X-ray and thermal investigations of LaFeTeO6 and LaCrTeO6 compounds

Article abstract of DOI:10.1016/j.jallcom.2005.09.044

LaFeTeO₆ and LaCrTeO₆ were prepared by the solid-state reaction of La₂O₃, M₂O₃ (M = Fe or Cr) and TeO₂ in 1:1:2 molar ratio. The compounds were characterised by X-ray and thermogravimetric techniques. Thermal and X-ray studies indicated that LaFeTeO₆ and LaCrTeO₆ vapourize incongruently according to the reactions:{A formula is presented}{A formula is presented}X-ray diffraction data of both the compounds have been indexed on the hexagonal system. Vapour pressures of TeO₂(g) over LaFeO₃(s) and LaCrO₃(s) were independently measured by employing the Knudsen effusion mass loss (KEML) technique. From the partial pressures of TeO₂(g) measured, the standard Gibbs free energy of formation of (Δ_fG°) LaFeTeO₆(s) and LaCrTeO₆(s) were obtained and could be represented by the following relations:{A formula is presented}.

Full text of DOI:10.1016/j.jallcom.2005.09.044

Journal of Alloys and Compounds 417 (2006) 300–303
X-ray and thermal investigations of LaFeTeO6 and
LaCrTeO6 compounds
Neeraj K. Guptaa, S.P. Roya, P.V. Joshib, G.A. Rama Raoa,∗
,
K. Krishnanc, K.D. Singh Mudherc
a Product Development Section, RC & I Group, Bhabha Atomic Research Centre, Mumbai 400085, India
b Radiopharmaceuticals Division, Bhabha Atomic Research Centre, Mumbai 400085, India
c Fuel Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India
Received 16 August 2005; received in revised form 24 September 2005; accepted 26 September 2005
Available online 18 November 2005
Abstract
LaFeTeO6 and LaCrTeO6 were prepared by the solid-state reaction of La2O3, M2O3 (M = Fe or Cr) and TeO2 in 1:1:2 molar ratio. The compounds
were characterised by X-ray and thermogravimetric techniques. Thermal and X-ray studies indicated that LaFeTeO6 and LaCrTeO6 vapourize
incongruently according to the reactions:
LaFeTeO6(s) → LaFeO3(s) + TeO2(g) + (1/2)O2(g)
LaCrTeO6(s) → LaCrO3(s) + TeO2(g) + (1/2)O2(g)
X-ray diffraction data of both the compounds have been indexed on the hexagonal system. Vapour pressures of TeO2(g) over LaFeO3(s) and
LaCrO3(s) were independently measured by employing the Knudsen effusion mass loss (KEML) technique. From the partial pressures of TeO2(g)
measured, the standard Gibbs free energy of formation of (ꢀfG◦) LaFeTeO6(s) and LaCrTeO6(s) were obtained and could be represented by the
following relations:
ꢀfG◦(LaFeTeO6(s)) 15 kJ/mol = −1902.0 + 0.5953T (1104–1205 K),
ꢀfG◦(LaCrTeO6(s)) 12 kJ/mol = −612.0 + 0.3488T (1106–1210 K)
© 2005 Elsevier B.V. All rights reserved.
Keywords: Knudsen effusion mass loss technique; LaFeTeO6; LaCrTeO6
1. Introduction
there is no such data available in the literature on quaternary
systems with lanthanum as one of the components though lan-
thanum is one of the prominent daughter products during fission.
In continuation of our earlier studies on the ternary systems of
tellurium bearing compounds [5–7], we report here, the X-ray,
thermal and Gibbs free energy of formation of the two new
phases LaFeTeO6 and LaCrTeO6.
Tellurium is one of the highly corrosive fission products that
can interact with clad components, fissile elements and other fis-
sion products of the oxide fuels within the reactor forming binary
and ternary oxides [1]. A number of uranates of strontium and
tellurium are reported in the literature [2,3]. Also, the prepara-
tion of tellurates with the general formula M3UO2(TeO3)4 and
M2U(TeO3)5 where M = Ba or Ca, was reported [4]. However,
2. Experimental
2.1. Preparation and characterisation of the compounds
∗
Corresponding author.
E-mail address: garrao@apsara.barc.ernet.in (G.A. Rama Rao).
LaFeTeO6 and LaCrTeO6 were prepared by heating a mixture of La2O3,
M2O3 (M = Fe or Cr) and TeO2 in 1:1:2 molar ratios in air at 1200 K. The
0925-8388/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2005.09.044

