Structure, thermodynamic, and magnetic properties of Ln4PdO7 with Ln = La, Nd, Sm, Eu, and Gd

The structure of Nd4PdO7 has been determined and refined using the Rietveld method and combined CuK alpha(1), X-ray and neutron powder data in space group PI with unit cell 15.972(2), b = 7.1927(7), c = 6.9160(6)Angstrom, alpha = 96.299(4), beta = 131.643(3), gamma = 121.438(3)degrees, V = 353.83(6) Angstrom(3) and Z = 2, to R-F =2.0% (neutron data) and R-F = 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 X-ray powder diffraction data show that Ln(4)PdO(7) with Ln = Sm, Eu,and Gd is isostructural with Nd4PdO7. The enthalpies of dissolution of Ln(4)PdO(7) (Ln = La, Nd) in 1.000 M HCl have been measured,vith an in-house built calorimeter, and from these values the enthalpies of formation for the compounds have been calculated. The decomposition temperatures of Ln(4)PdO(7) with Ln = La and Nd in oxygen have been determined by thermogravimetric measurements and found to decrease from 01645 +/- 10 K for La4PdO7 to 1540 +/- 10 K for Nd4PdO7. Using these data, an Ellingham diagram has been constructed assuming temperature-independent Delta H(f)degrees and Delta S(f)degrees. The magnetic susceptibilities of Ln(4)PdO(7) with Lit = La, Nd, Sm, Eu, Gd, recorded in the temperature range 10-320 K, were found to be in agreement with the expected ones for noninteracting Ln(3+) ions. (C) 1999 Academic Press.