RESUMO
Reactions of cerium and nickel in excess molten gallium were monitored by neutron diffraction during heating and cooling. The formation of binary intermediates CeGa2 and Ni2Ga3 was observed during heating. During cooling of the molten mixture from 900 °C, precipitation of BaAl4-type CeNi0.74Ga3.26 occurred at 850 °C. Upon cooling to 650 °C, this compound reacted in the flux to form Ce2NiGa10 and then Ce2NiGa12, the latter of which persisted to room temperature. Making use of this information, subsequent reactions were quenched at 750 °C to isolate crystals of CeNi0.74Ga3.26 for further study. Similar reactions replacing Ce with La and quenching above 750 °C yielded LaNi0.35Ga3.65 crystals. Magnetic susceptibility studies on CeNi0.74Ga3.26 indicate that the cerium is trivalent; the Ce3+ moments undergo a strongly anisotropic ferromagnetic ordering with moment perpendicular to the c axis below 7 K. Heat capacity data show little evidence of heavy fermion behavior. Resistivity measurements show that both LaNi0.35Ga3.65 and CeNi0.74Ga3.26 exhibit metallic behavior. Density of states calculations support this and indicate that Ni/Ga mixing in the compound stabilizes the structure.
RESUMO
La15(FeC6)4H was synthesized from the reaction of iron and anthracene in La/Ni eutectic flux. Anthracene was the source of both the carbon and hydrogen in the product. The structure of this metal carbide hydride features hydride ions in tetrahedral interstitial sites surrounded by lanthanum ions, which was confirmed by single-crystal neutron diffraction studies. The trigonal planar FeC6 units in which the central iron atom is coordinated by three ethylenide groups are similar to those found in La3.67FeC6, a previously reported compound that is formed in the absence of a hydride source. Magnetic susceptibility data confirm that the iron sites do not have magnetic moments. Density of states calculations indicate that La15(FeC6)4H is metallic and is stabilized by the incorporation of hydride anions.
