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Crystal structure of the R3Si1.25Se7 (R = Pr, Nd and Sm) compounds
Journal of Alloys and Compounds 458 (2008) 174–177
Crystal structure of the R3Si1.25Se7 (R = Pr, Nd and Sm) compounds L.D. Gulay ∗ , O.S. Lychmanyuk Department of General and Inorganic Chemistry, Volyn State University, Voli Avenue 13, 43009 Lutsk, Ukraine Received 18 February 2007; received in revised form 24 March 2007; accepted 26 March 2007 Available online 31 March 2007
Abstract The crystal structure of new ternary R3 Si1.25 Se7 (R = Pr, Nd and Sm) compounds (Dy3 Ge1.25 S7 structure type, Pearson symbol hP22.5, space group P63 , a = 1.05268 (3) nm, c = 0.60396 (3) nm, RI = 0.0897 for Pr3 Si1.25 Se7 ; a = 1.04760 (3) nm, c = 0.60268 (3) nm, RI = 0.0891 for Nd3 Si1.25 Se7 ; a = 1.04166 (6) nm, c = 0.59828 (6) nm for Sm3 Si1.25 Se7 ) was determined using X-ray powder diffraction. The nearest neighbours of the R and Si atoms are exclusively Se atoms. The latter form distorted trigonal prisms around the R atoms, octahedra around the Si1 atoms and tetrahedra around the Si2 atoms. Tetrahedral surrounding exists for Se1 and Se3 atoms. Six neighbours surround every Se2 atom. © 2007 Elsevier B.V. All rights reserved. Keywords: Chalcogenides; Rare earth compounds; Si compounds; Se compounds; Crystal structure; X-ray powder diffraction
1. Introduction Production of the compounds with increasingly complex compositions, such as ternary, quaternary, etc., has become a principal direction in a modern science of materials [1]. Among the multicomponent systems an important place belongs to the complex rare-earth chalcogenides. The rare-earth chalcogenides are being intensively studied during recent years due to their specific thermal, electrical and optical properties, which for example make them prospective materials in the field of infrared and nonlinear optics. Therefore the synthesis and the investigation of the crystal structures of complex chalcogenides is important step in the search for new materials. No ternary compounds in the R2 Se3 -SiSe2 (R = Pr, Nd and Sm) systems have been reported in literature. This paper presents part of a systematic investigation of rare earth chalcogenides. The crystal structure of new ternary R3 Si1.25 Se7 (R = Pr, Nd and Sm) compounds is given and discussed. 2. Experimental details The samples were prepared by melting the mixture of high purity elements (the purity of the ingredients was better than 99.9 wt.%) in evacuated silica
∗
Corresponding author. E-mail addresses: [email protected], [email protected], [email protected] (L.D. Gulay). 0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2007.03.127
ampoules. The synthesis was realized in a tube furnace. The ampoules were heated with a heating rate of 30 K/h to the maximal temperature, 1420 K. The samples were kept at the maximal temperature during 3 h. After that they were cooled slowly (10 K/h) to 870 K and annealed at this temperature during 240 h. After annealing the ampoules with the samples were quenched in cold water. X-ray powder diffraction patterns of the samples were recorded using a DRON-4-13 powder diffractometer (Cu K␣ radiation, 10◦ ≤ 2θ ≤ 100◦ , step scan mode with a step size of 0.05◦ and counting time of 20 s per data point). All calculations were performed using the CSD program [2].
