I. INTRODUCTION
It is of both academic interest and industrial necessity to study the properties of the Al–Ge–RE ternary compounds. However, up until now, a few researches about these ternary compounds have been reported (Wang et al., Reference Wang, Zhan, Pang and Du2011). The interesting structural chemistry and the rich magnetic properties make such materials worthy candidates for the investigation of the structural evolution and structure–properties relationships in rare-earth metal compounds (Zhang and Bobev, Reference Zhang and Bobev2013). The crystal structure of the RE2AlGe3 (RE = Y, Dy, Ho, Er, and Tm) compounds was studied for the first time by Johrendt et al. (Reference Johrendt, Mewis, Drescher, Wasser and Michels1996). These compounds are orthorhombic, space group Pnma (No. 62), with the Y2AlGe3 structure type. Later, the crystal structures of Sm2AlGe3 and Tb2AlGe3 were reported to have the same structure type (Mel'nyk et al., Reference Mel'nyk, Kuprysyuk, Gladyshevskii, Pikus and Staszczuk2005). So far, only two powder diffraction patterns of HoAl2.784Ge0.214 (Zhuravleva et al., Reference Zhuravleva, Rangan, Lane, Brazis, Kannewurf and Kanatzidis2001) and HoAl0.34Ge2 (Zeng et al., Reference Zeng, Qin, Chen, Liu, He and Nong2008) of the Ho–Al–Ge ternary system were included in the PDF (ICDD, Reference Kabekkodu2011). Therefore, in this paper, we present high-quality experimental powder X-ray diffraction (XRD) data for Ho2AlGe3.
II. EXPERIMENTAL
A. Synthesis
The sample of Ho2AlGe3 with a total mass of 2 g was prepared by arc melting using a non-consumable tungsten electrode and a water-cooled copper tray under argon atmosphere. Holmium (purity of 99.9%), aluminum (purity of 99.9%), and germanium (purity of 99.999%) were used as the starting materials. Titanium was used as an oxygen getter during the melting process. The sample was remelted three times in order to ensure the complete fusion and homogeneity. Weight losses were less than 1 wt%. After melting, the sample was enclosed in an evacuated quartz tube and annealed at 1073 K for 720 h, then cooled down at a rate of 10 K h−1 to room temperature. The sample was ground in an agate mortar and pestled to particle sizes no larger than 20 μm.
B. Data collection
XRD patterns of Ho2AlGe3 compound were collected at room temperature using a Rigaku Smart Lab 2006 powder diffractometer using CuKα radiation and a diffracted-beam graphite monochromator. The diffractometer was operated at 40 kV and 180 mA, the 2θ scan range was from 5° to 100° with a step size of 0.02°, and a count time of 6 s per step. Two sets of XRD data were collected, one with SRM 640 Si added as an internal standard to correct for possible systematic errors in the observed peak positions and the other without SRM 640 Si. The XRD pattern recorded from the specimen added with Si internal standard was used for indexing and for determining space group and unit-cell information, whereas the XRD pattern without Si internal standard was used for determining diffraction intensities. The 2θ obs values of the peaks were determined by the Savitzky–Golay second derivative using JADE 6.0 (Materials Data Inc., 2002) XRD Pattern Processing software of Materials Data, Inc. after smoothing the patterns, fitting and removing the background, and stripping the CuKα 2 peaks. Values of unit-cell parameters were then obtained by the least-squares method using JADE 6.0.
III. RESULTS
The experimental XRD pattern of compound Ho2AlGe3 is shown in Figure 1. All of the lines were successfully indexed using the Jade6.0 program in an orthorhombic system. By comparing the XRD data of Ho2AlGe3 with those of Y2AlGe3, it was found that Ho2AlGe3 and Y2AlGe3 (Johrendt et al., Reference Johrendt, Mewis, Drescher, Wasser and Michels1996) have the same structure type Pnma (No. 62). Using the corrected diffraction data of Ho2AlGe3, the accurate unit-cell parameters were obtained with a = 6.743 98(8) Å, b = 4.163 73(5) Å, c = 17.5834(2) Å, V = 493.74 Å3, Z = 4, and ρ x = 7.73 g cm−3. The figure of merit for indexing F N (Smith and Snyder, Reference Smith and Snyder1979) is F 30 = 202.7 (0.004, 37) and the value of RIR (RIR = 1.21) was obtained from the value of the ratio of the strongest line in the pattern to the strongest line of corundum in a 50–50 wt.% mixture of the two compounds. The observed and the calculated XRD data for Ho2AlGe3 are listed in Table I.
Figure 1. The powder X-ray diffraction pattern of Ho2AlGe3.
Table I. Powder diffraction data for Ho2AlGe3 (CuKα 1 , with λ = 1.540 60 Å).
aΔ2θ = 2θ obs–2θ cal.
ACKNOWLEDGEMENTS
This work was supported by the Natural Science Foundation of Guangxi (Grant No. 2011GXNSFA018034) and the Scientific Foundation of Guangxi High Education (Grant No. 2013ZD070).
