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Contribution to the structural characterization of a sodium yttrium titanate layered perovskite and its protonated forms
h4ateddsRosearchEadMin,Vol. 30, No. 8. pp. 925431.1995 Cqy@J1tQ1995Elswi~SoimosLb.l RiokdintheusA.Aurighlam8aved 0025~5408/95$9.50 + .OO
CONTRIBUTION TO THE STRUCTURAL CHARACTERIZATION OF A SODIUM YTTRIUM TITANATE LAYERED PEROVSKITE AND ITS PROTONATED FORMS
Mireille RICHARD,
Graziella GOGLIO
and Luc BROHAN
Institut des Mat6riaux de Names, Iaboratoire de Chimie des Solides UMR CNRS No 110 - Universit6 de Names 2, rue de la Houssin&e, 44072 NANTBS CBDEX 03, France (Received April 30, 1995; Communicated by P. Hagenmuller)
ABSTRACT
:The layered perovskite structures of NaYTiO, and homologous acid exchange form were investigated via powder X-ray diffraction and high resolution transmission electron microscopy. The NaYTiO? layered structure differs from the previous investigation of Blasse et al., by the mcorporation of pemvskite-like 2 octahedra thick lamellae instead of 1 octahedron thick lamellae and by a stacking of slabs which is primitive instead of I-centered with an (a+b)/2 gliding. The exchange of Na’ cations was performed in an acid medium. This experiment suggests that half of the Y3+ions occupy the perovskite lie cavities whereas the Na’ cations are localized in the interlayer space. Consequently, this structure is probably closer to TIBa,CaCulO, family compounds than to A,,rB,03,,, Ruddlesden-Popper type structure with n= 1.
MATERIALS
INDEX : titanate layered perovskite, acid-exchange,
htroductlu
electron microscopy.
.
Due to their potential application in catalysis for instance, there is a great interest in structures derived from perovskite. We are particularly interested in compounds known as RuddlesdenPopper structures, An+ 1B,Ojn+ l(1). Their connection with the perovskite lies in the structure of the layers. In An+IBn03,,+I, n perovskite slabs constitute each layer which is stacked with a 112 gliding along two of the cubic crystallographic directions of the 3D perovskite, namely a (a+b)/2 gliding. We reported elsewhere the structural investigations concerning the n = 3 term, A&n2Ti3OIo where A is an alkali or a proton and Ln is a rare earth or yttrium (2,3). In an attempt to synthesize other terms of this family, a compound with layers each containing two perovskite slabs was obtained. In this paper, the structural characterization of NaYTiOq and its protonated forms, using powder XRD and high resolution electron microscopy, is reported and discussed. 925
926
M. RICHARD et al.
Vol. 30, No. 8
The NaYTiO4 powder was prepared by conventional solid state method from excess sodium nitrate (20 X) and stoichiometric amount of yttrium oxide and titanium oxide. After grinding and decomposition of the alkali nitrate, the mixture was fired under air at 950°C for 1 day in a Pt crucible. The composition was checked using a scanning electron microscope equipped with a TRACOR probe. The powder XRD data were recorded using a D5000 Siemens diffractometer in a BraggBrentano geometry. The selected area electron diffraction (SAED) transmission microscopy studies were carried out using a CM30 Philips microscope. The sample studied by electron diffraction and transmission microscopy was prepared by grinding under liquid nitrogen or ethanol and then deposited on a polymer film supported by a copper grid. High Resolution Electron Microscopy was carried out with a Philips CM30 electron microscope equipped with a polar piece allowing a resolution better than 1.9 A. Acid-exchange of NaYTi04 was achieved at room temperature in an aqueous solution. The titanate powder was immersed in a lOO-fold excess (by weight) of 1M HNO3 for five days. The resulting product was retrieved by several cycles of centrifugation, washing with distilled water and finally acetone before drying under vacuum.
