Trussov, I.A. Male, L.L. Sanjuan, M.L. Orera, A. Slater, P.R. Understanding the complex structural features and phase changes in Na 2 Mg 2 (SO 4 ) 3 : A combined single crystal and variable temperature powder diffraction and Raman spectroscopy study J. solid state chem. 10.1016/j.jssc.2019.02.014 2019 2019