New phosphates: Na4C~.5Ti(P0,)B and Ni0.,TiOP04 Ann. Chim. Sci. Mat, 1998,23, pp. 7-10
PREPARATION AND STRUCTURAL CHARACTERIZATION OF TWO NEW TITANIUM PHOSPHATES NaCao,5Ti(P04)3 AND Nb,,TiOP04
A. EL JAZOULI, S. KRIMI, B. MANOUN, J.P. CHAMINADE*, P. GRAVEREAU*, D. DE WAAL**
Laboratoire de Chimie des Materiaux Solides, Faculte des Sciences Ben M’Sik, Avenue Idriss El Harti, B.P. 7955, Casablanca, Maroc.
* Institut de Chimie de la Mat&e Condens6e de Bordeaux, Avenue du Dr. A. Schweitzer, 33608 Pessac Cedex, France.
** Department of Chemistry, University of Pretoria, 0002 Pretoria, South Africa.
m : The titanium phosphate Na.&a, sTi(PO& crystallizes in the trigonal space group R32 (a,, = 9.008 f 0.002 A, ch = 21.814 f 0.003 A and Z = 6). Its structure belongs to the Nasicon type family.
The titanyl phosphate NicSTiOP04 ctystallizes in a monoclinic unit cell, Pfiic, (a = 7.383 * 0.001 A, b = 7.323 f 0.001 A, c = 7.344 f 0.001 A, 8 = 120.23 * 0.01” and Z = 4).
The structure of these two compounds is based on a three-dimensional framework built of Ti06 octahedra and PO4 tetrahedra.
The PO4 tetrahedra are isolated in both Na&ac rTi(PO& and Nio sTiOPO+ The TiO( octahedra are isolated in the former and linked together by “titanyl” oxygen atoms to form -Ti-O-Ti-O- infinite chains in the latter. These structural data are confirmed by the Raman spectroscopy study.
R6sumC : Prtoaration et camctCrisation structurale de deux nouveaux ohosohates Na&a~TilPO~)&&~+ Le phosphate de titane Na&a,, ,Ti(PO,), cristallise dam le groupe d’espace R32 (a+, = 9.008 + 0.002 A, ct, = 21.814 * 0.003 A et Z = 6). Sa structure appartient a la famille Nasicon.
Le phosphate de titanyl NicsTiOPOI cristallise dans une maille monoclinique, P2i/c, ( a = 7.383 f 0.001 A, b = 7.323 f 0.001 A,
c = 7,344 i 0.001 A, 8 = 120.23 f 0.01” et Z = 4).
La structure de ces dew composes est formee d’un reseau 3D d’octaedres TiOs et de tetratdres PO+ Les tttraedres POP sont isoles dam Na.,Ca, sTi(PO& et Nit sTiOPO+ Les octddres TiOs sont isolts dans le premier phosphate, alors que dans le second, ils sont lies par les sommets et forment des chaines intinies -Ti-0-Ti-0-. Ces donntes structurales sont contirmees par une etude par spectroscopic Raman.
1, INTRODUCTION
In the course of our investigation on titanium phosphates, reports have been published on glass or crystalline phases of M*lO - TiO2 - P2O5 (Mt = Na, Tl) and M’tO - Tiq - P205 (M” = Co, Ni, Mn,...) systems (l-8). The structures of Na5Ti(PO& (3) and M”u,5Ti#‘04)3 (M” = Co, Ni, Mn) (6-8) have been determined. All these compounds belong to the Nasicon-type structure. Their thermal stability has been estabilished (7). At high temperature the decomposition of N&Ti2(P04)3 yield to TiP2O7 and Nic.5TiPO5. The latter compound is a new titanyl oithophosphate (Nia.5TiOP04).
The compounds of this family continue to be the subject of increasing interest (9-16). The best known member is potassium titanyl orthophosphate KTiOP04 (KTP). Its non linear optical and electro-optical properties have found important applications. In this way we have developed a large program on the Mt20 - MU0 - Ti02 - P2O5 system with the aim of isolating interesting new compounds.
Reorints: A. EL JAZOIJLI, Laboratoire de Chimie des Materiaux Solides, Faculte des Sciences Ben M’Sik, Avenue Idriss El Harti, B. P. 7955, Casablanca, Maroc.
