BULK THERMAL-EXPANSION STUDIES OF BICASRCU2OX AND BI2CASR2CU2OX

The compounds BiCaSrCu2O(x) and Bi2CaSr2Cu2O(x) were prepared by ceramic techniques and characterized by X-ray powder diffractometry (XRD) and microthermogravimetry (mu-TG) and their bulk thermal expansion measurements were carried out using dilatometry in the temperature range 298 less-than-or-equal-to T less-than-or-equal-to 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 mu-TG analysis carried out in oxygen, air, and nitrogen shows negligible weight loss (approximately 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 (alpha-1) for both BiCaSrCu2O(x) and Bi2CaSr2CuO(x) is almost the same (alpha-1 almost-equal-to 10.5 x 10(-6) K-1) and is found to be nearly half of that for YBa2Cu3O7 (alpha-1 almost-equal-to 18 x 10(-6) K-1), suggesting that the interatomic bonding in both BiCaSrCu2O(x) and Bi2CaSr2Cu2O(x) is stronger as compared to YBa2Cu3O7.