ELECTRICAL-RESISTIVITY OF NONSUPERCONDUCTING LA4BACU5O13 AND LA5SRCU6O15-BASED COMPOUNDS DOWN TO THE MK TEMPERATURE-RANGE

We have measured the electrical resistivity of La4BaCu5O13 and La5SrCu 6O15-based compounds down to 39mK and 16mK, respectively, without obse rving superconductivity. When the resistivity rho - rho0 was proportio nal to T(gamma), the exponent gamma ranged from 1.18 to 1.83 for these compounds. where rho0 is residual resistivity and T is temperature. I t was ascertained from our measurements down to the mK range that thes e compounds were not superconducting because of a three-dimensional ne twork of CuO5 units.