Abstract T1 2 Ba 2 CaCu 2 O n (designated as T1-2212) has been synthesized using a precursor matrix reaction method. The superconducting phase with T c = 101 K was confirmed by microwave methods. A series of compounds T1 2 Ba 2 − y CaCu 2 O n with barium deficiency ( y = 0.0–0.75) were also prepared by the same route. The value of T c was found to monotonically decrease with deficiency of barium. Typically the value of T c reduced by about 20 K when barium concentration per formula unit reduced from 2.0 to 1.25 (keeping the concentration of all other compounds constant). The whole series of compounds were found to exhibit a single superconducting transition by microwave investigations. It was found that potassium substitution in barium deficient compounds enhanced the T c nearly to its original value. Further it was shown that even in thallium deficient compounds the lowering of T c was arrested and restored to its original value by substituting it with potassium. Thus it was shown that presence of potassium in T1-2212 has unique role of stabilizing the T c against the deteriorating effects due to possible T1/Ba nonstoichiometry. X-ray diffraction data suggests that thallium substitution occurs at barium site in the former case, whereas potassium substitutes at barium and thallium sites and the extent of substitution is dependent on the relative concentrations of thallium and barium in the starting composition.