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Lattice parameters variation with temperature of Ti2O3 and (Ti0.98V0.02)2O3 from single crystal X-ray data
Solid State Communications, Vol. 20, pp. 893—896, 1976.
Pergamon Press.
Printed in Great Britain
LATTICE PARAMETERS VARIATION WITH TEMPERATURE OF Ti203 AND (Tio 95V0 ~)2O3 FROM SINGLE CRYSTAL X-RAY DATA J.J. Cappom and M. Marezio Laboratoire des Rayons X, CNRS, BP 166X, 38042 Grenoble Cedex, France and J. Dumas and C. Schienker Groupe des Transitions de Phases, CNRS, BP 166X, 38042 Grenoble Cedex, France (Received 23 August 1976 by E. F Bertaut) The lattice parameters of Ti203 and (Tio.~Vo.o2)2O3have been measured as a function of temperature (24—670°Cfor Ti203 and 24—440 C for V-doped Ti2O3) from single crystal X-ray data. The high temperatures were attained by blowing hot argon directly on the crystal m?unted on an automatic Philips diffractometer. This experimental set-up gives standard deviations which are at least 10 times better than those of the previous measurements and allows to keep T1203 as such well above the transition. The variations of a, c, c/a ~hexagonalaxes) for pure Ti2O3 are m agreement with the previous results. On the contrary we did not observe any transition in the unit cell volume. The V-doping seems to attenuate the transition which is visible only on the a vs T curve AFTER it was found that the sesquioxide Ti203 undergoes a semiconductorto metal transition with an increase of the electrical conductivity of authors ~102inhave the tern1 several inperature range of 450—600 K, vestigated the variation of the lattice parameters as a 2~It has been found that, function temperature. while the of crystal structure remains corundum-type at all temperatures, the transition is accompanied by an abrupt variation of the lattice parameters. Between 450 and 600 K the a and c parameters show an anomalous decrease and increase, respectively. This gives rise to a strong increase in the c/a ratio. An anomaly in the specific heat has been found in the same temperature range.5 In order to explain this behavior it has been proposed that below the transition the ground state of the 3d electrons is a full a 1~bonding band with 3d orbitals metal—metal bonding along the c-axis and an empty e~ band a few 0.01 eV above. This band corresponds to 3d orbitals lying inplane. the basal plane to metal—metal bonding in this When the and temperature is increased the electrons are excited into the e~band and the
structural refinement of the two phases, i.e. by the direct determination of the Ti—Ti distances along the c-axis the shared (across(across the shared edges).face) and in the basal plane In the case of (Ti it hasthe been reported that the incorporation1_~V~)2O3, of V stabilizes metallic phase for values ofx larger than a few per cent, through an increase of the c/a ratio.7 More recent data show that the metallic phase is induced by V concentrations smaller than 1% in which case the stabilization is related to the formation of an impurity band.8 It has been proposed that the effect of the increase of the c/a ratio is important only at larger V concentrations.8 In order to measure the X-ray intensities of the metallic phase at high temperatures R. Argoud of our Laboratory has built a high-temperature attachment for
the Philips four-circle automatic diffractometer. Because of the high accuracy attained with this high-temperature set-up and because somereports discrepancies with earlier 3 thisofpaper the data of the lattice measurements, parameters variation with temperature of two crystals, one of pure Ti 203 and the other of a vanadium-doped metal—metal bonding becomes predominant in the basal Ti203. 6 This model is based mainly on the behavior of The Ti plane. 2O3 powder was obtained by pressing and arcthe lattice parameters with temperature. Now, the Ti—~fl melting under an argon atmosphere a 1:3 mixture of Ti separation along the c-axis does not necessarily follow metal and T1O2 (rutile powder). The V203 powder was the same behavior with temperature as the c-axis. In fact prepared by reducing V2O5 with hydrogen at 700°Cfor the titanium cations occupy OOz positions. The above three days. The proper stoichiornetric amounts of Ti203 model could receive a stronger support by a complete and V2O3 were mixed, pressed, and arc-melted in order 893
894
Ti2O3 AND (Ti0.98V0.0~O3FROM SINGLE CRYSTAL X-RAY DATA
Vol. 20, No.9
Table 1. Lattice parameters of Ti203
24°C 40 60 80 100 120 140 160 180 200 220 240 250 260 270 280 290 *
a
c
5.1556(3)* 5.1554(2) 5.1548(4) S.15S2(4)t 5.1546(5) S.i543(S)t 5.1525(5) S.l502(S)t
13.625(l)* 13.628(1) 13.636(2) i3.64O(2)t 13.651(2) i3.658(2)t 13.669(2) i3.69O(2)t 13.7!9(2)t i3.756(l)t l3.783(2)t i3.804(2)t 13.813(2) 13.822(1) 13.829(2) 13.835(1) 13.845(2)
S.l455(S)t S.1400(3)t 5.i3S9(4)t S.1332(4)t 5.1318(5) 5.1311(3) 5.1302(5)
5.1297(4) 5.1291(5)
300°C 320 340 360 380 400 420 440 460 480 500 520 670
a
c
S.l28O(7)t 5.1268(4) 5.1270(5) 5.1262(3) 5.1264(4) S.i268(S)t S.l2S9(4)t 5l254(5)t
l3.8Si(3)~ 13.865(2) 13.875(2) 13.866(1) 13.894(2) 13.904(2)t i3.91i(2)t i3.918(i)t 13.930(2) l3.937(i)t 13.946(2) i3.952(i)t 13.992(1)
5.1256(4) S.i258(3)t 5.1264(6) S.l268(4)t 5.1300(4)
Average value of five measurements.
