An X-Ray Diffraction and Thermogravimetric Study of Layered Perovskite Y_1−xBi_xBaCo₄O₇

Layer-structured oxides Y_1−xBi_xBaCo₄O₇(0.00 ≤ x ≤ 0.05) were successfully synthesized and their structural and oxygen absorption properties were investigated by x−ray diffraction and thermogravimetry. Though Bi solubility was limited to about 5%, corresponding to Y_0.95Bi_0.05BaCo₄O₇, it is found that the structure and oxygen absorption properties of Y_1−xBi_xBaCo₄O₇ are affected significantly as the Bi content x increases. Rietveld refinement results show that Y_1−xBi_xBaCo₄O₇(x ≤ 0.05) is single phase with a hexagonal crystal structure (space group P6₃mc). Unit cell parameters and volume are changed and CoO₄ tetrahedra are distorted along the c−axis in Bi doped YBaCo₄O₇. The TG results show that Y_1−xBi_xBaCo₄O₇ undergoes two oxygen absorption processes in oxygen from room temperature to 1000°C and the maximum mass increase of the doped samples is less than that of YBaCo₄O₇. Bi doping effects on the structure and oxygen absorption properties are discussed on the basis of average radius and disorder of the Y site, the valence of Bi and the oxygen activation energy.