N.K. Gupta et al. / Journal of Alloys and Compounds 417 (2006) 300–303
301
Table 1
X-ray powder diffraction data on LaCrTeO6 indexed on hexagonal system with
products were removed intermittently, ground and reheated to obtain pure phases
ofthecompounds. Theformationofthecompoundswereconfirmedbyrecording
their X-ray diffraction patterns on a STOE X-ray diffractometer using graphite
monochromatised Cu K␣1 radiation (␭ = 0.15406 nm).
˚
˚
cell parameters a = 5.1578(7) A, c = 10.3722(15) A
˚
˚
h k l
d (observed) (A)
d (calculated) (A)
I/I0
0 0 2
1 0 0
1 0 2
1 1 0
1 1 2
1 0 4
2 0 2
1 1 4
1 0 6
2 1 2
3 0 0
3 0 3
2 0 6
0 0 8
2 2 0
2 1 6
3 1 2
1 1 8
2 2 4
4 0 2
1 0 10
3 1 6
3 2 2
3 0 8
4 1 0
5.1798
4.4593
3.3805
2.5767
2.3072
2.2399
2.0493
1.8278
1.6118
1.6050
1.4884
1.3669
1.3669
1.2966
1.2901
1.2076
1.2049
1.1584
1.1548
1.0915
1.0105
1.0071
1.0051
0.9778
0.9750
5.1861
4.4668
3.3845
2.5789
2.3092
2.2426
2.0513
1.8285
1.6112
1.6054
1.4889
1.3675
1.3670
1.2965
1.2895
1.2078
1.2050
1.1584
1.1546
1.0917
1.0103
1.0070
1.0053
0.9778
0.9747
6
2.2. TG measurements
6
100
30
4
The thermal stability of LaFeTeO6(s) and LaCrTeO6(s) were studied by
recording their TG patterns with a Cahn microbalance thermal analyser. The
experiments were carried out in air in boron nitride cups at the heating rate
of 10 K/min up to 1475 K. Both the compounds were found to be stable up to
1100 K beyond which the vapourization of the compounds is initiated. The final
products at the end of the reaction were identified by X-ray powder diffraction
method as LaFeO3 in the case of LaFeTeO6 and LaCrO3 with LaCrTeO6. Their
thermal decomposition in air could be represented as
4
19
32
9
17
8
5
5
2
6
6
8
4
6
2
2
3
3
LaFeTeO6(s) → LaFeO3(s) + TeO2(g) + (1/2)O2(g)
LaCrTeO6(s) → LaCrO3(s) + TeO2(g) + (1/2)O2(g)
(1)
(2)
2.3. Vapour pressure measurements
The mass loss measurements due to vapourization were carried out in a Cahn
vacuum microbalance by the Knudsen effusion mass loss (KEML) technique.
Boron nitride cell with an orifice diameter of ≈1.0 mm at the center of the lid
was used as the Knudsen cell. Detailed experimental set-up and the Clausing
factor calibration for the Knudsen cell have been described in our earlier studies
[8].
2
3
3. Results and discussion
