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Synthesis, structure determination and magnetic susceptibilities of the oxides Ln3Li5Sb2O12 (Ln ≠ Pr, Nd, Sm)
J o m v m l o f Alloys e~nd Cornpou~wLs, I77 (1991) 2 5 1 - 2 5 7 JAL 0053
251
Synthesis, structure determination and magnetic susceptibilities of the oxides Ln,~Li,sSb20~2 (Ln = Pr, Nd, Sm) J. Isasi, M. L. Veiga, R. Saez-Puche, A. Jerez and C. Pico D e p a r t a m e n t o d e Q u i m i c a Ine~rgdnica I, U n i v e r s i d a d Cornplutense, F a c u l t a d d e Ciencicas Q u i m i c a s , E-28040 Mad.rid ( S p a i n ) (Received June 6, 1991)
Abstract The o x i d e s Ln:~Li.~Sb20~2 ( L n ~ P r , Nd, Sin) were p r e p a r e d in air by h e a t h l g a m i x t u r e of Ln20:~, LiNO:3 a n d Sb203 in t h e t e m p e r a t u r e r a n g e 1 0 2 3 - 1 2 4 3 K. Lattice p a r a m e t e r s as well as a t o m i c c o o r d i n a t e s in the s p a c e g r o u p I213 ( Z = 8 ) are e s t a b l i s h e d from Xray p o w d e r diffraction d a t a by t h e Rietveld m e t h o d . Magnetic susceptibilities f r o m 4.2 to 3 0 0 K follow a C u r i e - W e i s s law a b o v e 50 K ( L n = - P r ) or 70 K (Ln~-Nd). This is a t t r i b u t e d to t h e s p l i t t i n g of t h e g r o u n d s t a t e a s s o c i a t e d with the Ln a÷ ions by the influence of the crystal field. The m a g n e t i c m o m e n t s , 3.54 a n d 3.61 /ZB for p r a s e o d y n f i u m a n d n e o d y m i u m respectively, a g r e e with t h o s e c a l c u l a t e d by H u n d ' s fornmla. T h e Sm 3+ b e h a v i o u r c a n b e e x p l a i n e d by t a k i n g into a c c o u n t t h a t the splitting of t h e m u l t i p l e t s is n o t too large c o m p a r e d t o kT. The m a g n e t i c m o m e n t o b s e r v e d at r o o m t e m p e r a t u r e for this cation is 1.6 /xB.
1. I n t r o d u c t i o n A new series of mixed oxides, Ln3Li~Sb20,2 ( L n - L a , Pr, Nd, Sm, Eu), has recently been synthesized [1]. The unit cell is cubic (space group I2~3,
Z=8). In this paper we report the experimental magnetic susceptibilities for the oxides LnaLi~Sb2OL2 (Ln = Pr, Nd, Sm) in polycrystalline samples, which were also characterized by X-ray powder diffraction data, refined on the basis of the Rietveld analysis method.
2. E x p e r i m e n t a l d e t a i l s Ln3Li~Sb2Oi2 (Ln - Pr, Nd, Sm) samples were prepared from Ln203, LiNO3 and Sb203 (Merck). The initial mixture in stoichiometric ratio is heated to 1023 K for 6 h. The second step is a thermal treatment at 1243 K. In this process, sublimation of lithium oxide takes place and it is necessary to add an excess of 30%-40% LiNO3. Therefore the stoichiometry of this c o m p o u n d could not be fixed, but the tentative chemical formula of the phase La3LisSb2012
Elsevier Sequoia, Lausanne
252 [2] is proposed taking into account the structural analogy with the niobium (V) and tantalum (V) ternary oxides [3]. 3. R e s u l t s a n d d i s c u s s i o n
