Synthesis and structural characterization of the vividly colored first row transition metal-containing oxyfluoride antiperovskites Sr3-xMnxMO4F and Sr3-xMnxMO4-αF1-δ (M = Al, Ga)

Highlights: • Substitution of Mn²⁺ demonstrates Sr_3-xA_xMO₄F can tolerate divalent first row transition metals. • The colors of these materials vary from green to purple depending on anion stoichiometry. • Intense colors are likely due to small amounts of Mn³⁺ on the tetrahedral Al site. • Structural data is consistent with preferential occupation of eight-coordinate Sr(2) site by Mn²⁺. • Large off-center displacements are observed on the underbonded ten-coordinate Sr(1) site. - Abstract: Incorporation of dopant amounts of the divalent transition metal cation Mn²⁺ into the oxyfluoride material Sr_3-xMn_xMO₄F (M = Al, Ga; 0 ≤ x ≤ 0.1) yields green powders which vary in hue depending on the identity of M. Treatment of these phases with post-synthesis annealing under reducing conditions produces anion deficient phases according to Sr_3-xMn_xMO_4-αF_1-δ displaying vivid purple coloration. Intense colors are likely due to small amounts of Mn³⁺ on the tetrahedral M site. Full structural characterization based upon powder X-ray diffraction (PXRD), neutron powder diffraction (NPD), and thermogravimetric analysis (TGA) data are presented herein, demonstrating that the Sr_3-xA_xMO₄F (A = Ca, Sr, Ba; M = Al, Ga) anti-perovskite structure can readily accommodate first row transition metals.