Hejny, CliviaKahlenberg, VolkerSchmidmair, DanielaTribus, MartinaDe Villiers, J.P.R. (Johan)2016-09-222016-09Hejny, C, Kahlenberg, V, Schmidmair, D, Tribus, M & De Villiers, JPR 2016, 'β-alumina-14H and β-alumina-21R : two chromic Na2-δ(Al,Mg,Cr)17O25 polysomes observed in slags from the production of low-carbon ferrochromium', Journal of Solid State Chemistry, vol. 241, pp. 70-78.0022-459610.1016/j.jssc.2016.05.038http://hdl.handle.net/2263/56879The crystal structures of unknown phases found in slags from the production of low-carbon ferrochromium were studied by powder and single-crystal X-ray diffraction. Two phases of Na2−δ (Al, Mg, Cr)17O25 composition were found to be composed of an alternating stacking of a spinel-type and a Na-hosting block. Similar structures are known for β-alumina and β”- alumina, NaAl11O17. However, the spinel-type block in Na2-δ(Al, Mg, Cr)17O25 is composed of five cation layers in contrast to three cation layers in the β-alumina spinel-block. The two new phases, β-alumina-14H, P63/mmc, a=5.6467(2), c=31.9111(12) Å, and β-alumina-21R, R m, a=5.6515(3), c=48.068(3) Å have a 14-layer and 21-layer stacking with a 2 × (cccccch) and a 3 × (ccccccc) repeat sequence of oxygen layers in cubic and hexagonal close packing, respectively.en© 2016 Elsevier Inc. All rights reserved. Notice : this is the author’s version of a work that was accepted for publication in Journal of Solid State Chemistry. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. A definitive version was subsequently published in Journal of Solid State Chemistry, vol. 241, pp. 70-78, 2016. doi : 10.1016/j.jssc.2016.05.038.β-aluminaPolysomeCrystal structureEngineering, built environment and information technology articles SDG-07SDG-07: Affordable and clean energyEngineering, built environment and information technology articles SDG-08SDG-08: Decent work and economic growthEngineering, built environment and information technology articles SDG-09SDG-09: Industry, innovation and infrastructureEngineering, built environment and information technology articles SDG-12SDG-12: Responsible consumption and productionEngineering, built environment and information technology articles SDG-13SDG-13: Climate actionPostprint Article