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New compounds of the AB2O6 type
1122
Notes
values were an average of at least two determinations at each initial rare-earth concentration. The separation factors, distribution coefficients, and material balances deviated between the duplicate determinations by less than =t=2 Yo. The results show that the separation factor for Sm with respect to Nd is higher for chloride systems than for nitrate systems at all concentrations studied. One factor responsible for this difference is believed to be that a mechanism of extraction exists for the nitrate in addition to the ion exchange mcchanism.¢5) It was also observed that the separation factor for the chloride and nitrate systems were depressed significantly by the addition of acid. A less pronounced decrease in separation factors was observed when the aqueous rare-earth concentration was increased. It is concluded that the chloride system is preferable to the nitrate system as a separation process for Sin and Nd mixtures based on the fact that significantly higher separation factors were observed. The results also indicate that the extractions should be carried out at the lowest acidity that avoids the so-c.alled three dimensional polymerization, m C. BATTIffrA Institute for Atomic Research and C. Deportment o f Chemical Engineering, M. SMUTZ Iowa State University, Ames, Iowa (U.S.A.) ce~T. G. LENZ, Ames Laboratory of the AEC, Ames, Iowa, Private communication (1965). is) D. Fo PEPPARDand G. W. MASON,Nucl. Sci. andEngng. 16, 382 (1963).
J. lnorg. Nucl. Chem,. 1966. VoL 28, pp. 1122 to 1124. Pexgamon Press Ltd. Printed in Northern Ireland
New compounds of the A B 2 0 s type
(Received 27 October 1965) THIS NOTEreports some new compounds of the type ABsOe, where A is a large and B a small cation (ionic radii about 1.0 and 0.7 A respectively). They have one of the following three structure-types: orthorhombic CaNbsOem (fersmite, which is probably isomorphons with columbite), orthorhomhic CaTajO0cs~ or CaSbjOe typeJ s~ There are chains of Nb 5+ ions in the CaNhsOe structure. In the CaTaaOe structures pairs of Ta s+ ions occur. The CaSbaOe structure has alternate layers of Ca a+ and Sb~+ ions. Materials were prepared by sintering intimate mixtures of high-purity oxides or carbonates in oxygen at 1300°C (Sb-containingsamples at 1250°C and Mo-containing samples at 1150°C). X-ray powder diagrams were obtained on a Philips X-ray diffractometer using CuK~ radiation. Results are presented in Table 1. In a number of cases no single-phase material of the type ABsOs, but two phases, viz. ABO~ (seheelite) and BOa (futile) were obtained (see Table 2). The lattice parameters of the compounds ABaO, (B -----Ti and Nb or Ta) have been reported earlier by K o ~ o v . m The agreement between both sets of data is good. From Table 1 it is seen that the replacement of Nb s+ or Ta5+ in these compounds by Sb5+ or the combination 0.5 Tit+ + 0.5 W*+ is possible, but that structure is not maintained. This fact has been reported for other compounds t o 0 . (s)
m H. D. HEss and H. J. T R ~ U R , Am. Min. 44, 1 (1959); A.S.T.M. card 11-619; A.A. B ~ N , S. P. S. PORTOand A. YAm-V,Y. Appl. Phys. 34, 3155 (1963). ¢s~L. JAHNS~tO, Acta chem. Scand. 17, 2548 (1963). n ~A. MAON~J, Ark iv. Kemi, Min. Geol. 158, no. 3, 1, (1941) and Structure Reports 8, 156 (1940-1941). c4~L. H. BRIXNER,Inorg. Chem. 3, 600 (1964). c6J A. I. KOMKOV,Dokl. Akad. Nauk SSSR 126, 643 (1959). ~ej G. BLASSE, J. Inorg. Nuci. Chem. 26, 1191 (1964), 27, 993, 2117 (1965).
