UC Irvine

Measurements of specific heat cp(T) and thermal conductivity λ(T) give a detailed picture of the Tc(x) phase diagram of superconducting U1-xThxBe13 below 1 K. A distinct minimum for Tc is noted for x ≈ 0.018. Increasing x further results in increasing values for Tc1 and the occurence of a second phase transition in the superconducting state at Tc2 < Tc1. Two phase transitions are observed between 0.02 < x < 0.045. Tc2 is roughly constant with varying x. For x > 0.05, only one single transition occurs and Tc decreases with further increasing x. Anomalous behaviour is also observed for UBe13-yBy for y values between 0 and 0.05 in the sense that the cp anomalies at the superconducting transition are distinctly larger than the corresponding discontinuity observed in pure UBe13. The influence of B-doping on the phase diagram of U1-xThxBe13 has also been studied. © 1989.