Low frequency dielectric response of Cu0.5Tl0.5Ba2Ca2Cu3-xMxO10-δ (M = Cd, Zn, Ni; x=0, 1.5) superconductors

Abstract Cu 0.5 Tl 0.5 Ba 2 Ca 2 Cu 3-x M x O 10-δ (M = Cd, Zn, Ni; x = 0, 1.5) samples are synthesized by the two-step solid-state reaction method and extensively characterized by low frequency dielectric measurements. These samples have shown orthorhombic crystal structure in which the length of a-axis increases, but b & c-axes lengths suppress with the incorporation of Cd, Zn, Ni in the final compound. The T c (onset) and T c (R = 0) suppress with the doping of Cd whereas its values increase with the incorporation of Zn and Ni in the final compound. In ac-susceptibility measurements a suppression in the onset temperature of superconductivity observed in all doped samples, however, the maximum decrease is observed in Cd-doped samples. The vibrations of apical oxygen phonon modes of type Tl-O A -Cu(2) are hardened but the peak positions of other modes stay unchanged with the doping of Cd, Zn, Ni in the final compound. In the frequency dependent dielectric measurements the real (e / ) and imaginary (e // ) parts of the dielectric constants are suppressed with the increase of applied measurement frequency, however, their absolute values increase with the decrease of measurement temperature. In comparison with un-doped samples the absolute values of real e / and imaginary parts e // of dielectric constants suppress with the doping of Cd, Zn, Ni in the final compound; a maximum suppression is observed in Cd-doped samples. We have proposed from these results that doped Cd atoms in CuO 2 /CdO 2 planes produce an-harmonic oscillations, that in turn promotes the decrease in density of Cooper-pairs; it is reflected in the decrease of the dielectric constants of the final compound. Novel shift in dielectric loss (tanδ) from the negative to the positive value observed in the frequency region between 800 Hz and 1000 Hz in all Cu 0.5 Tl 0.5 Ba 2 Ca 2 Cu 3-x M x O 10-δ (M = Cd, Zn, Ni; 1.5) samples is attributed to be arising from the activation of various interfacial polarizations at different frequencies. An enhanced ac-conductivity jump is observed in pristine, Zn and Ni-doped samples which is altogether absent in Cd-doped samples providing unequivocal evidence of generation of an-harmonic oscillations and their pair breaking effects.