STRUCTURE, THERMODYNAMIC, AND MAGNETIC PROPERTIES OF Ln4PdO7 WITH Ln=La, Nd, Sm, Eu, AND Gd

摘要

The structure of Nd4PdO7 has been determined and refined using the Rietveld method and combined CuK alpha1 X-ray and neutron powder data in space group P-1 with unit cell a=15.972(2), b=7.1927(7), c=6.9160(6) angstroms, alpha=96.299(4), beta=131.643(3), gamma=121.438(3) degrees, V=353.83(6) angstroms3 and Z=2, to RF=2.0% (neutron data) and RF=6.2% (X-ray data). The structure is closely related to the monoclinic La4PdO7 structure and exhibits Nd atoms coordinated by seven O atoms and Pd atoms coordinated by a square of O atoms. Isolated chains of trans-corner-sharing PdO4 squares are straight in the La4PdO7 structure and staggered in the Nd4PdO7 structure. Electron and powder XRD data show that Ln4PdO7 with Ln=Sm, Eu, and Gd is isostructural with Nd4PdO7. The enthalpies of dissolution of Ln4PdO7 (Ln=La, Nd) in 1.000 M HCl have been measured with an in-house built calorimeter, and from these values the enthalpies of formation for the compounds have been calculated. The decomposition temperatures of Ln4PdO7 with Ln=La and Nd in O have been determined by thermogravimetric measurements and found to decrease from 1645+-10 K for La4PdO7 to 1540+-10 K for Nd4PdO7. Using these data, an Ellingham diagram has been constructed assuming temperature-independent DELTA H degreesf and DELTA S degreesf. The magnetic susceptibilities of Ln4PdO7 with Ln=La, Nd, Sm, Eu, Gd, recorded at 10-320 K, were found to be in agreement with the expected ones for noninteracting Ln3+ ions. 17 refs.