The Systems Ce–Al–(Si, Ge): Phase Equilibria and Physical Properties

Author： Flandorfer H. Kaczorowski D. Gröbner J. Rogl P. Wouters R. Godart C. Kostikas A.

ISSN： 0022-4596

Source： Journal of Solid State Chemistry, Vol.137, Iss.2, 1998-05, pp. : 191-205

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Abstract

The phase relations in the Ce-poor region of the ternary systems Al–Ce–(Ge, Si) were re-established at 600°C for Ce-concentrations up to 33 at.% Ce. The exact phase triangulation and structure determination for both systems were determined by EPMA and X-ray powder diffraction techniques. The homogeneity regions at 600°C were redetermined for the two phases within the section Ce(Al_xSi_1-x)₂: CeAl_1.46Si_0.54 (AlB₂-type) and CeAl_0.45–1.28Si_1.55–0.72 (ThSi₂-type). Besides these two phases, the only compound stable at 600°C in the system Al–Ce–Si was found to be CeAlSi₂ with a new structure type. CeAl₂Si₂ with the La₂O₂S-type, reported in earlier investigations, was shown to be metastable. Similarly, the existence of the phases reported earlier, “CeAl_1.25–1.75Si_2.75–2.25,” “Ce₂Al_3.5Si_4.5,” and “Ce₂Al₃Si₂,” was not confirmed at 500°C or 600°C. Ce₃Al₄Si₆ (Ce₃Al₄Si₆-type) was obtained in pure form after long-term annealing of melt spun samples at 500°C. For the Al–Ce–Ge system, our investigations at 600°C confirmed the five ternary compounds known from the existing literature. Homogeneity regions and location of the ternary phases were redefined. XAS and magnetic susceptibility measurements revealed a tripositive cerium ground state, ²F_5/2, in all the compounds studied. CeAl_1.2Si_0.8, CeAlSi₂, Ce₃Al₄Si₆, and Ce₂Al_1.6Ge_5.4 are antiferromagnets with T_N of 4.2, 3.7, 3.5, and 4.7 K, respectively. In turn, CeAl₂Si₂, CeAlGe, and Ce₂Al₃Ge₄ order ferromagnetically below 8, 5.6, and 11 K, respectively. The electrical resistivity of all these phases is characteristic of cerium intermetallics with pronounced crystal field effects.