Structural, magnetic and magnetocaloric properties of the Gd5Si4−x Sb x (x=0.5–3.5) phases

Substitution of Sb for Si in the Gd5Si4 phase results in the formation of ternary Gd5Si4−x Sb x phases with three different structure types. For x≤0.38 the Gd5Si4-type structure (Pnma space group) with all interslab T-T dimers intact exists (T is Si or Si/Sb mixture), in the x=1.21–1.79 region the Sm5Ge4-type structure (Pnma) with all interslab dimers broken is found. A further increase in the Sb concentration (x=2.27–3.1) leads to the appearance of the Eu5As4-type structure (Cmca) with broken but equivalent interslab T⋯T bonds. The Gd5Si4−x Sb x phases with 1.21≤x≤3.1 undergo ferromagnetic transitions in the temperature range from 164 to 295K. Magnetocaloric effect in terms of the isothermal entropy change, ΔS, reaches the maximum values of -3.7(4), -4.2(6) and -4.6(7)J/kgK for the Gd5Si2Sb2, Gd5Si1.5Sb2.5 and Gd5SiSb3 samples, respectively.