Abstract
Colored compounds A5(PO4)3Cu0.1OHz, where A = Ba1-xSrx (x=0,0.5,0.8), Sr1-y Cay (y=0,0.2, 0.5, 1), and Ba1/3Sr1/3Ca1/3 with an apatite structure containing copper ions in the hexagonal channels have been synthesized by the thermal treatment of the corresponding carbonates, oxides, and ammonium hydrophosphate at 1150°C. The use of the composition with A = Ba0.5Ca0.5 gives a multiphase product containing apatite (Ba1-xCax)5(PO4)3CuyOHz with x ∼ 0.2 as the major phase. The hexagonal lattice parameters of apatite depend linearly on the content of solid solution in the alkaline-earth metals. In the series of A = Ba, Ba-Sr, Sr, Sr-Ca, and Ca, the color of the samples changes smoothly from blue through violet to pink, whereas the samples with A = Ba0.5Ca0.5 and Ba1-3Sr1-3Ca1-3 are light gray. The diffuse reflectance electronic spectra exhibit two absorption bands characteristic of the copper ions in the hexagonal channels. Their positions depend on the alkaline-earth metal content of the compound. The third characteristic band appears in the spectrum of calcium apatite. Its relative intensity increases when calcium is gradually replaced by strontium and especially by barium, which results in worsening and even loss of the sample color. These spectral changes are presumably due to the transition of some copper ions from the hexagonal channels to other positions of the crystal lattice.
Published Version
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