- Email: [email protected]
Phase diagrams of SmI2CsI and SmI2NaI binary systems
Journal
of the Less-Common
PHASE DIAGRAMS X. Z. CHEN, Department (Received
September
149 (1989)
95 - 99
OF Sm12-CsI AND SmI,-NaI
S. H. WANG+ of Chemistry,
Metals,
95
BINARY
SYSTEMS*
and S. B. JIANG Beijing
Normal
University,
Beijing
(China)
14,1988)
Summary The SmI&sI and SmI,-NaI systems were studied by differential thermal analysis (DTA) and X-ray powder diffraction. The phase diagram of the Sm12-CsI system shows the presence of four compounds: CsSmJs, CsSmI,, Cs$mI, and Cs,SmI+ Cs,Sm& (which exists only at high temperature) has not been isolated as yet. The phase diagram of the SmI*--NaI system shows that no compound is formed at room temperature.
1. Introduction A considerable amount of work has been carried out on the phase diagrams of binary systems containing trivalent rare earth halides and alkali halides [l]. However, only a few phase diagrams of systems containing divalent rare earth (R) halides and alkali (A) halides have been presented in the literature [2 - 71. The compounds AEuCl, (A E Cs and Rb), AEu,Cl, (A ~CS, K, Rb, Na and Tl) and K*EuCl, have been found in the phase diagrams of the EuCl*--AC1 binary systems. In the YbI,-AI systems (A -_a, K, Rb and Cs) the compounds NaYb& (monoclinic), KYb13, RbYbI,, CsYbIs (orthorhombic), Rb4YbI,, Cs,YbI,, and Cs6YbIs have also been found [6]. It has recently been reported that some complexes of rare earth and alkali metal halides (such as NaSc14, CsCeL,, CsNd14 and CsLa14) and the divalent samarium compounds NaSmI, and CsSmIs [8 - 131 show higher vapour pressures than those of the rare earth salts alone. This has been confirmed by the observation of an increase in vapour pressure over a molten mixture of Ce3+ iodide and sodium iodide in high intensity discharge lamps
[W. Therefore it is of interest to ascertain the general pattern of the phase relationships of binary RX*--AX systems and to search for new filling materials for discharge lamps. In this paper the phase diagrams of the SmI,CsI and Sm12-NaI systems are reported. *Paper presented at the 18th Rare Earth Research Conference, September 12 - 16,1988. TAuthor to whom correspondence should be addressed. 0022-5088/89/$3.50
@ Elsevier
Sequoia/Printed
Lake
Geneva,
WI,
in The Netherlands
96
2. Experimental
details
SmI, was prepared by reaction of samarium with HgI, [14]. High purity c%mmercial reagent grade CsI and NaI (melting points, 626 and 661 “C) were used without further purification; however, they were dried by heating in vacuum (5 X 10d6 Torr) at 350 “C for 3 h before use. The purities of SmI,, CsI and NaI were checked by X-ray and thermal analyses. SmI,-CsI and SmI,-NaI samples with different molar ratios were prepared by weighing and mixing SmIz and CsI or NaI in a dry-box under an argon atmosphere. Each sample was sealed in a quartz ampoule in a vacuum (5 X 10V6 Torr). The SmI*-CsI samples were heated at 400 - 500 “C for 150 h and the SmI,-NaI samples were heated at 400 “C for 150 h for equilibration. Differential thermal analysis curves of the samples were recorded with a differential thermal analyser (model LCT-1; heating rate, 5 “C min-‘; temperature accuracy, ?l%). Phase analysis was performed on the basis of X-ray powder data, obtained with a 90 mm Guinier camera and Cu Ko radiation. SiOZ was used as an internal standard. The lattice parameters were refined by the program SOS11 [ 171. Relative powder intensities of the new compounds were calculated using the Lazy Pulverix program [ 181 and the atomic position parameters of a compound of the same type.
3. Results and discussion The phase diagrams of the binary systems Sm12-CsI and SmI*-NaI (obtained from their DTA curves) are shown in Figs. 1 and 2 respectively. In the SmI,-CsI system there is one congruently melting compound and three incongruently melting compounds having the compositions CsSmIs (i.e. SmI,:CsI = l:l), CsSm,I,, CssSmI, and Cs#mI,. Their melting
T°C 700 .