Powder X-ray diffraction patterns were registered at a rate of 0.1 ° (20) per minute by means of a Siemens Kristalloflex diffractometer powered by a D500 generator using nickel-filtered Cu Ka radiation. A 20 step scan of 0.04 ° was used and the Rietveld profile analysis method [4] was employed for refinement of X-ray diffraction patterns in the range 10°-120 ° (20) for 287 observed reflections. The structure of La3Li~(Nb,Ta)20,~ was used as a trial model. The Rietveld p r o g r a m m e minimizes the function X 2= (Rw~,/ RExp) 2. The reflection conditions are h + k + l = 2 n for (h, k, l), k + l = 2 n for (0, k, l) and h = 2 n for (h, 0, 0), compatible with the space group 12,3. The structural data for Ln3Li~Sb2012 ( L n - P r , Nd, Sin) are given in Table 1. The unit cell parameters decrease linearly in accordance with the lanthanide contraction effect. Table 2 lists the experimental bond lengths and angles of Ln3LisSb20,2 ( L n - P r , Nd, Sm). The structure of these c o m p o u n d s is isomorphous to La3Li~Sb20,2 and can be described as a three-dimensional framework of lanthanide, antimony and oxygen atoms. The SbO6 octahedra are located along the threefold axes of the unit cell and are associated with three lanthanide atoms, forming infinite chains of composition (Ln3Sb20,2)n. These chains are bonded with others by means oflanthanide and lithium atoms. Figure 1 shows the orientation of (Ln3Sb2012)n chains along a threefold axis. Magnetic susceptibility m e a s ur e m ent s were made using the Faraday m eth o d in the te m pe r at ur e range 4 . 2 - 3 0 0 K with a DMS5 Pendule susceptometer. The maximum magnetic field applied was 1 kG with H ( d H / d Z ) = 29 kG 2 c m - ' . The equipment was calibrated with Hg(Co(SCN)4) and Cd2(SO4)3" 8H20 and X was independent of the field in the temperature range of the measurements. Values of effective m o m e n t (~B) and Weiss constant (0) were obtained by least-squares fits from the linear part of the X - ' vs. T plots. The magnetic susceptibility of Pr3LisSb2Ol~. follows a Curie-Weiss law behaviour from 300 to 50 K. Below this t e m p e r a t u r e deviations upwards from linearity are observed, analogous to those found in some compounds of praseodymium [5, 6]. Since this cation has an even n u m b e r of f electrons, the lowest crystal field level could be a singlet and the upward deviations observed at the lower t e m p e r a t u r e s are probably due to the population of this singlet level (see Fig. 2). The reciprocal molar magnetic susceptibility for NdaLisSb2012 obeys a Curie-Weiss law, X= 1.63/T+ 14.8, above 70 K and the mo men t calculated from the X - ' vs. T plot suggests that crystal fields effects are probably present (Fig. 2). Similar remarks have previously b e en reported for different neodym i um c o m p o u n d s [7-9]. The observed and calculated magnetic m o m e n t s and Weiss constants for Ln 3+ in the oxides can be found in Table 3. In these cases negative