X-rav
diffraction
The positions and intensities of the diffraction peaks were determined by the PROLIX program (4). The crystal parameters refinement was performed with the U-FIT program (5). Table I gathers the principal peaks of the powder diffraction diagram with their corresponding indexations, d-spacings and relative intensities. Table I Indexations, d-spacings and relative intensities of the XRD peaks for NaYTiO4.
doba
hkl 001
dcalc(4
VI0
hkl
12.21
12.19
100
002 003 102 112 004 113 200 201 202 005 210 212 213 115 006 204
6.106 4.071 4.024 3.216 3.053 2.7713 2.6753 2.6133 2.4504 2.4425 2.3929 2.2279 2.0629 2.0521 2.0354 2.0121
6.103 4.071 4.025 3.216 3.055 2.7714 2.6753 2.6133 2.4506 2.4423 2.3926 2.2280 2.0627 2.0521 2.0356 2.0121
14 5 4 61 5 91 65 9 4 3 3 3 2 11 15 14
220 221 205 116 302 312 206 117 313 008 225 322 118 323 315 226 400
Q 35 1.8694 1.8038 1.7925 1.7120 1.6306 1.6199 1.5843 1.5624 1.5266 1.4956 1.4420 1.4157 1.3942 1.3909 1.3857 1.3376
1.8695 1.8040 1.7926 1.7123 1.6307 1.6199 1.5843 1.5624 1.5264 1.4956 1.4421 1.4157 1.3943 1.3908 1.3857 1.3375
3 14 5 5 12 13 2 23 1 2 2 3 1 4 9 6
can be indexed as a primitive tetragonal cell with the following refined The diffraction 2 = 5.3506(4) A and c = 12.213(l) A, where aP refers to the cubic cell parameters: a = a,, Yaks
Vol. 30. No. 8
parameter of the threedimensional mean deviation R = &C(28obs
927
LAYERED TITANATE
perovskite. The quality of the refinement
between 28,hs and 2&l, -2t3,~c)2=0.006,
D = -!--~~d(28)~=0.004”
is revealed by the
and the reliability
where nhkl is the number of reflections
factor
taken into
acco$
ani n, is the number of refined variables. Two layered structures can be proposed based orrthe refined cell parameters and the assumption that the thickness of TiO6 octahedron is close to 3.8 A. Inthe first model, each layer is constructed by one perovskite slab and are stacked one upon another with an (a+b)/2 glide. Consequently, the structure corresponds to the n = 1 term of the layered perovskites firstly reported by Ruddlesden and Popper, A,+lBn03,,+ 1. This model, illustrated in PIG. la), was already proposed by Blasse et al. (6) for the NaLnTiOq compounds with an ordered sequence of the Ln (Ln = Y or a rare earth) and Na cations along the c axis. The refined cell parameters for NaYTi04 are a = 3.77 A and c = 12.20 A. In the second model, each layer is constructed by two perovskite slabs and is stacked one upon another without any gliding. One NaCl-like layer is present in the interslab space. This structural model is adopted by TlBa$aC!t&j~ (7) and is shown in PIG. 1 b).
TiO2 2: A0 TiO2 A0 A=Na or Y 11 101
4
b) FIG. 1
Schematic structural models proposed for NaYTiO4 a) lst model b) 2” model
text).
Table II lists the indexations, calculated d-spacings and relative intensities of the three most intense peaks for both hypotheses. These calculations were done from the atomic parameters of idealized structures using the LAZY-PULVERIX program (8). The sodium and yttrium cations are statistically distributed among the available positions. Table II Indexations, calculated d-spacings and relative intensities of the most intense peaks for both proposed models.
Compared to the indexations and intensities observed from the experimental powder diffraction pattern, the second hypothesis leads to a better agreement. In order to determine this sequence, electron diffraction and high resolution microscopy studies were performed.
