Planar defects found in have been studied in detail. These planar defects are parallel to the a- b plane with the displacement vector . They arise from the movement of oxygen atoms within the structure. The dependence of the density of planar defects within has also been studied by varying the amount of the dopant Ca, i.e. with x = 0.05, 0.1, 0.2 and 0.4. There is no direct relationship between the density of the planar defects and the concentration of Ca.