I. INTRODUCTION
A large number of crystal structures of compounds in the Al–Nd–Ni ternary system have been reported in the ICSD (Inorganic Crystal Structure Database, 2015), such as AlNdNi, AlNdNi4, AlNd2Ni2, AlNd3Ni8, Al3NdNi2, Al4NdNi, etc. To our knowledge, there is no report about Al5NdNi2 compound. In this paper, the experimental X-ray powder diffraction (XRPD) pattern is presented, and the crystal structure of Al5NdNi2 is studied by the XRPD technique and Rietveld analysis.
II. EXPERIMENTAL
A. Al5NdNi2 preparation
The raw materials of pure metal with 99.99 wt.% aluminum, 99.99 wt.% neodymium, and 99.99 wt.% nickel were supplied by China New Metal Materials Technology Co., Ltd. The compound of Al5NdNi2 was prepared by melting the stoichiometric composition under argon atmosphere in an electric arc furnace. The total mass of the Al5NdNi2 sample is 2 g with the composition proportion of 34.02 wt.% Al, 36.38 wt.% Nd, and 29.60 wt.% Ni. In order to capture the residual oxygen, a titanium ingot was melted first before the alloy sample melting. In order to ensure that these elements fused together completely and the composition distributed uniformly, the sample was melted at least three times while being turned over in the gap. The melting processes were considered to be successful when the weight losses of the sample were <1 wt.%. Then, the sample ingot was enclosed in an evacuated quartz glass tube and annealed at the temperature of 1103 K for 1 month, and then cooled down at the rate of 0.2 K min−1 to ambient temperature. A sample was prepared for X-ray diffraction (XRD) testing by grinding Al5NdNi2 granules in a steel mortar.
B. Data collection and analyses
The XRPD data of Al5NdNi2 ternary compound were collected at the room temperature using the Rigaku Smart Lab (9) powder diffractometer which was equipped with a copper rotating anode powered with a voltage of 40 kV and current of 150 mA, and a diffracted-beam graphite monochromator. The goniometer radius is 300 mm, and the diffractometer was operated with the incident slit 1/2° and the receiving slit 0.3 mm. The scan range of diffraction angle (2θ) was from 10° to 100° with stepping-scanning mode, step size 0.02°, and 2.5 seconds per step. In order to calibrate systematic errors of 2θ locations in the experimental data, the internal standard method was employed, and the XRPD data for Al5NdNi2 mixed with high purity silicon as the internal standard material was collected.
The observed values of 2θ of the diffraction lines were chosen by the peak searching function of Jade 6.5 XRD pattern processing software (Materials Data Inc., 2002) based on the Savitzky–Golay 2nd derivatives combined with the counting statistics of intensity data. Structure refinement of Al5NdNi2 was performed by the Rietveld method using the DBWS-9807 program (Young et al., Reference Young, Larson and Paiva-Santos2000). In order to obtain the reference intensity ratio (RIR) value, the XRPD data of a mixture of 50 wt.% Al5NdNi2 and 50 wt.% NIST SRM 676a alumina was collected (Cline et al., Reference Cline, Von Dreele, Winburn, Stephens and Filliben2011).
III. RESULTS AND DISCUSSION
The experimental XRPD pattern of the Al5NdNi2 alloy is shown in Figure 1. All diffraction lines in the pattern were indexed successfully with an orthorhombic structure of space group Immm (No.71) using Jade 6.5. The lattice parameters were determined to be a = 7.0493 (1) Å, b = 9.5680 (1) Å, c = 3.9780 (1) Å, V = 268.30 Å3, ρ = 4.91 g cm−3, and Z = 2 by cell refinement from the list of peaks. Internal theta calibration was executed before locating the peaks. The F 30 (Smith–Snyder figure-of-merit) is 307.6(0.0030, 31) (Smith and Snyder, Reference Smith and Snyder1979). It was found that Al5NdNi2 and Al5CeNi2 share the same structure type as Al5NdNi2 by comparing crystal structure information with Al5CeNi2 from the report (Isikawa et al., Reference Isikawa, Mizushima, Sakurai, Mori, Munoz, Givord, Boucherle, Voiron, Oliveira and Flouquet1994). The calculated and observed values of XRPD data for Al5NdNi2 are listed in Table I.
Figure 1. Experimental XRPD pattern of Al5NdNi2.
Table I. Calculated and observed values of XRPD data for Al5NdNi2 (Cu Kα 1, with λ = 1.5406 Å).
aΔ2θ = 2θ cal–2θ obs.
bΔd = d cal–d obs.
Rietveld refinement of Al5NdNi2 was carried out with the DBWS-9807 program. The best results of Rietveld refinement for Al5NdNi2 were obtained when the 2b and 8n sites were only occupied by Al atoms, 2a sites were occupied by Nd atoms, and 4h sites were occupied by Ni atoms. The lattice parameters, refined by Rietveld refinement method, were a = 7.0508(1) Å, b = 9.5690(1) Å, c = 3.9792(1) Å, V = 268.47 Å3, ρ = 4.91 g cm−3, and Z = 2. The R factors were R p = 6.02%, R wp = 7.83%, R exp = 4.62%, S = 1.69, R B = 3.51, and R F = 2.50. The observed, calculated and residuals of XRPD pattern for Al5NdNi2 after Rietveld refinement are shown in Figure 2, and Table II shows the atomic sites and occupancy of Al5NdNi2 after refinement. The structure diagram of Al5NdNi2 is shown in Figure 3.
Figure 2. Observed, calculated, and residuals of XRPD pattern for Al5NdNi2 with Rietveld refinement.
Figure 3. (Color online) Crystal structure of the Al5NdNi2.
Table II. Atomic positions and occupancy of Al5NdNi2 with Rietveld refinement.
RIR is the ratio of the intensity of the strongest analyte line to the intensity of the (113) line of corundum when the analyte is mixed 50 : 50 by weight with corundum (Schreiner, Reference Schreiner1995). The XRPD data of a mixture of Al5NdNi2 and corundum in equal proportions by weight were shown in Figure 4. The corundum (113) line of 2θ 43.34° is the strongest peak for corundum, and the Al5NdNi2 (121) line of 2θ 31.87° is the strongest peak for Al5NdNi2. The peak height of these two non-overlapped peaks were determined by Jade 6.5, which were used to experimentally measure the RIR, and the RIR value is 1.23.
Figure 4. XRPD data of a mixture of Al5NdNi2 and corundum in equal proportions by weight.
ACKNOWLEDGEMENTS
This research was supported by International Centre for Diffraction Data (Grant No. 16-03), Guangxi Natural Science Foundation (Grant No. 2017JJA150615), Department of Education of Guangxi Zhuang Autonomous Region (Grant No. 2017KY0737), and Scientific Research Project of Baise University (Grant No. 2015KBN03).
SUPPLEMENTARY MATERIAL
The supplementary material for this article can be found at https://doi.org/10.1017/S088571561800026X
