The phase diagram of the Yb–Si system

doi:10.1016/S0925-8388(02)00809-5

Journal of Alloys and Compounds

Volume 348, Issues 1–2, 13 January 2003, Pages 100-104

https://doi.org/10.1016/S0925-8388(02)00809-5 Get rights and content

Abstract

The phase diagram of the Yb–Si system has been studied up to about 80 at.% Si by means of multitechnique investigations: differential thermal analysis (DTA), X-ray diffraction (XRD), optical microscopy (LOM), electron probe microanalysis (EMPA) and complemented with tensimetric measurements using the Knudsen effusion–mass spectrometry (KE–MS) and Knudsen effusion–weight loss (KE–WL) techniques. Besides the four already known intermediate phases: Yb₅Si₃ (Mn₅Si₃-type), YbSi (CrB-type), Yb₃Si₅ (Th₃Pd₅-type) and YbSi_2−x (AlB₂-type), two new compounds have been found and completely characterized: Yb₅Si₄ (Sm₅Ge₄-type) and Yb₃Si₄ (Ho₃Si₄-type). Two eutectics occur in this system: at less than 1 at.% Si (815 °C) and at about 82 at.% Si (1145 °C).

Introduction

Rare earths (R) and transition metal silicides form a class of fascinating materials for fundamental interface physics and for technological interest. This interest is even higher if Yb–Si intermediate phases are considered, where mixed valence instabilities can be compared between bulk silicides and interface reaction products.

Concerning the Yb–Si system, the phase diagram reported in Massalski [1] has been drawn simply considering the known existing phases and a presumed similarity with the Er–Si system. It seemed therefore worthwhile to study the whole system in order to provide information concerning phase equilibria and crystal chemistry, especially for the preparation of new compounds which could show interesting physical properties.

Recently, a paper of Grytsin et al. [2] reported the study of the Si-rich end of the Yb–Si system (above 60 at.% Si) with a careful examination of the complex crystal chemistry of the ytterbium disilicides and some physical properties of Yb₃Si₅. We substantially agree with their findings, even if with minor differences probably depending on the experimental techniques adopted.

In this paper we report, firstly, the results obtained in the determination of the phase diagram.

Section snippets

Experimental

Elemental silicon used in this investigation was ‘electronic grade’ type (purity 99.999 wt.%). Several samples of commercially available ytterbium were tested for their purity; it is well known that pure ytterbium metal, free of heavy pollutant elements, due to its high vapor pressure, can be easily obtained by sublimation techniques. However, other light elements, like hydrogen, may be present and affect greatly the melting point and the transformation temperature, raising the first and

Results and discussion

Fig. 1 shows the phase diagram of the Yb–Si system as obtained using the experimental techniques described in Section 2. Table 1 contains the crystallographic data for the intermediate phases formed in this system.

If we compare our findings with those reported by Grytsiv et al. [2] for the Si-rich side of the diagram, two main differences appear. A nearly systematic difference of about 10–15 degrees in the temperatures obtained from the thermal analysis (lower for Ref. [2]) depending probably

Concluding remarks

The phase diagram of the Yb–Si system has been investigated almost in the whole composition range finding two new intermediate phases: Yb₅Si₄ and Yb₃Si₄. Compared to the Ca–Si system, which is expected to be very similar, no great similarities appear: CaSi and YbSi are isotypic, CrB-type, then only two other phases have the same stoichiometry but not the crystal structure adopted, indicating that in this case valence electron concentration more than atomic dimensions drive compound formation

Acknowledgements

The authors thank the Italian Ministero dell’Istruzione, dell’Università e della Ricerca (MIUR) for financial support, under the National Research Program ‘Alloys and intermetallic compounds: thermodynamics, physical properties, reactivity’. The support by the Consiglio Nazionale delle Ricerche (CNR), under ‘Progetto finalizzato-Materiali speciali per tecnologie avanzate II’, is also acknowledged.

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The phase diagram of the Yb–Si system

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Concluding remarks

Acknowledgements

J. Solid State Chem.

J. Less-Common Metals

J. Alloys Comp.

J. Less-Common Metals

J. Solid State Chem.

J. Less-Common Metals

J. Alloys Comp.

Physica B

J. Less-Common Metals

J. Magn. Magn. Mater.

Thin Solid Films

Intermetallics