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254 TABLE 2 Bond lengths (angstroms) and bond angles (degrees) of Ln~Li,~Sb2Oje Ln ~ Pr Sb(1)-O(3) Sb(1)-O(4) Sb(2)-O(1) $b(2)-O(2) Pr(2)-O(2) Pr(2)-O(3) Li(1)-O(1) ai(1)-0(2) Li(1)-0(2) ai(1)-0(3) Li(1)-0(3) Li(1)-0(4)
2.61(7) 1.69(1) 2.26(7) 1.90(5) 2.62(5) 2.39(5) 2.01(0) 2.19(5) 2.69(5) 2.21(1) 2.00(0) 2.11 (2)
O(4)-Pr(1)-O(4) 0(2)-Pr(2)-0(2) O(3)-Sb(1)-O(4) O(1)-$b(2)-O(2) O(3)-Li(1)-0(1) O(3)-Li(1)-0(2) O(2)-Li(1)-O(4) 0(2)-Li(2)-0(4) O(1)-Li(2)-O(1) O(3)-Li(2)-0(4)
3x 3x 3x 3x 2x 2x
Pr(1)-O(4) Pr(1)-O(4) Pr(1)-O(1) Pr(1)-O(1) Pr(2)-O(2) Pr(2)-O(3) ai(2)-O(1) Li(2)-O(1) Li(2)-0(2) Li(2)-0(3) Li(2)-0(4) Li(2)-O(4 )
90.02 70.43 84.48 89.41 65.67 94.95 93.04 92.26 63.08 89.74
O(1)-Pr(1)-O(1) 0(3)-Pr(2)-0(3) O(4)-Sb(1)-O(3) 0(2)-Sb(2)-O(1) O(1)-Li(1)-O(3) 0(2)-Li(1)-0(2) 0(4)-Li(1)-0(3) 0(4)-Li(2)-0(1) 0(1)-Li(2)-0(3) O(4)-Li(2)-0(2)
3x 3x
Nd(1)--O(4) Nd(1)-O(4) Nd(1)-O(1) Sd(1)-O(1) Nd(2)-O(2) Nd(2)---0(3) Li(2)-O(1) Li(2)-O (1) Li(2)-0(2) Li(2)-0(3) Li(2)-O(4) Li(2)-0(4)
2.43(9) 2.60(6) 2.83(3) 2.90(4) 2.54(2) 2.52(0) 2.02(2) 2.34(3) 2.19(8) 2.19(4) 2.49(6) 2.52(2)
2x 2x 2x 2x 2x 2x
140.80 59.69 87.54 110.38 81.44 73.68 91.55 124.03 55.77 90.02
Ln~Nd
Sb(I)-0(3) Sb(1)-.0(4) Sb(2)-O(1) $b(2)-0(2) Nd(2)-0(2) Nd(2)-O(3) Li(l)-O(1 ) Li(1)--0(2) Li(1)-O(2) Li(l)-0(3) Li(1)--O(3) Li(1)-0(4) O(4)-Sd(1)-O(4) O(2)-Nd(2)-0(2) O(3)-$b(1)-O(4) O(1)-$b(2)-0(2) O(3)-Li(1)-O(1) O(3)-Li(1)-O(2) O(2),,-Li(1)-O(4) 0(2)-Li(2)-O(4) O(1)-Li(2)---O(1) O(3)-Li(2)-O(4)
1.73(9) 2.24(0) 2.06(0) 2.14(1) 2.14(1) 2.64(0) 2.55(1) 2.79 (9) 2.09(6) 2.10(4) 2.46(3) 2.20(1)
3x
3x 2x 2x
78.47 72.06 77.65 92.79 91.05 110.90 78.26 89.80 92.81 88.97
O(1)-Sd(1)-O(1) 0(3)-Nd(2)-O(3) O(4)-$b(1)--O(3) 0(2)--Sb(2)--O(1) O(1)-Li(1)---O(3) 0(2)-Li(I)-0(2) 0(4)-Li(1)-O(3) O(4),,-Li(2)-O(1) O(1)-Li(2)-O(3) O(4)--Li(2)-0(2)
2.62(2) 2.94(6) 2.24(0) 2.62(6) 2.46(9) 2.73(6) 2.14(6) 2.38(6) 2.42(7) 2.09(6) 2.08(0) 2.01(7)
2X 2x 2x 2x 2x 2x
68.29 84.57 89.61 69.99 79.74 89.02 64.27 108.90 85.78 90.20
(continu~ed)
255
TABLE 2. (corttinued) Ln -=Sm Sb(1)-O(3) Sb(1)-O(4) Sb(2)-O(1) Sb(2)-O(2) Sm(2)-O(2) Sm(2)-O(3) Li(1)-O(1) Li(1 ) - 0 ( 2 ) Li(1)-0(2) Li(1)-O(3) Li(1)-0(3) Li(1)-O(4)
2.00(3) 1.90(7) 2.04(1) 2.24(0) 2.26(6) 2.20(2) 2.09(4) 2.84(2) 2.10(0) 2.09(9) 2.27(1) 2.39(1)
O(4)-Sm(1)-O(4) O(2)-Sm(2)-O(2) O(3)-Sb(1)-O(4) O(1)-Sb(2)-O(2) O(3)-Li(1)-O(1) O(3)-Li(1)-O(2) O(2)-Li(1)-O(4) O(2)-Li(2)-0(4) O(1)-Li(2)-O(1) O(3)-Li(2}-O(4)
3× 3× 3× 3× 2× 2x
Sm(1)-O(4) Sm(1)-O(4) Sm(1)-O(1) Sm(1)-O(1) Sm(2)-O(2) Sm(2)-O(3) Li(2)-O(1) Li(2)-O(1) Li(2)-O(2) Li(2)-O(3) Li(2)-O(4) Li(2)-O(4)
66.72 77.54 102.85 89.54 88.81 98.99 99.42 73.07 70.70 96.61
O(1)-Sm(1)-O(1) 0(3)-Sm(2)-O(3) O(4)-$b(1)-O(3) O(2)-$b(2)-O(1) O(l)-Li(1)-O(3) O(2)-Li(1)-O(2) O(4)-Li(1)-O(3) O(4)-Li(2)--O(1) O(1)-Li(2)-O(3) O(4)-LJ(2)-O(2)
