Temperature and time dependence of phase formation of HgBa 2 Ca n −1 Cu n O 2( n +1)+ δ superconductors

We systematically studied the temperature and time dependence of phase formation of HgBa 2 Ca n −1 Cu n O 2( n +1)+ δ [Hg-12( n − 1) n , n = 1, 2, 3, 4] superconductors by a single step firing method. All samples were synthesized from high-purity HgO, BaO, CaO, and CuO in a sealed quartz tube. The phase formation of Hg-12( n − 1) n was examined by both x-ray diffraction (XRD) analysis and dc susceptibility measurement. A single-phase HgBa 2 CuO 4+ δ (Hg-1201) was obtained in a relatively wide temperature range (600–850 °C), while single-phase HgBa 2 CaCu 2 O 6+8 (Hg-1212) and HgBa 2 Ca 2 Cu 3 O 8+ δ (Hg-1223) were obtained only in narrow temperature and time ranges for the synthesis. The optimum temperatures for Hg-1212 and Hg-1223 were found to be 665 and 710 °C, respectively, when the sintering time was fixed for about 50 h. The HgBa 2 Ca 3 Cu 4 O 10+ δ (Hg-1234) phase was obtained as a mixture with Hg-1223.