Abstract
Two superconducting phases of Re3W have been found with different physical properties. One phase crystallizes in a noncentrosymmetric cubic (alpha-Mn) structure and has a superconducting transition temperature T-c of 7.8 K. The other phase has a hexagonal centrosymmetric structure and is superconducting with a T-c of 9.4 K. Switching between the two phases is possible by annealing the sample or remelting it. The properties of both phases of Re3W have been characterized by powder neutron diffraction, magnetization, and resistivity measurements. The temperature dependences of the lower and upper critical fields have been measured for both phases. These are used to determine the penetration depths and the coherence lengths for these systems.