8 A. El Jazouli et al.
In this publication we report on the preparation and structural characterization using X-ray powder dieaction and Raman spectroscopy of the two new titanium phosphates Na&q.sTi(PO& and Nio sTiOP04.
2. EXPERIMENTAL
Na&q,sTi(PO4)3 and Nio.sTiOP04 were obtained by a sol-gel method as described elsewhere (6) or by conventional solid state reaction techniques. Powder crystalline samples have been prepared from mixtures of Na2CO3, CaC03, NiO, TiO2 and (NH&HP04 in stoichiometric proportions and heated progressively from 200 up to 650°C for Na&ar,5Ti(P04)3 and 950°C for Nio.sTiOP04, with intermediate regrinding. Na&ao.sTi(PO& can also be obtained by heating the glass of identical composition at 600°C. The obtained final products are white for Na&ar.STi(P04)3 and green for Nio,5TiOP04. The X-ray diffraction data were collected at room temperature with a Philips PW17lO diffractometer (Cu Ka). The Rietveld refinement was performed using the Fullprof program (17). The Raman spectra were recorded using the microprobe on the XY Dilor Multichannel instrument. Excitation was accomplished with the 514.5 nrn line of an Argon ion laser. Incident power was approximately 100 mW.
3. RESULTS AND DISCUSSION
3.1 Structure of Na&aQSTi(POd_ll and NiuTiOP04 -_
The structures of Na&ao5Ti(PO& and Nio,sTiOP04 have been determined by Rietveld refinement of the X-ray diffraction patterns. Here we give a summary of this study, details of with will be published elsewhere (18).
The XRD pattern of Na&m,sTi(PO& can be indexed assuming an hexagonal cell (a+, = 9.008 f 0.002 i\, ch = 21.814 + 0.003 A and Z = 6). The d values of the diffraction lines are given in table 1. The observed reflexion conditions are consistent with the space groups R 5 and R32. Attempts to resolve the structure in R 7 group led to bad results. The structure was then resolved in R32 group. Several cationic distributions are assuming for the Rietveld refinement : [Na3lM(2$%SOO 51bf(1)[NaV&Q4)3, [NaZ.SlM(tz)bhJ 5Cao 5lM(1)[NaTilA(P04)3 and
[Na2,5]~(2)[Na]M~I)[Nao,jCao,sTi]A(PO4)3. The best results are obtained for the third one. The structure of this material consists of a three dimensional network of PO4 tetrahedra and A06 octahedra (A = Ti, Na, Ca) sharing common comers (fieure I). The Ti06 octahedra are isolated. The Ti-0 distances (1.92-2.00 A) are of the same magnitude as those found in NasTi(P04)3 (1.88- 1.96 A) (3). The PO4 tetrahedra are also isolated and more distorted than in NasTi(P04)3.
A new titanyl orthophosphate Nio,STiOP04 was obtained during the study of the NiO-Ti02-P205 system (7). Its structure was determined ab-initio in P2Jc space group (18). The monoclinic unit cell parameters are a=7.383~0.001& b=7.323fO.OOlA, c=7.344*0.001& ~=120.23~0.01” and Z=4. The d values of the dieaction lines are given in table 2. The structure of Nio.STiOP04 can be described as a three-dimensional network based on TiO6 octahedra and PO4 tetrahedra . The Ni atoms occupy a triangle based antiprism sharing hvo faces with TiO6 octahedra [fierure 2). The PO4 tehahedra are isolated and the P-O distances are normal (ml.52 A). The TiO6 octahedra are distorted. They are formed by four oxygen atoms belonging to the PO4 groups and by two bridging
“titanyl” oxygens. The Ti-0 (PO4) distances (1.88. 1.90, 2.07, 2.10 A) are fairly uniform with a mean of 1.99 A. There are differences in the lengths of the titanium-titanyl oxygen bonds in the chain of titanium octahedra. There is altemance of a very short Ti-0 bond (1.70 A) and a very long one (2.23 A). In this aspect, the structure of Nio.sTiOP04 is similar to that of M’TiOPOd (M’ = K, Na, Li) where octahedral chains have been also detected (10, 12, 14, 15).
