Mesure du pouvoir thermoélectrique des phases intermédiaires stables à 900 C dans les systèmes ternaires Ce-Fe-Si et U-Fe-Si.

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1 GdR-Thermoélectrique, Caen 28/29 juin 2007 Mesure du pouvoir thermoélectrique des phases intermédiaires stables à 900 C dans les systèmes ternaires Ce-Fe-Si et U-Fe-Si. D. Berthebaud 1, A. P. Gonçalves 3, D. Kaczorowski 2, O. Tougait 1, E. B. Lopes 3, A. Pikul 2 et H. Noël 1 1. Chimie du Solide et Matériaux. UMR CNRS 6226, Université de Rennes 1, 263 Avenue de Général Leclerc, Rennes, France 2. Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, Wrocław, Poland. 3. Departamento de Química, Instituto Tecnológico e Nuclear/CFMC-UL, P Sacavém, Portugal

2 GdR-Thermoélectrique, Caen 28/29 juin 2007 Thermoelectrical power of the intermediate phases of the Ce-Fe-Si and U-Fe-Si ternary systems, D. Berthebaud 1, A. P. Gonçalves 3, D. Kaczorowski 2, O. Tougait 1, E. B. Lopes 3, A. Pikul 2 et H. Noël 1 1. Chimie du Solide et Matériaux. UMR CNRS 6226, Université de Rennes 1, 263 Avenue de Général Leclerc, Rennes, France 2. Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, Wrocław, Poland. 3. Departamento de Química, Instituto Tecnológico e Nuclear/CFMC-UL, P Sacavém, Portugal

3 Motivation : heavy fermion thermoelectricity Ce- & U- based intermetallics Competing interactions unstable valence : Ce 3+/4+, U 3+/4+ long range RKKY : localized f- ē crystal field effect Kondo effects heavy fermion behavior.. complicated S(T) 1,2 hybridisation f-states and s-, p-, d- states of the ligands interatomic distances chemical substitutions pressure 1 D. Jaccard, J. Sierro in: P. Wachter, H. Boppart (Eds) Valence Instabilities, North-Holland, 1982 p A.K. Bhattachajee, B. Coqblin, Phys. Rev. B., 13 (1976) 3441

4 Remarkable feature of the Ce-Fe and U-Fe compounds RFe 2 : R = Y, Ce, Gd and U C15, cubic Laves phases neutron diffraction and XMCD experiments RFe 2 YFe 3 2 GdFe 3 2 CeFe 4 2 UFe 5 2 Tc (K) µ m (µb/fe) µ m (µb/r) Strong hybridization between 4f or 5f and 3d electrons 6 3 H. Kirchmayr, C.A. Poldy, in K.A. Gschneidner, L. Eyring (Eds), Handbook on the Physics and Chemistry of Rare Earth, chap.14, North-Holland, L. Paolasini, G.H. Lander, S.M. Shapio, R. Caciuffo, L. Lebech, L.P. Regnault, B. Roessli, J.M. fournier, Phys. Rev. B, 54 (1996) M. Wulff, G.H. Lander, B. Lech, A. Delapalme, Phys. Rev. B, 39 (1989) M.M.S. Brooks, O. Erikson, B. Johanson, J.JM. Franse, P.H. Frings, J. Phys. F., 18 (1988) L33.

5 transport properties of CeFe 2 ρ (T) and S (T) : idiosyncratic features 7 + subsequent experiments pressure H(T) alloying. electronic instability hybridization between Ce - 4f and Fe - 3d electrons Project : Systematic investigations of the crystal-chemistry and electronic properties of the intermediate phases of the Ce - & U Fe Si ternary systems 7 E. Gratz, E. Bauer, H. Nowotny, A.T. Burkov, M.V. Vedernikov, Solid State Comm., 69 ( 1989) 1007.

