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X-ray investigation of alloys with composition Th37.5M25M′37.5; M=Al,Ga, M′=Si,Ge
Journal of Alloys and Compounds 365 (2004) 173–177
X-ray investigation of alloys with composition Th37.5M25M37.5; M=Al,Ga, M=Si,Ge V. Kaveˇcanský a,b , Peter Rogl a,∗ , H. Noel c , M. Mihalik b , K. Wochowski d , R. Troc d a
c
Institut für Physikalische Chemie, Univ. Wien, Währingerstr. 42, A-1090 Wien, Austria b Institute of Experimental Physics, Slovak Acad. Sciences, Košice, Slovakia Laboratoire de Chemie du Solide et Inorganique Moléculaire, Université de Rennes I, UMR-CNRS 6511, Avenue du Général Leclerc, F-35042 Rennes, cedex, France d W. Trzebiatowski Institute for Low Temperature and Structure Research, Polish Academy of Sciences, P-50-950 Wroclaw, P.O. Box 1410, Poland Received 10 June 2003; accepted 16 June 2003
Abstract Alloys with composition Th37.5 M25 M 37.5 (or ‘Th3 M2 M 3 ’), where M = Al,Ga; M = Si,Ge, prepared by arc melting, have been investigated by means of X-ray Rietveld analyses. No ternary compounds were observed bearing isotypism with the homologous U3 Ga2 Ge3 type of structure. In all cases the major phase corresponds to a solid solution of the M-metal component in binary ThSi2−y or ThGe2−y , respectively. © 2003 Elsevier B.V. All rights reserved. Keywords: Actinide compounds; Crystal structure; X-ray diffraction
1. Introduction U3 Si2 dispersion in an aluminium matrix has proven to be a useful high-density uranium and proliferation-resistant fuel for research and test reactors [1]. Preliminary investigations of analogous gallium-containing fuels revealed rather high changes in volume after heat treatment for 100 h at 400 ◦ C and these fuels were therefore rated with poor irradiation performance [2]. In a recent paper we have dealt with the crystal structure of novel compounds with the formula U3 M2 M 3 , where M and M are metals from the third and fourth main group, respectively [3]. Neutron powder diffraction studies as well as investigation of single crystals U3 Al2 Si(Ge)3 revealed a noncollinear ferromagnetic spin structure for the uranium atoms in the eight-fold position [4]. For proper derivation of the uranium ground-state from low temperature specific heat measurements on these materials, however, comparison with an isotypic nonmagnetic ∗ Corresponding author. Tel.: +43-1-4277-52456; fax: +43-1-4277-9524. E-mail address: [email protected] (P. Rogl).
0925-8388/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0925-8388(03)00658-3
material would be of benefit. As no La, Y, Lu-containing isotype of U3 M2 M 3 could be found, we decided to inspect the homologous systems with thorium, particularly as there is hitherto no information available on phase relations within systems Th–M–M with M = Al,Ga and M = Si,Ge [5].
2. Experimental Alloys, Th37.5 M25 M 37.5 ,with a total amount of ∼1 g were prepared by argon arc-melting ingots of the elements. Starting from a nominal composition, 37.5 at.% Th, 25.0 at.% Al or Ga and 37.5 at.% Si or Ge, well-crystallized products were obtained. For homogenisation the samples were wrapped in Ta-foil, sealed in evacuated silica tubes and annealed at 900 ◦ C for 4 days and quenched. Further details of sample preparation and heat treatment as well as handling of the specimens in glove boxes can be found from our previous paper [3]. A Jeol-JSM 6400 scanning electron microscope was used to reveal the microstructure of the samples. The composition of the phases was analysed by
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energy dispersive X-ray spectroscopy (EMPA-EDS) with an Oxford-Link-Isis Si/Li analyser. Precise lattice parameters and standard deviations were obtained from a least squares refinement of room temperature Guinier–Huber image plate X-ray powder data, using monochromatic CuK␣1 radiation with an internal standard of 6N-pure Ge (aGe = 0.5657906 nm at RT). Rietveld refinements were performed using the gsas software package [6].
