X-ray diffraction experiments on Y₄Co₃ single crystals suggest that the positions of the Co atoms in the channels between the Y prism columns ('c axis sites') are only weakly correlated with the rest of the structure. The Y₄Co₃ phase can be stabilised by silicon such that peritectic rather than peritectoid formation occurs. The substitution of about 2 at.% Co by Si destroys both superconductivity and magnetism.