Intense turquoise colors of apatite-type compounds with Mn5þ in tetrahedral coordination

The solid solutions of chlorapatite compounds Ba5Mn3 xVxO12Cl (x 1⁄4 0e3.0) and Ba5Mn3 xPxO12Cl (x 1⁄4 0 e3.0) have been synthesized through solid state reactions and Pechini or solegel method using citric acid. The colors of the samples change from white (x 1⁄4 3.0) through turquoise (x 1⁄4 1.5) to dark green (x 1⁄4 0) with increasing amount of manganese. Optical measurements reveal that the origin of the color is presumably a combination of ded transitions of Mn5þ and cation-anion charge transfer from transition metals to oxygens. Near IR reflectance measurements indicate that synthesized compounds are promising materials for “cool pigments” applications. Magnetic measurements verify that manganese has two unpaired electrons and exhibits 5 þ oxidation state. The IR spectra change systematically with sample compositions and the fingerprint region (700 cm 1 to 1100 cm 1) indicates characteristic bands belonging to (MnO4) , (VO4) and (PO4) functional groups. Structure refinements using neutron data confirm that Mn5þ, V5þ and P5þ cations occupy the tetrahedral sites in the apatite structure. © 2015 Elsevier Masson SAS. All rights reserved.