Frequency dependent losses in REBa2Cu3O7 (RE = Dy, Ce)

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Abstract
Frequency dependent response of DyBa2Cu3O7 and CeBa2Cu3O7−x is measured by a simple contactless method over a wide frequency range (1 KHz to 13 MHz) at 300 and 77 K. The volume fraction of the superconducting phase can be easily estimated by the method. It is seen that χ′ (≈ −1/4π × Meissner fraction) for DyBa2Cu3O7 at 77 K is independent of frequency up to 10 MHz in the Meissner state. For CeBa2Cu3O7−x which is a non‐superconducting insulator, χ′ is positive and increases with frequency both at 300 and 77 K (χ′ (77 K) < χ′ (300 K)). The relaxation mechanism for the ac conduction in DyBa2Cu3O7 in the normal state is suggested to be primarily due to tunnelling and hopping of 2p hole polarons located at oxygen sites.