I. INTRODUCTION
The AB5-type hydrogen storage alloy is widely used in nickel-metal hydride batteries as anode material because of its good comprehensive performance, such as easy activation, dynamic performance, moderate capacity, relatively low price, etc. Researchers have done a lot of work with experimental and theoretical studies since LaNi5 hydrogen storage alloy was found in the 1960s of the past century, resulting in the development of a large number of AB5-type hydrogen storage alloys using the method of element substitution. At present, the structure of AB5 alloy materials has been investigated, and several AB5-type alloys have been confirmed, such as LaNi4.5Si0.5, LaMn3Ni2, LaMnNi4, LaNi4.25Al0.75, LaNi4.75Sn0.25, FeLaNi4, Cu3LaNi2, Ga1.2LaNi3.8, La0.5Ni5Y0.5, Ce0.5La0.5Ni5, Co2.5LaNi2.5, Cr0.5Cu1.5LaNi3, CuFeLaNi3, Al0.3Co0.75LaMn0.4Ni3.55, and others. The X-ray diffraction (XRD) patterns of a new phase in the Ce–Co–Ni ternary system have not been extensively studied, and there are very few reports about the structure of a CeCoNi phase from inorganic crystal structure database (Da et al., Reference Da, Brochado Oliveira and Harris1983) and ICDD's PDF4+ database (Klyamkin et al., Reference Klyamkin, Zakharkina and Tsikhotskaya2005).
So far, the experimental X-ray power diffraction data of the CeCo3Ni2 phase have not been included in the ICDD's Master Database. We report here the high-quality powder XRD data for the compound CeCo3Ni2.
II. EXPERIMENTAL
A. Synthesis
The sample of CeCo3Ni2 was generated from the melt of stoichiometric amounts of elemental constituents (99.9 wt% Ce, 99.99 wt% Co, and 99.99 wt% Ni by China New Metal Materials Technology Co. Ltd.) under high-purity argon atmosphere in a vacuum arc furnace, which has a tungsten electrode and a water-cooled copper tray. During the melting process, titanium was used as an oxygen capture agent. In order to ensure fused together and uniform composition, multiple melting processes (three times in this experiment) have been executed. Weight losses of the sample were <1 wt% with a total mass of 2 g. After melting, the sample was enclosed in an evacuated quartz tube and annealed at 1173 K for 480 h, and then cooled down to room temperature at a rate of 18 K h−1. Finally, the sample was ground to powder with a particle size smaller than 20 µm, in an agate mortar.
B. Data collection
The X-ray powder diffraction data for CeCo3Ni2 compound were collected at room temperature using a Rigaku SmartLab X-ray powder diffractometer, using CuKα radiation and a diffraction beam graphite monochromator. The diffractometer was operated at 40 kV and 150 mA, the scan range of 2θ was from 10° to 100° with a step size of 0.02° and a count-time of 10 s step−1.
X-ray powder diffraction data for the mixture of CeCo3Ni2 and an internal standard material (SRM Si) were collected. The obtained values of the Bragg angle, 2θ, were calibrated for instrumental errors using a parabolic fit with reference material SRM Si. Once the 2θ values were corrected, precise lattice parameters were obtained by a least-squares refinement (Zeng et al., Reference Zeng, He, Qin and Wei2007). The observed intensity (peak heights) of each diffraction peak was determined from the XRD data of a pure CeCo3Ni2 sample. The RIR value was calculated from the XRD data that were collected from a mixture of 50 wt% CeCo3Ni2 and 50 wt% corundum.
III. RESULTS
The experimental XRD pattern for the pure CeCo3Ni2 compound is shown in Figure 1. All peaks were successfully indexed by Jade 6.0 (2002, Materials Data Inc.) software with a hexagonal structure. It was found that CeCo3Ni2 and LaNi5 (Kisi et al., Reference Kisi, Buckley and Gray1992) have the same structure type (P6/mmm, No.191) by comparing the X-ray powder diffraction pattern of CeCo3Ni2 with that of LaNi5. The accurate lattice parameters were obtained with a = b = 4.9081(2) Å, c = 4.0034(2) Å, V = 83.52 Å3, Z = 1, and the density is 8.6347 g cm−3 by indexing and refining for the corrected X-ray powder diffraction data of CeCo3Ni2. The figure of merit for indexing F N (Smith and Snyder, Reference Smith and Snyder1979) is F 30 = 112.7(0.0089, 30) and the intensity ratio RIR value is 0.48. The observed and the calculated X-ray powder diffraction data for CeCo3Ni2 are listed in Table I.
Figure 1. The X-ray powder diffraction pattern of CeCo3Ni2.
Table I. X-ray powder diffraction data for CeCo3Ni2 (CuK α 1, with λ = 1.5406 Å).
aΔ2θ = 2θ obs − 2θ cal
bΔd = d obs − d cal.
ACKNOWLEDGMENTS
This work was supported by the Guangxi Natural Science Foundation (Grant No. 2011GXNSFA018034) and the scientific foundation of Guangxi high education (Grant No. 2013ZD070).