3. Results and discussion The formation of the R3 Si1.25 Se7 (R = Pr, Nd and Sm) compounds was observed during the investigation of the phase relations in the R2 Se3 -SiSe2 (R = Pr, Nd and Sm) systems. Similarity of the X-ray powder diffraction patterns of these compounds proved that they are isostructural. Crystal structures of these compounds were investigated using X-ray powder diffraction. All of the peaks of the X-ray powder diffraction pattern of the Pr3 Si1.25 Se7 sample were indexed in a hexagonal unit cell with the lattice parameters listed in Table 1. Composition of the sample, intensities of the reflections and obtained lattice parameters proved that this compound is isostructural with Dy3 Ge1.25 S7 (space group P63 , a = 0.9730 nm, c = 0.5820 nm) [3]. Results of the crystal structure determination of the Pr3 Si1.25 Se7 compound are given in Table 1, whereas atomic coordinates and temperature factors are listed in Table 2. Complete crystal structure determination was performed for Nd3 Si1.25 Se7 also
L.D. Gulay, O.S. Lychmanyuk / Journal of Alloys and Compounds 458 (2008) 174–177
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Table 1 Crystal data and structure refinement details of R3 Si1.25 Se7 (R = Pr and Nd) Empirical formula Formula weight Space group
Pr3 Si1.25 Se7 1010.55 P63 (no. 173)
Nd3 Si1.25 Se7 1020.55 P63 (no. 173)
Unit cell dimensions (nm)
a = 1.05268 (3) c = 0.60396 (3)
a = 1.04760 (3) c = 0.60268 (3)
Volume (nm3 ) Number of formula units per unit cell Calculated density (g/cm3 ) Absorption coefficient (mm−1 ) F(0 0 0) Diffractometer 2θ range for data collection Refinement method Structure solution and refinement RI RP Texture axis and parameter
0.57960 (6) 2
0.57281 (6) 2
5.7899 118.082
5.9166 124.345
865 DRON-4-13 10.00–100.00 Full profile CSD
871 DRON-4-13 10.00–100.00 Full profile CSD
0.0897 0.1815 [1 1 0] and 0.52 (3)
0.0891 0.1967 [1 1 0] and 0.48 (4)
(Tables 1 and 2). The site occupancy factor for the Si1 atom was fixed at the value 0.25 to satisfy charge balance requirements. The X-ray powder diffraction pattern of Sm3 Si1.25 Se7 was not good quality for reliable crystal structure determination. Only lattice parameters were determined for this compound: a = 1.04166 (6) nm, c = 0.59828 (6) nm. The experimental and calculated diffractograms and the corresponding difference diagrams for the Pr3 Si1.25 Se7 (a) and Nd3 Si1.25 Se7 (b) compounds are shown in Fig. 1. Relevant interatomic distances (δ, nm) and coordination numbers (C.N.) of the atoms in the structures of the R3 Si1.25 Se7 (R = Pr and Nd) compounds are listed in Table 3. The interatomic distances agree well with the sum of the respective ionic radii [4]. The unit cell and the coordination polyhedra of the Pr (a), Si1 (b), Si2 (c), Se1 (d), Se2 (e) and Se3 (f) atoms in the structure of the Pr3 Si1.25 Se7 compound are shown in Fig. 2. The nearest neighbours of the Pr and Si atoms are exclusively Se
Fig. 1. The experimental and calculated diffractograms and the corresponding difference diagrams for the Pr3 Si1.25 Se7 (a) and Nd3 Si1.25 Se7 (b) compounds.
atoms. The latter form distorted trigonal prisms around the Pr atoms, octahedra around the Si1 atoms and tetrahedra around the Si2 atoms. Tetrahedral surrounding exists for Se1 and Se3 atoms. Six neighbors surround every Se2 atom. High values of temperature factors for Se2 (Table 2) correlate well with higher coordination numbers (C.N. = 6) for these atoms when compared with the respective values for Se1 and Se3 (C.N. = 4). The packing of the Pr-centered trigonal prisms, Si1-centered octahedra and Si2-centered tetrahedra in the structure of the
Table 2 Atomic coordinates and temperature factors for the R3 Si1.25 Se7 (R = Pr and Nd) compounds Atom
Position
x/a
y/b
z/c
Occupation
Biso. × 102 (nm2 )
Pr3 Si1.25 Se7 Pr Si1 Si2 Se1 Se2 Se3
6c 2a 2b 2b 6c 6c
0.2296 (2) 0 1/3 1/3 0.9081 (5) 0.4188 (5)
0.3565 (2) 0 2/3 2/3 0.1558 (5) 0.8975 (5)
0.739 (1) 0.99 (2) 0.333a 0.951 (2) 0.728 (2) 0.480 (1)
1.00 0.25 1.00 1.00 1.00 1.00
0.6 (1) 0.5 0.5 0.5 (3) 1.8 (2) 0.7 (2)
Nd3 Si1.25 Se7 Nd Si1 Si2 Se1 Se2 Se3
6c 2a 2b 2b 6c 6c
0.2267 (2) 0 1/3 1/3 0.9078 (5) 0.4170 (5)
0.3563 (2) 0 2/3 2/3 0.1566 (5) 0.8925 (6)
0.711 (1) 0.98 (2) 0.333a 0.929 (2) 0.692 (1) 0.447 (1)
1.00 0.25 1.00 1.00 1.00 1.00
0.66 (4) 0.5 0.5 0.64 (8) 1.48 (7) 0.69 (7)
a
Fixed.
