Bulk thermal expansion studies of BiCaSrCu₂O _x and Bi₂CaSr₂Cu₂O _x

Abstract

The compounds BiCaSrCu₂O _x and Bi₂CaSr₂Cu₂O _x were prepared by ceramic techniques and characterized by X-ray powder diffractometry (XRD) and microthermogravimetry (μTG) and their bulk thermal expansion measurements were carried out using dilatometry in the temperature range 298⩽T⩽1073 K in air. The results have been analyzed and are compared with those obtained earlier for YBa₂Cu₃O₇. The XRD analysis shows that both BiCaSrCu₂O _x and Bi₂CaSr₂Cu₂O _x are single phase in nature, having an orthorhombic symmetry. The μTG analysis carried out in oxygen, air, and nitrogen shows negligible weight loss (R~0.1%) on heating to 1073 K, indicating that these two compounds, unlike YBa₂Cu₃O₇, are quite stable. The analysis of bulk thermal expansion data reveals that the average linear thermal expansion coefficient (α ₁) for both BiCaSrCu₂O _x and Bi₂CaSr₂Cu₂O _x is almost the same (α ₁≈ 10.5×10⁻⁶ K⁻¹) and is found to be nearly half of that for YBa₂Cu₃O₇ (α ₁≈ 18×10⁻⁶ K⁻¹), suggesting that the interatomic bonding in both BiCaSrCu₂O _x and Bi₂CaSr₂Cu₂O _x is stronger as compared to YBa₂Cu₃O₇.