2.62(5) 2.26(1) 2.77(4) 2.93(8) 2.79(7) 2.39(8) 2.12(3) 2.40(6) 2.19(3) 2.09(6) 2.41 (4) 2.19(5)
2x 2x 2x 2× 2x 2x
69.03 61.92 90.38 77.62 83.96 79.44 84.55 137.57 119.33 88.81
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0 0
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Fig. 1. A threefold axis along which chains of (Ln3Sb20~2),~ (Ln-=Pr, Nd, Sin) are disposed and location of lithium atoms (circles). v a l u e s f o r t h e W e i s s c o n s t a n t (0) a r e f o u n d . I t is o b v i o u s t h a t t h e W e i s s c o n s t a n t v a l u e s a r e d u e t o t h e c r y s t a l field e f f e c t s . A d i f f e r e n t b e h a v i o u r in t h e t e m p e r a t u r e d e p e n d e n c e o f t h e m a g n e t i c p r o p e r t i e s o f S m s L i s S b 2 0 1 2 is o b s e r v e d ( F i g . 3). T h e s u s c e p t i b i l i t y o f
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Sm3LisSb,~O12 r e m a i n s a l m o s t c o n s t a n t b e t w e e n 100 and 2 4 0 K. This characteristic b e h a v i o u r is attributed to the fact that the e n e r g y differences o f the 6H multiplet levels for Sm ~+ are c o m p a r a b l e to kT, and for this r e a s o n Van Vleck c a n be u s e d in a first a p p r o x i m a t i o n [10 ], n e g l e c t i n g the J - m i x i n g a n d crystal-field-splitting effects, a l t h o u g h this gives a p o o r fit of the ex-
257 TABLE 3 Magnetic parameters for Ln3LisSb2Oj~ Ln
Ground state of the free ion
#~ (/x~)
bt" (bt/~)
0 (K)
Pr Nd Sm
3H4 41"/z 6H5/2
3.58 3.62 1.6
3.54 3.61 1.6 ~
- 16.0 - 14.8 --
~Calculated at 298 K.
p e r i m e n t a l and calculated susceptibilities, as Fig. 3 shows, and a value of A = 298 c m - 1 for the orbit-coupling c o n s t a n t is obtained.
Acknowledgments W e t h a n k F. Rojas for the m a g n e t i c m e a s u r e m e n t s . This work is s u p p o r t e d by the CICYT P B 8 9 - 1 3 4 (Spain). J. Isasi is grateful to the UCM for a " B e c a Complutense".
References 1 2 3 4 5 6 7 8 9 10
J. Isasi, M. L. Lopez, M. L. Veiga and C. Pico, Anal. Quire., in the press. J. Isasi, M. L. Veiga, A. Jerez and C. Pico, J. L e s s - C o m m o n Met., 157 (1991) 381. H. Hyooma and K. Hayashi, Mater. Res. Bull., 23 (1988) 1399. J. Rodriguez-Carvajal, P r o g r a m FULLPROF, ILL, Grenoble, 1990. R. Saez-Puche, M. Norton, T. R. White and W. S. Glaussinger, J. S o l i d S t a t e Chem., 50 (1983) 281. Y. Laureiro, M. L. Veiga, F. Fernandez, R. Saez-Puche, A. Jerez and C. Pico, J. LessC o m m o n Met., 167 (1991) 387. L. Beaury, J. Derouet, P. Porcher, P. Caro and P. G. Fedman, J. L e s s - C o m m o n Met., 126 (1986). Y. Laureiro, M. L. Veiga, F. Fernandez, R. Saez-Puche, A. Jerez and C. Pico, J. LessC o m m o n Met., 335 (1990) 157. M. L. Lopez, M. L. Veiga, F. Fernandez, A. Jerez and C. Pico, J. Less-Cornmon Met., 166 (1990) 367. J. H. van V]eck, The Theory o f E l e c t r i c a n d M a g n e t i c Susceptibilities, Oxford University Press, Oxford, 1965.