6 Outline : Part 1: The Ce-Fe-Si ternary system 1. the isothermal section at 900 C 2. the new compound 3. the magnetic properties of the ternary compounds 4. the electrical resistivity behavior 5. the thermoelectrical power Part 2 : the U-Fe-Si ternay system 1. the isothermal section 2. the new compounds and their electronic properties 3. transport properties of the ternary compounds Part 3: conclusion

7 Isothermal section at 900 C Ce-Fe-Si 10 Si phase Pearson code Structure type A Ce 2 FeSi 3 hp3 AlB B CeFeSi 2 oc16 CeNiSi 2 CeSi 2-α C CeFeSi tp6 Cu 2 Sb 90 CeSi 2-α2 CeSi 50 Ce 5 Si 4 Ce 3 Si 2 60 Ce 5 Si L 40 E B C D βfesi 2 60 FeSi 50 40Fe 5 Si 3 G 30 α1 F 20 α2 10 D CeFe 2 Si 2 ti10 CeAl 2 Ga 2 E F G Ce 5 Fe 2 Si 8 hp3 AlB 2 CeFe 13-x Si x 2.4<x<2.6 CeFe 13-y Si y 3.5<y<5 cf112 NaZn 13 ti56 Ce 2 Ni 17 Si 9 Ce CeFe 2 Ce 2 Fe 17 0 Fe CeFe 13-y Si y 3.5<y<5 D. Berthebaud et al., J Alloys Compd., in press. G: peritectoïd reaction Tt < 1200 C

8 Rietveld Refinement of CeFe 9 Si 4 Formula CeFe 9 Si 4 (Ce 2 Ni 17 Si 9 -type) Space group I4/mcm (No. 140) Lattice parameters (Ǻ) a : c : R-factors (%) R B : Rp Rexp Rwp χ (1) (1) D8 Bruker diffractometer Sol-X detector, monochromatized CuKα1 radiation

9 Magnetic properties of the ternary phases χ 1 [mol Fe /emu] CeFe 9 Si 4 B = 0.1 T σ [emu/g] µ eff = 2.9 µ B θ p = 77 K T = 2 K χ 0 = emu/mol Fe B [T] T [K] Ferromagnet : CeFe 13-x Si x, x = 2,4 (Tc = 202 K) σ [emu/g] Pauli paramagnet : CeFeSi, CeFeSi 2, CeFe 2 Si 2, Ce 5 Fe 2 Si 8 8 Y. Zhao, J. Liang, W. Tang, Y. Guo, G. Rao, J. Appl. Phys., 78 ( 1995) 2866.

10 ρ(t) of Ce-Fe-Si ternary compounds Metallic or semi-metallic behaviors

11 S(T) of Ce-Fe-Si ternary compounds modest values of the thermoelectrical power CeFeSi (S =40µV/K à 150K) et CeFeSi 2 (S = 30µV/K à 300K)

12 Isothermal section at 900 C Si Phase Pearson code Type structural U U-Fe-Si USi 3 80 USi 30 2-z H 70 βfesi U Si 5 C 60 USi 50 FeSi U 5 Si A I 4 50 U 3 Si 60 B 2 G 40 J Fe 5 Si 3 70 U 3 Si K α1 D E F α Liquide U 6 Fe UFe 2 (<805 C) Fe A B C D E U 2 FeSi 3 UFe 2 Si 2 U 3 Fe 2 Si 7 U 2 Fe 3 Si UFe 12-x Si x hp3 ti10 oc24 hp12 ti26 AlB 2 Al 4 Ba U 3 Fe 2 Si 7 MgZn 2 ThMn 12 1<x<3 F U 2 Fe 17-x Si x hp38 Th 2 Ni 17 X=3.2 à 4 G H UFeSi U 1.2 Fe 4 Si 9.7 op12 hp30 TiNiSi Er 1.2 Fe 4 Si 9.7 I U 2 Fe 3 Si 5 ms40 Lu 2 Co 3 Si 5 J UFe 5 Si 3 tp9 UFe 5 Si 3 K U 6 Fe 16 Si 7 cf116 Mg 6 Cu 16 Si 7

