Magnetic-susceptibility and heat-capacity measurements on Pr-rich PrBa2-xPrxCu3O7-y compounds.

Abstract

The compound ${\mathrm{PrBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathit{y}}$, though isostructural to the 90-K superconducting compounds, R${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathit{y}}$ (R=rare earth and Y), is semiconducting. Moreover, it orders magnetically with ${\mathit{T}}_{\mathit{N}}$\ensuremath{\sim}16 K and also exhibits a large electronic specific-heat coefficient \ensuremath{\gamma}. We have prepared Pr-rich ${\mathrm{PrBa}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Pr}}_{\mathit{x}}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathit{y}}$ (0\ensuremath{\le}x\ensuremath{\le}1) compounds to study the effect of excess Pr at the Ba site on the structure, magnetic ordering, and electronic specific-heat coefficient of this system. It is observed that single-phase compounds in the above series form up to x\ensuremath{\sim}0.8. The stoichiometric ${\mathrm{PrBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathit{y}}$ is orthorhombic but the compounds with excess Pr form in the closely related tetragonal structure. Magnetic-susceptibility and heat-capacity measurements reveal that both ${\mathit{T}}_{\mathit{N}}$ and \ensuremath{\gamma} decrease with increasing Pr concentration suggesting a common origin underlying the two.