our earlier studies on Ni3TeO6 compound in Ni–Te–O sys-
tem and Cr2TeO6 and Fe2TeO6 in Cr/Fe–Te–O systems [6,11].
The mathematical derivation for the rate of mass loss is given
below:
3.1. X-ray and thermal studies
The products formed by reacting La2O3, M2O3 (M = Fe or
Cr) and TeO2 in 1:1:2 molar ratio in air at 1200 K were char-
acterised by XRD. X-ray diffraction data of LaCrTeO6 in the
present study matched well with the data reported by Kaspar [9].
The X-ray powder diffraction data of LaFeTeO6 could also be
indexed on the hexagonal system as they are iso-structural. Their
unit cell parameters were refined by the least squares method
using the computer program LATPAR [10]. The indexed diffrac-
tion data of both the compounds are given in Tables 1 and 2.
dw/dt = dw1/dt + dw2/dt
(3)
Table 2
X-ray powder diffraction data on LaFeTeO6 indexed on hexagonal system with
˚
˚
cell parameters, a = 5.2017(4) A, c = 10.3393(12) A
˚
˚
h k l
d (observed) (A)
d (calculated) (A)
I/I0
0 0 2
1 0 0
1 0 1
1 0 2
1 1 0
1 1 2
1 0 4
2 0 2
1 1 4
2 1 2
3 0 0
2 0 6
3 0 4
3 1 2
2 1 6
2 2 4
4 0 2
3 2 2
3 1 6
4 1 0
3 0 8
5.1706
4.5019
4.1286
3.3950
2.5993
2.3225
2.2426
2.0641
1.8329
1.6170
1.5016
1.3682
1.2985
1.2146
1.2113
1.1618
1.1004
1.0134
1.0114
0.9831
0.9797
5.1697
4.5048
4.1298
3.3963
2.6008
2.3234
2.2420
2.0649
1.8334
1.6172
1.5016
1.3686
1.2984
1.2144
1.2112
1.1617
1.1004
1.0134
1.0115
0.9830
0.9796
5
3
4
100
34
6
3.2. Vapour pressure measurements
3.2.1. LaFeTeO6
The equilibrium vapour pressures of TeO2(g) and (1/2)O2(g)
were measured in the temperature range 1104 to 1205 K over
a mixture of LaFeTeO6(s) by employing the Knudsen effusion
mass loss (KEML) technique. The detailed experimental set-up
of KEML is similar to our earlier reported results in [6]. The
total mass loss due to TeO2(g) and (1/2)O2(g) was apportioned
in terms of their molar masses using their mole fraction for
reaction (1) and could be given as
3
23
39
22
12
5
8
8
10
6
3
dw/dt = dw1/dt + dw2/dt
(3)
4
5
3
4
where dw/dt is the experimentally measured combined rate of
mass loss of TeO2(g) and (1/2)O2(g), dw1/dt and dw2/dt are the
individual rate of mass loss of TeO2(g) and (1/2)O2(g), respec-
tively. Similar apportionation procedure has been followed in

