Synchrotron X-ray and neutron diffraction studies of NaAlH 4 containing Ti additives

Abstract

NaAlH 4, Na 3AlH 6 and NaH samples with Ti additives have been investigated by synchrotron X-ray diffraction and neutron diffraction. Directly after ball milling there are no signs of any Ti-containing phases, and the unit-cell dimensions of NaAlH 4, Na 3AlH 6 and Al give no indication of any solid solutions. Combined refinements of X-ray and neutron diffraction of Na 1−3 x Ti x AlD 4 and NaAl 1− x Ti x D 4 show no indications of such solid solutions. Hence it is concluded that the Ti is in an amorphous state directly after ball milling. After cycling, however, a shoulder on the high-angle side of the Al reflections appears that is interpreted as a fcc solid solution Al 1− x Ti x with x≈0.07. Furthermore, addition of TiF 3 by ball milling results in different phases compared to TiCl 3/TiCl 4. The chlorides give NaCl, whereas no NaF is formed by the fluoro additive. It has not yet been possible to determine by X-ray diffraction where the fluorine is in the sample.