A new ordered triple Hollandite: Ba1.33Sb2.66Al5.33O16

Ba1.33Sb2.66Al5.33O16 is a triple Hollandite, which crystallizes in a tetragonal cell (I4/m no. 87) with a=b=9.86090(5) Å and c=8.77612(6) Å. Its crystal structure was characterized using electron diffraction and X-ray powder diffraction; it is isotypic to K1.33Mg3.11Sb4.89O16, K1.76Mg3.25Sb4.75O16 and to K1.8Li2.45Sb5.55O16. In the rutile chains of Ba1.33Sb2.66Al5.33O16, the ordering of Al and Sb atoms into unmixed sites induces the tripling of the c parameter compared to a ‘single’ Hollandite structure. The Ba2+ cations are dispersed along c, in the largest tunnels on non-split and fully occupied sites. They lie into Ba–Ba pairs separated by vacancies. Their regular arrangement has been confirmed by high resolution electron microscopy. Electrochemical experiments have also been performed in Li-ion cell but no Li insertion was detected.