Comments on “Thermoelectric properties of rare earth containing type-I clathrate compound, Dy8Al16Si30”
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In the paper by K. Rajput and S. Vitta published in the present journal the synthesis and the thermoelectric properties of the dysprosium containing clathrate Dy8Al16Si30 were reported. We prepared two samples following exactly to the technique described in the paper. Our XRD and SEM/EDX investigations do not confirm the presence of any amount of a Dy-containing clathrate phase in the sample.
KeywordsDiffraction Pattern Powder Diffraction Ionic Radius Clathrate Annealed Sample
In the recent paper by K. Rajput and S. Vitta  the synthesis and the thermoelectric properties of the dysprosium containing clathrate Dy8Al16Si30 were reported. The authors obtained by melting the elementary metals a polyphase material containing, as claimed by the authors, the clathrate phase. This conclusion was made on the basis of X-ray powder diffraction (XRD) of the polyphase sample. However, in our opinion, the diffraction pattern and the Rietveld analysis given in the paper do not provide strong evidence of the presence of the clathrate phase. The authors investigated the sample also using the scanning electron microscopy (SEM) with energy dispersive X-ray spectral analysis (SEM/EDX). However, only the total composition of the sample and not that of the individual phases was reported.
No clathrate phase was detected in both our samples. Although the diffraction pattern of the Dy-clathrate is not available, it can be simulated based on the existing Ba- and Sr-containing analogues. Substitution of Ba with its ionic radius (r ion ) of 1.47 Å by Sr with r ion = 1.31 Å results in a contraction of the unit cell from a = 10.632 to 10.465 Å [2, 3]. Linear extrapolation to the ionic radius of Dy3+ r ion = 1.083 Å leads to a value of a = 10.23 Å for the lattice constant of the Dy-clathrate. Using this value and replacing the scattering factor of Ba by that of Dy we obtained the diffraction pattern of a hypothetical Dy-clathrate which is shown in Fig. 1 as a line diagram.
No phase with the generic composition A8B46 characteristic of a type-I clathrate was found.
Thus both XRD and SEM/EDX do not confirm the presence of any amount of a Dy-containing clathrate phase in the sample prepared according to .
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