Table 1 Crystallographic data for binary phases (extracted from Villars et al. [7]) Phase
ThSi2 ThSi ThGa2 ThGe2 ThGe
Structure type
Space group
a
Unit cell dimensions (nm) b
c
V
␣-ThSi2 FeB ␣-ThSi2 ␣-ThSi2 NaCl
I41 /amd Pnma I41 /amd I41 /amd ¯ Fm3m
0.4118 0.788 0.4247 0.4106 0.6046
=a 0.415 =a =a =a
1.4221 0.589 1.4701 1.4193 =a
0.2412 0.1926 0.2652 0.2393 0.2210
3. Results and discussion Phase relations in the vicinity of the composition Th37.5 M25 M 37.5 (‘Th3 M2 M 3 ’) were evaluated on the base of analysis of corresponding binary phase diagrams [5]. A compilation of crystallographic data of the binary compounds ThM2 (ThM 2 ) and ThM (ThM ) is presented in Table 1. Measured diffraction patterns were processed in two steps. At first, a structureless fitting of the whole X-ray pattern was performed using the LeBail method [8]. In this way numerical values of all nonstructural parameters were refined (e.g. background, analytical description of the peak profile, parameters for the description of the experimental equipment as well as the unit cell dimensions of all phases involved). When convergence of the least squares calculations was achieved, the refined values were fixed and the crystal structure parameters of the phases with sufficient weight fraction were refined. Fractional occupations of the atom sites were constrained in accordance with the chemical composition of the phases determined by EMPA. Finally a full profile Rietveld refinement of all structural and structureless parameters was performed.
This refinement strategy proved successful to minimize the correlations among the large number of parameters to be refined. The quality of the fit is characterised by residuals Rw and Rwp . Final refinement results are summarized in Figs. 1–4. Crystallographic data are compiled in Table 2. 3.1. Rietveld refinement of the alloys Th37.5 Al25 Si37.5 and Th37.5 Ga25 Si37.5 The majority phases in these alloys are formed by (i) a tetragonal phase of ␣ThSi2 type (space group I41 /amd) and (ii) an orthorhombic phase of the FeB type (Pnma). While Th37.5 Al25 Si37.5 consists only from these two phases [Th(Alx Si1−x )2 and Th(Alx Si1−x )], the phase composition of Th37.5 Ga25 Si37.5 was found to be more complicated. Besides the two phases, [Th(Gax Si1−x )2 and Th(Gax Si1−x )], secondary phases were identified: (i) another ␣ThSi2 type phase, Th(Gax Si1−x )2 , with significantly different lattice parameters, which are close to those of ThGa2 and (ii) traces of probably Th3 (Gax Si1−x )5 (defect AlB2 -type, P6/mmm). The difference in the X-ray
Fig. 1. Rietveld refinement of alloy Th37.5 Al25 Si37.5 .
V. Kaveˇcansk´y et al. / Journal of Alloys and Compounds 365 (2004) 173–177
175
Fig. 2. Rietveld refinement of alloy Th37.5 Ga25 Si37.5 .
scattering factors for Ga and Si enabled the refinement of the occupancy factors for the Si(Ga) positions though the process was considerably complicated by strong correlations between temperature and occupancy parameters. However, the estimated value of x for Th(Gax Si1−x )2 does not correspond to the determined values of the lattice parameters since the determined unit cell volume is smaller than that of pure ␣ThSi2 . This discrepancy may hint towards defect formation and should be the subject of further investigation.
3.2. Rietveld refinement of the alloys Th37.5 Al25 Ge37.5 and Th37.5 Ga25 Ge37.5 The phase constitution of the two samples is very similar concerning not only its quality but even the weight fractions of the determined phases are close. The majority phase for both compounds is the tetragonal ␣ThSi2 type Th(Alx Ge1−x )2 and/or Th(Gax Ge1−x )2 , respectively while the second one was identified as face centred cubic Th(Alx Ge1−x ) and/or Th(Gax Ge1−x ). No other phases were
Fig. 3. Rietveld refinement of alloy Th37.5 Al25 Ge37.5 .
