Co2P2O7‐Ni2P2O7 solid solutions: Structural characterization and color

NH4[Co1−yNiyPO4]·H2O (0 ≤ y ≤ 1) single crystals were fired to prepare Co2−xNixP2O7 0 ≤ x ≤ 2 solid solutions between 800 and 1200°C. The structure of these solid solutions is α‐M2P2O7 (M = Co, Ni). The contraction of the unit cell with increasing x confirmed the formation of these solid solutions. The UV–vis–NIR spectra of these solid solutions were consistent with Co(II) and Ni(II) ions in the two different crystallographic sites (octahedral site and square pyramidal site) in the α‐M2P2O7 structure. Due to their thermal stability, Co2−xNixP2O7 (0 ≤ x ≤ 2) solid solutions with α‐M2P2O7 structure can be used as a blue, green, brown or yellow ceramic pigment