t Average value of two measurements. The numbers between parentheses represent the standard deviations on the last decimal figure. The least~guaresrefinement was based on the following reflections: 164, 2410, 25~,5~16,6~0,3116, 1~16,3612, 3410, 5510, 2016. to prepare the (Tio 9sVo.o~)203 powder. Single crystals of Table 2. Lattice parameters of Ti0 98V0 ~)2O3 Ti203 and of (Ti0 98V0 ~)2O3 were grown by the Czochralsky technique in a commercial triarc furnace a c (Centorr Associates). The absence of V203 and Ti305 in 24°C 5.1331(7) 13.705(3) the pure and doped crystals was checked by specific heat ioo 5.1309(3) 13.738(2) thermal analysis. V203 and Ti3O5 show first order tran120 5.1297(5) 13.750(2) sitions at 150 and 450 K, respectively and small amounts 140 5.1288(5) 13.760(2) can be easily detected. The vanadium9content was deter160 5.1265(4) 13.776(2) In general it was 180 5.1254(5) 13.790(2) mined by atomic absorption analysis. found to be approximately lO%less than the nominal 200 5.1242(4) 13.805(2) composition. 220 5.1225(5) 13.814(2) Small pieces of large crystals were ground into 240 5.1218(4) 13.829(2) spheres of 0.22 and 0.20 mm dia. for the pure Ti 2O3 and 280 5.1202(4) 13.856(2) the V-doped sample, respectively. Then they were 320 5.1195(5) 13.875(2) mounted on a Philips, four circle, automatic, diffracto360 5.1196(4) 13.893(2) meter equipped with a graphite monochromator and 400 5.1184(4) 13.915(2) MoK~3radiation. The use of the ~3radiation reduced the 440 5.1194(5) 13.925(2) intensity of the reflection by a factor of “-‘3, however its monochromaticity made the search for the orientation The numbers between parentheses represent the stanmatrix much easier after a variation of the temperature. dard deviations on the last decimal figure. The high temperatures were attained by blowing a hot The least-squares refinement was based on the following stream of commercial argon* directly on the crystal. A reflections: 1~4,2410, 256, 5516, 060, 6012, 3116, 1416. *
Air liquid U quality with a typical composition: 99.995% argon (in volume) 5 ppm 02, 5 ppm H20, 40 ppm N2.
