Layered Lanthanide Research Articles

The synthesis and physical properties of the new layered lanthanide alkaline earth cobalt oxides [Ln 2MCo 2O 7 (Ln=Sm, Gd; M=Sr, Ba)

Three new oxides Sm 2SrCo 2O 7, Sm 2BaCo 2O 7 and Gd 2SrCo 2O 7 have been successfully synthesized by a solid state reaction method. The X — Ray diffraction spectra show that they are all isostructural with Sr 3Ti 2O 7. Ln 2SrCo 2O 7 (Ln=Sm, Gd) crystallized in the tetragonal system, Sm 2BaCo 2O 7 in the orthorhombic system. The Co-O bonds in CoO 2 planes of Ln 2SrCo 2O 7 are shorter than those of LnSrCoO 4 (Ln=Sm, Gd), thus their d electrons are more delocalized and their electrical resistivities are smaller. The electrical resistivities versus temperature in the range 300− 1100K showed that the five oxides represent weakly localized systems. In the lower temperature range, the magnetic behavior of Gd 2SrCo 2O 7 and GdSrCoO 4 fits the Curie-Weiss law well. The magnetic exchange reaction in the CoO sublattice of Gd 2 SrCo 2O 7 is ferromagnetic, but in GdSrCoO 4 is antiferromagnetic. The other three oxides with Sm +3 showed complex magnetic behavior which is perhaps related to the complexity of Sm +3.

Intercalation studies of several layered lanthanide oxychlorides with pyridine

Abstract A series of new intercalation compounds of the layered lanthanide oxychlorides, LnOC1 (Ln = Ho, Er, Tm and Yb), with pyridine has been successfully obtained at both room and high temperature (85 °C). The intercalated pyridine stoichiometries (χ) in the (py) x LnOCl compounds, determined by thermal gravimetric analysis, are independent of the reaction temperature and time after 2 weeks with the (py) x ErOCl and (py) x YbOCl, but are affected by the reaction temperature and time with the (py) x HoOCl and (py) x TmOCl. An average interlayer expansion of ∼5 a between the LnOCl layers upon pyridine intercalation suggests that the pyridine ring is oriented perpendicular to the host layers. The pyridine species inserted between the host layers are neutral pyridine molecules. The presence of water in pyridine leads to the pyridinium ion that also intercalates and has been identified by IR spectroscopy.

New Intercalation Compounds of Layered Lanthanide Oxychlorides LnOCl (Ln = Ho, Er, Tm, and Yb) with Pyridine and Substituted Pyridines

The lanthanide oxychlorides of Ho, Er, Tm, and Yb crystallize in the hexagonal space group, R[bar 3]m as a mixture of the SmSI- and YOF-type layered structures. The oxychlorides are prepared by heating Ln[sub 2]O[sub 3] (Ln = Ho, Er, Tm, and Yb) with excess NH[sub 4]Cl, followed by pyrohydrolysis. Crystalline phases of the lanthanide oxychlorides are obtained by heating LnOCl in LiCl/KCl fluxes at 450[degrees]C. The cell parameters obtained from X-ray powder diffraction are as follows: HoOCl, a = 3.7697, c = 27.766 [angstrom]; ErOCl, a = 3.745, c = 27.719 [angstrom]; TmOCl, a = 3.708, c = 27.72 [angstrom]; YbOCl, a = 3.704, c = 27.68 [angstrom]. A series of new pyridine intercalation compounds, (py)[sub x]LnOCl, have been prepared by reactions of pyridine with the LnOCl hosts. Intercalation compounds are characterized by X-ray powder diffraction, mass spectroscopy, elemental analysis, thermal gravimetric analysis, infrared spectroscopy, and temperature-dependent magnetic susceptibility. There is no reduction in the host lattice and pyridine apparently intercalates as the neutral molecule. An acid-base interaction is proposed for the mode of intercalation of pyridine into the lanthanide oxychlorides. Further studies on the intercalation of substituted pyridines, 4-ethylpyridine, and 2,6-lutidine, indicate that the C[sub 2] axis ofmore » pyridine is oriented perpendicular to the LnOCl layers. 38 refs., 7 figs., 6 tabs.« less

Magnetic properties of the new rare earth carbide fluoride layered compound: Ho 2CF 2

We present magnetic susceptibility, specific heat and neutron diffraction data of the new layered rare earth carbide flouride Ho 2CF 2. The susceptibility displays a rounded maximum centered around 4.6 K and a Curie-Weiss law at higher temperatures with a paramagnetic Curie temperature of -4.9(2) K. The specific heat shows a sharp anomaly at 3.61(5) K indicating the onset of long range ordering but also a considerable high temperature tail pointing to low dimensional magnetic behaviour. Low temperature neutron powder diffraction reveals additional magnetic Bragg peaks with significant critical scattering remaining well above the long range ordering temperature.

Oxygen excess in layered lanthanide nickelates

Density measurements on large single-crystal specimens of La 2NiO 4+δ and Pr 2NiO 4+δ show that oxygen nonstoichiometry arises from the presence of excess lattice oxygen. X-ray photoelectron spectra as well as X-ray absorption edge studies provide no evidence for the existence of Ni 3+ in these oxygen-excess nickelates under the conditions of the measurements. Transmission electron microscopy has revealed a novel type of exsolution process of the stoichiometric phase out of nonstoichiometric La 2NiO 4 during heating in CO 2 at 870 K for 3 h. An interpretation of the results in terms of the existence of peroxide species within the conducting layers is proposed.