Ordered CoSn-type ternary phases in Co3Sn3−xGex

► Ge substitutes preferentially for one of the two Sn sites in CoSn. ► We identified two new ordered phases: Co3Sn2Ge and Co3SnGe2. ► Co3Sn2Ge occurs in a two phase region. ► Phases show enhanced resistivity and reduced density of states at the Fermi level.