In this paper we have shown that polycrystalline films corresponding to Tl-2223 phase can be grown by employing high thalliation temperatures and short thalliation times. Ultrasonically deposited precursor films corresponding to Ba₂Ca_2.2Cu_3.3O_x(Ag_y) have been thalliated under high vacuum (∼ 10^-5 torr) at 890°C to obtain single phase Tl-2223 films. An off-stoichiometric and unreacted pellet of composition Tl_2.05Ba₂Ca₂Cu₃O_z has been used as source of Tl. We have shown that oxygen ambient is not necessary for the growth of Tl-2223 phase. The as-thalliated films have T_c’s in the range 123 K ±0.70 K. TheT_c has been found to be independent of the addition of AgNO₃ to the precursor. The zero field transportJ_c has been observed to be > 1.2 X 10⁵ A/cm² at 77 K. NearT_c (110 K-122 K),J_c has been observed to follow the power lawJ_c ∞ (1-T/T_c)_p,p 2. A power law withp tt 1.4 has been observed for the temperature range 70 K-110 K. An optimum doping of Ag has been observed to induce about 25% increase inJ_c and it also leads to uniform and enlarged grain growth. The surface morphology of Ag free samples contains plate like grains having arbitrary shapes. In contrast to this 0.35 Ag doped sample exhibits nearly rectangular plate like grains

In this paper we have reported investigations on the effect of simultaneous substitution of Bi and Tl at the H𝑔 site in the oxygen deficient H𝑔O_𝛿 layer of H𝑔Ba₂Ca₂Cu₃O_8+𝛿 cuprate superconductor. Bulk polycrystalline samples have been prepared by the two-step solid state reaction process (precursor route). It has been observed that the as grown H𝑔Bi_0.2–𝑥Tl_𝑥Ba₂Ca₂Cu₃O_8+𝛿 (with 𝑥 = 0.00, 0.05, 0.10, 0.15, 0.20) corresponds to the 1223 phase. It has been found that the 𝑇_c varies with the average cationic size $\langle R_d \rangle$ of the dopantcations. The optimum 𝑇_c of ∼ 131 K has been found for the composition H𝑔Bi_0.15Tl_0.05Ba₂Ca₂Cu₃O_8+𝛿. This composition leads to the average dopant cation size of ∼ 1.108 Å which is very close to the size of H𝑔²⁺ (∼ 1.11 Å). The microstructure for H𝑔Bi_0.15Tl_0.05Ba₂Ca₂Cu₃O_8+𝛿 has been found to be most dense and this phase exhibits the highest stability. The 𝐽_c of the optimum material H𝑔Bi_0.15Tl_0.05Ba₂Ca₂Cu₃O_8+𝛿 is found to be ∼ 1.29 × 10³ A/cm² at 77 K.