THE SYSTEM La–Ni–In: PHASE EQUILIBRIA AND CRYSTAL STRUCTURES OF COMPOUNDS

Abstract

Interaction between the components in the La–Ni–In system was investigated by X-ray powder diffraction and, partially, scanning electron microscopy with energy-dispersive X-ray spectroscopy. Isothermal section of the phase diagram was constructed in full concentration range at 870 K (0–0.333 at. part La) and 670 K (> 0.333 at. part La). The samples were synthesized in an arc-furnace on a water-cooled Cu-plate under an argon atmosphere and annealed in silica tubes at 870 K for one month (range 0–0.333 at. part. La) and at 670 K (range > 0.333 at. part. La) for two months. The phase analysis was performed by X-ray powder diffraction method. Microstructures of polished samples and quantitative and qualitative analysis were carried out on a Tescan Vega 3 LMU scanning electron microscope equipped with an Oxford Instruments SDD X-MaxN20 detector. Fourteen ternary compounds, namely LaNi7In6 (LaNi7In6-type structure), LaNi9In2 (YNi9In2-type structure), LaNi3In6 (LaNi3In6-type structure), LaNi5In (CeNi5Sn-type structure), LaNi3In2 (HoNi2.6Ga2.4-type structure), LaNiIn4 (YNiAl4-type structure), La4Ni7In8 (Ce4Ni7In8-type structure), La5Ni6In11 (Pr5Ni6In11-type structure), LaNi2In (PrCo2Ga-type structure), LaNiIn (ZrNiAl-type structure), LaNi0.5–0.25In1.5–1.75 (AlB2-type structure), La2Ni2In (Mo2FeB2-type structure and о-La2Ni2In-type structure), La11Ni4In9 (Nd11Pd4In9-type structure), La12Ni6In (Sm12Ni6In-type structure) exist in the La–Ni–In system at the temperature of investigation. The crystal structure of о-La2Ni2In and La12Ni6In compounds was refined using powder data (STOE STADI P, Cu Kα1–radiation). The substitution of Ni for In was observed for compounds with AlB2- and YNi9In2-types structure and its composition can be described by the formulas LaNi0.5–0.25In1.5–1.75 and LaNi9–8.2In2–2.8 respectively. Binary compound LaNi5 dissolves up to 8.5 at. % of In and La2In – up to 5 at. % of Ni. Compounds of the La–Ni–In system can be divided into three groups: nickel-rich compounds are complex multi-layered with high values of coordination numbers of atoms; compounds of the middle part of the concentration triangle – two-layered compounds with coordination polyhedra in the form of prisms; compounds rich in lanthanum are complex multi-layered compounds with relatively low values of coordination numbers of atoms.