T“c 700
SmI2-CSI
SmI24aI
I 600'
“‘0
2;
40
60
8:
i 100
CsI mol% Fig. 1. The SmI&sI
phase diagram.
NaI mol% Fig. 2. The SmIz-NaI
phase diagram.
1
CsSm~Is, a little SmIz
SmI2, a little CsSmzIs
CSSrX&
21 CsSm&
3:2
2:1
SmI2, a little NaI
4:r
SmXz, a little NaX
Molar ratio: Smjlz:NaI
SmIz, NaI
1:t
CSkhIJ
1.-l
NaI, a little Smiz
1:2
a little CsSmI3
Results of phase analysis (25 “C) from X-ray powder diffraction
TABLE 2
‘#:_I
9:t
Molar ratio SmI~CsI
Results of phase analysis (25 “C) from X-ray powder diffraction
TM&E
Cs&nIs
1:3
NaI, a little SmXz
1:4
Cs$3mIs, a little CsSmIs
1:2
NaI, very little Smiz
1:6
--
CsX, a little Cs$%rrI.j
1:9
98
points are 610,474, 487 and 535 “C!respectively. There are also two eutectic points located at 443 and 508 “C with 17.5 and 72.5 mol.% CsI; these were estimated using the Tammann Trigon method. The formation of three of these compounds has been confirmed by X-ray diffraction measurements at room temperature (see Table 1). The failure to detect CszSm14 by X-ray diffraction at room temperature may be due to the decomposition of this compound on cooling to 500 “C. The AB and CD lines observed in the SmI,-CsI phase diagram may be attributed to phase transformations of CsSm& and CssSmI, respectively. The results of the X-ray powder diffraction phase analyses at room temperature in other regions of the phase diagram are presented in Table 1. These results are inconsistent with those obtained from the DTA data. The EF and GH lines may be regarded as an indication of the presence of two compounds which are unstable at room temperature. While their X-ray diffraction data have not yet been obtained at room temperature it is not unreasonable to speculate that these compounds have the possible compositions CsSm,& and CsgmI, respectively. The phase diagram of the SmI,-NaI system shows that there is no compound present at room temperature. This is consistent with the X-ray diffraction data shown in Table 2. However, a eutectic point appears at 381 “C with 27 mol.% NaI. In Table 3 the lattice constants and densities of CsSm,I, and CsSmI, (obtained from their X-ray diffraction data) are summarized. It is of interest to compare the phase diagrams of the SmI,-CsI and SmI,,-NaI systems with those of the YbI,-AI (A - Na, K, Rb and Cs) [ 5 - 71 and MF,-AF (M = alkaline earth metal; A = alkali metal) [19] systems. In the YbI,-AI and MF?--AF systems, the larger the ionic radius of the alkali, the larger ther number of compounds with different compositions that can be formed. A similar trend is observed in SmI*-CsI and SmIz-NaI systems; however, the EuCl,-AC1 (A = alkali metal) systems do not follow this rule.
TABLE 3 Lattice constants and properties of CsSmzIS and CsSmI3
Colour Crystal system type Space group a (A) b (A) c(A) P (deg) D, (g CIII-~) ;O
02 cmv3)
MV, (cm3 mol-‘)
CsSmzIs
CsSmZ3
Blackish green Monoclinic p2 1/c 10.219(3) 9.093(2) 14.300(6) 90.35(4) 5.34 5.26 4 200.0
Bright green Orthorhombic Pmmm 8.631(3) 17.999(6) 12.564(5) 4.52 4.76 8 146.9
99
Acknowledgments We thank Mr. Che-Guang Chan for his assistance in X-ray powder diffraction measurement and for many useful discussions on the data analysis. We acknowledge the National Natural Science Foundation of China for support of this research.