928
M. RICHARD et al.
Vol. 30, No. 8
After grinding in ethanol the powder was deposited on a copper grid. The [0 0 l] zone axis pattern is presented in FIG. 2. This pattern revealed the existence of extra-reflections localized in (3 n, 3 m, e) directions with n and m odd which implies a doubled cell at 4S’ with respect to the former one and with the a parameter close to 2ap instead of aPd2. The labelled cell takes into account this new cell.
FIG. 2 [0 0 l] zone axis electron diffraction pattern of NaYTiO4. In order to obtain structural information concerning the gliding type, high resolution image was recorded perpendicularly to the layers. By referring to the cell parameters refined from the powder XRD data, the crystallite orientation is [ 1 lo]. The image and the diffraction patterns are shown in FIG. 3 and FIG. 4, respectively.
FIG. 3 [ 1 1 O] high resolution image showing the extended sequence with thickness of two perovskite slabs in NaYTi04.
Vol. 30, No. 8
LAYERED TITANATE
929
FIG. 4 [ 1 1 0] zone axis electron diffraction pattern corresponding to the former image.
Based on the fact light contrasts are associated with the heavy atoms, yttrium and titanium, the electron diffraction pattern indicates that each layer is made of two perovskite slabs and that these layers are stacked one upon another. This study suggests the second model, since the lattice seems to be primitive and no gliding is observed. A gliding along only one direction would obviously result in an orthorhombic cell because of the loss of the 4-fold rotation axis along the stacking axis, c. According to the tetragonal cell parameters relined from electron and X-ray diffraction data, this hypothesis is not retained.
exchange In an attempt to differentiate the positions of Na+ and Y3+ cations, an acid-exchange was performed as previously described. The alkali acid-exchange will only be possible if the sodium is situated in the interslab space.
98
2
96
.I
i
94 92 90 -
100
Thermogravimetric
200
300
400
500
600
Y2Ti20,
700 800 Temperature (“C)
FIG. 5 analysis curve of the exchanged compound obtained from NaYTiO4 (at 1OWmin).
M. RICHARD et al.
930
Vol. 30, No. 8
The thermogravimetric analysis (IGA) was performed under air with a TGS 2 Perk&Elmer apparatus. The exchange rate was checked by semi-quantitative analysis in a 35C Jeol scanning electron microscope equipped with a TRACOR probe. At the end of the treatment, the exchange rate is close to 90%. The thermogravimetric analysis curve, shown in the PIG. 5, reveals a monotonous weight loss which is achieved at 600°C. The XRD pattern of the final compound obtained at 800°C is characteristic of the pyrochlore YzTi&. Since the final product is known and considering on one hand that 10% sodium is still present in the compound and on the other hand that all the weight loss can be associated to a water departure, the exchanged product can be expressed HugNaolYTi04,0.7H20. The slope change observed around 200°C corresponds then to the nominal composition HofiaolYTiO4.
L
NaYTiO,,
.,YTiO,, 0.7H,O 0
10
20
30
40
50
60
70
20 0 PIG. 6 Powder XRD pattern of the exchanged compound compared to the NaYTiO4 one. As shown in PIG. 6, the XRD pattern of the exchanged compound reveals a close relationsh’ with the pattern of the patent phase. Tab ‘pe III lists indexations, positions and intensities of the diffraction peaks for the exchanged product. The diagram can be indexed using a tetragonal cell sli htly different from the cell used for NaYTiO4. The refined parameters are thus a = 3.725(l) 1 and c = 22.86(2) A. The c parameter is twice that of the precursor phase whereas a is J2-fold smaller. The characteristic R= &C(2%L%
factors
are
as
- 2e,alc)2 =0.021.
