Phase equilibria and crystal structures in the system Eu–Pd–B

Phase equilibria in the ternary system Eu–Pd–B have been determined from X-ray powder diffraction for the isothermal section at 850 °C in the concentration range up to 34 at.% Eu. Phase relations at 850 °C are governed by one ternary phase, Eu2Pd14.9B4.9, which crystallizes with the Nd2Pd14+xB5−y-type structure. Rietveld refinement of X-ray powder intensity data confirmed space group I41/amd, a = 0.85653(3) nm, c = 1.66124(6) nm, x = 0.9, y = 0.1 (RF2 = Σ|F02−Fc2|/ΣF02 = 0.054). At 850 °C Eu2Pd14.9B4.9 appears without any significant homogeneity region. At temperatures below 730 ± 10 °C the tetragonal phase decomposes and a new monoclinic phase was found to form: Eu3Pd25−xB8−y. Rietveld refinement of X-ray powder data proved isotypism with the La3Pd25−xB8−y-type structure (space group P21/c, a = 1.17103(3) nm, b = 1.05623(2) nm, c = 1.60102(4), β = 102.199(1), x = 1.7, y = 0.07; RF2 = 0.054).At 850 °C, the solubilities of third component in europium borides and palladium borides are generally insignificant, but binary Eu1−xPd3+x is an exception (AuCu3-type structure, 0.01 < x < 0.10) as it exhibits an extended solid solution for boron extending into the ternary at 850 °C up to EuPd3By (y = 0.55). Furthermore, a rather large homogeneity region of fcc-Pd(Eu,B) extends into the ternary system.