Effect of alkali metal carbonate A2CO3 (A = Li, Na, K) on AC susceptibility and superconducting properties of YBa2Cu3O7−δ

The effect of alkali metal carbonate (A 2 CO 3 ) x addition on YBa 2 Cu 3 O 7−δ with A = K, Na and Li for x = 0, 0.3, 0.5 and 1.0 wt% has been investigated. XRD patterns showed a single YBa 2 Cu 3 O 7−δ phase for all samples. The resistance versus temperature measurements showed that all samples exhibited metallic normal state behavior. The addition of Li 2 O 3 suppressed the superconductivity of YBa 2 Cu 3 O 7−δ more than Na 2 CO 3 and K 2 CO 3 . The AC susceptibility measurements showed a decrease in T c χ ′ for Li 2 CO 3 addition. T c χ ′ was not much affected with Na 2 CO 3 and K 2 CO 3 addition which was around 93–94 K for x = 0–1.0 wt%. However, T c χ ′ was very much suppressed in the Li 2 O 3 -added samples with T c χ ′ decreasing from 94 K for x = 0 to 83 K for x = 1.0 wt%. The peak temperature T p of the imaginary part of the susceptibility χ ″ shifted to lower temperatures for Li 2 CO 3 , Na 2 CO 3 and K 2 CO 3 addition. This indicated the intergranular coupling and flux pinning force were suppressed when alkali metal carbonate was added. This work also showed that alkali metals with smaller ionic radius, Li, suppressed superconductivity of YBa 2 Cu 3 O 7−δ more than the larger ionic radius, Na and K.