• Sangeetha, Nediadath S.
• Pecharsky, Vitalij K.
• Mudring, Anja-Verena
• Smetana, Volodymyr
• Manfrinetti, Pietro
• Gschneidner, Karl A.
• Provino, Alessia
• Dhar, Sudesh K.

Abstract

<p>The phases reported in the literature as "R₂Pd₃" (R = rare earth element) have been reinvestigated. The exact stoichiometric composition of this series of compounds, which form for R = Sc, Y, and from Gd to Lu, including Yb, was found to be R₃Pd₅. All of them crystallize in the orthorhombic Pu₃Pd₅ structure type (oS32-Cmcm). The crystal structure has been refined from both single crystal (for Tb₃Pd₅) and powder X-ray diffraction data (for Tb₃Pd₅, Ho₃Pd₅, and Tm₃Pd₅). These compounds represent the first example of a binary phase formed by R and Pd adopting the Pu₃Pd₅-type featuring two crystallographic nonequivalent sites for the R atoms in the unit cell (the Wyckoff sites 4c and 8e). The variation of the lattice parameters and unit cell volume along the series strictly follows the trend of the lanthanide contraction. An extrapolation of the volume contraction versus the R³⁺ ionic radius gives an atomic volume of 29.74 ų for Yb in the hypothetical trivalent metallic state (under normal conditions). The formation temperatures and mechanisms, a peritectic reaction, and stability ranges have also been investigated. It turns out that Gd₃Pd₅ is a high temperature phase; it was not possible to quench this compound as a metastable phase, at room temperature, to be measured. In the light of our results, most of the R-Pd phase diagrams need to be revised. The magnetization, heat capacity, and electrical resistivity have been measured for Tb₃Pd₅, Dy₃Pd₅, Ho₃Pd₅, and Er₃Pd₅. They order antiferromagnetically at low temperatures, each undergoing two transitions, T_N1 and T_N2 (with T_N1 going from 13.5 to 5.1 K and T_N2 going from 6.5 to 3.6 K, respectively for Tb and Ho compounds). From our data we cannot distinguish whether the two rare earth sublattices sequentially order magnetically at T_N1 and T_N2, respectively, or whether they are simultaneously involved in both transitions. The electronic structure calculations predict antiferromagnetic ordering also for Gd₃Pd₅. Y₃Pd₅ is a Pauli paramagnet.</p>

Topics

• impedance spectroscopy
• compound
• single crystal
• resistivity
• powder X-ray diffraction
• phase diagram
• magnetization
• Lanthanide
• heat capacity
• rare earth metal
• metastable phase