Growth and anisotropic resistivity of PrBa2Cu4O8 and Pr2Ba4Cu7O15-gamma single crystals: A direct probe of metallic Cu-O double chains

We have successfully grown single crystals of PrBa2Cu4O8 (Pr124) and Pr2Ba4 Cu7O15-y (Pr247) by means of a flux method under high pressure oxygen gas o f 11 atm in Al2O3 or MgO crucibles. The most appropriate starting compositi on for the crystal growth was found to be Pr:Ba:Cu=1:2:3 for both Pr124 and Pr247, by examining the generated phases in samples prepared with widely v arying composition and sintering temperature. The temperature dependence of resistivity of Pr124 single crystals exhibited no superconductivity, at le ast down to 2 K. Resistivity along the b-axis direction showed a highly con ductive behavior, of which the origin is attributed to the double-chain sit e because of the large anisotropy between a- and b-axis resistivities. The anisotropy in resistivity between the a- and b-axis directions was found to be about 17 at room temperature, 275 at 85 K, and 190 at 5 K.