control unit was used in order to monitor the temperature and control the proper gas flow. By using this gas blower on a thermocouple of about the same size as the
11203 AND (Ti0~98V0.0~O3 FROM SINGLE CRYSTAL X-RAY DATA
Vol. 20, No.9
895
~T~O3V
(3
100
200
300
‘.00
500
600
700
Temp.C
0
1(30
200
300
400
500
600
700
Temp.C
Fig. 1. Variation of a, c, c/a, and unit cell volume (hexagonal axes) vs flC) for 11203 and (Tio. 98V0.0~O3. sphere it was found that at 500°C, for instance, the ternperature was constant 3. within two degrees inside A calibration curve was adrawn volume of about 1 mm in order to obtain the temperature of the sample from that set on the control unit. Details of this high temperature attachment will be published elsewhere.’°The 0 angles of 11 reflections for the ‘11203 sample and of 8 for the V-doped one, were measured. The zero of the 0-circle was determined by measuring for each reflection the 0 and —0 values. The lattice parameters were obtamed by11the least-squares refinement program PARAM. Tables 1 and 2 give the lattice parameters a and c (hexagonal axes) for the pure Ti 203 crystal and for the V-doped one, respectively. Since the lattice parameters of Ti2O3 are very sensitive to the stoichiometry of the crystal which can vary easily with atemperature, accurate determination represents good test fortheir the inertness of the atmosphere around the crystal in our gas-blower set-up. The lattice parameters of pure Ti 2O3 were measured with increasing temperature in this sequential fashion: from room temperature to 520°C, back to room temperature, up to 670°Candup finally back to room temperature. The values obtained, corresponding to the same temperature, differed from each other within the standard deviations. This proved that no oxidation had taken place at high temperatures up to 670°C. It should be pointed out that our data are quite an improvement with respect to those published by Eckers and Bradt4 who stated that 300°Cappeared to be the
maximum temperature of stability for Ti2O3 in an atmosphere of ofthe commercial-purity helium. The lattice parameters V-doped Ti 203 crystal were determined with increasing temperature. At the end of the measurements the lattice parameters at room temperature were redetermined in order to check whether the stoichiometiy had remained the same. No change was detected. The stability of this crystal was determined up to 440°C. Figure 1 shows the variation of the lattice parameters, c/a ratio and unit cell volume as a function of temperature thethe pure Ti203crystal crystalthe andsemiconductor of the V-doped one.ofFor former to metal transition is clearly seen in the a and c parameter curves as well as in the c/a ratio one. At the transition one observes a sharp drop of the a parameter and sharp increases of the c parameter and of the c/a ratio.2~the This is in agreement with thein previous measurements, only difference being the precision of the data. We can estimate that our standard deviations are between 10 and 20 times better than the previous ones. No transition is observed in the unit cell volume. This3 iswho contrary to calculated what has been reported by Rao et al. that the transition is accompanied by a 7% drop in the unit cell volume. Actually, if one calculates the volume from the lattice parameters reported by these authors, the V vs T curve does not show any anomaly. It seems, therefore, that the drop is due to erroneous calculations. It can be seen from Fig. 1 that the V-doping attenuate the transition which is visible only in the a vs T curve. ‘I’his is in agreement with the data of reference 8 from
896
11203 AND (Tio.~Vo.o~OFROM 3 SINGLE CRYSTAL X-RAY DATA
Vol. 20, No.9
which it was concluded that the lattice distortion caused by the incorporation of cations was important at concentrations larger than 1%. REFERENCES 1.
MORIN F.J., Phys. Rev. Lett. 3, 34 (1959).
2.
PEARSON D.,J. Phys. Chem. Solids 5,316 (1958).
3. 4.
RAO C.N.R., LEOHMAN R.E. & HONIG J.M.,Phys. Lett. 27A, 271 (1968). ECKERS L.J. & BRADT R.C., J. Appl. Phys. 44,3470 (1973).
5.
BARROW H.L., CHANDRASHEKIIARG.V., CHI T.V., HONIG J.M. & SLADEK R.J.,Phys. Rev. B7, 5147 (1973); COEY J.M.D., ROUIX-BUISSON H., SCHLENKER C., LAKKIS S. & DUMAS J., [to be published in Revue Géndrale de Thermique (1976)].
6.
GOODENOUGH J.B., 1. Solid State Chem. 5, 145 (1972).
7.
CHANDRASHEKHARG.V.,WONCHOI Q.,MOYOJ. &HONIGJ.M.,Mat. Res. BulL 5, 999 (1970).
8.
DUMAS J. & SCHLENKER C., Colloque C.N.RS. sur les Transitions Metal—Non Metal, Autrans, (28 June— 1st July 1976)1. de Phys. (to be published). See also: DUMAS J., SCHLENKER C. & NATOLI RC., Solid State Commun. 16,493 (1975); DUMAS J., SCHLENKER C., THOLENCE J.L. & TOURNIER it, Solid State Commun. 17, 1215 (1975); Conf. on Magn. and Magn. Mat., Philadelphia (Dec. 1975), A.I.P. Proc. (to be published).
9.
The analysis was performed at the Larec Laboratory of the University of Grenoble.
10. 11.
ARGOUD R. & CAPPONI J.J. (to be published). STEWART J.M., X-ray 63 System (July 1971 version). TR-64-6, N56-398. Computer Science Center, Univ. of Maryland, College Park, MD, U.S.A.
