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On the phase relations in the MoCaS, SMoO and CaSO systems at 1373 K
Journal of the Less-Common Metals, 161(1990) 257-262
ON THE PHASE RELATIONS IN THE Mo-Ca-S, Ca-S-O SYSTEMS AT 1373 K R. ANDRUSZKIEWICZ
257
S-MO-O AND
and R. HORYril
Institute for Low Temperature and Structure Research, Polish Academy of Sciences, ul. Ok&a 2, SO-422 Wroctaw (Poland) (Received October 19,1989)
Summary Phase equilibria in the Mo-Ca-S, S-MO-O and Ca-S-O systems have been revealed by X-ray powder diffractometry. The sole ternary phase, previously known as &MO& (Chevrel type), has been identified. Experiments with arcsealed molybdenum crucibles have not confirmed the theoretical predictions of the existence of equilibrated phases in the Mo-Ca system. The existence of the CaO,,,S,.01 solid solution in the Ca-S-O system has been established. A gravimetric method for calcium determination is presented.
1. Introduction Due to some interest in the oxygen-defected Chevrel-type phases [l, 21, the present work has been motivated by lack of data on the phase regions surrounding the CaMo,S, phase in the Mo-Ca-S-O system. In the course of experiments with calcium-containing samples we have observed some measurable losses of calcium during temperature homogenization at 1373 K. We describe a new gravimetric method of calcium determination to control this undesirable process. Phase relations in the binary MO-S system were well recognized at higher temperatures [3]. Monoclinic MO& and rhombohedral or hexagonal MoS, phases also belong to the system. Further details of the MO-S phases are given in our earlier work [4]. CaS, the sole phase in the Ca-S system at 1373 K, has been well known for a long time [5]. This compound (m.p. 2798 K [6]) crystallizes with an NaCl-type structure [7] with a lattice constant a = 5.686 A [8], 5.6836 A [9] or 5.6903 A [lo]. The phase can be obtained from the elements [ 111; however, several other methods have also been described in the literature [12-141. The sulphur-rich Ca-S phases, polysulphides, stable in non-aqueous solutions, decompose during heating [ 15,161. Because of the instability of ozonide CaO, [ 171, superoxide CaO, [ 18,191 and peroxide CaO, [20,21], the sole CaO phase probably exists in the Ca-0 system at 0022-5088/90/$3.50
Q Elsevier Sequoia/Printed in The Netherlands
258
elevated temperatures. The CaO phase (m.p. 2886 K [17]) may be prepared by burning metallic calcium in oxygen [22]. This oxide crystallizes just like CaS, with a lattice constant a = 4.7990 A [9,23]. Only one condensed phase (monoclinic MOO,) is known in the entire MO-O system [24,25] at 1373 K. Apart from theoretical considerations on molybdenum solubility in liquid calcium [26] and on the existence of Mo-Ca phases [27, 281 there have been no experimental data of phase relations in the Mo-Ca system. The complete Mo-Ca-0 phase diagram will be published separately.
2. Experimental details 2.1. Materialsand procedure Ternary samples of total mass 2 g were prepared from powdered molybdenum (purity, 99.95%), calcium (purity, 99.92%), CaS (obtained from the elements [111) and stoichiometric MO&. Pellets of different chemical composition were reacted in evacuated quartz ampoules for 70 h at 1373 K, whereas calciumrich specimens were heated in arc-sealed molybdenum capsules. The phase composition of the samples was analyzed by X-ray powder diffractometry using silicon as an internal standard. 2.2. Gravimetric method of calcium determination The method described below is based on weighing the pure CaMoO, phase. The Mo-Ca-S material with the ratio (Ca)/(Mo) < 1 undergoes conversion during oxidation in air or in oxygen to the very stable CaMoO, compound (powellite); sulphur and redundant molybdenum are carried away in the form of volatile SO, and MOO, oxides. This property was confirmed in numerous experiments on the oxidation of the Mo-Ca-S samples performed in the temperature range 1073-1373 K. X-ray powder spectra always revealed pure calcium molybdate (pale-yellow crystals, present as the solid residue in the crucible). The X-ray powder diagram of the tetragonal CaMoO, compound [29] was distinct and invariable, regardless of the initial composition of the samples. The duration of sample oxidation vs. T was examined with great care. Unfortunately, the data obtained for the lowest temperature (1073 K) were not useful for analysis (the crucible with its contents was brought to constant weight after about 2 weeks). However, burning of the samples carried out at 1373 K reduced the time of oxidation to about 3 days. Let us consider the phase diagram of the Mo-Ca-S ternary system (Fig. 1). For the purpose of further discussion we divide it into two right-angled triangles (dotted line). Every sample from the left-hand part has sufficient amounts of molybdenum to transform alI of the calcium into CaMoO,. In the right-hand triangle the above condition is not fulfilled ((Ca)/(Mo) > 1); in this case some molybdenum or MOO, should be added to the samples.