1123
Notes TABLE l : - - C o M P O U N D S OF THE TYPE A B t O e
Structure type
Composition
Lattice parameters (A0
YTiNbOs
CaNbIOs
a = 5"57
b = 14"62
c = 5"19
YTiTaO6
CaNbiO6
5.56
14"60
5-19
GdTiNbO6
CaNbsO6
5.59
14.68
5-24
LaTil.sMo0.sO6
CaNblOs
5.60
15.01
5-27
YTiSbOe
CaTa2Oe*
a = 5.24
b = 10"90
c = 7.38
YTil.sWo.6Oe
CaTa~O8
5-22
10.83
7.32
LaTiNbOe
CaTatOs
5"45
10"98
7"59
LaTiTaO6
CaTa,Os
5.46
10.96
7.59
GdTiSbO6
CaTa2Oe
5-26
10.95
7.42
GdTiTaOe
CaTasOe
5"27
10-98
7"43
GdTi:.sWo.~Oe
CaTa~Oe
5.23
10"88
7"36
LaTiSbOe
CaSbiOe1"
a = 5-21
c = 5.18
LaTil.sWo.6Os
CaSb2Oe~/
a = 5"21
b = 8"78
c = 10.15
fl = 92030 • * Orthorhombic modification t Hexagonal With monoclinic distortion
Of the three structure types mentioned above, anion polarization is most important for the CaSb,Os type (layer-structure), whereas metal-metal ion bonding as suggested earlier by ns~s) is important for the CaNbaOs type (chains of Nb s+ ions) and to a less extent for the CaTa,O. type (pairs of T # + ions). TABLE 2 . - - R E A C T I O N PRODUCTS OF PREPARATIONS
Intended composition
UNSUCCESSFUL
Reaction products Scheelite
Rutile
CaTiWOe
CaWO4
TiOs
CaTiMoO6
CaMoO4
TiOs
CaSnWO6
CaWO4
SnOa
YTivsMoe.506
YTi0.sMoe.sO4 ")
TiOs
GdTil.sMoe.sOe
GdTio.sMoo.~O~ (4)
TiOi
In general the former effect dominates in Sb 5+ compounds, the latter in Nb s+ compounds, whereas the Ta 5+ compounds are in between them. Mo 6+ is probably analogous to Nb 5+ and W 6+ to T # +. This is also realized in the present compounds, especially if it is recalled that the larger the A ion (e.g. La *+) the smaller the influence of metal--metal ion bonding (larger distance). The X-ray diagram of LaTil.6We.sOe resembles that of LaTiSbOe, but many lines are split and
1124
Notes
new weak lines appear. It was possible to index the diagram using a unit cell with approximate lattice parameters a' = a, b' --- a~/3, c' = 2c and a small monoclinic distortion (primed parameters refer to LaTil.~W0.~O~, unprimed parameters to LaTiSbOe). it is not clear what the reason for this is. A possible explanation is long-range order of Ti ~+ and W e+ in the CaSbiOe structure. Finally we mention that we were able to reproduce MAGNI~LI'Sresult that the compounds ASh~O~ (.4, = Ca, St, Pb, Ba) are all isomorphous and have the CaSb~O~ structure. ~ Completely different results were obtained by COFF~N, t~ but it seems to us that this was due to an incomplete reaction between his starting materials.
Philips Research Laboratories, N. V. Philips' Gloeilampenfabrieken, Eindhoven, Netherlands
G. BLASSE
tv~ W. W. COr~EEN,J. Am, Ceram. Soc. 39, 154 (1956) and A.S.T.M. card 11-45.
