Papers by Keyword: Cuprates

Abstract: The size factor was analyzed as criterion for the formation of M₁₄Cu₂₄O₄₁ phases. Attempts to replace Sr and/or Ca in Sr₈Ca₆Cu₂₄O₄₁, the best-known spin-ladder compound, by Mg or Ba were carried out. No significant solubility was observed for Mg, whereas the Ca atoms, and up to 4 Sr atoms per formula unit in Sr₁₄Cu₂₄O₄₁, could be replaced by Ba. Based on the present investigation and literature data the minimum “critical” value of the average radius of the cations M above which an M₁₄Cu₂₄O₄₁ phase is formed was found to be close to 1.21 Å and the maximum “critical” value close to 1.40 Å.

Abstract: Since the discovery of the high Tc superconductors, several works have been made about the different properties of these materials. Anelastic spectroscopy experiments are sensitive tools to the study of defects in solids and phase transitions. By this technique, we can distinguish the different types of atomic jumps that happen to different temperatures. The intensity of the peaks in the anelastic spectrum and the "step" in the torsional modulus are related with the concentration of the relaxing entities, and the position of the peaks is determined by its mobility. In this paper, the study on Bi and Sm based superconducting oxides was made by anelastic relaxation measurements using a torsion pendulum. The samples were submitted to successive thermal treatments in high vacuum, in the temperature range between 100 K and 650 K, heating rate about 1 K/min. For Bi based superconducting oxides the results shown two peaks, that were associated to interstitial oxygen mobility and to orthorhombic to monoclinic phase transition. For Sm based superconducting oxides the results shown a relaxation peak that was attributed to the jumps of the oxygen atoms in the inter-chains O1 and O5 of the lattice.