Pergamon Press.
Printed in Great Britain
LATTICE PARAMETERS VARIATION WITH TEMPERATURE OF Ti203 AND (Tio 95V0 ~)2O3 FROM SINGLE CRYSTAL X-RAY DATA J.J. Cappom and M. Marezio Laboratoire des Rayons X, CNRS, BP 166X, 38042 Grenoble Cedex, France and J. Dumas and C. Schienker Groupe des Transitions de Phases, CNRS, BP 166X, 38042 Grenoble Cedex, France (Received 23 August 1976 by E. F Bertaut) The lattice parameters of Ti203 and (Tio.~Vo.o2)2O3have been measured as a function of temperature (24—670°Cfor Ti203 and 24—440 C for V-doped Ti2O3) from single crystal X-ray data. The high temperatures were attained by blowing hot argon directly on the crystal m?unted on an automatic Philips diffractometer. This experimental set-up gives standard deviations which are at least 10 times better than those of the previous measurements and allows to keep T1203 as such well above the transition. The variations of a, c, c/a ~hexagonalaxes) for pure Ti2O3 are m agreement with the previous results. On the contrary we did not observe any transition in the unit cell volume. The V-doping seems to attenuate the transition which is visible only on the a vs T curve AFTER it was found that the sesquioxide Ti203 undergoes a semiconductorto metal transition with an increase of the electrical conductivity of authors ~102inhave the tern1 several inperature range of 450—600 K, vestigated the variation of the lattice parameters as a 2~It has been found that, function temperature. while the of crystal structure remains corundum-type at all temperatures, the transition is accompanied by an abrupt variation of the lattice parameters. Between 450 and 600 K the a and c parameters show an anomalous decrease and increase, respectively. This gives rise to a strong increase in the c/a ratio. An anomaly in the specific heat has been found in the same temperature range.5 In order to explain this behavior it has been proposed that below the transition the ground state of the 3d electrons is a full a 1~bonding band with 3d orbitals metal—metal bonding along the c-axis and an empty e~ band a few 0.01 eV above. This band corresponds to 3d orbitals lying inplane. the basal plane to metal—metal bonding in this When the and temperature is increased the electrons are excited into the e~band and the
structural refinement of the two phases, i.e. by the direct determination of the Ti—Ti distances along the c-axis the shared (across(across the shared edges).face) and in the basal plane In the case of (Ti it hasthe been reported that the incorporation1_~V~)2O3, of V stabilizes metallic phase for values ofx larger than a few per cent, through an increase of the c/a ratio.7 More recent data show that the metallic phase is induced by V concentrations smaller than 1% in which case the stabilization is related to the formation of an impurity band.8 It has been proposed that the effect of the increase of the c/a ratio is important only at larger V concentrations.8 In order to measure the X-ray intensities of the metallic phase at high temperatures R. Argoud of our Laboratory has built a high-temperature attachment for
the Philips four-circle automatic diffractometer. Because of the high accuracy attained with this high-temperature set-up and because somereports discrepancies with earlier 3 thisofpaper the data of the lattice measurements, parameters variation with temperature of two crystals, one of pure Ti 203 and the other of a vanadium-doped metal—metal bonding becomes predominant in the basal Ti203. 6 This model is based mainly on the behavior of The Ti plane. 2O3 powder was obtained by pressing and arcthe lattice parameters with temperature. Now, the Ti—~fl melting under an argon atmosphere a 1:3 mixture of Ti separation along the c-axis does not necessarily follow metal and T1O2 (rutile powder). The V203 powder was the same behavior with temperature as the c-axis. In fact prepared by reducing V2O5 with hydrogen at 700°Cfor the titanium cations occupy OOz positions. The above three days. The proper stoichiornetric amounts of Ti203 model could receive a stronger support by a complete and V2O3 were mixed, pressed, and arc-melted in order 893
894
Ti2O3 AND (Ti0.98V0.0~O3FROM SINGLE CRYSTAL X-RAY DATA
Vol. 20, No.9
Table 1. Lattice parameters of Ti203
24°C 40 60 80 100 120 140 160 180 200 220 240 250 260 270 280 290 *
a
c
5.1556(3)* 5.1554(2) 5.1548(4) S.15S2(4)t 5.1546(5) S.i543(S)t 5.1525(5) S.l502(S)t
13.625(l)* 13.628(1) 13.636(2) i3.64O(2)t 13.651(2) i3.658(2)t 13.669(2) i3.69O(2)t 13.7!9(2)t i3.756(l)t l3.783(2)t i3.804(2)t 13.813(2) 13.822(1) 13.829(2) 13.835(1) 13.845(2)
S.l455(S)t S.1400(3)t 5.i3S9(4)t S.1332(4)t 5.1318(5) 5.1311(3) 5.1302(5)
5.1297(4) 5.1291(5)
300°C 320 340 360 380 400 420 440 460 480 500 520 670
a
c
S.l28O(7)t 5.1268(4) 5.1270(5) 5.1262(3) 5.1264(4) S.i268(S)t S.l2S9(4)t 5l254(5)t
l3.8Si(3)~ 13.865(2) 13.875(2) 13.866(1) 13.894(2) 13.904(2)t i3.91i(2)t i3.918(i)t 13.930(2) l3.937(i)t 13.946(2) i3.952(i)t 13.992(1)
5.1256(4) S.i258(3)t 5.1264(6) S.l268(4)t 5.1300(4)
Average value of five measurements.