251
Synthesis, structure determination and magnetic susceptibilities of the oxides Ln,~Li,sSb20~2 (Ln = Pr, Nd, Sm) J. Isasi, M. L. Veiga, R. Saez-Puche, A. Jerez and C. Pico D e p a r t a m e n t o d e Q u i m i c a Ine~rgdnica I, U n i v e r s i d a d Cornplutense, F a c u l t a d d e Ciencicas Q u i m i c a s , E-28040 Mad.rid ( S p a i n ) (Received June 6, 1991)
Abstract The o x i d e s Ln:~Li.~Sb20~2 ( L n ~ P r , Nd, Sin) were p r e p a r e d in air by h e a t h l g a m i x t u r e of Ln20:~, LiNO:3 a n d Sb203 in t h e t e m p e r a t u r e r a n g e 1 0 2 3 - 1 2 4 3 K. Lattice p a r a m e t e r s as well as a t o m i c c o o r d i n a t e s in the s p a c e g r o u p I213 ( Z = 8 ) are e s t a b l i s h e d from Xray p o w d e r diffraction d a t a by t h e Rietveld m e t h o d . Magnetic susceptibilities f r o m 4.2 to 3 0 0 K follow a C u r i e - W e i s s law a b o v e 50 K ( L n = - P r ) or 70 K (Ln~-Nd). This is a t t r i b u t e d to t h e s p l i t t i n g of t h e g r o u n d s t a t e a s s o c i a t e d with the Ln a÷ ions by the influence of the crystal field. The m a g n e t i c m o m e n t s , 3.54 a n d 3.61 /ZB for p r a s e o d y n f i u m a n d n e o d y m i u m respectively, a g r e e with t h o s e c a l c u l a t e d by H u n d ' s fornmla. T h e Sm 3+ b e h a v i o u r c a n b e e x p l a i n e d by t a k i n g into a c c o u n t t h a t the splitting of t h e m u l t i p l e t s is n o t too large c o m p a r e d t o kT. The m a g n e t i c m o m e n t o b s e r v e d at r o o m t e m p e r a t u r e for this cation is 1.6 /xB.
1. I n t r o d u c t i o n A new series of mixed oxides, Ln3Li~Sb20,2 ( L n - L a , Pr, Nd, Sm, Eu), has recently been synthesized [1]. The unit cell is cubic (space group I2~3,
Z=8). In this paper we report the experimental magnetic susceptibilities for the oxides LnaLi~Sb2OL2 (Ln = Pr, Nd, Sm) in polycrystalline samples, which were also characterized by X-ray powder diffraction data, refined on the basis of the Rietveld analysis method.
2. E x p e r i m e n t a l d e t a i l s Ln3Li~Sb2Oi2 (Ln - Pr, Nd, Sm) samples were prepared from Ln203, LiNO3 and Sb203 (Merck). The initial mixture in stoichiometric ratio is heated to 1023 K for 6 h. The second step is a thermal treatment at 1243 K. In this process, sublimation of lithium oxide takes place and it is necessary to add an excess of 30%-40% LiNO3. Therefore the stoichiometry of this c o m p o u n d could not be fixed, but the tentative chemical formula of the phase La3LisSb2012
Elsevier Sequoia, Lausanne
252 [2] is proposed taking into account the structural analogy with the niobium (V) and tantalum (V) ternary oxides [3]. 3. R e s u l t s a n d d i s c u s s i o n
Powder X-ray diffraction patterns were registered at a rate of 0.1 ° (20) per minute by means of a Siemens Kristalloflex diffractometer powered by a D500 generator using nickel-filtered Cu Ka radiation. A 20 step scan of 0.04 ° was used and the Rietveld profile analysis method [4] was employed for refinement of X-ray diffraction patterns in the range 10°-120 ° (20) for 287 observed reflections. The structure of La3Li~(Nb,Ta)20,~ was used as a trial model. The Rietveld p r o g r a m m e minimizes the function X 