U 6 Fe 16 Si 7 U 6 Fe 16 Si 7 Cubic, Fm3m,

7206(5)Ǻ Th 6 Mn 23 Mg 6 Cu 16 Si 7 & U 6

7814(2)Ǻ Ir 4 Sc 11 (Ir 7 IrSc 16 Sc 6 )

13 U 6 Fe 16 Si 7 U 6 Fe 16 Si 7 Cubic, Fm3m, a = (5)Ǻ Th 6 Mn 23 Mg 6 Cu 16 Si 7 & U 6 Fe 16 Si 7 C U 6 Fe 16 Si 7 C Cubic, Fm3m, a = (2)Ǻ Ir 4 Sc 11 (Ir 7 IrSc 16 Sc 6 ) Zr 6 Zn 23 Si Perspective view of the crystal structure of U 6 Fe 16 Si 7 C

14 Magnetic properties of U 6 Fe 16 Si 7 & U 6 Fe 16 Si 7 C U 6 Fe 16 Si 7 : - Pauli paramagnet - delocalized system U 6 Fe 16 Si 7 C : - reduced magnetic moment on U atoms - partially localized system

15 Transport properties of U 6 Fe 16 Si 7 & U 6 Fe 16 Si 7 C metallic behavior few µv/k

16 UFe 5 Si 3 Peritectoïd formation : UFe 2 Si 2 + Fe 3 Si UFe 5 Si 3 Synthesis : rapid solidification of the melt (splat cooling) annealing at 900 C for 10 days Formula UFe 5 Si 3 Space group P4/mmm (No. 123) Parameters (Ǻ) a : c : R-factors (%) R B : Rp Rexp Rwp χ (5) (1) D8 Bruker diffractometer Sol-X detector, monochromatized CuKα1 radiation

17 Crystal Structure & Magnetic behavior of UFe 5 Si 3 Ferromagnet : Tc = 310(2) K c a b d( Fe-Fe) = 2.44 Ǻ d(fe-fe)iron = 2.48 Ǻ σs = 3µB/ f.u.

18 Transport properties of UFe 5 Si 3 ρ(t) = ρ0 + AT 2, T < 120K S(T) : anomaly at T = 70K Kondo scattering?

19 Transport properties of U-Fe-Si ternary compounds ρ (µω m) U 2 FeSi 3 U 2 Fe 3 Si 5 U 1.2 Fe 4 Si T(K) UFe 2 Si 2 U 3 Fe 2 Si 7 Thermopower (µv/k) U 3 Fe 2 Si 7 UFe 2 Si 2 U 1.2 Fe 4 Si U 2 Fe 3 Si T (K) U 2 FeSi 3 metallic or semi-metallic behaviors modest values of the thermoelectrical power

20 Conclusion : U & Ce Fe Si compounds Initerant : (Ce &U)FeSi, (Ce&U)Fe 2 Si 2 CeFeSi 2, CeFe 9 Si 4 Ce 5 Fe 2 Si 8, U 2 FeSi 3, U 6 Fe 16 Si 7 U 2 Fe 5 Si 3, U 2 Fe 3 Si 7, UFe 10 Si 2 partially localized : U 6 Fe 16 Si 7 C U 1.2 Fe 4 Si 9.7 U and Ce, f electrons hybridize with s-, p- or d- electrons of Si or Fe metallic or semi-metallic behaviors, modest values of thermoelectrical power, (CeFeSi, 40µV/K about 150 K) no simple relation between ρ(t) and S(T) hybridization of f and s-, p- or d- electrons and S(T) Future : Ge-compounds to move the system toward localization of the f electrons

21 Acknowledgements Dr. M. Potel, Dr. T. Roisnel, Dr. M. Pasturel J. Le Lannic, S. Casale Pr. R. Troc D. Badurski Dr. K. Gofryk Financial Support Dr. O. Sologub Dr. J.C Waerenborgh Dr. L. Pereira PAI Pessoa : ( ) PAI Polonium : ( ) CNRS-Polish Academy of Sciences ( )

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