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Crystal Chemistry and Phase Equilibria of the CaO-½Dy2O3-CoOz System at 885 °C in Air



Winnie K. Wong-Ng, William J. Laws, James A. Kaduk


The CaO-½Dy2O3-CoOz system prepared at 885 °C in air consists of two calcium cobaltate compounds, namely, the 2D thermoelectric oxide solid solution, (Ca3-xDyx)Co4O9-z (0 x 0.6) which has a misfit layered structure, and the 1D Ca3Co2O6 which consists of chains of alternating CoO6 trigonal prisms and CoO6 octahedra. Ca3Co2O6 was found to be a stoichiometric compound without the substitution of Dy on the Ca site. No solid solution of the distorted perovskite, (Dy1-xCax)CoO3-z was established at this temperature (confirmed by X-ray Rietveld refinements). In the peripheral binary system of CaO-Dy2O3, while a small solid solution region was identified for (Dy1-xCax)O(3-z)/2 (0 x 0.075), Dy was not present in the Ca site of CaO. In addition, neither the reported Dy2CoO4 phase in the Dy2O -CoOz system nor the Ca- doped (Dy1+xCa1-x)CoO4-z phase was present at 885 °C. Three solid solution tie-line regions and four three-phase regions were determined in the CaO-½Dy2O3-CoOz system, which is substantially different from the other CaO-½R2O3-CoOz systems where R=La, Nd, Sm, Eu, and Gd. A comparison of the phase diagrams between the CaO-½Dy2O3-CoOz system and the CaO-½La2O3-CoOz system and the CaO-½Gd2O3-CoOz system is also presented in this paper.
Solid State Sciences


Phase diagram of CaO-½Dy2O3-CoOz, thermoelectric oxide (Ca3-xDyx)Co4O9-z, phase relationships


Wong-Ng, W. , Laws, W. and Kaduk, J. (2018), Crystal Chemistry and Phase Equilibria of the CaO-½Dy2O3-CoOz System at 885 °C in Air, Solid State Sciences, [online], (Accessed May 28, 2022)
Created December 13, 2018, Updated April 26, 2020