259 S
cn
MO Fig. 1. The Mo-Ca-S
phase diagram.
The oxidation of samples of average mass 0.5 g was carried out in 2 g beryllia crucibles using a partially closed electric furnace. The conversion factor for Ca/ CaMoO, is 0.20038. The method proposed here was tested by analysis of unreacted samples (a mixture of CaS, MO and MO&) of nominal chemical com~sition CaMo,S,. The calcium index was found to be 1.009 (the calcium excess was 0.04 wt.%). Analytical methods based on the molybdates are widely known [30, 3 11. Our “dry” method is restricted to samples which can transform into non-volatile CaMoO,, the only residue after the burning process. Such conditions are realized, for example, in the Mo-Ca, Mo-Ca-S, Mo-Ca-0 and Mo-Ca-S-O systems.
3. Result and discussion 3.1. The MO-Ca-S system Phase relations obtained in the Mo-Ca-S system indicate the existence of one ternary phase, Ch-CaMo,S,, being equilibrated with molybdenum, Mo2,&, 2HMoS, and CaS phases (see Fig. 1). The Ch phase, first reported by Chevrel et al. and Fischer [32,33] is characterized by a small homogeneous region along the ChCa line. The calcium index of the phase (0.9-l .O) was determined by precise X-ray spectrometric measurements [34], The superconducting properties of the Ch phase have been discussed in detail by Geantet et al. 134,351 and Lachal et al, 1361. Apart from the Ch phase setting, the 2H-MoS,-S-CaS and Mo-CaS-Ca phase equilibria were also found. The compositions of representative samples are collected in Table 1. Considering the Ch phase setting (samples 1-3, 5,6), it should be noted here that in some Me-MO-S systems the Chevrel-type phase is in equilibrium with the elemental Me metal [37]. The 2H-MoS,-S-CaS region of the system has been identified due to calcium losses from the sample (sample 4) of the Mo,,Ca,,S,, initial chemical composition ( Ch-CaS line). The chemical analysis of the reacted sample, taking into account the
260
elemental sulphur involved, has revealed a new chemical composition of the sample, belonging to the three-phase part of the system. The Mo-CaS-Ca region has been established by means of arc-sealed molybdenum capsule tests. Two sample compositions (samples 7 and 8) have been prepared from MO + CaS + Ca and MO + MoS, + Ca substrates. In both cases the final phase composition was the same, i.e. MO + CaS + Ca. This result does not corroborate the theoretical suggestions of the existence of equilibrated Mo-Ca phases [27,28]. In all the cases accurate X-ray measurements of the molybdenum cell constant exhibit a characteristic value (3.147( 1) A) for pure metallic molybdenum [38] (see samples 1, 6-8). This finding rejects the possibility of the existence of significant molybdenum solid solutions in the Mo-Ca-S system. Owing to experimental difficulties, molybdenum solubility in molten calcium has not been investigated. However, the dashed line in Fig. 1 represents the theoretical prediction of the existence of the Ca(Mo) solution [26]. The authors published an estimated thermodynamic equation In( x)~~ = - 17 800/T+ 2.2 (where x is the molar fraction and T is the absolute temperature) for calculating the solubility of molybdenum in liquid calcium in the temperature range 1112-l 750 K.Inthecaseof1373K,x,,is2.1X10-5. In Table 1, a samples characterize, by way of example, the quantitative changes in the chemical composition during temperature treatment. 3.2. The S-MO-O and Ca-S-O system The easily interpreted X-ray spectra indicate the domination of binary phases in both equilibrated systems (see Figs. 2 and 3). The S-MO-O system is composed of Mo-Mo~,~,$,-MoO,, MO,,&-MoS,MOO, and gas (0, + SO,)-MoS,-MOO* phase fields.