2= (Rw~,/ RExp) 2. The reflection conditions are h + k + l = 2 n for (h, k, l), k + l = 2 n for (0, k, l) and h = 2 n for (h, 0, 0), compatible with the space group 12,3. The structural data for Ln3Li~Sb2012 ( L n - P r , Nd, Sin) are given in Table 1. The unit cell parameters decrease linearly in accordance with the lanthanide contraction effect. Table 2 lists the experimental bond lengths and angles of Ln3LisSb20,2 ( L n - P r , Nd, Sm). The structure of these c o m p o u n d s is isomorphous to La3Li~Sb20,2 and can be described as a three-dimensional framework of lanthanide, antimony and oxygen atoms. The SbO6 octahedra are located along the threefold axes of the unit cell and are associated with three lanthanide atoms, forming infinite chains of composition (Ln3Sb20,2)n. These chains are bonded with others by means oflanthanide and lithium atoms. Figure 1 shows the orientation of (Ln3Sb2012)n chains along a threefold axis. Magnetic susceptibility m e a s ur e m ent s were made using the Faraday m eth o d in the te m pe r at ur e range 4 . 2 - 3 0 0 K with a DMS5 Pendule susceptometer. The maximum magnetic field applied was 1 kG with H ( d H / d Z ) = 29 kG 2 c m - ' . The equipment was calibrated with Hg(Co(SCN)4) and Cd2(SO4)3" 8H20 and X was independent of the field in the temperature range of the measurements. Values of effective m o m e n t (~B) and Weiss constant (0) were obtained by least-squares fits from the linear part of the X - ' vs. T plots. The magnetic susceptibility of Pr3LisSb2Ol~. follows a Curie-Weiss law behaviour from 300 to 50 K. Below this t e m p e r a t u r e deviations upwards from linearity are observed, analogous to those found in some compounds of praseodymium [5, 6]. Since this cation has an even n u m b e r of f electrons, the lowest crystal field level could be a singlet and the upward deviations observed at the lower t e m p e r a t u r e s are probably due to the population of this singlet level (see Fig. 2). The reciprocal molar magnetic susceptibility for NdaLisSb2012 obeys a Curie-Weiss law, X= 1.63/T+ 14.8, above 70 K and the mo men t calculated from the X - ' vs. T plot suggests that crystal fields effects are probably present (Fig. 2). Similar remarks have previously b e en reported for different neodym i um c o m p o u n d s [7-9]. The observed and calculated magnetic m o m e n t s and Weiss constants for Ln 3+ in the oxides can be found in Table 3. In these cases negative
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~
C'~ C~'] O~ ~"0
Cq C'X1 O0 O0 " ~ ~ ~ ~ ~'~ " ~ --~ ~ C'q C'X1C'q C~1C'q C~1
~-,~.~,_~
"~
2.
"~
~
,~
,.0 ~
c'q
eq cm ~
,~
.~'~ .~'~ ~--''~-J ~-~ ~--~
::::3
c~
II
~ oo ~ 9 0 "~'~' 0
~
~
~.~
~
--
'-
0
0
~
5 5 5 5 5 5 5 5 d d
0
II
C; ;> m
II
~ C~~
II ~-
b
II
% o
.3
o
o
~
o
~
~
0 0 0 0 0 0 0 0 0 0
o
~
0
0
0
~
~
dddddddddd
III
~ ~
II
" ' ~
~
I~
L
254 TABLE 2 Bond lengths (angstroms) and bond angles (degrees) of Ln~Li,~Sb2Oje Ln ~ Pr Sb(1)-O(3) Sb(1)-O(4) Sb(2)-O(1) $b(2)-O(2) Pr(2)-O(2) Pr(2)-O(3) Li(1)-O(1) ai(1)-0(2) Li(1)-0(2) ai(1)-0(3) Li(1)-0(3) Li(1)-0(4)
2.61(7) 1.69(1) 2.26(7) 1.90(5) 2.62(5) 2.39(5) 2.01(0) 2.19(5) 2.69(5) 2.21(1) 2.00(0) 2.11 (2)