follows
:
D = -J--~ld(20)l=0.015°
and
Vol. 30, No. 8
931
LAYERED TITANATEI
Table III Indexations, positions and intensities of the XRD peaks for the exchanged product HogNao.1YTi04,0.7H2G. hkl 002 004 006 104 106 110 112 115 10 10 118 200 205 214 216
dcalc (A) 11.43 5.715 3.810 3.120 2.6635 2.6338 2.5666 2.2822 1.9484 1.9367 1.8624 1.7248 1.5992 1.5263
?e . -5 5.717 3.813 3.117 2.6612 2.6339 2.5669 2.2816 1.9486 1.9371 1.a635 1.7239 1.5996 1.5263
21 5 30 21 11 2 9 4 4 7 7 4 2
The capability to exchange the alkali in an acid medium suggests that the sodium ions are localized in the interlayer space and consequently that the 12-fold coordmatcd sites are occupied by the yttrium ions. Unfortunately, this additional information did not allow us to determine the cation distribution in the structure from powder diffraction pattern
Conclusion Both XRD pattern and the electron microscopy of NaYTiO4 suggest a structuml model close to TIBa2CaCu208& in which each layer is constructed by two perovskite slabs and is stacked one upon another instead of by one perovskite slab stacked with a l/2 gliding along two directions, as previously reported by Blasse et al. (6). Moreover, since the sodium exchange is possible, this suggests that the alkali are situated in the interlayer space and therefore the yttrium occupies the 12fold coordinated intmlayer perovskite site. The crystal structure refinement is still in progress.
1. S.N. Ruddlesden and P. Popper, Acta Cryst., 1 l., 54-55, (1957) 2. M. Richard, L. Brohan and M. Toumoux, J. Sohd State Chem., 112,345, (1994) 3. M. Richard, L. Brohan, A.M. Marie, C. Roucau and M. Toumoux, submitted to J. Solid State Chem. 4. Treatment of INEL X-Ray curve detector powder diffraction data : chain program and experimental results, J.M. Barbet, M. Evain, P. Deniard and R. Brec. 5. U-Fit : a cell parameter refinement program, M. Evain, IMN Names, (1992) 6. G. Blasse, J. Inorg. Chem., 30,656, (1968) 7. M. Hervieu, A. Maignan, C. Martin, C. Michel, J. Provost and B. Raveau, J. Solid State Chem., 75, 212, (1988) 8. R. Yvon, W. Jeitschko et E. Parthe, J. Appl. Crystallogr., 10,73, (1977)
CONTRIBUTION TO THE STRUCTURAL CHARACTERIZATION OF A SODIUM YTTRIUM TITANATE LAYERED PEROVSKITE AND ITS PROTONATED FORMS
Mireille RICHARD,
Graziella GOGLIO
and Luc BROHAN
Institut des Mat6riaux de Names, Iaboratoire de Chimie des Solides UMR CNRS No 110 - Universit6 de Names 2, rue de la Houssin&e, 44072 NANTBS CBDEX 03, France (Received April 30, 1995; Communicated by P. Hagenmuller)
ABSTRACT
:The layered perovskite structures of NaYTiO, and homologous acid exchange form were investigated via powder X-ray diffraction and high resolution transmission electron microscopy. The NaYTiO? layered structure differs from the previous investigation of Blasse et al., by the mcorporation of pemvskite-like 2 octahedra thick lamellae instead of 1 octahedron thick lamellae and by a stacking of slabs which is primitive instead of I-centered with an (a+b)/2 gliding. The exchange of Na’ cations was performed in an acid medium. This experiment suggests that half of the Y3+ions occupy the perovskite lie cavities whereas the Na’ cations are localized in the interlayer space. Consequently, this structure is probably closer to TIBa,CaCulO, family compounds than to A,,rB,03,,, Ruddlesden-Popper type structure with n= 1.
MATERIALS
INDEX : titanate layered perovskite, acid-exchange,
htroductlu
electron microscopy.
.
