Superconductivity up to 90 K in a New Family of the (Pb,Hg)Sr₂(Ca,Y)Cu₂O₇ System

A new family of superconductors were observed in the (Pb_0.5Hg_0.5)Sr₂(Ca_1-xY_x )Cu₂O_7-δ system for the composition range 0.5 ≤ x ≤ 0.2, with a maximum T_c of 90 K (at x = 0.3) as determined by electrical resistance and magnetization measurements. We have investigated the crystal structure across the entire composition range by X-ray diffraction, by which we identify the phase responsible for the superconductivity to be similar to that of (Pb,Cu)Sr₂CaCu₂O₇ (the so-called Pb-based 1212 phase) with a space group of P4/mmm and lattice constants of a ranging from 3.8159(6) Å for x = 0.5 to 3.8082(4) Å for x = 0.2, and c ranging from 11.950(2) Å for x = 0.5 to 12.022(2) Å for x = 0.2. Moreover, the chemical composition of one sample in the series having nominal composition (Pb_0.5Hg_0.5)Sr₂(Ca_0.5Y_{0 .5})Cu₂O_7-δ(x = 0.5) was determined to be [Pb_0.6Hg_0.2Cu_0.2]Sr_2.0[Ca _0.42Y_0.51Hg_0.07] Cu₂O_{7- δ} by energy-dispersive spectrometry.