References 1 J. Kutscher and A. Schneider, 2. Anorg. Allg. Chem., 408 (1984) 135 - 145. 2 G. I. Novikov, 0. G. Polyachenok and S. A. Frid, J. Inorg. Chem. (USSR), 9 (1964) 412 - 415. 3 H. Fink and H. J. Seihert, 2. Anorg. Allg. Chem., 466 (1980) 87. 4 A. K. Molodkin, A. M. Karagodina, D. G. Dudareva and V. A. Krokhin, J. Znorg. Chem. (USSR), 28 (1983) 2985. 5 S. H. Wang, S. B. Jiang, Z. G.“Tang and H. Z. Yang, J. Chin. Rare-Earth Sot., 2 (1984) 25. 6 Z. G. Tang, H. Z. Yang and S. H. Wang, J. Chin. Rare-Earth Sot., 4 (1986) 71 - 73. 7 S. H. Wang and M. Zhao, J. Less-Common Met., 127 (1987) 219 - 224. 8 W. A. McAllister, J. Efectrochem. Sot., 132 (1985) 2798 - 2800. 9 R. J. Zollweg, C. S. Liu, C. Hirayama and J. W. McNall, J. Illurn. Eng. Sot., 4 (1975) 249 - 253. 10 C. S. Liu and C. Hirayama, J. Zllum. Eng. Sot., 8 (1970) 147 - 151. 11 C. Hirayama, J. Illurn. Eng. Sot., 6 (1977) 209 - 214. 12 C. Hirayama, in E. Lundin (ed.), Proc. 12th Rare-Earth Research Conf., Vail, CO, 1976, Vol. 2, pp. 1044 - 1053. 13 C. Hirayama and P. M. Castle, in J. M. Haschke and H. A. Eick (eds.), Proc. 11th Rare-Earth Research Conf., Travers City, MI, October 7 - 10, 1974, National Technical Information Service, Springfield, VA, 1974, Vol. 2, pp. 1048 - 1057. 14 S. H. Wang and H. Z. Yang, Proc. 1st Chinese Rare-Earth Conf., Be&ng, October 1980, Abstracts, p. 46. 15 F. G. Ras, D. J. W. Ijdo and G. G. Vesschoor, Acta Crystallogr. Sect. B, 33 (1977) 259. 16 A. dePretis, D. Minichelli, F. Riceiardiello, Rev. Znt. Hautes Temp. Refract., 22 (1985) 215 - 219. 17 G. Meyer, personal communication (Justus-Liebig UniversitPt, Giessen, F.R.G.) 18 K. Yvon, W. Jeitschko and E. Parthe, J. Appl. Crystallogr., 10 (1977) 73. 19 R. E. Thoma, lnorg. Chem., 1 (1962) 259.
of the Less-Common
PHASE DIAGRAMS X. Z. CHEN, Department (Received
September
149 (1989)
95 - 99
OF Sm12-CsI AND SmI,-NaI
S. H. WANG+ of Chemistry,
Metals,
95
BINARY
SYSTEMS*
and S. B. JIANG Beijing
Normal
University,
Beijing
(China)
14,1988)
Summary The SmI&sI and SmI,-NaI systems were studied by differential thermal analysis (DTA) and X-ray powder diffraction. The phase diagram of the Sm12-CsI system shows the presence of four compounds: CsSmJs, CsSmI,, Cs$mI, and Cs,SmI+ Cs,Sm& (which exists only at high temperature) has not been isolated as yet. The phase diagram of the SmI*--NaI system shows that no compound is formed at room temperature.
1. Introduction A considerable amount of work has been carried out on the phase diagrams of binary systems containing trivalent rare earth halides and alkali halides [l]. However, only a few phase diagrams of systems containing divalent rare earth (R) halides and alkali (A) halides have been presented in the literature [2 - 71. The compounds AEuCl, (A E Cs and Rb), AEu,Cl, (A ~CS, K, Rb, Na and Tl) and K*EuCl, have been found in the phase diagrams of the EuCl*--AC1 binary systems. In the YbI,-AI systems (A -_a, K, Rb and Cs) the compounds NaYb& (monoclinic), KYb13, RbYbI,, CsYbIs (orthorhombic), Rb4YbI,, Cs,YbI,, and Cs6YbIs have also been found [6]. It has recently been reported that some complexes of rare earth and alkali metal halides (such as NaSc14, CsCeL,, CsNd14 and CsLa14) and the divalent samarium compounds NaSmI, and CsSmIs [8 - 131 show higher vapour pressures than those of the rare earth salts alone. This has been confirmed by the observation of an increase in vapour pressure over a molten mixture of Ce3+ iodide and sodium iodide in high intensity discharge lamps
[W. Therefore it is of interest to ascertain the general pattern of the phase relationships of binary RX*--AX systems and to search for new filling materials for discharge lamps. In this paper the phase diagrams of the SmI,CsI and Sm12-NaI systems are reported. *Paper presented at the 18th Rare Earth Research Conference, September 12 - 16,1988. TAuthor to whom correspondence should be addressed. 0022-5088/89/$3.50
@ Elsevier
Sequoia/Printed
Lake
Geneva,
WI,
in The Netherlands
96
2. Experimental
details
