Effects of chemical substitution in CeRu₂Si₂, a well-studied heavy fermion system and YbPd₂Si₂ have been investigated through magnetic susceptibility and x-ray diffraction in the systems CeRu_xSi₂, CeRu_2−xOs_xSi₂, CeRu₂Si_2−xGe_x and YbPd₂Si_2−xGe_x. Replacing silicon by germanium generates normal chemical pressure effect, namely, Ce and Yb atoms in CeRu₂Si₂ and YbPd₂Si₂ became more and less magnetic respectively. With increasing Ge concentration, CeRu₂Si_2−xGe_x exhibits larger susceptibility at low temperature, goes to an antiferromagnetic state and finally becomes ferromagnetic. In YbPd₂Si_2−xGe_x, increasing Ge concentration drives Yb atoms to more divalent state. Electronic effects are more pronounced in CeRu_2−xOs_xSi₂ though CeRu₂Si₂ and CeOs₂Si₂ have very nearly the same lattice parameters. It is conjectured that CeRu₂Si_2−xGe_x may be the first Ce-based heavy fermion having a magnetic ground state.

Effect of incorporation of Sb in place of Bi in the bismuth cuprate superconductors has been examined. The nominal compositions studied are MCa_1·5Sr_1·5Cu₂O_8+δ and MCa₂Sr₂Cu₃O_10+δ, whereM=Bi_2−xSb_x or Bi_1·5−xSb_xPb_0·5. Different preparative routes such as the ceramic method, the matrix route as well as the melt route were employed to prepare the materials. No indication of either Sb entering the lattice or enhancement ofT_c is noted from resistivity, magnetic susceptibility and microwave absorption measurements.