t Average value of two measurements. The numbers between parentheses represent the standard deviations on the last decimal figure. The least~guaresrefinement was based on the following reflections: 164, 2410, 25~,5~16,6~0,3116, 1~16,3612, 3410, 5510, 2016. to prepare the (Tio 9sVo.o~)203 powder. Single crystals of Table 2. Lattice parameters of Ti0 98V0 ~)2O3 Ti203 and of (Ti0 98V0 ~)2O3 were grown by the Czochralsky technique in a commercial triarc furnace a c (Centorr Associates). The absence of V203 and Ti305 in 24°C 5.1331(7) 13.705(3) the pure and doped crystals was checked by specific heat ioo 5.1309(3) 13.738(2) thermal analysis. V203 and Ti3O5 show first order tran120 5.1297(5) 13.750(2) sitions at 150 and 450 K, respectively and small amounts 140 5.1288(5) 13.760(2) can be easily detected. The vanadium9content was deter160 5.1265(4) 13.776(2) In general it was 180 5.1254(5) 13.790(2) mined by atomic absorption analysis. found to be approximately lO%less than the nominal 200 5.1242(4) 13.805(2) composition. 220 5.1225(5) 13.814(2) Small pieces of large crystals were ground into 240 5.1218(4) 13.829(2) spheres of 0.22 and 0.20 mm dia. for the pure Ti 2O3 and 280 5.1202(4) 13.856(2) the V-doped sample, respectively. Then they were 320 5.1195(5) 13.875(2) mounted on a Philips, four circle, automatic, diffracto360 5.1196(4) 13.893(2) meter equipped with a graphite monochromator and 400 5.1184(4) 13.915(2) MoK~3radiation. The use of the ~3radiation reduced the 440 5.1194(5) 13.925(2) intensity of the reflection by a factor of “-‘3, however its monochromaticity made the search for the orientation The numbers between parentheses represent the stanmatrix much easier after a variation of the temperature. dard deviations on the last decimal figure. The high temperatures were attained by blowing a hot The least-squares refinement was based on the following stream of commercial argon* directly on the crystal. A reflections: 1~4,2410, 256, 5516, 060, 6012, 3116, 1416. *
Air liquid U quality with a typical composition: 99.995% argon (in volume) 5 ppm 02, 5 ppm H20, 40 ppm N2.