176
L.D. Gulay, O.S. Lychmanyuk / Journal of Alloys and Compounds 458 (2008) 174–177
Table 3 Interatomic distances (δ, nm) and coordination numbers (C.N.) of the atoms in R3 Si1.25 Se7 (R = Pr and Nd) Atoms
δ (nm)
C.N.
Pr3 Si1.25 Se7
Nd3 Si1.25 Se7
0.2886 (6) 0.2951 (7) 0.2962 (6) 0.3092 (7) 0.312 (1) 0.3152 (6)
0.2892 (6) 0.2965 (7) 0.2926 (6) 0.3067 (8) 0.306 (1) 0.3146 (6)
6
Si1 –3Se2 –3Se2
0.270 (8) 0.278 (8)
0.261 (8) 0.288 (8)
6
Si2 –1Se1 –3Se3
0.230 0.230
0.243 0.218
4
Se1 –1Si2 –3R
0.230 0.3152 (6)
0.243 0.3146 (6)
4
Se2 –1Si1 –1Si1 –1R –1R –1R –1R
0.270 (8) 0.278 (8) 0.2886 (6) 0.2962 (6) 0.312 (1) 0.324 (1)
0.261 (8) 0.288 (8) 0.2892 (6) 0.2926 (6) 0.306 (1) 0.328 (1)
6
Se3 –1Si2 –1R –1R –1R
0.230 0.2951 (7) 0.3092 (7) 0.3158 (7)
0.218 0.2965 (7) 0.3067 (7) 0.3188 (7)
4
R –1Se2 –1Se3 –1Se2 –1Se3 –1Se2 –1Se1
Pr3 Si1.25 Se7 compound is shown in Fig. 3. Two neighbour layers are shown. Three Pr-centered prisms form the block. The prisms inside the block are connected to each other by corners (Se2 atoms). The columns of the Si1-centered octahedra are situated inside these blocks along Z-axis. The blocks of three Prcentered trigonal prisms are connected to each other by edges
Fig. 2. The unit cell and the coordination polyhedra of the Pr (a), Si1 (b), Si2 (c), Se1 (d), Se2 (e) and Se3 (f) atoms in the structure of the Pr3 Si1.25 Se7 compound.
(Se1 and Se3 atoms) and form the layers perpendicular to Zaxis. The Si2-centered tetrahedra are situated in the rings of six Pr-centered trigonal prisms. The Pr-centered prisms of the neighboring layers are connected to each other by corners (Se2 atoms). The dependence of the lattice parameters (a and c) and unit cell volume (V) of the R3 Si1.25 Se7 (R = Pr, Nd and Sm) compounds on the ionic radii of the rare earth elements are shown
Fig. 3. The packing of the Pr-centered trigonal prisms, Si1-centered octahedra and Si2-centered tetrahedra in the structure of the Pr3 Si1.25 Se7 compound.
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in Fig. 4 reflecting the well known lanthanide contraction when going from Pr to Sm. The decreasing of the unit cell volumes agrees well with the decreasing of the ionic radii of rare earth element. References
Fig. 4. The dependence of the lattice parameters (a and c) and unit cell volume (V) of the R3 Si1.25 Se7 (R = Pr, Nd and Sm) compounds on the ionic radii of the rare earth elements.
[1] A.A. Eliseev, G.M. Kuzmichyeva, Handbook on the Physics and Chemistry of Rare Earths, vol. 13, Elsevier Science Publishers B.V., 1990 (Chapter 89) pp. 191–281. [2] L.G. Aksel’rud, Yu.N. Grin’, P.Yu. Zavalij, V.K. Pecharsky, V.S. Fundamensky, Collected Abstracts of the 12th European Crystallographic Meeting, vol. 3, Moscow, August, Izv. Acad. Nauk SSSR, Moscow, 1989, p. 155. [3] A. Michelet, A. Mazurier, G. Collin, P. Laruelle, J. Flahaut, J. Solid State Chem. 13 (1975) 65. [4] N. Wiberg, Lehrbuch der Anorganischen Chemie, Walter de Gruyter, Berlin, 1995, pp. 1838–1841.
