Mn0msoTi2(PO&-NaTi2(P04)3 solid solutions Ann. Chim. Sci. Mat, 1998,23, pp. 81-84
CHEMICAL, STRUCTURAL AND MAGNETIC STUDIES OF Mn0.50Ti2(PO& AND ITS SOLID SOLUTION WITH NaTiz(PO&
H. FAKRANE, A. AATIQ’y2, M. LAMIRE, A. EL JAZOULIl, C. DELMAS2 Lahoratoire de Chimie du Solide, Faculti des Sciences Ain Chock, Casablanca, Maroc.
1 Laboratoire de Chimie des Matiriaux Solides, Facultk des Sciences Ben M’Sik, Casablanca, Maroc.
2 Laboratoire de Chimie de la Mat&e Condens& de Bordeaux, Universitk de Bordeaux I, France.
SmarV : N~~.&fn,Tiz(PO& (0 5 x 50.5) phosphates have been prepared by solid state reaction and by sol-gel m&hod. ne X-ray diffraction study shows that these materials belong to the N&con-type structure. The structure of i%O.sTiz(PO& has been solved in the R? space group. Mn*’ ions are ordered in half of M(1) sites. The magnetic study undertaken on Mno.sTi2(P04), shows a pammagnetic behaviour with absence of Mn”-h4n2’ interactions even at low temperature.
R&me : Etudes chimiaue. structurale et mam&iaue de &SoTi,[PO,), et sa solution solide avec NaTi,(PO,),. yes phosphates Na(,.2.yn,TiZ(P0& (0 5 x ( 0,5) ont ti ptiparts par r&ction B [‘&at solide et par une m&ode sol-gel. L&de par diffraction des rayons X montre que ces mhiaux appartiennent au type structural Nasicon. La structure de Mq,lTiz(PO,), a &&
r&oh&e dans Ie groupe d’espace R 3 Les ions Mn’+ s’ordonnent dans la moitit des sites M(1). L’Ctude magnttique effect&e sur Mm,5Ti2(P04)3 montre un comportement paramagnt%ique avec I’absence d’interactions Mn*+-Mn2’mmCme it basse temptcature.
1 - INTRODUCTION
Titanium phosphates &,~oTi2(P04)3 have been largely studied for their catalytic properties (M = Cu) (1,2) or for their low thermal expansion coefficient (M = Mg, Ca, Sr, Ba) (3). Recently, structures of Mo.soTiz(PO& (M = Cu, Mg,
Co, Ca) (4-S) have been determined. To our knowledge, the phosphate &.,T&(PO& has not been studied. We present in this paper the results obtained for the N~~.&vln~“Ti&‘O& system : chemical, structure and magnetic properties.
2- ELABORATION AND CRYSTALLOCHEMICAL CHARACTERIZATION
N~~&ln~Ti2(PO& (0 5 x 5 0.5) materials have been obtained by the general preparation method of phosphates according to the reaction :
(I-2x)NazCOs + 2x(MnC03, nHzO) + 4Ti02 + 6NsHzP0, +2Na(,.2,MnxTi2(P0,), + CO2 + 6NH, + (9 + Zxn)H*O.
Five thermal processings with intermittent regrinding at 200°C (24h), 600°C (48h), 8OO’C (96h), 900°C (48h) and 950°C (48h) are necessary to obtain these compounds without impurities. They can also be prepared by a sol-gel method as described elsewhere for Co0,50Ti2(P0.& (6). In this case, the materials are amorphous at low temperatie and crystallize at high temperature (fieure 1).
X-ray powder patterns of Na(,.&n,Ti2(P0& (0 5 x < 0:5) phases obtained by solid state reaction are shown in fiaure 2. Observed reflections are compatible with R32 and R? groups except for x = 0 ( R~c). Values of the hexagonal latiice parameters and densities are given in table.
&&@ : M. LAMIRE, L. C. S. Fawlte des Sciences Ain Chock, D&p&meat de Chimie,km8 Route d’Eljadida, B.P. 5366 Maarif, Casablanca MAROC.
82 H. Fakrane et al.
The progressive substitution of sodium by manganese provokes a decrease of the ch parameter and a very slight variation of the ah parameter. This decrease of Ch is in favor of the occupation of M(1) sites by the manganese (ri= 0.82A) of size smaller than the sodium one (ri = 1.021%). The x = 0.5 composition (Mn0.sTiz(P04)3) is a new phosphate of the h&Ti2(PO& series. The chemical analysis of this compound obtained by the two ways of preparation, carried out in the Analysis Service of CNRS (Vernaison-France), gives experimental atomic ratios in good agreement with the calculated values (Q@Q.