TABLE 1 RepresentativeMo-Ca-S samples and values of a for parameter of molybdenum Number
Initialsample composition
1 2 3
Phases observed (1373 K) MO,
Mo,.o,S,,
Mo,.o,S,,
Cell constant a(A) 3.148
Ch
MO%
Ch
MO&, Ch MO&, S, CaS MoS,, CaS, Ch MO, Ch, CaS MO,CaS, Ca MO,CaS, Ca
“Real chemical composition of the reacted samples.
3.147 3.147 3.147
261
Fig. 2. The S-MO-O phase diagram. Fig. 3. The Ca-S-O
phase diagram.
TABLE 2 Representative Number
S-MO-O and Ca-S-O Initial sample composition
samples and values of a for CaS and CaO Phases observed (1373 K)
MO, MO&, MOO, MO& MO&, MOO, MoS,, MOO, MoS,, MOO, Ca, CaS, CaO CaS, CaO CaS, CaO
Cell constant a (A) CaS
CaO
5.692( 1)
4.809( 1)
Two phase fields, gas (0, + SO,)-CaS-CaO and Ca-CaS-CaO, characterize the Ca-S-O system. However, a slightly enlarged CaO cell parameter, 4.809 A, solid solution and, consequently, the indicates the existence of CaO,,&,,, presence of very narrow Ca-CaO(S),, and CaO(S),,-0 phase fields. The observed sulphur solubility in the CaO phase is somewhat large when compared with results for higher temperatures published by Kor and Richardson [39] and Sharma and Richardson [40]. The nominal compositions of the investigated specimens are collected in Table 2. References 1 D. W. Capone, II, R. P. Guertin, S. Foner, D. G. Hinks and Hung-Chen Li, Phys. Rev. Lett., 51 (1983)601. 2 G. K. Shenoy, D. G. Hinks, A. M. Umaji and C. W. Kimball, Solid State Cornmun., 51(1984) 621.
262 3 W. B. Johnson, W. S. Hong and D. W. Readey, Ser. Metall., I7( 1983) 919. R. Andruszkiewicz and R. Horyii, J. Less-Common Met., 138 (1988) 87. M. Vaquelin, Ann. Chim. Whys., 6 (18 17) 35. R. Juza and K. Biinzen, Z. Phys. Chem., 17( 1958) 82. M. Komac, L. Golie, D. Kolar and B. S. BrEid, J. Less-Common Met., 24 (1971) 121.
4 5 6 7
Phys. Chem., 128(1927) 154. W. Primak, H. Kaufman and R. Ward, .I. Am. Chem. Sot., 70 (1948) 2043. 0. J. Giintert and A. Faessler, Z. Kristullogr., 107( 1956) 357. P. J. Walker and R. C. C. Ward, Muter. Res. Bull., 19 (1984) 717. V. H. Valey,J. Chem. Sot., 47(1885) 478. L. Marino, Gaz. Chim. Ital., 43 ( 19 13) 4 16. T. Petzel, Z. anorg. a&. Chem., 3% (1973) 173. P. L. Robinson and W. E. Scott, J. Chem. Sot., 134 (1931) 693. E. V. Dulepov and S. S. Batsanov, Zh. Strukt. Khim., I3 (1972) 347. T. B. Massalski (ed.), Binary Alloys Phase Diagrams, Vol. 1, American Society for Metals, Metals Park, OH, 1986, p. 627. P. Sadhukhan and A. T. Bell, J. Solid State Chem., 29 (1979) 97. C. Brosset and N.-G. Vannerberg, Nature, I77( 1956) 238. W. Traube and W. Schulze, Ber., 54 (1921) 1626. J. Conroy (ref. by R. Gerstl), Ber., 6 (1873) 769. W. P. Davey, Phys. Rev., 21( 1923) 2 13. W. Gerlach, Z. Phys., 9 (1922) 184. L.Kihlborg,ArkivKemi, 21(1963)471. L. L. Y. Chang and B. Phillips, J. Am. Cerum. Sot., 52 (1969) 527. L. Brewer and R. H. Lamoreaux, in 0. Kubaschewscki (ed.), Phase Diagrams. Atomic Energy Review, Special Issue No. 7, International Atomic Energy Agency, Vienna, 1980, p. 225. E. M. Savitskii and V. B. Tribulya, Neorg Muter., 7( 1971) 1097. A. E. Vol and I. K. Kagan, Slroenie i svoistva dvoi’nykh metallicheskikh sistem, Vol. 4, Nauka, Moskva, 1979, p. 505. V. B. Aleksandrov, L. V. Gorbatyi and V. V. Ilyukhin, Kristallografiya, 13 (1968) 5 12. G. A. Parker, Analytical Chemistry of Molybdenum, Springer, Berlin, 1983, p. 26. W. L. Hillebrand and G. E. F. Lundell, Applied Inorganic Analysis, Wiley, New York, 1953, Chap. 40. R. Chevrel, M. Sergent and J. Prigent, J. SolidState Chem., 3 (1971) 515. 0. Fischer,Appl. Phys., 16(1978) 1. C. Geantet, J. Padiou, 0. Peiia, M. Sergent and R. Horyri, Solid State Commun., 64 (1987) 1363. C. Geantet, R. Horyli, J. Padiou, 0. Peiia and M. Sergent, Proc. Znt. Conf on High Temperature