Due to their potential application in catalysis for instance, there is a great interest in structures derived from perovskite. We are particularly interested in compounds known as RuddlesdenPopper structures, An+ 1B,Ojn+ l(1). Their connection with the perovskite lies in the structure of the layers. In An+IBn03,,+I, n perovskite slabs constitute each layer which is stacked with a 112 gliding along two of the cubic crystallographic directions of the 3D perovskite, namely a (a+b)/2 gliding. We reported elsewhere the structural investigations concerning the n = 3 term, A&n2Ti3OIo where A is an alkali or a proton and Ln is a rare earth or yttrium (2,3). In an attempt to synthesize other terms of this family, a compound with layers each containing two perovskite slabs was obtained. In this paper, the structural characterization of NaYTiOq and its protonated forms, using powder XRD and high resolution electron microscopy, is reported and discussed. 925
926
M. RICHARD et al.
Vol. 30, No. 8
The NaYTiO4 powder was prepared by conventional solid state method from excess sodium nitrate (20 X) and stoichiometric amount of yttrium oxide and titanium oxide. After grinding and decomposition of the alkali nitrate, the mixture was fired under air at 950°C for 1 day in a Pt crucible. The composition was checked using a scanning electron microscope equipped with a TRACOR probe. The powder XRD data were recorded using a D5000 Siemens diffractometer in a BraggBrentano geometry. The selected area electron diffraction (SAED) transmission microscopy studies were carried out using a CM30 Philips microscope. The sample studied by electron diffraction and transmission microscopy was prepared by grinding under liquid nitrogen or ethanol and then deposited on a polymer film supported by a copper grid. High Resolution Electron Microscopy was carried out with a Philips CM30 electron microscope equipped with a polar piece allowing a resolution better than 1.9 A. Acid-exchange of NaYTi04 was achieved at room temperature in an aqueous solution. The titanate powder was immersed in a lOO-fold excess (by weight) of 1M HNO3 for five days. The resulting product was retrieved by several cycles of centrifugation, washing with distilled water and finally acetone before drying under vacuum.
X-rav
diffraction
The positions and intensities of the diffraction peaks were determined by the PROLIX program (4). The crystal parameters refinement was performed with the U-FIT program (5). Table I gathers the principal peaks of the powder diffraction diagram with their corresponding indexations, d-spacings and relative intensities. Table I Indexations, d-spacings and relative intensities of the XRD peaks for NaYTiO4.
doba
hkl 001
dcalc(4
VI0
hkl
12.21
12.19
100
002 003 102 112 004 113 200 201 202 005 210 212 213 115 006 204
6.106 4.071 4.024 3.216 3.053 2.7713 2.6753 2.6133 2.4504 2.4425 2.3929 2.2279 2.0629 2.0521 2.0354 2.0121
6.103 4.071 4.025 3.216 3.055 2.7714 2.6753 2.6133 2.4506 2.4423 2.3926 2.2280 2.0627 2.0521 2.0356 2.0121
14 5 4 61 5 91 65 9 4 3 3 3 2 11 15 14
220 221 205 116 302 312 206 117 313 008 225 322 118 323 315 226 400
Q 35 1.8694 1.8038 1.7925 1.7120 1.6306 1.6199 1.5843 1.5624 1.5266 1.4956 1.4420 1.4157 1.3942 1.3909 1.3857 1.3376
1.8695 1.8040 1.7926 1.7123 1.6307 1.6199 1.5843 1.5624 1.5264 1.4956 1.4421 1.4157 1.3943 1.3908 1.3857 1.3375
3 14 5 5 12 13 2 23 1 2 2 3 1 4 9 6
can be indexed as a primitive tetragonal cell with the following refined The diffraction 2 = 5.3506(4) A and c = 12.213(l) A, where aP refers to the cubic cell parameters: a = a,, Yaks
Vol. 30. No. 8
parameter of the threedimensional mean deviation R = &C(28obs
927
LAYERED TITANATE
perovskite. The quality of the refinement
between 28,hs and 2&l, -2t3,~c)2=0.006,
D = -!--~~d(28)~=0.004”
is revealed by the
and the reliability
where nhkl is the number of reflections
factor
taken into
acco$
ani n, is the number of refined variables. Two layered structures can be proposed based orrthe refined cell parameters and the assumption that the thickness of TiO6 octahedron is close to 3.8 A. Inthe first model, each layer is constructed by one perovskite slab and are stacked one upon another with an (a+b)/2 glide. Consequently, the structure corresponds to the n = 1 term of the layered perovskites firstly reported by Ruddlesden and Popper, A,+lBn03,,+ 1. This model, illustrated in PIG. la), was already proposed by Blasse et al. (6) for the NaLnTiOq compounds with an ordered sequence of the Ln (Ln = Y or a rare earth) and Na cations along the c axis. The refined cell parameters for NaYTi04 are a = 3.77 A and c = 12.20 A. In the second model, each layer is constructed by two perovskite slabs and is stacked one upon another without any gliding. One NaCl-like layer is present in the interslab space. This structural model is adopted by TlBa$aC!t&j~ (7) and is shown in PIG. 1 b).
