Synthesis and structure of complex phosphates Na3,5MII 0,5Fe1,5(PO4)3 (MII — Mg, Ni), obtained under condition of the crystallization of multicomponent self-fluxes - Yu. Strutynska; A. B. Spivak; V. M. Baumer; M. S. Slobodianyk (Reports of the National Academy of Sciences of Ukraine, 2021)