8 J.Oftedale,Z. 9 10 11 12 13 14 15 16 17
18 19 20
21 22 23
24 25 26
27 28
29 30
31 32 33 34 35
Superconductors, 29-March 4,1988.
36 37
38 39 40
and Materials
and Mechanisms
of Superconductivity,
Znterlaken,
February
p. 481. B. Lachal, R Baillif, A. Junod and J. Muller, Solid State Commun., 45 (1983) 849. H. A. Wagner and H. C. Freyhardt, J. Phys. Chem. Solids, 43 (1982) 177. K.-H, Hellwege (ed.), Landolt-Biintstein Data and Functional Relationships in Science and Technology, Vol. 6, Springer, Berlin, 1971, p. 16. G. J. W. Kor and F. D. Richardson, Trans. Inst. Min. Merall., C79( 1970) 148. R. A. Sharma and F. D. Richardson, Trans. AZME, 233( 1965) 1586.
ON THE PHASE RELATIONS IN THE Mo-Ca-S, Ca-S-O SYSTEMS AT 1373 K R. ANDRUSZKIEWICZ
257
S-MO-O AND
and R. HORYril
Institute for Low Temperature and Structure Research, Polish Academy of Sciences, ul. Ok&a 2, SO-422 Wroctaw (Poland) (Received October 19,1989)
Summary Phase equilibria in the Mo-Ca-S, S-MO-O and Ca-S-O systems have been revealed by X-ray powder diffractometry. The sole ternary phase, previously known as &MO& (Chevrel type), has been identified. Experiments with arcsealed molybdenum crucibles have not confirmed the theoretical predictions of the existence of equilibrated phases in the Mo-Ca system. The existence of the CaO,,,S,.01 solid solution in the Ca-S-O system has been established. A gravimetric method for calcium determination is presented.
1. Introduction Due to some interest in the oxygen-defected Chevrel-type phases [l, 21, the present work has been motivated by lack of data on the phase regions surrounding the CaMo,S, phase in the Mo-Ca-S-O system. In the course of experiments with calcium-containing samples we have observed some measurable losses of calcium during temperature homogenization at 1373 K. We describe a new gravimetric method of calcium determination to control this undesirable process. Phase relations in the binary MO-S system were well recognized at higher temperatures [3]. Monoclinic MO& and rhombohedral or hexagonal MoS, phases also belong to the system. Further details of the MO-S phases are given in our earlier work [4]. CaS, the sole phase in the Ca-S system at 1373 K, has been well known for a long time [5]. This compound (m.p. 2798 K [6]) crystallizes with an NaCl-type structure [7] with a lattice constant a = 5.686 A [8], 5.6836 A [9] or 5.6903 A [lo]. The phase can be obtained from the elements [ 111; however, several other methods have also been described in the literature [12-141. The sulphur-rich Ca-S phases, polysulphides, stable in non-aqueous solutions, decompose during heating [ 15,161. Because of the instability of ozonide CaO, [ 171, superoxide CaO, [ 18,191 and peroxide CaO, [20,21], the sole CaO phase probably exists in the Ca-0 system at 0022-5088/90/$3.50
Q Elsevier Sequoia/Printed in The Netherlands
258
elevated temperatures. The CaO phase (m.p. 2886 K [17]) may be prepared by burning metallic calcium in oxygen [22]. This oxide crystallizes just like CaS, with a lattice constant a = 4.7990 A [9,23]. Only one condensed phase (monoclinic MOO,) is known in the entire MO-O system [24,25] at 1373 K. Apart from theoretical considerations on molybdenum solubility in liquid calcium [26] and on the existence of Mo-Ca phases [27, 281 there have been no experimental data of phase relations in the Mo-Ca system. The complete Mo-Ca-0 phase diagram will be published separately.