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Fig. 4. Rietveld refinement of alloy Th37.5 Ga25 Ge37.5 . Table 2 Crystallographic data for alloys with composition Th37.5 M25 M 37.5 (M = Al,Ga, M = Si,Ge) Parameter/nominal Th37.5 Al25 Si37.5 Th37.5 Ga25 Si37.5 Th37.5 Al25 Ge37.5 composition of alloy (at.% ) X-ray data collection Image plate Radiation CuK␣1 2θ angular range 8 ≤ 2θ ≤ 100 a Rwp 0.138 0.1102 0.1295 Rp a 0.089 0.0737 0.0815 Phase I—Structure type ␣-ThSi2 , space group I41 /amd Formula Th(Alx Si1−x )2−y Th(Gax Si1−x )2−y Th(Alx Ge1−x )2−y xb 0.4 0.15 0.36 yb 0.22 0.37 0.26 EMPA in at.% Th36 Al25.3 Si38.7 Th38.0 Ga9.5 Si52.5 Th36.5 Al23 Ge40.5 Atom site occupancy fAl = 0.35; fSi = 0.54 fGa = 0.12; fSi = 0.69 fAl = 0.32; fGe = 0.56 Atom fract. coord. zSi = 0.2893(7) zSi = 0.2945(10) zGe = 0.2925(3) a (nm) 0.417118(7) 0.41136(3) 0.419281(5) c (nm) 1.43485(4) 1.3993(2) 1.44115(3) 3 0.249647(9) 0.23678(4) 0.253349(6) V (nm) c Weight fraction (%) 84 46 92 Phase II Structure type FeB FeB NaCl ¯ Space group Pnma Pnma Fm3m Formula Th(Alx Si1−x ) Th(Gax Si1−x ) ThGe xb 0.09 0.1 – EMPA in at.% Th50 Al4.4 Si45.6 Th50.5 Ga5.0 Si44.5 Th50 Al0 Ge50 Atom site occupancy fAl = 0.09; fSi = 0.91 fGa = 0.1; fSi =0.9 – a (nm) 0.79314(11) 0.79424(6) 0.605300(2) b (nm) 0.41395(5) 0.41378(3) =a c (nm) 0.59235(7) 0.59259(4) =a 3 V (nm) 0.19448(4) 0.19475(2) 0.221775(1) Weight fraction (%)c 16 36 8 Phase III—Structure type: ␣-ThSi2 , space group: I41 /amd, formula: Th(Gax Si1−x )2−y ; EMPA unresolved Atom site occupancy – fGa = 0.93; fSi = 0.07 – xb – 0.93 – – 0.0 – yb a (nm) – 0.42330(7) – c (nm) – 1.4704(5) – 0.2635(1) V (nm)3 Weight fraction (%)c – 18 – 1 a R 2 2 wp = { wi [(yoi −yci )(yoi −ybi )/yoi ] / wi (yoi −ybi ) } 2 ; Rp ={ |yoi −yci |.|yoi −ybi |/yoi }/ |yoi −ybi |. b Determined from refined values of fractional occupancy of the atom site (constrained according to c The sample is assumed to consist only of the determined phases. The sum of the weight fractions
Th37.5 Ga25 Ge37.5
0.1435 0.0954 Th(Gax Ge1−x )2−y 0.36 0.38 Th38.2 Ga22 Ge39.8 fGa = 0.29; fGe = 0.52 zGe = 0.2925(4) 0.418581(5) 1.42920(3) 0.250410(7) 88 NaCl ¯ Fm3m ThGe – Th50 Ga0 Ge50 – 0.60441(2) =a =a 0.22080(1) 12 – – – – – –
chemical composition derived by EMPA). is constrained to 1.0.