SmI, was prepared by reaction of samarium with HgI, [14]. High purity c%mmercial reagent grade CsI and NaI (melting points, 626 and 661 “C) were used without further purification; however, they were dried by heating in vacuum (5 X 10d6 Torr) at 350 “C for 3 h before use. The purities of SmI,, CsI and NaI were checked by X-ray and thermal analyses. SmI,-CsI and SmI,-NaI samples with different molar ratios were prepared by weighing and mixing SmIz and CsI or NaI in a dry-box under an argon atmosphere. Each sample was sealed in a quartz ampoule in a vacuum (5 X 10V6 Torr). The SmI*-CsI samples were heated at 400 - 500 “C for 150 h and the SmI,-NaI samples were heated at 400 “C for 150 h for equilibration. Differential thermal analysis curves of the samples were recorded with a differential thermal analyser (model LCT-1; heating rate, 5 “C min-‘; temperature accuracy, ?l%). Phase analysis was performed on the basis of X-ray powder data, obtained with a 90 mm Guinier camera and Cu Ko radiation. SiOZ was used as an internal standard. The lattice parameters were refined by the program SOS11 [ 171. Relative powder intensities of the new compounds were calculated using the Lazy Pulverix program [ 181 and the atomic position parameters of a compound of the same type.
3. Results and discussion The phase diagrams of the binary systems Sm12-CsI and SmI*-NaI (obtained from their DTA curves) are shown in Figs. 1 and 2 respectively. In the SmI,-CsI system there is one congruently melting compound and three incongruently melting compounds having the compositions CsSmIs (i.e. SmI,:CsI = l:l), CsSm,I,, CssSmI, and Cs#mI,. Their melting
T°C 700 .
T“c 700
SmI2-CSI
SmI24aI
I 600'
“‘0
2;
40
60
8:
i 100
CsI mol% Fig. 1. The SmI&sI
phase diagram.
NaI mol% Fig. 2. The SmIz-NaI
phase diagram.
1
CsSm~Is, a little SmIz
SmI2, a little CsSmzIs
CSSrX&
21 CsSm&
3:2
2:1
SmI2, a little NaI
4:r
SmXz, a little NaX
Molar ratio: Smjlz:NaI
SmIz, NaI
1:t
CSkhIJ
1.-l
NaI, a little Smiz
1:2
a little CsSmI3
Results of phase analysis (25 “C) from X-ray powder diffraction
TABLE 2
‘#:_I
9:t
Molar ratio SmI~CsI
Results of phase analysis (25 “C) from X-ray powder diffraction
TM&E
Cs&nIs
1:3
NaI, a little SmXz
1:4
Cs$3mIs, a little CsSmIs
1:2
NaI, very little Smiz
1:6
--
CsX, a little Cs$%rrI.j
1:9
98
points are 610,474, 487 and 535 “C!respectively. There are also two eutectic points located at 443 and 508 “C with 17.5 and 72.5 mol.% CsI; these were estimated using the Tammann Trigon method. The formation of three of these compounds has been confirmed by X-ray diffraction measurements at room temperature (see Table 1). The failure to detect CszSm14 by X-ray diffraction at room temperature may be due to the decomposition of this compound on cooling to 500 “C. The AB and CD lines observed in the SmI,-CsI phase diagram may be attributed to phase transformations of CsSm& and CssSmI, respectively. The results of the X-ray powder diffraction phase analyses at room temperature in other regions of the phase diagram are presented in Table 1. These results are inconsistent with those obtained from the DTA data. The EF and GH lines may be regarded as an indication of the presence of two compounds which are unstable at room temperature. While their X-ray diffraction data have not yet been obtained at room temperature it is not unreasonable to speculate that these compounds have the possible compositions CsSm,& and CsgmI, respectively. The phase diagram of the SmI,-NaI system shows that there is no compound present at room temperature. This is consistent with the X-ray diffraction data shown in Table 2. However, a eutectic point appears at 381 “C with 27 mol.% NaI. In Table 3 the lattice constants and densities of CsSm,I, and CsSmI, (obtained from their X-ray diffraction data) are summarized. It is of interest to compare the phase diagrams of the SmI,-CsI and SmI,,-NaI systems with those of the YbI,-AI (A - Na, K, Rb and Cs) [ 5 - 71 and MF,-AF (M = alkaline earth metal; A = alkali metal) [19] systems. In the YbI,-AI and MF?--AF systems, the larger the ionic radius of the alkali, the larger ther number of compounds with different compositions that can be formed. A similar trend is observed in SmI*-CsI and SmIz-NaI systems; however, the EuCl,-AC1 (A = alkali metal) systems do not follow this rule.