2. Experimental details 2.1. Materialsand procedure Ternary samples of total mass 2 g were prepared from powdered molybdenum (purity, 99.95%), calcium (purity, 99.92%), CaS (obtained from the elements [111) and stoichiometric MO&. Pellets of different chemical composition were reacted in evacuated quartz ampoules for 70 h at 1373 K, whereas calciumrich specimens were heated in arc-sealed molybdenum capsules. The phase composition of the samples was analyzed by X-ray powder diffractometry using silicon as an internal standard. 2.2. Gravimetric method of calcium determination The method described below is based on weighing the pure CaMoO, phase. The Mo-Ca-S material with the ratio (Ca)/(Mo) < 1 undergoes conversion during oxidation in air or in oxygen to the very stable CaMoO, compound (powellite); sulphur and redundant molybdenum are carried away in the form of volatile SO, and MOO, oxides. This property was confirmed in numerous experiments on the oxidation of the Mo-Ca-S samples performed in the temperature range 1073-1373 K. X-ray powder spectra always revealed pure calcium molybdate (pale-yellow crystals, present as the solid residue in the crucible). The X-ray powder diagram of the tetragonal CaMoO, compound [29] was distinct and invariable, regardless of the initial composition of the samples. The duration of sample oxidation vs. T was examined with great care. Unfortunately, the data obtained for the lowest temperature (1073 K) were not useful for analysis (the crucible with its contents was brought to constant weight after about 2 weeks). However, burning of the samples carried out at 1373 K reduced the time of oxidation to about 3 days. Let us consider the phase diagram of the Mo-Ca-S ternary system (Fig. 1). For the purpose of further discussion we divide it into two right-angled triangles (dotted line). Every sample from the left-hand part has sufficient amounts of molybdenum to transform alI of the calcium into CaMoO,. In the right-hand triangle the above condition is not fulfilled ((Ca)/(Mo) > 1); in this case some molybdenum or MOO, should be added to the samples.
259 S
cn
MO Fig. 1. The Mo-Ca-S
phase diagram.
The oxidation of samples of average mass 0.5 g was carried out in 2 g beryllia crucibles using a partially closed electric furnace. The conversion factor for Ca/ CaMoO, is 0.20038. The method proposed here was tested by analysis of unreacted samples (a mixture of CaS, MO and MO&) of nominal chemical com~sition CaMo,S,. The calcium index was found to be 1.009 (the calcium excess was 0.04 wt.%). Analytical methods based on the molybdates are widely known [30, 3 11. Our “dry” method is restricted to samples which can transform into non-volatile CaMoO,, the only residue after the burning process. Such conditions are realized, for example, in the Mo-Ca, Mo-Ca-S, Mo-Ca-0 and Mo-Ca-S-O systems.