control unit was used in order to monitor the temperature and control the proper gas flow. By using this gas blower on a thermocouple of about the same size as the
11203 AND (Ti0~98V0.0~O3 FROM SINGLE CRYSTAL X-RAY DATA
Vol. 20, No.9
895
~T~O3V
(3
100
200
300
‘.00
500
600
700
Temp.C
0
1(30
200
300
400
500
600
700
Temp.C
Fig. 1. Variation of a, c, c/a, and unit cell volume (hexagonal axes) vs flC) for 11203 and (Tio. 98V0.0~O3. sphere it was found that at 500°C, for instance, the ternperature was constant 3. within two degrees inside A calibration curve was adrawn volume of about 1 mm in order to obtain the temperature of the sample from that set on the control unit. Details of this high temperature attachment will be published elsewhere.’°The 0 angles of 11 reflections for the ‘11203 sample and of 8 for the V-doped one, were measured. The zero of the 0-circle was determined by measuring for each reflection the 0 and —0 values. The lattice parameters were obtamed by11the least-squares refinement program PARAM. Tables 1 and 2 give the lattice parameters a and c (hexagonal axes) for the pure Ti 203 crystal and for the V-doped one, respectively. Since the lattice parameters of Ti2O3 are very sensitive to the stoichiometry of the crystal which can vary easily with atemperature, accurate determination represents good test fortheir the inertness of the atmosphere around the crystal in our gas-blower set-up. The lattice parameters of pure Ti 2O3 were measured with increasing temperature in this sequential fashion: from room temperature to 520°C, back to room temperature, up to 670°Candup finally back to room temperature. The values obtained, corresponding to the same temperature, differed from each other within the standard deviations. This proved that no oxidation had taken place at high temperatures up to 670°C. It should be pointed out that our data are quite an improvement with respect to those published by Eckers and Bradt4 who stated that 300°Cappeared to be the
maximum temperature of stability for Ti2O3 in an atmosphere of ofthe commercial-purity helium. The lattice parameters V-doped Ti 203 crystal were determined with increasing temperature. At the end of the measurements the lattice parameters at room temperature were redetermined in order to check whether the stoichiometiy had remained the same. No change was detected. The stability of this crystal was determined up to 440°C. Figure 1 shows the variation of the lattice parameters, c/a ratio and unit cell volume as a function of temperature thethe pure Ti203crystal crystalthe andsemiconductor of the V-doped one.ofFor former to metal transition is clearly seen in the a and c parameter curves as well as in the c/a ratio one. At the transition one observes a sharp drop of the a parameter and sharp increases of the c parameter and of the c/a ratio.2~the This is in agreement with thein previous measurements, only difference being the precision of the data. We can estimate that our standard deviations are between 10 and 20 times better than the previous ones. No transition is observed in the unit cell volume. This3 iswho contrary to calculated what has been reported by Rao et al. that the transition is accompanied by a 7% drop in the unit cell volume. Actually, if one calculates the volume from the lattice parameters reported by these authors, the V vs T curve does not show any anomaly. It seems, therefore, that the drop is due to erroneous calculations. It can be seen from Fig. 1 that the V-doping attenuate the transition which is visible only in the a vs T curve. ‘I’his is in agreement with the data of reference 8 from
896
11203 AND (Tio.~Vo.o~OFROM 3 SINGLE CRYSTAL X-RAY DATA
Vol. 20, No.9
which it was concluded that the lattice distortion caused by the incorporation of cations was important at concentrations larger than 1%. REFERENCES 1.
MORIN F.J., Phys. Rev. Lett. 3, 34 (1959).
2.
PEARSON D.,J. Phys. Chem. Solids 5,316 (1958).
3. 4.
RAO C.N.R., LEOHMAN R.E. & HONIG J.M.,Phys. Lett. 27A, 271 (1968). ECKERS L.J. & BRADT R.C., J. Appl. Phys. 44,3470 (1973).
5.
BARROW H.L., CHANDRASHEKIIARG.V., CHI T.V., HONIG J.M. & SLADEK R.J.,Phys. Rev. B7, 5147 (1973); COEY J.M.D., ROUIX-BUISSON H., SCHLENKER C., LAKKIS S. & DUMAS J., [to be published in Revue Géndrale de Thermique (1976)].
6.
GOODENOUGH J.B., 1. Solid State Chem. 5, 145 (1972).
7.
CHANDRASHEKHARG.V.,WONCHOI Q.,MOYOJ. &HONIGJ.M.,Mat. Res. BulL 5, 999 (1970).
8.
DUMAS J. & SCHLENKER C., Colloque C.N.RS. sur les Transitions Metal—Non Metal, Autrans, (28 June— 1st July 1976)1. de Phys. (to be published). See also: DUMAS J., SCHLENKER C. & NATOLI RC., Solid State Commun. 16,493 (1975); DUMAS J., SCHLENKER C., THOLENCE J.L. & TOURNIER it, Solid State Commun. 17, 1215 (1975); Conf. on Magn. and Magn. Mat., Philadelphia (Dec. 1975), A.I.P. Proc. (to be published).
9.
The analysis was performed at the Larec Laboratory of the University of Grenoble.
10. 11.
ARGOUD R. & CAPPONI J.J. (to be published). STEWART J.M., X-ray 63 System (July 1971 version). TR-64-6, N56-398. Computer Science Center, Univ. of Maryland, College Park, MD, U.S.A.