Table 1 : Lattice parameters and densities of
Na(l.&ln~TiZ(PO& (0 I: x < 0.5) phases. I (A.U.) 113 C
104 125 :
a..-. 711 303 k
0.500 8.515(4) 121.09(l) 1 1325(2) 3.10 13.08(2) ] Table 2 : Chemical analysis of IvhoTiZ(PO& prepared by solid state reaction (a) and sol-gel method (b).
10 15 20 25 30 35 40
Atomic ratios Mn/Ti Mn/P TilP 2ecu
calculated 0.260 0.167 0.667
Experimental (a) Fig. 1 : X-ray powder patterns at different
0.248 0.162 0.646
Experimental (b) temperatures of ~.SOTi2(P0& prepared by
0.253 0.161 0.646 sol-gel : 300°C (a), 4OO’C (b) and 750°C (c)
3 - STRUCTURAL DETERMINATION OF Mno.mTidPO&
The refinement of the crystal structure of MnO.~oTiz(PO& has been realized in the R? space group by supposing a vacancy-manganese order in the M(1) sites. The initial atomic coordinate were those of Ch.5Ti2(P04)3 (8). The experimental conditions and results of the refmement as well as the different structural parameters are given in tables 3 and 4. Firmre 3 shows observed, calculated and difference X-ray profiles for M&.5TiZ(P04)s. The refinement realiid with the R32 space group which does not require manganese-vacancy ordering leads to significantly bad results.
113
parameters of Iv& soTi,(PO&.
Table 3 : Structural data and X-ray Rietveld refinement i 003 101 0’2
---- r
1 IO 006 214 125
I 202 024 ‘I6
. 300 303 104
Space group
a(A)
CiAi
Volume (As) Wavelength (A) Angular r&ge (deg. 20) Step width (deg. 20) Count time Refinement program
Analytical function for profil shape
Number of reflections RP
RWP RS=l%
RF
(2 = 6 felagonal system)
a.515 21.09 1325 1.54178 IO-120
0.02 40s
PZ%-%igSt \%J
PV = qL + (I-q)G (q= 0.2103)
924 8.0 % 12.1 %
4.5 % 3.2 %
1 A
- - . - _.. .- . . - .-... .-- ._,,__ -.;
piiq j
A Al A I I j
10 15 20 25 30 35 40
2BCu Fig.2 - X-ray powder patterns of N~l-2x$&Ti2(PO&
(0 < x < 0.5) prepared by solid state reaction
1 10 20.30 40 50 60 70 80 90 100110
Mn0.50Ti,(P04)3-NaTi,(P04)3 solid solutions 83
Table 4: Reduced coordinates and thermal vibration factors of ~.~JiDU.
Fig. 3 : Final observed (...) calculated (-) and difference X-ray profiles for Mn0,soTi2(P0&
4- DESCRIPTION OF THE STRUCTURE AND DISCUSSION
Mno.soTiz(PO& presents the Nasicon-type structure which is constituted of a sequence of [TiO,J octahedra and PO.,]
tetrahedra connected by the corners (fieure 4). Manganese ions occupy half of M( 1) sites in an ordered manner. The [MnOJ octahedron is regular. The [Mn-O(l)] distance (2.26A) is close to that calculated (2.22A) from ionic radius.
Electrostatic repulsions between oxygen plans surrounding M(1) site are more important when this site is empty [d(O-0) = 2.364A > d(Mn-0) = 2.26& -5).
The vacancy-manganese ordering implies the existence of two titanium ions types, Ti(l) neighboring the manganese and Ti(2) neighboring the vacancy. Tbe [Ti(2)06] octahedron, having a common face with the empty M(1) site [OO,], is slightly distorted. The Ti(2>0(2) distance (l.SSlA) is similar to that of Ti(2)-O(4) (1.863&1) (table 5). On the other hand, the [Ti( 1)06] octahedron, having a common face with the full M(I) site [MnOc], is more distorted. The Ti( l)-0( 1) distance (2.014A) is superior to the Ti(l)-O(3) distance (1.891A). The [Ti(l)Os] octahedron is notably deformed as a result of the strong electrostatic repulsions between Mr?+ and Ti” ions. Moreover, the Mn-Ti(1) distance (3.098& is larger than the q -Ti(2) one (2.849A) (figure 5). The 0-Ti(l)-0 angles vary between 78.34” and 95.23” while O-Ti(2)-0 angles are found between 88.06” and 91.44’, explaining thus the distortion of the [Ti(l)06] octahedra in comparison with the [Ti(2)0,] ones.
The [PO,] tetrahedra are slightly distorted with phosphorus-oxygen distances (1.509-1.582,k) close to those generally found for Nasicon-like phosphates (4-8). O-P-O angles vary 6om 105.46” to 115.05”.
