Structural, magnetic, and heat-capacity studies on Zn- and Ga-substituted PrBa2Cu3O7- delta.

Abstract

The compound ${\mathrm{PrBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ is not superconducting and exhibits antiferromagnetic ordering of the Pr moments with N\'eel temperature ${\mathit{T}}_{\mathit{N}}$ of \ensuremath{\sim}17 K. We have carried out magnetic, heat-capacity, and neutron-diffraction structural studies on Zn- and Ga-substituted ${\mathrm{PrBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$. The Zn and Ga dopants presumably substitute at the plane and the chain Cu sites, respectively. Our measurements reveal that ${\mathit{T}}_{\mathit{N}}$ is reduced in both cases; the reduction being faster for Ga substitution than for Zn substitution. For 10 at. % Zn substitution ${\mathit{T}}_{\mathit{N}}$ is \ensuremath{\sim}15--16 K, while for the same substitution level of Ga it is \ensuremath{\sim}12--14 K. It is rather unusual that the plane-site substitution has relatively less effect on ${\mathit{T}}_{\mathit{N}}$ than the chain-site substitution. From neutron-diffraction studies the cause of such contrasting behavior may be understood in terms of changed planar Cu-${\mathrm{O}}_{2}$ and Pr-${\mathrm{O}}_{2}$ bond lengths. The electronic specific-heat coefficient \ensuremath{\gamma} of the substituted samples is found to be large as in the parent ${\mathrm{PrBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ compound.