V. Kaveˇcansk´y et al. / Journal of Alloys and Compounds 365 (2004) 173–177
determined. In the case of the Th–Al–Ge system, the occupancy factor of the Ge(Al) positions could be refined. The estimated value of x is in good agreement with the unit cell volume of the Th(Alx Ge1−x )2 phase. 4. Summary The combined analyses (EMPA and XRD) of the constitution of alloys Th37.5 M25 M 37.5 (or Th3 M2 M 3 , M = Al,Ga; M = Si,Ge) revealed in all cases a multiphase structure where the major phase corresponds to a solid solution of the M-metal component in binary ThSi2−y or ThGe2−y , respectively. No isotypes to the U3 Ga2 Ge3 structure were found. Acknowledgements This research was sponsored by the Austrian–Slovak bilateral project 33s33, the Austrian–Polish bilateral Project 14/2001 and by the INTAS-project 234.
177
References [1] G.L. Garner, K.E. Bogacik, J.E. King, Trans. Am. Nucl. Soc. USA 55 (1987) 284. [2] T.C. Wiencek, R.F. Domagala, Trans. Am. Nucl. Soc. USA 55 (1987) 284. [3] F. Weitzer, M. Potel, H. Noël, P. Rogl, J. Solid State Chem. 111 (1994) 275. [4] A.G. Gukasov, P. Rogl, P.J. Brown, M. Mihalik, A.A. Menovsky, J. Phys. Condens. Matter 14 (2002) 8841. [5] P. Villars, A. Prince, H. Okamoto, Handbook of Ternary Alloy Phase Diagrams (1995) ASM InternationalMaterials Park, OH. [6] A.C. Larson, R.B. Von Dreele, GSAS—Generalised Crystal Structure Analysis System, Los Alamos National Laboratory, Los Alamos NM, 1990. [7] P. Villars, L.D. Calvert, Pearson’s Handbook of Crystallographic Data For Intermetallic Phases, 2nd Edition, ASM International, Materials Park, OH, 1991. [8] A. LeBail, Accuracy in Powder Diffraction II E. Prince J.K. Stalick (Eds.), Proceedings of the International Conference, May 26–29, NIST Special Publication 846 (1992) 213.
X-ray investigation of alloys with composition Th37.5M25M37.5; M=Al,Ga, M=Si,Ge V. Kaveˇcanský a,b , Peter Rogl a,∗ , H. Noel c , M. Mihalik b , K. Wochowski d , R. Troc d a
c
Institut für Physikalische Chemie, Univ. Wien, Währingerstr. 42, A-1090 Wien, Austria b Institute of Experimental Physics, Slovak Acad. Sciences, Košice, Slovakia Laboratoire de Chemie du Solide et Inorganique Moléculaire, Université de Rennes I, UMR-CNRS 6511, Avenue du Général Leclerc, F-35042 Rennes, cedex, France d W. Trzebiatowski Institute for Low Temperature and Structure Research, Polish Academy of Sciences, P-50-950 Wroclaw, P.O. Box 1410, Poland Received 10 June 2003; accepted 16 June 2003
Abstract Alloys with composition Th37.5 M25 M 37.5 (or ‘Th3 M2 M 3 ’), where M = Al,Ga; M = Si,Ge, prepared by arc melting, have been investigated by means of X-ray Rietveld analyses. No ternary compounds were observed bearing isotypism with the homologous U3 Ga2 Ge3 type of structure. In all cases the major phase corresponds to a solid solution of the M-metal component in binary ThSi2−y or ThGe2−y , respectively. © 2003 Elsevier B.V. All rights reserved. Keywords: Actinide compounds; Crystal structure; X-ray diffraction
1. Introduction U3 Si2 dispersion in an aluminium matrix has proven to be a useful high-density uranium and proliferation-resistant fuel for research and test reactors [1]. Preliminary investigations of analogous gallium-containing fuels revealed rather high changes in volume after heat treatment for 100 h at 400 ◦ C and these fuels were therefore rated with poor irradiation performance [2]. In a recent paper we have dealt with the crystal structure of novel compounds with the formula U3 M2 M 3 , where M and M are metals from the third and fourth main group, respectively [3]. Neutron powder diffraction studies as well as investigation of single crystals U3 Al2 Si(Ge)3 revealed a noncollinear ferromagnetic spin structure for the uranium atoms in the eight-fold position [4]. For proper derivation of the uranium ground-state from low temperature specific heat measurements on these materials, however, comparison with an isotypic nonmagnetic ∗ Corresponding author. Tel.: +43-1-4277-52456; fax: +43-1-4277-9524. E-mail address: [email protected] (P. Rogl).