O(4)-Pr(1)-O(4) 0(2)-Pr(2)-0(2) O(3)-Sb(1)-O(4) O(1)-$b(2)-O(2) O(3)-Li(1)-0(1) O(3)-Li(1)-0(2) O(2)-Li(1)-O(4) 0(2)-Li(2)-0(4) O(1)-Li(2)-O(1) O(3)-Li(2)-0(4)
3x 3x 3x 3x 2x 2x
Pr(1)-O(4) Pr(1)-O(4) Pr(1)-O(1) Pr(1)-O(1) Pr(2)-O(2) Pr(2)-O(3) ai(2)-O(1) Li(2)-O(1) Li(2)-0(2) Li(2)-0(3) Li(2)-0(4) Li(2)-O(4 )
90.02 70.43 84.48 89.41 65.67 94.95 93.04 92.26 63.08 89.74
O(1)-Pr(1)-O(1) 0(3)-Pr(2)-0(3) O(4)-Sb(1)-O(3) 0(2)-Sb(2)-O(1) O(1)-Li(1)-O(3) 0(2)-Li(1)-0(2) 0(4)-Li(1)-0(3) 0(4)-Li(2)-0(1) 0(1)-Li(2)-0(3) O(4)-Li(2)-0(2)
3x 3x
Nd(1)--O(4) Nd(1)-O(4) Nd(1)-O(1) Sd(1)-O(1) Nd(2)-O(2) Nd(2)---0(3) Li(2)-O(1) Li(2)-O (1) Li(2)-0(2) Li(2)-0(3) Li(2)-O(4) Li(2)-0(4)
2.43(9) 2.60(6) 2.83(3) 2.90(4) 2.54(2) 2.52(0) 2.02(2) 2.34(3) 2.19(8) 2.19(4) 2.49(6) 2.52(2)
2x 2x 2x 2x 2x 2x
140.80 59.69 87.54 110.38 81.44 73.68 91.55 124.03 55.77 90.02
Ln~Nd
Sb(I)-0(3) Sb(1)-.0(4) Sb(2)-O(1) $b(2)-0(2) Nd(2)-0(2) Nd(2)-O(3) Li(l)-O(1 ) Li(1)--0(2) Li(1)-O(2) Li(l)-0(3) Li(1)--O(3) Li(1)-0(4) O(4)-Sd(1)-O(4) O(2)-Nd(2)-0(2) O(3)-$b(1)-O(4) O(1)-$b(2)-0(2) O(3)-Li(1)-O(1) O(3)-Li(1)-O(2) O(2),,-Li(1)-O(4) 0(2)-Li(2)-O(4) O(1)-Li(2)---O(1) O(3)-Li(2)-O(4)
1.73(9) 2.24(0) 2.06(0) 2.14(1) 2.14(1) 2.64(0) 2.55(1) 2.79 (9) 2.09(6) 2.10(4) 2.46(3) 2.20(1)
3x
3x 2x 2x
78.47 72.06 77.65 92.79 91.05 110.90 78.26 89.80 92.81 88.97
O(1)-Sd(1)-O(1) 0(3)-Nd(2)-O(3) O(4)-$b(1)--O(3) 0(2)--Sb(2)--O(1) O(1)-Li(1)---O(3) 0(2)-Li(I)-0(2) 0(4)-Li(1)-O(3) O(4),,-Li(2)-O(1) O(1)-Li(2)-O(3) O(4)--Li(2)-0(2)
2.62(2) 2.94(6) 2.24(0) 2.62(6) 2.46(9) 2.73(6) 2.14(6) 2.38(6) 2.42(7) 2.09(6) 2.08(0) 2.01(7)
2X 2x 2x 2x 2x 2x
68.29 84.57 89.61 69.99 79.74 89.02 64.27 108.90 85.78 90.20
(continu~ed)
255
TABLE 2. (corttinued) Ln -=Sm Sb(1)-O(3) Sb(1)-O(4) Sb(2)-O(1) Sb(2)-O(2) Sm(2)-O(2) Sm(2)-O(3) Li(1)-O(1) Li(1 ) - 0 ( 2 ) Li(1)-0(2) Li(1)-O(3) Li(1)-0(3) Li(1)-O(4)
2.00(3) 1.90(7) 2.04(1) 2.24(0) 2.26(6) 2.20(2) 2.09(4) 2.84(2) 2.10(0) 2.09(9) 2.27(1) 2.39(1)
O(4)-Sm(1)-O(4) O(2)-Sm(2)-O(2) O(3)-Sb(1)-O(4) O(1)-Sb(2)-O(2) O(3)-Li(1)-O(1) O(3)-Li(1)-O(2) O(2)-Li(1)-O(4) O(2)-Li(2)-0(4) O(1)-Li(2)-O(1) O(3)-Li(2}-O(4)
3× 3× 3× 3× 2× 2x
Sm(1)-O(4) Sm(1)-O(4) Sm(1)-O(1) Sm(1)-O(1) Sm(2)-O(2) Sm(2)-O(3) Li(2)-O(1) Li(2)-O(1) Li(2)-O(2) Li(2)-O(3) Li(2)-O(4) Li(2)-O(4)
66.72 77.54 102.85 89.54 88.81 98.99 99.42 73.07 70.70 96.61
O(1)-Sm(1)-O(1) 0(3)-Sm(2)-O(3) O(4)-$b(1)-O(3) O(2)-$b(2)-O(1) O(l)-Li(1)-O(3) O(2)-Li(1)-O(2) O(4)-Li(1)-O(3) O(4)-Li(2)--O(1) O(1)-Li(2)-O(3) O(4)-LJ(2)-O(2)
2.62(5) 2.26(1) 2.77(4) 2.93(8) 2.79(7) 2.39(8) 2.12(3) 2.40(6) 2.19(3) 2.09(6) 2.41 (4) 2.19(5)
2x 2x 2x 2× 2x 2x
69.03 61.92 90.38 77.62 83.96 79.44 84.55 137.57 119.33 88.81
Sb Li .,~---~0
0 0
La ~
0
0
Fig. 1. A threefold axis along which chains of (Ln3Sb20~2),~ (Ln-=Pr, Nd, Sin) are disposed and location of lithium atoms (circles). v a l u e s f o r t h e W e i s s c o n s t a n t (0) a r e f o u n d . I t is o b v i o u s t h a t t h e W e i s s c o n s t a n t v a l u e s a r e d u e t o t h e c r y s t a l field e f f e c t s . A d i f f e r e n t b e h a v i o u r in t h e t e m p e r a t u r e d e p e n d e n c e o f t h e m a g n e t i c p r o p e r t i e s o f S m s L i s S b 2 0 1 2 is o b s e r v e d ( F i g . 3). T h e s u s c e p t i b i l i t y o f
256
e•
-'~Pr
~.2 o -...~ Nd
•
3.0~
%
o•
°
• .0.::...