Crystal structure of the R3Si1.25Se7 (R = Pr, Nd and Sm) compounds L.D. Gulay ∗ , O.S. Lychmanyuk Department of General and Inorganic Chemistry, Volyn State University, Voli Avenue 13, 43009 Lutsk, Ukraine Received 18 February 2007; received in revised form 24 March 2007; accepted 26 March 2007 Available online 31 March 2007
Abstract The crystal structure of new ternary R3 Si1.25 Se7 (R = Pr, Nd and Sm) compounds (Dy3 Ge1.25 S7 structure type, Pearson symbol hP22.5, space group P63 , a = 1.05268 (3) nm, c = 0.60396 (3) nm, RI = 0.0897 for Pr3 Si1.25 Se7 ; a = 1.04760 (3) nm, c = 0.60268 (3) nm, RI = 0.0891 for Nd3 Si1.25 Se7 ; a = 1.04166 (6) nm, c = 0.59828 (6) nm for Sm3 Si1.25 Se7 ) was determined using X-ray powder diffraction. The nearest neighbours of the R and Si atoms are exclusively Se atoms. The latter form distorted trigonal prisms around the R atoms, octahedra around the Si1 atoms and tetrahedra around the Si2 atoms. Tetrahedral surrounding exists for Se1 and Se3 atoms. Six neighbours surround every Se2 atom. © 2007 Elsevier B.V. All rights reserved. Keywords: Chalcogenides; Rare earth compounds; Si compounds; Se compounds; Crystal structure; X-ray powder diffraction
1. Introduction Production of the compounds with increasingly complex compositions, such as ternary, quaternary, etc., has become a principal direction in a modern science of materials [1]. Among the multicomponent systems an important place belongs to the complex rare-earth chalcogenides. The rare-earth chalcogenides are being intensively studied during recent years due to their specific thermal, electrical and optical properties, which for example make them prospective materials in the field of infrared and nonlinear optics. Therefore the synthesis and the investigation of the crystal structures of complex chalcogenides is important step in the search for new materials. No ternary compounds in the R2 Se3 -SiSe2 (R = Pr, Nd and Sm) systems have been reported in literature. This paper presents part of a systematic investigation of rare earth chalcogenides. The crystal structure of new ternary R3 Si1.25 Se7 (R = Pr, Nd and Sm) compounds is given and discussed. 2. Experimental details The samples were prepared by melting the mixture of high purity elements (the purity of the ingredients was better than 99.9 wt.%) in evacuated silica
∗
Corresponding author. E-mail addresses: [email protected], [email protected], [email protected] (L.D. Gulay). 0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2007.03.127
ampoules. The synthesis was realized in a tube furnace. The ampoules were heated with a heating rate of 30 K/h to the maximal temperature, 1420 K. The samples were kept at the maximal temperature during 3 h. After that they were cooled slowly (10 K/h) to 870 K and annealed at this temperature during 240 h. After annealing the ampoules with the samples were quenched in cold water. X-ray powder diffraction patterns of the samples were recorded using a DRON-4-13 powder diffractometer (Cu K␣ radiation, 10◦ ≤ 2θ ≤ 100◦ , step scan mode with a step size of 0.05◦ and counting time of 20 s per data point). All calculations were performed using the CSD program [2].
