Synthesis and excess conductivity analysis of TlBa 2 (Ca 32y Be y )Cu 4 O 122d superconductors Nawazish A. Khan • M. Shamraiz • S. Qamar Abbass Received: 12 October 2013 / Accepted: 3 January 2014 / Published online: 20 January 2014 Ó Springer-Verlag Berlin Heidelberg 2014 Abstract TlBa 2 (Ca 3-y Be y )Cu 4 O 12-d (y = 0, 0.5, 1.0, 1.5, 2) samples are synthesized at normal pressure and the influence of doped Be-atoms on the superconductivity parameters at the microscopic level is investigated by carrying out excess conductivity analyses of conductivity data. The samples have shown tetragonal structure and the unit cell volume decreases with increased Be-doping. The onset temperature of superconductivity [T c (onset)] and zero resistivity critical temperature [T c (R = 0)] decrease with increased Be, however, the magnitude of diamagnetism is enhanced with Be (except for Be-doping of y = 1.0). The apical oxygen mode of the type Tl–O A –Cu(2) and CuO 2 planar oxygen mode are softened as observed in FTIR absorption measurements. The FIC analyses of conductiv- ity data have shown an increase in the coherence length along the c-axis and inter-plane coupling. The values of B c0 (T), B c1 (T), J c (0), s u are improved with the doping of Be. These observations suggested that due to the proximity effect there is less suppression in the value of the order parameter of the Cooper pairs from |w| 2 = 1 value in the CuO 2 planes in Be-doped samples that maintains the den- sity of carriers in the conducting CuO 2 planes [since the |w| 2 = n/2] which promotes enhancement in the magnitude of superconductivity. 1 Introduction The high irreversibility fields and J c values in supercon- ductors are needed for the potential use of a material in the device fabrication and wire application. In the family of thallium-based superconductors, TlBa 2 Ca 3 Cu 4 O 12-d is a potential candidate that has a charge reservoir layer (CRL) and four conducting CuO 2 planes (CP) [1–3]. The CRL has more vacant states in comparison with the conducting CuO 2 planes and, therefore, has Fermi level higher than conducting planes which forces the flow of the carriers from CRL to the CP. The outer two CuO 2 planes (OCP) situated in the immediate neighborhood of CRL are over- doped with carriers, whereas the inner two CuO 2 planes (ICP) being farther from the CRL are under-doped with the carriers [4]. The carrier deficiency of ICP induces some of the moments of Cu atoms to be aligned in anti-ferromag- netic fashion [5–7]; such materials turn insulating and marginalize the over-all superconducting properties of the final compound [8–19]. However, the direction of such anti-ferromagnetic aligned spin can be reversed by doping the inner CuO 2 planes with excess carriers. The density of the carriers in ICP can be increased by self-doping exper- iments accomplished by post-annealing of the samples in the oxygen atmosphere [14]. In such experiments, the intercalation of O d oxygen atoms controls the flows of the carriers to the CuO 2 planes [14, 15]. The self-doping experiments take longer time and reproducibility of the experiments is linked with purity of the oxygen supply. However, the self-doping experiments can be replaced by doping smaller sized Be-atom at Ca sites in the unit cell of TlBa 2 Ca 3 Cu 4 O 12-d superconductors. It is expected that doped Be-atom would suppress the distance between the conducting planes and homogenize the carrier’s concen- tration in various CuO 2 planes. The atomic radius of Be N. A. Khan (&)  M. Shamraiz  S. Q. Abbass Department of Physics, Materials Science Laboratory, Quaid-i-Azam University, Islamabad 45320, Pakistan e-mail: nawazishalik2@yahoo.com 123 Appl. Phys. A (2014) 116:1307–1313 DOI 10.1007/s00339-014-8225-6 ｄｯｷｮｬｯ｡､･､＠｢ｹ＠ｨｴｴｰＺＯＯｩｲ｡ｮｰ｡ｰ･ｲＮｩｲ＠ﺘﺎﺏ罇＠ﺎﻥ＠ﻣﻘﺎﻟﻪ＠ﻭ荿 ﺳﺎﻣﺎﻧﻪ＠ﺩﺍﻧﻠﻮﺩ＠ﺭﺍﯾ