J, Inorg. NucL Chem., 1966. VoL 28, pp. 1124 to 1125. Pergamon Press Ltd. Printed in Northern Ireland
Polymorphism of BiaMoO o (Received 27 October 1965) THE CRYSTALstructure of natural Bi~MoOe (koechlinite) has been described b~ ZEMANNo(1) It is orthorhombic with lattice parameters a = 5"50 A, b = 5-49 A and c = 16.24 A and" consists of alternate layers perpendicular to the c-axis with composition MoO4 and BisOi. The MoO4 layer contains MoO6 octahedra sharing corners in the ab plane. The BiiOi layer is built up in the same way as in BiOCI. cs~ This note reports a high temperature modification of Bi2MoO6. BisWOe was studied simultaneously. Samples were prepared by fling intimate mixtures of Bi~O, and MoOs or WOs at 750°C for several hours. X-ray diagrams were obta/ned on a Philips diffractometer using copper radiation. BitMoO6 prepared in this way is isomorphous with LaIMoOe, the structure of which compound has been reported by S[LI~N and LUNDBERG.(8) This structure differs from the koechlinite strUCture in one aspect, viz. the MoO4 layer consists of MoO~ tetrahedra having no anions in common. The transition from the low- to the high-temperature modification of Bi~MoO6 can therefore be described as follows. The Bi2Os layers and the Me positions remain unaltered. Only the oxygen anions in the MoO4 layer are rearranged. The X-ray pattern of the high-temperature form of Bi~MoO~ for low values of 0 is given in Table 1. The structure is tetragonal with lattice parameters a = 3.95 A and c = 17.21 A. A comparison between the lattice parameters of Bi~MoOo and La~MoO8 is noteworthy. LasMoOo has a = 4.09 and c = 15"99 A. c8~ This means that Bi~MoO6 is strongly elongated along the c-axis in comparison to LaiMoO,. The same phenomenon occurs for the 0xyhaiides. Compare for example the ismorphous BiOC1 (tetragonal, a = 3.891 and c = 7.369 A) and LaOC1 (a = 4.119 and c ----• 6-883 A). GdOC1 and YOC1 (also isomorphous with BiOCI) have the same e/a ratio as LaOC1. ~4~ The structure of the oxyhalides contains also a BitO~ or Lanes layer like that of Bi2MoO6 and LalMoOe. A possible explanation for the elongation is the presence of an outer electron pair on the BP + ion (6 sffi). If this pair is on the apex of the tetragonal Bier-pyramid, as has been suggested for isoelectronic Pb ~+ in, e.g. PbO, C1~it causes an extra repulsion between the MoO~ and the Bi202 layer, since the apex of the BiO~ pyramid is directed towards the MoO~ layer. It has indeed been observed that
~1~j. ZEMANN, Heidelberger Beitr. Mineral Petro~r. $, 139 (1956) and Structural Reports 20, 449 (1956). ~ See e.g., A. F. Wm,LS, Structural Inorganic Chemistry (3rd Ed.). Oxford University Press (1962), ta~ L. G. SILLENand K. LUI~BOgO, Z. Anorg. Chem. 252, 2 (1943). c*~R. W. G. WYcgol~l*, Crystal Structures, 1, p. 294. 8¢~. Ed. Interscienc~, NeW York.
Notes
values were an average of at least two determinations at each initial rare-earth concentration. The separation factors, distribution coefficients, and material balances deviated between the duplicate determinations by less than =t=2 Yo. The results show that the separation factor for Sm with respect to Nd is higher for chloride systems than for nitrate systems at all concentrations studied. One factor responsible for this difference is believed to be that a mechanism of extraction exists for the nitrate in addition to the ion exchange mcchanism.¢5) It was also observed that the separation factor for the chloride and nitrate systems were depressed significantly by the addition of acid. A less pronounced decrease in separation factors was observed when the aqueous rare-earth concentration was increased. It is concluded that the chloride system is preferable to the nitrate system as a separation process for Sin and Nd mixtures based on the fact that significantly higher separation factors were observed. The results also indicate that the extractions should be carried out at the lowest acidity that avoids the so-c.alled three dimensional polymerization, m C. BATTIffrA Institute for Atomic Research and C. Deportment o f Chemical Engineering, M. SMUTZ Iowa State University, Ames, Iowa (U.S.A.) ce~T. G. LENZ, Ames Laboratory of the AEC, Ames, Iowa, Private communication (1965). is) D. Fo PEPPARDand G. W. MASON,Nucl. Sci. andEngng. 16, 382 (1963).