3. Results and discussion The formation of the R3 Si1.25 Se7 (R = Pr, Nd and Sm) compounds was observed during the investigation of the phase relations in the R2 Se3 -SiSe2 (R = Pr, Nd and Sm) systems. Similarity of the X-ray powder diffraction patterns of these compounds proved that they are isostructural. Crystal structures of these compounds were investigated using X-ray powder diffraction. All of the peaks of the X-ray powder diffraction pattern of the Pr3 Si1.25 Se7 sample were indexed in a hexagonal unit cell with the lattice parameters listed in Table 1. Composition of the sample, intensities of the reflections and obtained lattice parameters proved that this compound is isostructural with Dy3 Ge1.25 S7 (space group P63 , a = 0.9730 nm, c = 0.5820 nm) [3]. Results of the crystal structure determination of the Pr3 Si1.25 Se7 compound are given in Table 1, whereas atomic coordinates and temperature factors are listed in Table 2. Complete crystal structure determination was performed for Nd3 Si1.25 Se7 also
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Table 1 Crystal data and structure refinement details of R3 Si1.25 Se7 (R = Pr and Nd) Empirical formula Formula weight Space group
Pr3 Si1.25 Se7 1010.55 P63 (no. 173)
Nd3 Si1.25 Se7 1020.55 P63 (no. 173)
Unit cell dimensions (nm)
a = 1.05268 (3) c = 0.60396 (3)
a = 1.04760 (3) c = 0.60268 (3)
Volume (nm3 ) Number of formula units per unit cell Calculated density (g/cm3 ) Absorption coefficient (mm−1 ) F(0 0 0) Diffractometer 2θ range for data collection Refinement method Structure solution and refinement RI RP Texture axis and parameter
0.57960 (6) 2
0.57281 (6) 2
5.7899 118.082
5.9166 124.345
865 DRON-4-13 10.00–100.00 Full profile CSD
871 DRON-4-13 10.00–100.00 Full profile CSD
0.0897 0.1815 [1 1 0] and 0.52 (3)
0.0891 0.1967 [1 1 0] and 0.48 (4)
(Tables 1 and 2). The site occupancy factor for the Si1 atom was fixed at the value 0.25 to satisfy charge balance requirements. The X-ray powder diffraction pattern of Sm3 Si1.25 Se7 was not good quality for reliable crystal structure determination. Only lattice parameters were determined for this compound: a = 1.04166 (6) nm, c = 0.59828 (6) nm. The experimental and calculated diffractograms and the corresponding difference diagrams for the Pr3 Si1.25 Se7 (a) and Nd3 Si1.25 Se7 (b) compounds are shown in Fig. 1. Relevant interatomic distances (δ, nm) and coordination numbers (C.N.) of the atoms in the structures of the R3 Si1.25 Se7 (R = Pr and Nd) compounds are listed in Table 3. The interatomic distances agree well with the sum of the respective ionic radii [4]. The unit cell and the coordination polyhedra of the Pr (a), Si1 (b), Si2 (c), Se1 (d), Se2 (e) and Se3 (f) atoms in the structure of the Pr3 Si1.25 Se7 compound are shown in Fig. 2. The nearest neighbours of the Pr and Si atoms are exclusively Se
Fig. 1. The experimental and calculated diffractograms and the corresponding difference diagrams for the Pr3 Si1.25 Se7 (a) and Nd3 Si1.25 Se7 (b) compounds.
atoms. The latter form distorted trigonal prisms around the Pr atoms, octahedra around the Si1 atoms and tetrahedra around the Si2 atoms. Tetrahedral surrounding exists for Se1 and Se3 atoms. Six neighbors surround every Se2 atom. High values of temperature factors for Se2 (Table 2) correlate well with higher coordination numbers (C.N. = 6) for these atoms when compared with the respective values for Se1 and Se3 (C.N. = 4). The packing of the Pr-centered trigonal prisms, Si1-centered octahedra and Si2-centered tetrahedra in the structure of the
Table 2 Atomic coordinates and temperature factors for the R3 Si1.25 Se7 (R = Pr and Nd) compounds Atom
Position
x/a
y/b
z/c
Occupation
Biso. × 102 (nm2 )
Pr3 Si1.25 Se7 Pr Si1 Si2 Se1 Se2 Se3
6c 2a 2b 2b 6c 6c
0.2296 (2) 0 1/3 1/3 0.9081 (5) 0.4188 (5)
0.3565 (2) 0 2/3 2/3 0.1558 (5) 0.8975 (5)
0.739 (1) 0.99 (2) 0.333a 0.951 (2) 0.728 (2) 0.480 (1)
1.00 0.25 1.00 1.00 1.00 1.00
0.6 (1) 0.5 0.5 0.5 (3) 1.8 (2) 0.7 (2)
Nd3 Si1.25 Se7 Nd Si1 Si2 Se1 Se2 Se3
6c 2a 2b 2b 6c 6c
0.2267 (2) 0 1/3 1/3 0.9078 (5) 0.4170 (5)
0.3563 (2) 0 2/3 2/3 0.1566 (5) 0.8925 (6)
0.711 (1) 0.98 (2) 0.333a 0.929 (2) 0.692 (1) 0.447 (1)
1.00 0.25 1.00 1.00 1.00 1.00
0.66 (4) 0.5 0.5 0.64 (8) 1.48 (7) 0.69 (7)
a
Fixed.