3. Result and discussion 3.1. The MO-Ca-S system Phase relations obtained in the Mo-Ca-S system indicate the existence of one ternary phase, Ch-CaMo,S,, being equilibrated with molybdenum, Mo2,&, 2HMoS, and CaS phases (see Fig. 1). The Ch phase, first reported by Chevrel et al. and Fischer [32,33] is characterized by a small homogeneous region along the ChCa line. The calcium index of the phase (0.9-l .O) was determined by precise X-ray spectrometric measurements [34], The superconducting properties of the Ch phase have been discussed in detail by Geantet et al. 134,351 and Lachal et al, 1361. Apart from the Ch phase setting, the 2H-MoS,-S-CaS and Mo-CaS-Ca phase equilibria were also found. The compositions of representative samples are collected in Table 1. Considering the Ch phase setting (samples 1-3, 5,6), it should be noted here that in some Me-MO-S systems the Chevrel-type phase is in equilibrium with the elemental Me metal [37]. The 2H-MoS,-S-CaS region of the system has been identified due to calcium losses from the sample (sample 4) of the Mo,,Ca,,S,, initial chemical composition ( Ch-CaS line). The chemical analysis of the reacted sample, taking into account the
260
elemental sulphur involved, has revealed a new chemical composition of the sample, belonging to the three-phase part of the system. The Mo-CaS-Ca region has been established by means of arc-sealed molybdenum capsule tests. Two sample compositions (samples 7 and 8) have been prepared from MO + CaS + Ca and MO + MoS, + Ca substrates. In both cases the final phase composition was the same, i.e. MO + CaS + Ca. This result does not corroborate the theoretical suggestions of the existence of equilibrated Mo-Ca phases [27,28]. In all the cases accurate X-ray measurements of the molybdenum cell constant exhibit a characteristic value (3.147( 1) A) for pure metallic molybdenum [38] (see samples 1, 6-8). This finding rejects the possibility of the existence of significant molybdenum solid solutions in the Mo-Ca-S system. Owing to experimental difficulties, molybdenum solubility in molten calcium has not been investigated. However, the dashed line in Fig. 1 represents the theoretical prediction of the existence of the Ca(Mo) solution [26]. The authors published an estimated thermodynamic equation In( x)~~ = - 17 800/T+ 2.2 (where x is the molar fraction and T is the absolute temperature) for calculating the solubility of molybdenum in liquid calcium in the temperature range 1112-l 750 K.Inthecaseof1373K,x,,is2.1X10-5. In Table 1, a samples characterize, by way of example, the quantitative changes in the chemical composition during temperature treatment. 3.2. The S-MO-O and Ca-S-O system The easily interpreted X-ray spectra indicate the domination of binary phases in both equilibrated systems (see Figs. 2 and 3). The S-MO-O system is composed of Mo-Mo~,~,$,-MoO,, MO,,&-MoS,MOO, and gas (0, + SO,)-MoS,-MOO* phase fields.
TABLE 1 RepresentativeMo-Ca-S samples and values of a for parameter of molybdenum Number
Initialsample composition
1 2 3
Phases observed (1373 K) MO,
Mo,.o,S,,
Mo,.o,S,,
Cell constant a(A) 3.148
Ch
MO%
Ch
MO&, Ch MO&, S, CaS MoS,, CaS, Ch MO, Ch, CaS MO,CaS, Ca MO,CaS, Ca
“Real chemical composition of the reacted samples.
3.147 3.147 3.147
261
Fig. 2. The S-MO-O phase diagram. Fig. 3. The Ca-S-O
phase diagram.
TABLE 2 Representative Number
S-MO-O and Ca-S-O Initial sample composition
samples and values of a for CaS and CaO Phases observed (1373 K)
MO, MO&, MOO, MO& MO&, MOO, MoS,, MOO, MoS,, MOO, Ca, CaS, CaO CaS, CaO CaS, CaO
Cell constant a (A) CaS
CaO
5.692( 1)
4.809( 1)
Two phase fields, gas (0, + SO,)-CaS-CaO and Ca-CaS-CaO, characterize the Ca-S-O system. However, a slightly enlarged CaO cell parameter, 4.809 A, solid solution and, consequently, the indicates the existence of CaO,,&,,, presence of very narrow Ca-CaO(S),, and CaO(S),,-0 phase fields. The observed sulphur solubility in the CaO phase is somewhat large when compared with results for higher temperatures published by Kor and Richardson [39] and Sharma and Richardson [40]. The nominal compositions of the investigated specimens are collected in Table 2. References 1 D. W. Capone, II, R. P. Guertin, S. Foner, D. G. Hinks and Hung-Chen Li, Phys. Rev. Lett., 51 (1983)601. 2 G. K. Shenoy, D. G. Hinks, A. M. Umaji and C. W. Kimball, Solid State Cornmun., 51(1984) 621.