New phosphates: Na,Ca0.5Ti(P0,), and Ni,,TiOP04 9
tP04
cAo6
FIG. I-The smxture of Na&q,5Ti(P04)3 viewed along [I 1 O] FIG.2-The structure of Nio 5TiOP04 along 11 OO]
TABLE I-X-ray diffraction data for Na&q.sTi(PO& TABLE 2-X-ray diffraction data for Nio 5TiOP04
hkl dobs (A) deal (A) III,
101 DO3 012 I IO 104 021 113 01s 202 006 024 211 205 107 I22 116 300 214 018 303 125 027 009 220 208 131 223 217 119 312 306 10 IO 134 128 401 315 01 II 042 226 0210 0012
7.346 6.343 4.491 4470 3.829
3.639 3.172 2.924
2832 2602 2.571
2.449
2.252 2.237
2.153
2.125 2.108 2.004 I.941
1919 1.820
7346 7271 6.345 4.504 4.470 3.840 3 829 3 808 3673 3 636 3.173 2.922 2.908 2894 2.846 2.829 2.601 2.594 2574 2.449 2.443 2.435 2.424 2.252 2.235 2.153 2.151 2.142 2.134 2 122 2 I15 2101 2.011 2.002 1.943 1.938 1.922 1.920 1915 1.904 1818
21 8
I4 28 91
21 I5 24
IO0 48 2 6 3 s II
38 7
hkl dabs(A) deal (A) l/I0
100 6.372 6380 15
I I -I 4814
110 4.801 4.811 30
01 I 4.797
020 3.659 3.662 4
2 1 -I 3.297
1 I -2 3.281 3.284 100
III 3.281
2 0 -2 3 194
200 3 190
12-l 3 I76 3 177 42
120 3.176
002 3.174
02 -I 3 172
2 I -2 2.928
210 2.922 2.925 5
012 2.913
2 2 -I 2.600
I 2 -2 2.595 2.594 21
121 2.592
3 0 -2 2.417
2 2 -2 2.415 2 407 6
220 2.405
022 2397 2399 6
3 I -2 2.296
3 I -I 2.294
2 I -3 2.294 2.288 IO
211 2.285
I I -3 2.283
II2 2.281 2.281 20
13-l 2.281
I30 2.280
031 2.279
3 I -3 2.045
310 2.040 2.042 IO
23-l 2.037
I 3 -2 2.034
013 2.032 2.033 IO
I31 2.033
2 2 -3 2.013
221 2.011
I 2 -3 2.009 2.009 6
122 2.008
10 A. El Jazouli et al.
Figure3 represents Ratnan spectra of NaTiz(PO&, Na&an STi(PO&, Nio.sTiOP04 and LiTiOPO+ A full vibrational analysis and assignment of the bands in the spectra will be published elsewhere. The comparison of these spectra allows us to make some remarks. The Na&ac sTi(PO.& bands are more broad than those of the other phosphates due to the disorder in the M(2) and A sites. The strong band around 750-800 cm” observed in the titanyi orthophosphates (NaTiOP04 : 745 cm.’ (19), LiTiOP04 : 783 cm-‘, NinjTiOP04 : 750 cm-‘) and absent in the Nasicon titanium phosphates NaTil(PO& and Na&anSTi(PO& is assigned to the Ti-0 vibrations in the -Ti-O-Ti-O- chains (19,20). The bands observed in the high energy region 860-l 170 cm-’ are due to the isolated phosphate groups. They are assigned to symetrical and antisymetrical stretching vibrations vr and vs. These bands are relatively very weak in the oxyphosphates where TiO6 octahedra form -Ti-O-Ti-O- chains but are the strongest in the Nasicon compounds containing isolated TiO6 octahedra. The bands observed between 350 and 600 cm-’ are attributed to O-P-O deformations (~2 and v4 PO4 modes) and Ti-0 vibrations. The bands observed below 300 cm” are attributed to lattice vibrations.
T
(c)
(4
FIG. 3 - Raman spectra of (a) NaTiZ(PO&; (b) Na&ao.sTi(PO&; (c) LiTiOP04; (d) Niu.sTiOPO4.
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