J. lnorg. Nucl. Chem,. 1966. VoL 28, pp. 1122 to 1124. Pexgamon Press Ltd. Printed in Northern Ireland
New compounds of the A B 2 0 s type
(Received 27 October 1965) THIS NOTEreports some new compounds of the type ABsOe, where A is a large and B a small cation (ionic radii about 1.0 and 0.7 A respectively). They have one of the following three structure-types: orthorhombic CaNbsOem (fersmite, which is probably isomorphons with columbite), orthorhomhic CaTajO0cs~ or CaSbjOe typeJ s~ There are chains of Nb 5+ ions in the CaNhsOe structure. In the CaTaaOe structures pairs of Ta s+ ions occur. The CaSbaOe structure has alternate layers of Ca a+ and Sb~+ ions. Materials were prepared by sintering intimate mixtures of high-purity oxides or carbonates in oxygen at 1300°C (Sb-containingsamples at 1250°C and Mo-containing samples at 1150°C). X-ray powder diagrams were obtained on a Philips X-ray diffractometer using CuK~ radiation. Results are presented in Table 1. In a number of cases no single-phase material of the type ABsOs, but two phases, viz. ABO~ (seheelite) and BOa (futile) were obtained (see Table 2). The lattice parameters of the compounds ABaO, (B -----Ti and Nb or Ta) have been reported earlier by K o ~ o v . m The agreement between both sets of data is good. From Table 1 it is seen that the replacement of Nb s+ or Ta5+ in these compounds by Sb5+ or the combination 0.5 Tit+ + 0.5 W*+ is possible, but that structure is not maintained. This fact has been reported for other compounds t o 0 . (s)
m H. D. HEss and H. J. T R ~ U R , Am. Min. 44, 1 (1959); A.S.T.M. card 11-619; A.A. B ~ N , S. P. S. PORTOand A. YAm-V,Y. Appl. Phys. 34, 3155 (1963). ¢s~L. JAHNS~tO, Acta chem. Scand. 17, 2548 (1963). n ~A. MAON~J, Ark iv. Kemi, Min. Geol. 158, no. 3, 1, (1941) and Structure Reports 8, 156 (1940-1941). c4~L. H. BRIXNER,Inorg. Chem. 3, 600 (1964). c6J A. I. KOMKOV,Dokl. Akad. Nauk SSSR 126, 643 (1959). ~ej G. BLASSE, J. Inorg. Nuci. Chem. 26, 1191 (1964), 27, 993, 2117 (1965).
1123
Notes TABLE l : - - C o M P O U N D S OF THE TYPE A B t O e
Structure type
Composition
Lattice parameters (A0
YTiNbOs
CaNbIOs
a = 5"57
b = 14"62
c = 5"19
YTiTaO6
CaNbiO6
5.56
14"60
5-19
GdTiNbO6
CaNbsO6
5.59
14.68
5-24
LaTil.sMo0.sO6
CaNblOs
5.60
15.01
5-27
YTiSbOe
CaTa2Oe*
a = 5.24
b = 10"90
c = 7.38
YTil.sWo.6Oe
CaTa~O8
5-22
10.83
7.32
LaTiNbOe
CaTatOs
5"45
10"98
7"59
LaTiTaO6
CaTa,Os
5.46
10.96
7.59
GdTiSbO6
CaTa2Oe
5-26
10.95
7.42
GdTiTaOe
CaTasOe
5"27
10-98
7"43
GdTi:.sWo.~Oe
CaTa~Oe
5.23
10"88
7"36
LaTiSbOe
CaSbiOe1"
a = 5-21
c = 5.18
LaTil.sWo.6Os
CaSb2Oe~/
a = 5"21
b = 8"78
c = 10.15
fl = 92030 • * Orthorhombic modification t Hexagonal With monoclinic distortion
Of the three structure types mentioned above, anion polarization is most important for the CaSb,Os type (layer-structure), whereas metal-metal ion bonding as suggested earlier by ns~s) is important for the CaNbaOs type (chains of Nb s+ ions) and to a less extent for the CaTa,O. type (pairs of T # + ions). TABLE 2 . - - R E A C T I O N PRODUCTS OF PREPARATIONS
Intended composition
UNSUCCESSFUL
Reaction products Scheelite
Rutile
CaTiWOe
CaWO4
TiOs
CaTiMoO6
CaMoO4
TiOs
CaSnWO6
CaWO4
SnOa
YTivsMoe.506
YTi0.sMoe.sO4 ")
TiOs
GdTil.sMoe.sOe
GdTio.sMoo.~O~ (4)
TiOi
In general the former effect dominates in Sb 5+ compounds, the latter in Nb s+ compounds, whereas the Ta 5+ compounds are in between them. Mo 6+ is probably analogous to Nb 5+ and W 6+ to T # +. This is also realized in the present compounds, especially if it is recalled that the larger the A ion (e.g. La *+) the smaller the influence of metal--metal ion bonding (larger distance). The X-ray diagram of LaTil.6We.sOe resembles that of LaTiSbOe, but many lines are split and
1124
Notes
new weak lines appear. It was possible to index the diagram using a unit cell with approximate lattice parameters a' = a, b' --- a~/3, c' = 2c and a small monoclinic distortion (primed parameters refer to LaTil.~W0.~O~, unprimed parameters to LaTiSbOe). it is not clear what the reason for this is. A possible explanation is long-range order of Ti ~+ and W e+ in the CaSbiOe structure. Finally we mention that we were able to reproduce MAGNI~LI'Sresult that the compounds ASh~O~ (.4, = Ca, St, Pb, Ba) are all isomorphous and have the CaSb~O~ structure. ~ Completely different results were obtained by COFF~N, t~ but it seems to us that this was due to an incomplete reaction between his starting materials.