TiO2 2: A0 TiO2 A0 A=Na or Y 11 101
4
b) FIG. 1
Schematic structural models proposed for NaYTiO4 a) lst model b) 2” model
text).
Table II lists the indexations, calculated d-spacings and relative intensities of the three most intense peaks for both hypotheses. These calculations were done from the atomic parameters of idealized structures using the LAZY-PULVERIX program (8). The sodium and yttrium cations are statistically distributed among the available positions. Table II Indexations, calculated d-spacings and relative intensities of the most intense peaks for both proposed models.
Compared to the indexations and intensities observed from the experimental powder diffraction pattern, the second hypothesis leads to a better agreement. In order to determine this sequence, electron diffraction and high resolution microscopy studies were performed.
928
M. RICHARD et al.
Vol. 30, No. 8
After grinding in ethanol the powder was deposited on a copper grid. The [0 0 l] zone axis pattern is presented in FIG. 2. This pattern revealed the existence of extra-reflections localized in (3 n, 3 m, e) directions with n and m odd which implies a doubled cell at 4S’ with respect to the former one and with the a parameter close to 2ap instead of aPd2. The labelled cell takes into account this new cell.
FIG. 2 [0 0 l] zone axis electron diffraction pattern of NaYTiO4. In order to obtain structural information concerning the gliding type, high resolution image was recorded perpendicularly to the layers. By referring to the cell parameters refined from the powder XRD data, the crystallite orientation is [ 1 lo]. The image and the diffraction patterns are shown in FIG. 3 and FIG. 4, respectively.
FIG. 3 [ 1 1 O] high resolution image showing the extended sequence with thickness of two perovskite slabs in NaYTi04.
Vol. 30, No. 8
LAYERED TITANATE
929
FIG. 4 [ 1 1 0] zone axis electron diffraction pattern corresponding to the former image.
Based on the fact light contrasts are associated with the heavy atoms, yttrium and titanium, the electron diffraction pattern indicates that each layer is made of two perovskite slabs and that these layers are stacked one upon another. This study suggests the second model, since the lattice seems to be primitive and no gliding is observed. A gliding along only one direction would obviously result in an orthorhombic cell because of the loss of the 4-fold rotation axis along the stacking axis, c. According to the tetragonal cell parameters relined from electron and X-ray diffraction data, this hypothesis is not retained.
exchange In an attempt to differentiate the positions of Na+ and Y3+ cations, an acid-exchange was performed as previously described. The alkali acid-exchange will only be possible if the sodium is situated in the interslab space.
98
2
96
.I
i
94 92 90 -
100
Thermogravimetric
200
300
400
500
600
Y2Ti20,
700 800 Temperature (“C)
FIG. 5 analysis curve of the exchanged compound obtained from NaYTiO4 (at 1OWmin).
