)0.5 phases. Cristobalite-type BPO4 crystallizes in the tetragonal lattice, space group I-4 (No. 82) [1]. Variable-Temperature Powder X-ray diffraction (VT-PXRD) patterns of this material were analysed by the sequential Rietveld refinement protocol. This method was used to determine the temperature dependency of the lattice parameters and linear thermal expansion coefficient. The refinement reveals significant anisotropy along the a- and c- crystallographic axes as a function of temperature, with thermal expansion coefficients of 10.6 x 10-6 /°C and 2.83 x 10-6 /°C, respectively. Structural changes accompanying this thermoresponsive behaviour will be discussed, including the variation of the interatomic distances and P-O-B (inter-polyhedral angle) with temperature. The open framework borophosphate (NH4)0.5Co1.25(H2O)2(BP2O8)(H2O)0.5 was synthesized under mild hydrothermal conditions at 180°C. The crystal structure was refined in the hexagonal lattice, space group P65 (no. 170) [2]. The compound is composed of NH4+ and H2O molecules located within the helical channels running along the [001] direction. Thermoresponsive investigation conducted by TGA analysis reveal a four step mass loss process, with the final step observed at 500-700°C range. Preliminary VT-PXRD results of this compound will also be presented.
Primary author
Mr
Mashikoane Mogodi
(University of the Witwatersrand)
Co-author
Prof.
David Billing
(University of the Witwatersrand)
