Volume dependence of the superconducting transition temperature for the high-temperature superconductorHgBa2Ca2−xPbxCu3O8+δ

The homologous series ${\mathrm{HgBa}}_2$ ${\mathrm{Ca}}_{\mathit{n}\mathrm{-}1}$ ${\mathrm{Cu}}_{\mathit{n}}$ ${\mathrm{O}}_{2\mathit{n}+2+\mathrm{\delta }}$ (n=1,2,3,4) is the newest and most promising of the layered high-${\mathit{T}}_{\mathit{c}}$ superconducting materials, as demonstrated in setting the highest ${\mathit{T}}_{\mathit{c}}$ among the known superconducting materials. We slightly doped ${\mathrm{HgBa}}_2$ ${\mathrm{Ca}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{8+\mathrm{\delta }}$ with Pb, producing ${\mathrm{HgBa}}_2$ ${\mathrm{Ca}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Pb}}_{\mathit{x}}$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{8+\mathrm{\delta }}$ with ${\mathit{T}}_{\mathit{c}}$ about 133 K. The Pb dopant helped material growth and still kept ${\mathit{T}}_{\mathit{c}}$ close to that of the optimally doped ${\mathrm{HgBa}}_2$ ${\mathrm{Ca}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{8+\mathrm{\delta }}$. The superconducting transition temperature as a function of pressure, ${\mathit{T}}_{\mathit{c}}$(P), was measured to 3 GPa. ${\mathit{T}}_{\mathit{c}}$ increases monotonicaly with ${\mathit{dT}}_{\mathit{c}}$(P)/dP≊1.5 K/GPa near ambient pressure. The lattice parameters as a function of pressure were measured to 5 GPa. The volume decreases monotonically and is represented by an isothermal bulk modulus of ${\mathit{B}}_{\mathit{V}}$=143±15 GPa. Both results were combined to produce ${\mathit{T}}_{\mathit{c}}$(V), which is readily comparable to theoretical models.