M. RICHARD et al.
930
Vol. 30, No. 8
The thermogravimetric analysis (IGA) was performed under air with a TGS 2 Perk&Elmer apparatus. The exchange rate was checked by semi-quantitative analysis in a 35C Jeol scanning electron microscope equipped with a TRACOR probe. At the end of the treatment, the exchange rate is close to 90%. The thermogravimetric analysis curve, shown in the PIG. 5, reveals a monotonous weight loss which is achieved at 600°C. The XRD pattern of the final compound obtained at 800°C is characteristic of the pyrochlore YzTi&. Since the final product is known and considering on one hand that 10% sodium is still present in the compound and on the other hand that all the weight loss can be associated to a water departure, the exchanged product can be expressed HugNaolYTi04,0.7H20. The slope change observed around 200°C corresponds then to the nominal composition HofiaolYTiO4.
L
NaYTiO,,
.,YTiO,, 0.7H,O 0
10
20
30
40
50
60
70
20 0 PIG. 6 Powder XRD pattern of the exchanged compound compared to the NaYTiO4 one. As shown in PIG. 6, the XRD pattern of the exchanged compound reveals a close relationsh’ with the pattern of the patent phase. Tab ‘pe III lists indexations, positions and intensities of the diffraction peaks for the exchanged product. The diagram can be indexed using a tetragonal cell sli htly different from the cell used for NaYTiO4. The refined parameters are thus a = 3.725(l) 1 and c = 22.86(2) A. The c parameter is twice that of the precursor phase whereas a is J2-fold smaller. The characteristic R= &C(2%L%
factors
are
as
- 2e,alc)2 =0.021.
follows
:
D = -J--~ld(20)l=0.015°
and
Vol. 30, No. 8
931
LAYERED TITANATEI
Table III Indexations, positions and intensities of the XRD peaks for the exchanged product HogNao.1YTi04,0.7H2G. hkl 002 004 006 104 106 110 112 115 10 10 118 200 205 214 216
dcalc (A) 11.43 5.715 3.810 3.120 2.6635 2.6338 2.5666 2.2822 1.9484 1.9367 1.8624 1.7248 1.5992 1.5263
?e . -5 5.717 3.813 3.117 2.6612 2.6339 2.5669 2.2816 1.9486 1.9371 1.a635 1.7239 1.5996 1.5263
21 5 30 21 11 2 9 4 4 7 7 4 2
The capability to exchange the alkali in an acid medium suggests that the sodium ions are localized in the interlayer space and consequently that the 12-fold coordmatcd sites are occupied by the yttrium ions. Unfortunately, this additional information did not allow us to determine the cation distribution in the structure from powder diffraction pattern
Conclusion Both XRD pattern and the electron microscopy of NaYTiO4 suggest a structuml model close to TIBa2CaCu208& in which each layer is constructed by two perovskite slabs and is stacked one upon another instead of by one perovskite slab stacked with a l/2 gliding along two directions, as previously reported by Blasse et al. (6). Moreover, since the sodium exchange is possible, this suggests that the alkali are situated in the interlayer space and therefore the yttrium occupies the 12fold coordinated intmlayer perovskite site. The crystal structure refinement is still in progress.
1. S.N. Ruddlesden and P. Popper, Acta Cryst., 1 l., 54-55, (1957) 2. M. Richard, L. Brohan and M. Toumoux, J. Sohd State Chem., 112,345, (1994) 3. M. Richard, L. Brohan, A.M. Marie, C. Roucau and M. Toumoux, submitted to J. Solid State Chem. 4. Treatment of INEL X-Ray curve detector powder diffraction data : chain program and experimental results, J.M. Barbet, M. Evain, P. Deniard and R. Brec. 5. U-Fit : a cell parameter refinement program, M. Evain, IMN Names, (1992) 6. G. Blasse, J. Inorg. Chem., 30,656, (1968) 7. M. Hervieu, A. Maignan, C. Martin, C. Michel, J. Provost and B. Raveau, J. Solid State Chem., 75, 212, (1988) 8. R. Yvon, W. Jeitschko et E. Parthe, J. Appl. Crystallogr., 10,73, (1977)