0925-8388/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0925-8388(03)00658-3
material would be of benefit. As no La, Y, Lu-containing isotype of U3 M2 M 3 could be found, we decided to inspect the homologous systems with thorium, particularly as there is hitherto no information available on phase relations within systems Th–M–M with M = Al,Ga and M = Si,Ge [5].
2. Experimental Alloys, Th37.5 M25 M 37.5 ,with a total amount of ∼1 g were prepared by argon arc-melting ingots of the elements. Starting from a nominal composition, 37.5 at.% Th, 25.0 at.% Al or Ga and 37.5 at.% Si or Ge, well-crystallized products were obtained. For homogenisation the samples were wrapped in Ta-foil, sealed in evacuated silica tubes and annealed at 900 ◦ C for 4 days and quenched. Further details of sample preparation and heat treatment as well as handling of the specimens in glove boxes can be found from our previous paper [3]. A Jeol-JSM 6400 scanning electron microscope was used to reveal the microstructure of the samples. The composition of the phases was analysed by
174
V. Kaveˇcansk´y et al. / Journal of Alloys and Compounds 365 (2004) 173–177
energy dispersive X-ray spectroscopy (EMPA-EDS) with an Oxford-Link-Isis Si/Li analyser. Precise lattice parameters and standard deviations were obtained from a least squares refinement of room temperature Guinier–Huber image plate X-ray powder data, using monochromatic CuK␣1 radiation with an internal standard of 6N-pure Ge (aGe = 0.5657906 nm at RT). Rietveld refinements were performed using the gsas software package [6].
Table 1 Crystallographic data for binary phases (extracted from Villars et al. [7]) Phase
ThSi2 ThSi ThGa2 ThGe2 ThGe
Structure type
Space group
a
Unit cell dimensions (nm) b
c
V
␣-ThSi2 FeB ␣-ThSi2 ␣-ThSi2 NaCl
I41 /amd Pnma I41 /amd I41 /amd ¯ Fm3m
0.4118 0.788 0.4247 0.4106 0.6046
=a 0.415 =a =a =a
1.4221 0.589 1.4701 1.4193 =a
0.2412 0.1926 0.2652 0.2393 0.2210
3. Results and discussion Phase relations in the vicinity of the composition Th37.5 M25 M 37.5 (‘Th3 M2 M 3 ’) were evaluated on the base of analysis of corresponding binary phase diagrams [5]. A compilation of crystallographic data of the binary compounds ThM2 (ThM 2 ) and ThM (ThM ) is presented in Table 1. Measured diffraction patterns were processed in two steps. At first, a structureless fitting of the whole X-ray pattern was performed using the LeBail method [8]. In this way numerical values of all nonstructural parameters were refined (e.g. background, analytical description of the peak profile, parameters for the description of the experimental equipment as well as the unit cell dimensions of all phases involved). When convergence of the least squares calculations was achieved, the refined values were fixed and the crystal structure parameters of the phases with sufficient weight fraction were refined. Fractional occupations of the atom sites were constrained in accordance with the chemical composition of the phases determined by EMPA. Finally a full profile Rietveld refinement of all structural and structureless parameters was performed.