Table 5 : Interatomic distances (A) and angles (“) in Mn0.s0Ti2(P0&.
Distances (A) Angles (“)
h-O(l) (x6) 2.262(l) O-O(2) (x6) 2.364(4) Ol-Mn-01 68.44(g)
0(1)-O(l) (x6) 2.544(5) 0(2)-O(2) (x6) 2.646(2) 111.55(1)
(x6) 3.740(7) (x6) 3.918(9) 02-o-02 68.05(7)
(x32..5?!C?I .__.,..._... G%%%!m..,.
. . . . . . . . . . 111.94(3)
X(1)-0(1) (x3) 2.014(3) Ti(2)-O(2) (x3) 1.851(2) 03-Ti(l)-03 95.10(7) Ti(l)-O(3) (x3) 1.891(7) Ti(2)-O(4) (x3) 1.863(8) 04-Ti(2)-04 89.29(2)
Mn-Ti(1) 3.098(2) Mn-X(2) 4.963(5) Ol-Ti(l)-01 78.34(3)
3-Ti(1) 4.936(4) D-li(2) 2.849(8) 02-Ti(2)-02 91.23(g)
0(1)-O(l) (x3) 2.544(5) 0(2)-O(2) (x3) 2.646(2) 03-Ti(l)-01 95.23(4)
0(3)-O(3) (x3) 2.791(7) 0(4)-O(4) (x3) 2.619(8) 90.32(2)
04-Ti(2)-02 91.44(l) .._.,....__.____..__...,...,... . . . 88.06(l)
P-O(l) (xl) 1.668(Q) P-O(3) (xl) 1.509(l) 02-P-01 108.81(l)
P-O(2) (xl) 1567(Q) P-O(4) (xl) 1.582(6) 01-P-04 108.24(8)
0(1)-O(2) (xl) 2.550(8) 0(1)-O(3) (xl) 2.514(4) 03-P-01 109.53(3) 0(1)-O(4) (xl) 2.553(7) 0(2)-O(3) (xl) 2.448(Q) 04-P-02 115.05(5) 0(2)-O(4) (xl) 2.658(l) 0(3)-O(4) (xl) 2.527(2) 03-P-04 109.63(l)
03-P-02 105.46(5)
84 H. Fakrane et at.
C I
Mn
Ti(2)Oe -PO4
TWO6
Fig. 4 : Representation of tbe structnre of Mn0.50Ti2(P04)3 a long to the c-axis.
5- MAGNETIC BEHAVIOUR OF Mtq59Ti&4)3
Fig. 5 : Electrostatic interactions and interatomic distances in MnusoTi2(P0&.
The thermal variation of the reciprocal molar susceptibility of Iv&s0Ti2(PO& follows strictly a Curie law (figure 6).
This behavionr clearly shows that there is no magnetic interaction between divalent manganese ions. The experimental value of the Curie constant Cq.= 4.40 is in good agreement with the calculated one r&=4.375 for Mn” (3d5 high spin).
150
100 X’(uem) ...-’
*. em . . 50
flzzI
*. --
*:- .-
0 /** T(K)
0 100 200 300
Fig. 6 : Thermal variation of the reciprocal susceptibility of Mn0.50Ti2(P04)3.
7- CONCLUSION
New Nasicon-type phosphates Na(i.$4n,Ti,(PO& (0 5 x 5 0.5) have been prepared by solid state reaction (950°C) and by sol-gel method (75O’C). The b&.soTir(PO& structure has been solved in R? space group. Mn2’ ions.occupy one of the two positions of the M(1) site [3a (0, 0, O)], the other [3b (0, 0, l/2)] is empty. This phosphate shows a paramagnetic behavionr with the absence of h4n2+-Mn*+ interactions.
8 - REFERENCES
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(4) Olazcusga (R.), Le Flem(G.), Boireau (A.), Soubeyroux (J. L.), Adv. Mat. Res., 1994, -2, 177.
(5) Barth (S.), Olazcuaga (R.), Gravereau (P.), Le Flem (G.), Hagemnuller (P.), Mater. Letters, 1993, & 96 (6) El Bouari (A.), El Jszouli (A.), Dance (J. M.), Le Flem (G.), Olazcuaga (R.), Adv. Mat. Res., 1994, &, 173.
(7) Senbbagaraman (S.), Guru Row (T. N.), Umarji (A, M.), Solid State Comm., 1989, m 609.
(8) Mentrc (0.). Abraham (F.), Deffontsiues (B.), Vast (P.), Solid State Ionics, 1994,22.293.
(9) Wiles (D. B.), Young (R.) J. Aoul. Crvst., 1981, & 149.