TABLE 3 Lattice constants and properties of CsSmzIS and CsSmI3
Colour Crystal system type Space group a (A) b (A) c(A) P (deg) D, (g CIII-~) ;O
02 cmv3)
MV, (cm3 mol-‘)
CsSmzIs
CsSmZ3
Blackish green Monoclinic p2 1/c 10.219(3) 9.093(2) 14.300(6) 90.35(4) 5.34 5.26 4 200.0
Bright green Orthorhombic Pmmm 8.631(3) 17.999(6) 12.564(5) 4.52 4.76 8 146.9
99
Acknowledgments We thank Mr. Che-Guang Chan for his assistance in X-ray powder diffraction measurement and for many useful discussions on the data analysis. We acknowledge the National Natural Science Foundation of China for support of this research.
References 1 J. Kutscher and A. Schneider, 2. Anorg. Allg. Chem., 408 (1984) 135 - 145. 2 G. I. Novikov, 0. G. Polyachenok and S. A. Frid, J. Inorg. Chem. (USSR), 9 (1964) 412 - 415. 3 H. Fink and H. J. Seihert, 2. Anorg. Allg. Chem., 466 (1980) 87. 4 A. K. Molodkin, A. M. Karagodina, D. G. Dudareva and V. A. Krokhin, J. Znorg. Chem. (USSR), 28 (1983) 2985. 5 S. H. Wang, S. B. Jiang, Z. G.“Tang and H. Z. Yang, J. Chin. Rare-Earth Sot., 2 (1984) 25. 6 Z. G. Tang, H. Z. Yang and S. H. Wang, J. Chin. Rare-Earth Sot., 4 (1986) 71 - 73. 7 S. H. Wang and M. Zhao, J. Less-Common Met., 127 (1987) 219 - 224. 8 W. A. McAllister, J. Efectrochem. Sot., 132 (1985) 2798 - 2800. 9 R. J. Zollweg, C. S. Liu, C. Hirayama and J. W. McNall, J. Illurn. Eng. Sot., 4 (1975) 249 - 253. 10 C. S. Liu and C. Hirayama, J. Zllum. Eng. Sot., 8 (1970) 147 - 151. 11 C. Hirayama, J. Illurn. Eng. Sot., 6 (1977) 209 - 214. 12 C. Hirayama, in E. Lundin (ed.), Proc. 12th Rare-Earth Research Conf., Vail, CO, 1976, Vol. 2, pp. 1044 - 1053. 13 C. Hirayama and P. M. Castle, in J. M. Haschke and H. A. Eick (eds.), Proc. 11th Rare-Earth Research Conf., Travers City, MI, October 7 - 10, 1974, National Technical Information Service, Springfield, VA, 1974, Vol. 2, pp. 1048 - 1057. 14 S. H. Wang and H. Z. Yang, Proc. 1st Chinese Rare-Earth Conf., Be&ng, October 1980, Abstracts, p. 46. 15 F. G. Ras, D. J. W. Ijdo and G. G. Vesschoor, Acta Crystallogr. Sect. B, 33 (1977) 259. 16 A. dePretis, D. Minichelli, F. Riceiardiello, Rev. Znt. Hautes Temp. Refract., 22 (1985) 215 - 219. 17 G. Meyer, personal communication (Justus-Liebig UniversitPt, Giessen, F.R.G.) 18 K. Yvon, W. Jeitschko and E. Parthe, J. Appl. Crystallogr., 10 (1977) 73. 19 R. E. Thoma, lnorg. Chem., 1 (1962) 259.