Nearly single-phase superconductors have been fabricated by the solid state reaction method. Resistance and magnetization measurements indicated that the samples annealed at for 6 h in had a superconducting transition temperature with and . The thermal stability of the Hg(Tl)-1223 phase was studied with the help of thermogravity, differential thermal analysis and the Raman spectrum. The thermal processes of Hg(Tl)-1223 phase decomposition indicated that the percentage of reversible oxygen evaporation was smaller and the onset temperature () of Hg(Tl)-1223 phase complete decomposition was much higher than those of the undoped Hg-system superconductor. Raman measurements showed that there existed a strong peak at with a small shoulder peak at and several other weak bands at 126, 142, 232 and . The strongest peak at may originate from the vibration mode of both interstitial site oxygens and apical oxygens. The addition of thallium introduced more oxygen atoms and stronger bonding into HgO planes, raising the vibration frequency of oxygen atoms and stabilizing the crystal structure of the Hg-1223 phase.