Intense Turquoise and Green Colors in Brownmillerite-Type Oxides Based on Mn⁵⁺ in Ba₂In_2–<i>x</i>Mn_<i>x</i>O_5+<i>x</i>

Brownmillerite-type oxides Ba₂In_2–<i>x</i>Mn_<i>x</i>O_5+<i>x</i> (<i>x</i> = 0.1–0.7) have been prepared and characterized. Magnetic measurements indicate that manganese in as-prepared samples is substituting predominantly as Mn⁵⁺ for all values of <i>x</i> with observed paramagnetic spin-only moments close to values expected for two unpaired electrons. Electron paramagnetic resonance measurements indicate that this Mn⁵⁺ is present in a highly distorted tetrahedral environment. Neutron diffraction structure refinements show that Mn⁵⁺ occupies tetrahedral sites for orthorhombic (<i>x</i> = 0.1) and tetragonal (<i>x</i> = 0.2) phases. For Mn ≥ 0.3 samples, neutron refinements show that the phases are cubic with disordered cations and oxygen vacancies. The colors of the phases change from light yellow (<i>x</i> = 0) to intense turquoise (<i>x</i> = 0.1) to green (<i>x</i> = 0.2, 0.3) or to dark green (<i>x</i> ≥ 0.4). Under reducing conditions, Mn⁵⁺ is reduced to Mn³⁺, and Ba₂In_2–<i>x</i>Mn_<i>x</i>O_5+<i>x</i> phases become black Ba₂In_2–<i>x</i>Mn_<i>x</i>O₅ phases still with the brownmillerite structure

Intense Turquoise and Green Colors in Brownmillerite-Type Oxides Based on Mn⁵⁺ in Ba₂In_2–<i>x</i>Mn_<i>x</i>O_5+<i>x</i>

Brownmillerite-type oxides Ba₂In_2–<i>x</i>Mn_<i>x</i>O_5+<i>x</i> (<i>x</i> = 0.1–0.7) have been prepared and characterized. Magnetic measurements indicate that manganese in as-prepared samples is substituting predominantly as Mn⁵⁺ for all values of <i>x</i> with observed paramagnetic spin-only moments close to values expected for two unpaired electrons. Electron paramagnetic resonance measurements indicate that this Mn⁵⁺ is present in a highly distorted tetrahedral environment. Neutron diffraction structure refinements show that Mn⁵⁺ occupies tetrahedral sites for orthorhombic (<i>x</i> = 0.1) and tetragonal (<i>x</i> = 0.2) phases. For Mn ≥ 0.3 samples, neutron refinements show that the phases are cubic with disordered cations and oxygen vacancies. The colors of the phases change from light yellow (<i>x</i> = 0) to intense turquoise (<i>x</i> = 0.1) to green (<i>x</i> = 0.2, 0.3) or to dark green (<i>x</i> ≥ 0.4). Under reducing conditions, Mn⁵⁺ is reduced to Mn³⁺, and Ba₂In_2–<i>x</i>Mn_<i>x</i>O_5+<i>x</i> phases become black Ba₂In_2–<i>x</i>Mn_<i>x</i>O₅ phases still with the brownmillerite structure