176
L.D. Gulay, O.S. Lychmanyuk / Journal of Alloys and Compounds 458 (2008) 174–177
Table 3 Interatomic distances (δ, nm) and coordination numbers (C.N.) of the atoms in R3 Si1.25 Se7 (R = Pr and Nd) Atoms
δ (nm)
C.N.
Pr3 Si1.25 Se7
Nd3 Si1.25 Se7
0.2886 (6) 0.2951 (7) 0.2962 (6) 0.3092 (7) 0.312 (1) 0.3152 (6)
0.2892 (6) 0.2965 (7) 0.2926 (6) 0.3067 (8) 0.306 (1) 0.3146 (6)
6
Si1 –3Se2 –3Se2
0.270 (8) 0.278 (8)
0.261 (8) 0.288 (8)
6
Si2 –1Se1 –3Se3
0.230 0.230
0.243 0.218
4
Se1 –1Si2 –3R
0.230 0.3152 (6)
0.243 0.3146 (6)
4
Se2 –1Si1 –1Si1 –1R –1R –1R –1R
0.270 (8) 0.278 (8) 0.2886 (6) 0.2962 (6) 0.312 (1) 0.324 (1)
0.261 (8) 0.288 (8) 0.2892 (6) 0.2926 (6) 0.306 (1) 0.328 (1)
6
Se3 –1Si2 –1R –1R –1R
0.230 0.2951 (7) 0.3092 (7) 0.3158 (7)
0.218 0.2965 (7) 0.3067 (7) 0.3188 (7)
4
R –1Se2 –1Se3 –1Se2 –1Se3 –1Se2 –1Se1
Pr3 Si1.25 Se7 compound is shown in Fig. 3. Two neighbour layers are shown. Three Pr-centered prisms form the block. The prisms inside the block are connected to each other by corners (Se2 atoms). The columns of the Si1-centered octahedra are situated inside these blocks along Z-axis. The blocks of three Prcentered trigonal prisms are connected to each other by edges
Fig. 2. The unit cell and the coordination polyhedra of the Pr (a), Si1 (b), Si2 (c), Se1 (d), Se2 (e) and Se3 (f) atoms in the structure of the Pr3 Si1.25 Se7 compound.
(Se1 and Se3 atoms) and form the layers perpendicular to Zaxis. The Si2-centered tetrahedra are situated in the rings of six Pr-centered trigonal prisms. The Pr-centered prisms of the neighboring layers are connected to each other by corners (Se2 atoms). The dependence of the lattice parameters (a and c) and unit cell volume (V) of the R3 Si1.25 Se7 (R = Pr, Nd and Sm) compounds on the ionic radii of the rare earth elements are shown
Fig. 3. The packing of the Pr-centered trigonal prisms, Si1-centered octahedra and Si2-centered tetrahedra in the structure of the Pr3 Si1.25 Se7 compound.
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in Fig. 4 reflecting the well known lanthanide contraction when going from Pr to Sm. The decreasing of the unit cell volumes agrees well with the decreasing of the ionic radii of rare earth element. References
Fig. 4. The dependence of the lattice parameters (a and c) and unit cell volume (V) of the R3 Si1.25 Se7 (R = Pr, Nd and Sm) compounds on the ionic radii of the rare earth elements.
[1] A.A. Eliseev, G.M. Kuzmichyeva, Handbook on the Physics and Chemistry of Rare Earths, vol. 13, Elsevier Science Publishers B.V., 1990 (Chapter 89) pp. 191–281. [2] L.G. Aksel’rud, Yu.N. Grin’, P.Yu. Zavalij, V.K. Pecharsky, V.S. Fundamensky, Collected Abstracts of the 12th European Crystallographic Meeting, vol. 3, Moscow, August, Izv. Acad. Nauk SSSR, Moscow, 1989, p. 155. [3] A. Michelet, A. Mazurier, G. Collin, P. Laruelle, J. Flahaut, J. Solid State Chem. 13 (1975) 65. [4] N. Wiberg, Lehrbuch der Anorganischen Chemie, Walter de Gruyter, Berlin, 1995, pp. 1838–1841.