Powder XRD patterns of (A) as-grown; and (B) annealed Bi2Sr2−xKxCo2Oy textured samples. The peaks of thermoelectric phase are shown by the diffraction planes. *, o, and # correspond to Bi0.75Sr0.25Oy, CoCo2O4, and Bi3.8Sr11.4Co8O28.875 secondary phases, respectively. Here, a, b, c, d, e, f, and g correspond to x=0.0, 0.025, 0.050, 0.075, 0.10, 0.125, and 0.15, respectively.