Influence of Be substitution on the superconducting properties of (Cu0.5Tl0.5)Ba2(Ca2−yBey)(Cu2.5Cd0.5)O10−δ (y = 0, 0.1, 0.2, 0.35, 0.5) samples

Abstract

Be doped (Cu0.5Tl0.5)Ba2(Ca2−yBey)(Cu2.5Cd0.5)O10−δ (y = 0, 0.1, 0.2, 0.35, 0.5) superconductive samples are synthesized by solid state reaction method at normal pressure. The X-ray diffraction of these samples reveals a suppression in the c-axis length with the enhanced Be contents, reflecting the incorporation of Be at the inter plane Ca sites. The critical temperature Tc (R = 0) and onset temperature of diamagnetism Tc (onset) are found to increase with the increasing Be-contents up to y = 0.2 and decrease beyond this doping level. The room temperature resistivity, ρ(290K), is decreased in y = 0.1 and 0.2 samples, and raised to higher values beyond y = 0.2 in comparison to y = 0 samples. This improvement most likely arises due to the better interplane coupling caused by incorporation of Be at the Ca sites in the unit cell. The magnitude of diamagnetism is suppressed in all the Be-doped samples in comparison to un-doped sample. The FTIR absorption spectra show systematic hardening of the vibrational modes of apical oxygen with the increasing Be concentration. It confirms the incorporation of Be at the interplane Ca sites which results in the enhanced interplane coupling and hence the better superconducting properties in y = 0.1 and 0.2 samples. This hardening of the apical oxygen modes also complements our XRD results. The suppression of superconductivity parameters in samples with higher Be contents, namely y = 0.35 and 0.5, is attributed to the presence of heavier Cd at the Cu planar sites in CuO2/CdO2 planes. Cd atoms suppress the phonon’s population due to anharmonic oscillations it produces. Such anharmonicity is further promoted due to the enhanced interplane coupling caused by Be doping which further suppresses the phonon’s density and hence the superconductivity in the samples with higher Be-contents i.e. y = 0.35 and 0.5. These results stress on the vital role the electron–phonon interactions in the mechanism of superconductivity in cuprate superconductors.