Abstract
In the current work, a full description of the strong effect of Ca substitution in Ba sites of YBa2−xCaxCu3Oδ ceramics prepared by the sol-gel method on structural, electrical, and dielectric properties has been presented. XRD accompanied with Rietveld refinements confirm the significant structural change from orthorhombic phase (Pmmm) for (x = 0) YBa2Cu3Oδ (YBCO) to tetragonal phase for (x = 2) YCa2Cu3Oδ with a P4/mmm spatial group. XPS was performed comparing the two extremums on the Y3d, Cu2p, and O1s, showing a shift in all peaks, confirming the change in structure. SEM study also supports the large change that will take place as Ba sites are substituted by Ca, and the correct stoichiometry of the prepared ceramics was verified with EDS analysis. Such structural changes impact directly transport properties. Temperature-dependent resistivity measurements reveal a superconducting aspect in YBa2Cu3Oδ whereas YCa2Cu3Oδ ceramics are characterized by an insulating to metallic phase transition. The electrical properties in YCa2Cu3Oδ phase is mainly analyzed in terms of the temperature coefficient of resistivity (the TCR effect). YCa2Cu3Oδ ceramics are distinguished by excellent dielectric properties, including a colossal dielectric constant (εr′ ≈ 104) accompanied by low dielectric loss over a wide range of temperatures (298K–448K) and frequencies (10–105 Hz).
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