Synthesis and crystal structure of 3R and 1T′ polytypes of NH4Sc(SO4)2

Anhydrous complex scandium-ammonium sulfate NH4Sc(SO4)2 is a technologically important compound for affordable production of scandium oxide. This compound may exist in stable 3R and metastable 1T′ polytypic forms with very similar physical properties and the phase diagram characterized by irreversible 1T′→3R phase transition.208