We report resistivity, structural, and magnetic susceptibility [${\chi }^{\mathrm{spin}\left(\mathrm{T}\right)]}$ measurements for the compounds ${\mathrm{Pr}}_1$${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ and ${\mathrm{Nd}}_1$${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$. The Nd compound is superconducting with an onset transition temperature of 90 K, while the Pr compound is semiconducting above 4 K. The lattice parameters for these two materials have been determined using x-ray diffraction techniques, and both appear to be tetragonal, although the ${\mathrm{Nd}}_1$${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ compound may exhibit some orthorhombic splitting. The high-temperature effective moments in the two systems are within a few percent of the free-ion moments. In each case the presence of significant curvature in the inverse susceptibility versus T behavior on the scale of 100 K suggests the presence of crystalline electric field splittings on the same energy scale. For the Pr compound this is further confirmed by a finite value for ${\chi }^{\mathrm{spin}}$(0) and a residual large constant term at high temperatures. The possible origin of semiconducting behavior as compared with superconducting behavior in the Nd and other rare-earth compounds is discussed in terms of differences in charge-carrier density and possible role of valence fluctuations among Pr rare-earth ions.

• Received 23 October 1987

DOI:https://doi.org/10.1103/PhysRevB.37.7454