This refinement strategy proved successful to minimize the correlations among the large number of parameters to be refined. The quality of the fit is characterised by residuals Rw and Rwp . Final refinement results are summarized in Figs. 1–4. Crystallographic data are compiled in Table 2. 3.1. Rietveld refinement of the alloys Th37.5 Al25 Si37.5 and Th37.5 Ga25 Si37.5 The majority phases in these alloys are formed by (i) a tetragonal phase of ␣ThSi2 type (space group I41 /amd) and (ii) an orthorhombic phase of the FeB type (Pnma). While Th37.5 Al25 Si37.5 consists only from these two phases [Th(Alx Si1−x )2 and Th(Alx Si1−x )], the phase composition of Th37.5 Ga25 Si37.5 was found to be more complicated. Besides the two phases, [Th(Gax Si1−x )2 and Th(Gax Si1−x )], secondary phases were identified: (i) another ␣ThSi2 type phase, Th(Gax Si1−x )2 , with significantly different lattice parameters, which are close to those of ThGa2 and (ii) traces of probably Th3 (Gax Si1−x )5 (defect AlB2 -type, P6/mmm). The difference in the X-ray
Fig. 1. Rietveld refinement of alloy Th37.5 Al25 Si37.5 .
V. Kaveˇcansk´y et al. / Journal of Alloys and Compounds 365 (2004) 173–177
175
Fig. 2. Rietveld refinement of alloy Th37.5 Ga25 Si37.5 .
scattering factors for Ga and Si enabled the refinement of the occupancy factors for the Si(Ga) positions though the process was considerably complicated by strong correlations between temperature and occupancy parameters. However, the estimated value of x for Th(Gax Si1−x )2 does not correspond to the determined values of the lattice parameters since the determined unit cell volume is smaller than that of pure ␣ThSi2 . This discrepancy may hint towards defect formation and should be the subject of further investigation.
3.2. Rietveld refinement of the alloys Th37.5 Al25 Ge37.5 and Th37.5 Ga25 Ge37.5 The phase constitution of the two samples is very similar concerning not only its quality but even the weight fractions of the determined phases are close. The majority phase for both compounds is the tetragonal ␣ThSi2 type Th(Alx Ge1−x )2 and/or Th(Gax Ge1−x )2 , respectively while the second one was identified as face centred cubic Th(Alx Ge1−x ) and/or Th(Gax Ge1−x ). No other phases were
Fig. 3. Rietveld refinement of alloy Th37.5 Al25 Ge37.5 .
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Fig. 4. Rietveld refinement of alloy Th37.5 Ga25 Ge37.5 . Table 2 Crystallographic data for alloys with composition Th37.5 M25 M 37.5 (M = Al,Ga, M = Si,Ge) Parameter/nominal Th37.5 Al25 Si37.5 Th37.5 Ga25 Si37.5 Th37.5 Al25 Ge37.5 composition of alloy (at.% ) X-ray data collection Image plate Radiation CuK␣1 2θ angular range 8 ≤ 2θ ≤ 100 a Rwp 0.138 0.1102 0.1295 Rp a 0.089 0.0737 0.0815 Phase I—Structure type ␣-ThSi2 , space group I41 /amd Formula Th(Alx Si1−x )2−y Th(Gax Si1−x )2−y Th(Alx Ge1−x )2−y xb 0.4 0.15 0.36 yb 0.22 0.37 0.26 EMPA in at.% Th36 Al25.3 Si38.7 Th38.0 Ga9.5 Si52.5 Th36.5 Al23 Ge40.5 Atom site occupancy fAl = 0.35; fSi = 0.54 fGa = 0.12; fSi = 0.69 fAl = 0.32; fGe = 0.56 Atom fract. coord. zSi = 0.2893(7) zSi = 0.2945(10) zGe = 0.2925(3) a (nm) 0.417118(7) 0.41136(3) 0.419281(5) c (nm) 1.43485(4) 1.3993(2) 1.44115(3) 3 0.249647(9) 0.23678(4) 0.253349(6) V (nm) c Weight fraction (%) 84 46 92 Phase II Structure type FeB FeB NaCl ¯ Space group Pnma Pnma Fm3m Formula Th(Alx Si1−x ) Th(Gax Si1−x ) ThGe xb 0.09 0.1 – EMPA in at.