'X
O.' i 0.6
•
Q
~-S~.''° 0
I
80
I
I
I
160
240
320
&O0
T (K)
Fig. 2. Temperature dependence of reciprocal magnetic susceptibility for Ln3Li~Sb2012 p e r mole of Ln 3÷ (Ln~-Pr, Nd).
!
i
1.(
6
I
!.\ I
IOg
1
2{~
~I~
Fig. 3. Temperature variation of magnetic susceptibility per mole of Sm3LisSb20]2. Full lines r e p r e s e n t calculated values.
Sm3LisSb,~O12 r e m a i n s a l m o s t c o n s t a n t b e t w e e n 100 and 2 4 0 K. This characteristic b e h a v i o u r is attributed to the fact that the e n e r g y differences o f the 6H multiplet levels for Sm ~+ are c o m p a r a b l e to kT, and for this r e a s o n Van Vleck c a n be u s e d in a first a p p r o x i m a t i o n [10 ], n e g l e c t i n g the J - m i x i n g a n d crystal-field-splitting effects, a l t h o u g h this gives a p o o r fit of the ex-
257 TABLE 3 Magnetic parameters for Ln3LisSb2Oj~ Ln
Ground state of the free ion
#~ (/x~)
bt" (bt/~)
0 (K)
Pr Nd Sm
3H4 41"/z 6H5/2
3.58 3.62 1.6
3.54 3.61 1.6 ~
- 16.0 - 14.8 --
~Calculated at 298 K.
p e r i m e n t a l and calculated susceptibilities, as Fig. 3 shows, and a value of A = 298 c m - 1 for the orbit-coupling c o n s t a n t is obtained.
Acknowledgments W e t h a n k F. Rojas for the m a g n e t i c m e a s u r e m e n t s . This work is s u p p o r t e d by the CICYT P B 8 9 - 1 3 4 (Spain). J. Isasi is grateful to the UCM for a " B e c a Complutense".
References 1 2 3 4 5 6 7 8 9 10
J. Isasi, M. L. Lopez, M. L. Veiga and C. Pico, Anal. Quire., in the press. J. Isasi, M. L. Veiga, A. Jerez and C. Pico, J. L e s s - C o m m o n Met., 157 (1991) 381. H. Hyooma and K. Hayashi, Mater. Res. Bull., 23 (1988) 1399. J. Rodriguez-Carvajal, P r o g r a m FULLPROF, ILL, Grenoble, 1990. R. Saez-Puche, M. Norton, T. R. White and W. S. Glaussinger, J. S o l i d S t a t e Chem., 50 (1983) 281. Y. Laureiro, M. L. Veiga, F. Fernandez, R. Saez-Puche, A. Jerez and C. Pico, J. LessC o m m o n Met., 167 (1991) 387. L. Beaury, J. Derouet, P. Porcher, P. Caro and P. G. Fedman, J. L e s s - C o m m o n Met., 126 (1986). Y. Laureiro, M. L. Veiga, F. Fernandez, R. Saez-Puche, A. Jerez and C. Pico, J. LessC o m m o n Met., 335 (1990) 157. M. L. Lopez, M. L. Veiga, F. Fernandez, A. Jerez and C. Pico, J. Less-Cornmon Met., 166 (1990) 367. J. H. van V]eck, The Theory o f E l e c t r i c a n d M a g n e t i c Susceptibilities, Oxford University Press, Oxford, 1965.