262 3 W. B. Johnson, W. S. Hong and D. W. Readey, Ser. Metall., I7( 1983) 919. R. Andruszkiewicz and R. Horyii, J. Less-Common Met., 138 (1988) 87. M. Vaquelin, Ann. Chim. Whys., 6 (18 17) 35. R. Juza and K. Biinzen, Z. Phys. Chem., 17( 1958) 82. M. Komac, L. Golie, D. Kolar and B. S. BrEid, J. Less-Common Met., 24 (1971) 121.
4 5 6 7
Phys. Chem., 128(1927) 154. W. Primak, H. Kaufman and R. Ward, .I. Am. Chem. Sot., 70 (1948) 2043. 0. J. Giintert and A. Faessler, Z. Kristullogr., 107( 1956) 357. P. J. Walker and R. C. C. Ward, Muter. Res. Bull., 19 (1984) 717. V. H. Valey,J. Chem. Sot., 47(1885) 478. L. Marino, Gaz. Chim. Ital., 43 ( 19 13) 4 16. T. Petzel, Z. anorg. a&. Chem., 3% (1973) 173. P. L. Robinson and W. E. Scott, J. Chem. Sot., 134 (1931) 693. E. V. Dulepov and S. S. Batsanov, Zh. Strukt. Khim., I3 (1972) 347. T. B. Massalski (ed.), Binary Alloys Phase Diagrams, Vol. 1, American Society for Metals, Metals Park, OH, 1986, p. 627. P. Sadhukhan and A. T. Bell, J. Solid State Chem., 29 (1979) 97. C. Brosset and N.-G. Vannerberg, Nature, I77( 1956) 238. W. Traube and W. Schulze, Ber., 54 (1921) 1626. J. Conroy (ref. by R. Gerstl), Ber., 6 (1873) 769. W. P. Davey, Phys. Rev., 21( 1923) 2 13. W. Gerlach, Z. Phys., 9 (1922) 184. L.Kihlborg,ArkivKemi, 21(1963)471. L. L. Y. Chang and B. Phillips, J. Am. Cerum. Sot., 52 (1969) 527. L. Brewer and R. H. Lamoreaux, in 0. Kubaschewscki (ed.), Phase Diagrams. Atomic Energy Review, Special Issue No. 7, International Atomic Energy Agency, Vienna, 1980, p. 225. E. M. Savitskii and V. B. Tribulya, Neorg Muter., 7( 1971) 1097. A. E. Vol and I. K. Kagan, Slroenie i svoistva dvoi’nykh metallicheskikh sistem, Vol. 4, Nauka, Moskva, 1979, p. 505. V. B. Aleksandrov, L. V. Gorbatyi and V. V. Ilyukhin, Kristallografiya, 13 (1968) 5 12. G. A. Parker, Analytical Chemistry of Molybdenum, Springer, Berlin, 1983, p. 26. W. L. Hillebrand and G. E. F. Lundell, Applied Inorganic Analysis, Wiley, New York, 1953, Chap. 40. R. Chevrel, M. Sergent and J. Prigent, J. SolidState Chem., 3 (1971) 515. 0. Fischer,Appl. Phys., 16(1978) 1. C. Geantet, J. Padiou, 0. Peiia, M. Sergent and R. Horyri, Solid State Commun., 64 (1987) 1363. C. Geantet, R. Horyli, J. Padiou, 0. Peiia and M. Sergent, Proc. Znt. Conf on High Temperature
8 J.Oftedale,Z. 9 10 11 12 13 14 15 16 17
18 19 20
21 22 23
24 25 26
27 28
29 30
31 32 33 34 35
Superconductors, 29-March 4,1988.
36 37
38 39 40
and Materials
and Mechanisms
of Superconductivity,
Znterlaken,
February
p. 481. B. Lachal, R Baillif, A. Junod and J. Muller, Solid State Commun., 45 (1983) 849. H. A. Wagner and H. C. Freyhardt, J. Phys. Chem. Solids, 43 (1982) 177. K.-H, Hellwege (ed.), Landolt-Biintstein Data and Functional Relationships in Science and Technology, Vol. 6, Springer, Berlin, 1971, p. 16. G. J. W. Kor and F. D. Richardson, Trans. Inst. Min. Merall., C79( 1970) 148. R. A. Sharma and F. D. Richardson, Trans. AZME, 233( 1965) 1586.