% Th50 Al4.4 Si45.6 Th50.5 Ga5.0 Si44.5 Th50 Al0 Ge50 Atom site occupancy fAl = 0.09; fSi = 0.91 fGa = 0.1; fSi =0.9 – a (nm) 0.79314(11) 0.79424(6) 0.605300(2) b (nm) 0.41395(5) 0.41378(3) =a c (nm) 0.59235(7) 0.59259(4) =a 3 V (nm) 0.19448(4) 0.19475(2) 0.221775(1) Weight fraction (%)c 16 36 8 Phase III—Structure type: ␣-ThSi2 , space group: I41 /amd, formula: Th(Gax Si1−x )2−y ; EMPA unresolved Atom site occupancy – fGa = 0.93; fSi = 0.07 – xb – 0.93 – – 0.0 – yb a (nm) – 0.42330(7) – c (nm) – 1.4704(5) – 0.2635(1) V (nm)3 Weight fraction (%)c – 18 – 1 a R 2 2 wp = { wi [(yoi −yci )(yoi −ybi )/yoi ] / wi (yoi −ybi ) } 2 ; Rp ={ |yoi −yci |.|yoi −ybi |/yoi }/ |yoi −ybi |. b Determined from refined values of fractional occupancy of the atom site (constrained according to c The sample is assumed to consist only of the determined phases. The sum of the weight fractions
Th37.5 Ga25 Ge37.5
0.1435 0.0954 Th(Gax Ge1−x )2−y 0.36 0.38 Th38.2 Ga22 Ge39.8 fGa = 0.29; fGe = 0.52 zGe = 0.2925(4) 0.418581(5) 1.42920(3) 0.250410(7) 88 NaCl ¯ Fm3m ThGe – Th50 Ga0 Ge50 – 0.60441(2) =a =a 0.22080(1) 12 – – – – – –
chemical composition derived by EMPA). is constrained to 1.0.
V. Kaveˇcansk´y et al. / Journal of Alloys and Compounds 365 (2004) 173–177
determined. In the case of the Th–Al–Ge system, the occupancy factor of the Ge(Al) positions could be refined. The estimated value of x is in good agreement with the unit cell volume of the Th(Alx Ge1−x )2 phase. 4. Summary The combined analyses (EMPA and XRD) of the constitution of alloys Th37.5 M25 M 37.5 (or Th3 M2 M 3 , M = Al,Ga; M = Si,Ge) revealed in all cases a multiphase structure where the major phase corresponds to a solid solution of the M-metal component in binary ThSi2−y or ThGe2−y , respectively. No isotypes to the U3 Ga2 Ge3 structure were found. Acknowledgements This research was sponsored by the Austrian–Slovak bilateral project 33s33, the Austrian–Polish bilateral Project 14/2001 and by the INTAS-project 234.
177
References [1] G.L. Garner, K.E. Bogacik, J.E. King, Trans. Am. Nucl. Soc. USA 55 (1987) 284. [2] T.C. Wiencek, R.F. Domagala, Trans. Am. Nucl. Soc. USA 55 (1987) 284. [3] F. Weitzer, M. Potel, H. Noël, P. Rogl, J. Solid State Chem. 111 (1994) 275. [4] A.G. Gukasov, P. Rogl, P.J. Brown, M. Mihalik, A.A. Menovsky, J. Phys. Condens. Matter 14 (2002) 8841. [5] P. Villars, A. Prince, H. Okamoto, Handbook of Ternary Alloy Phase Diagrams (1995) ASM InternationalMaterials Park, OH. [6] A.C. Larson, R.B. Von Dreele, GSAS—Generalised Crystal Structure Analysis System, Los Alamos National Laboratory, Los Alamos NM, 1990. [7] P. Villars, L.D. Calvert, Pearson’s Handbook of Crystallographic Data For Intermetallic Phases, 2nd Edition, ASM International, Materials Park, OH, 1991. [8] A. LeBail, Accuracy in Powder Diffraction II E. Prince J.K. Stalick (Eds.), Proceedings of the International Conference, May 26–29, NIST Special Publication 846 (1992) 213.