We have synthesized CaBaLaCu₃O_7−δ and related compounds Ca_0.9BaLaCu₃O_7−δ, Ca₁₁ BaLaCu₃O_7−δ and Ca_0.9Ce_0.1 BaLaCu₃O_7−δ in order to investigate the effect of doping and non-stoichiometry at Ca-sites on the superconducting behaviour of tetragonal superconductor CaBaLaCu₃O_7−δ. The superconducting transition temperature (T_c) of Ca_0.9 BaLaCu₃O_7−δ is the same as that of pure CaBaLaCu₃O_7−δ(67 ± 1 K). Calcium excess compound Ca_1.1 BaLaCu₃O_7−δ showed a drop inT_c to 72 K while the cerium-substituted compound Ca_0.9 Ce_0.1 BaLaCu₃ O_7−δ showed a drop inT_c to 43 K. The results are explained on the basis of difference in valency between the host and the dopant ion.

Doppler-broadened annihilation radiation spectra have been measured as a function of temperature from 77 K to 300 K, for several high temperature oxide superconductors viz single-phase YBCO, single- and mixed-phase Tl-Ca-Ba-Cu-O and Bi-Ca-Sr-Cu-O compounds. The temperature-dependent parameters extracted respond to a change at the onset of superconducting transition. The observations point to involvement of oxygen valence electrons at the onset of superconducting transition. Also a possible structural change and/or increase in electron density at the oxygen vacancy/defect sites seem to accompany the transition. In addition, the parameters derived are seen to be sensitive to the presence of more than one superconducting phases in mixed phase samples.

Single-phase 2122 samples of thallium and bismuth superconductors were made by the precursor matrix method. The thermopower of these samples was measured in the temperature range 250 K-T_c. The thermopower was positive and decreased linearly with increasing temperature aboveT_c (onset). The exponential enhancement of thermopower seen in the undoped and doped YBCO was not observed in these samples. The linear variation of thermopower can be explained on the basis of either a two-band model or a narrow band model.