<p> New metal-rich Gd5T4 magnetocaloric phases (T - p-element) were designed, synthesized and characterized. These phases exhibit a close relationship between the valence electron count, size effect, crystal structure and physical properties. The targeted cleavage of the interslab T-T dimers was achieved in the Gd5Si4-xPx, Gd5Si4-xSbx and GdsSi4_xBix systems. While in the Gd5Si4-xPx system only a change in the valence electron count was employed for the desired structural transformations, in the Gd5Si4-xSbx and Gd5Si4-xBix systems both the valence electron count and size effect were used to break the interslab dimers. Incorporation of large Bi atoms into the Gd5Si4 phase resulted in the complete cleavage of the interslab T-T bonds and lead to novel slab stacking sequences accompanied by stacking faults. </p> <p> The Gd5Si4_xPx and Gd5Si4-xSbx phases undergo ferromagnetic transitions within a wide temperature range. Values of the corresponding magnetic entropy changes indicate the presence of a conventional magnetocaloric effect. This is likely due to the temperature stability of the structures with the broken dimers which hinders first-order coupled magnetostructural transitions. </p> <p> Metal-rich ferromagnetic phases of the RE5NixT3-x composition with RE = Gd, Dy, Lu, T = Sb, Bi were derived from the parent RE5T3 binaries. Incorporation of nickel stabilizes the orthorhombic Yb5Sb3-type structures at 800 °C. The Gd5Ni0.96Sb2.04, Gd5Ni0.71Bi2.29 and Dy5Ni0.66Bi2.34 phases show relatively low values of magnetocaloric effect. </p> / Thesis / Doctor of Philosophy (PhD)

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