Philips Research Laboratories, N. V. Philips' Gloeilampenfabrieken, Eindhoven, Netherlands
G. BLASSE
tv~ W. W. COr~EEN,J. Am, Ceram. Soc. 39, 154 (1956) and A.S.T.M. card 11-45.
J, Inorg. NucL Chem., 1966. VoL 28, pp. 1124 to 1125. Pergamon Press Ltd. Printed in Northern Ireland
Polymorphism of BiaMoO o (Received 27 October 1965) THE CRYSTALstructure of natural Bi~MoOe (koechlinite) has been described b~ ZEMANNo(1) It is orthorhombic with lattice parameters a = 5"50 A, b = 5-49 A and c = 16.24 A and" consists of alternate layers perpendicular to the c-axis with composition MoO4 and BisOi. The MoO4 layer contains MoO6 octahedra sharing corners in the ab plane. The BiiOi layer is built up in the same way as in BiOCI. cs~ This note reports a high temperature modification of Bi2MoO6. BisWOe was studied simultaneously. Samples were prepared by fling intimate mixtures of Bi~O, and MoOs or WOs at 750°C for several hours. X-ray diagrams were obta/ned on a Philips diffractometer using copper radiation. BitMoO6 prepared in this way is isomorphous with LaIMoOe, the structure of which compound has been reported by S[LI~N and LUNDBERG.(8) This structure differs from the koechlinite strUCture in one aspect, viz. the MoO4 layer consists of MoO~ tetrahedra having no anions in common. The transition from the low- to the high-temperature modification of Bi~MoO6 can therefore be described as follows. The Bi2Os layers and the Me positions remain unaltered. Only the oxygen anions in the MoO4 layer are rearranged. The X-ray pattern of the high-temperature form of Bi~MoO~ for low values of 0 is given in Table 1. The structure is tetragonal with lattice parameters a = 3.95 A and c = 17.21 A. A comparison between the lattice parameters of Bi~MoOo and La~MoO8 is noteworthy. LasMoOo has a = 4.09 and c = 15"99 A. c8~ This means that Bi~MoO6 is strongly elongated along the c-axis in comparison to LaiMoO,. The same phenomenon occurs for the 0xyhaiides. Compare for example the ismorphous BiOC1 (tetragonal, a = 3.891 and c = 7.369 A) and LaOC1 (a = 4.119 and c ----• 6-883 A). GdOC1 and YOC1 (also isomorphous with BiOCI) have the same e/a ratio as LaOC1. ~4~ The structure of the oxyhalides contains also a BitO~ or Lanes layer like that of Bi2MoO6 and LalMoOe. A possible explanation for the elongation is the presence of an outer electron pair on the BP + ion (6 sffi). If this pair is on the apex of the tetragonal Bier-pyramid, as has been suggested for isoelectronic Pb ~+ in, e.g. PbO, C1~it causes an extra repulsion between the MoO~ and the Bi202 layer, since the apex of the BiO~ pyramid is directed towards the MoO~ layer. It has indeed been observed that
~1~j. ZEMANN, Heidelberger Beitr. Mineral Petro~r. $, 139 (1956) and Structural Reports 20, 449 (1956). ~ See e.g., A. F. Wm,LS, Structural Inorganic Chemistry (3rd Ed.). Oxford University Press (1962), ta~ L. G. SILLENand K. LUI~BOgO, Z. Anorg. Chem. 252, 2 (1943). c*~R. W. G. WYcgol~l*, Crystal Structures, 1, p. 294. 8¢~. Ed. Interscienc~, NeW York.