302
N.K. Gupta et al. / Journal of Alloys and Compounds 417 (2006) 300–303
Table 3
Gibbs free energy of formation of LaFeTeO6 at different temperatures
Temperature
(K)
p(TeO2)
(Pa)
p◦(TeO2)
(Pa)
p(O2)
(Pa)
ꢀfG◦(LaFeTeO6)
(kJ/mol)
1104
1132
1136
1145
1150
1152
1165
1173
1175
1180
1205
0.4172
1.1080
1.2676
1.6575
2.0004
2.1888
3.2923
4.4824
4.6056
5.2440
11.4456
144.7319
257.8357
279.3570
333.8927
368.2218
382.8312
491.3923
571.4187
593.1937
650.9700
1024.1379
0.2043
0.5426
0.6224
0.8641
0.9849
1.0738
1.6165
2.2025
2.2640
2.5764
5.6311
−1244.78
−1228.12
−1255.74
−1220.38
−1217.41
−1203.71
−1208.48
−1203.71
−1202.52
−1199.55
−1184.66
ꢀ
dw2/dt = dw1/dt × 1/2 × 32/159.6
dw1/dt = (dw/dt)(0.819)
(4)
(5)
By substituting the value of dw1/dt in Eq. (4), we can calculate
dw2/dt. Thus by inserting the individual mass loss of dw1/dt
and dw2/dt in the rate mass loss equation (3)
ꢀ
p (Pa) = [(dw/dt)(1/kA) T/M]
(6)
where p is the partial pressures of the evolved gas, k the Clausing
factor, A the area of the orifice diameter, T the temperature and
M is the molecular weight of the evolved gaseous species, the
individual partial pressures contributed by TeO2(g) and O2(g)
were determined and are given in Table 3. The corresponding
least squares fit of log p(TeO2(g)) versus 1/T is shown in Fig. 1
and could be represented by the relation:
Fig. 1. Temperature dependence of the partial pressures of TeO2(g) over
LaFeTeO6(s) and LaFeO3(s).
corresponding least squares fit of log p(TeO2(g)) against 1/T for
LaCrTeO6 is shown in Fig. 2, which could be represented by the
relation:
log p (kPa) 0.01 = −43 742/T + 31.1694 (1104–1205 K)
(7)
log p (kPa) 0.01 = −42 994/T + 30.0024 (1106–1210 K)
(10)
The standard Gibbs free energy of formation of LaFeTeO6(s) is
represented by the relation:
By usingthevapourpressure dataof TeO2(g), thestandardGibbs
free energy formation data of LaCrTeO6(s) could be obtained
ꢀfG◦(LaFeTeO6(s))
= ꢀfG◦(LaFeO3(s)) + ꢀfG◦(TeO2(l)) + 0.5RT ln p(O2(g))
+ RT ln(p(TeO2)/p◦(TeO2))
(8)
Table 4
Gibbs free energy of formation of LaCrTeO6 at different temperatures
Where p◦(TeO2) is the partial pressure of TeO2(g) over TeO2(l)
and the vapour pressure data are taken from reported values [12].
By using the Gibbs free energy formation of TeO2(l) and that
of LaFeO3 from the literature data [1,13], the standard Gibbs
free energy formation of LaFeTeO6(s) could be obtained and is
represented by the relation:
Temperature
(K)
p(TeO2)
(Pa)
p◦(TeO2)
(Pa)
p(O2)
(Pa)
ꢀfG◦(LaCrTeO6)
(kJ/mol)
1106
1123
1127
1136
1138
1140
1148
1150
1158
1172
1185
1199
1209
1210
0.3411
0.5943
0.6971
0.8776
0.9578
0.9586
1.2945
1.3327
1.7168
2.8929
4.1820
6.6021
9.1828
9.3702
150.9726
214.8322
233.0640
279.3570
290.7207
302.5044
354.1220
368.2218
429.8830
560.8060
713.8136
920.1858
1099.2354
1118.7733
0.2043
0.2958
0.3471
0.4364
0.4762
0.6244
0.6436
0.6437
0.8545
1.4405
2.0823
3.2876
4.5676
4.6661
−226.23
−220.30
−218.90
−215.76
−215.06
−214.37
−211.58
−210.88
−208.09
−203.21
−198.67
−193.79
−190.30
−189.95
ꢀfG◦(LaFeTeO6(s)) 15 kJ/mol
= −1902.0 + 0.5953T (1104–1205 K)
(9)
3.2.2. LaCrTeO6
The equilibrium vapour pressures of TeO2(g) over LaCrO3(s)
were calculated at various temperatures (1106–1210 K) for the
reaction shown in Eq. (2) and the values are given in Table 4. The

N.K. Gupta et al. / Journal of Alloys and Compounds 417 (2006) 300–303
303
4. Conclusion
The data on the Gibbs free energy of formation of the com-
pounds LaFeTeO6 and LaCrTeO6 are being reported for the first
time in the La–M–Te–O system. Both the compounds have been
indexed on the hexagonal system and their lattice cell parameters
were refined.
From the TG studies, it was observed that both the com-
pounds vapourize incongruently with the loss of TeO2 and the
finalproductswereidentifiedasLaFeO3 inthecaseofLaFeTeO6
and LaCrO3 in the case of LaCrTeO6.
Acknowledgements
The authors are thankful to Shri B.K. Sen, Head, Product
Development Section and Dr. V. Venugopal, Director, Radio-
chemistry & Isotope Group for their keen interest in the
work.
References
[1] E.H.P. Cordfunke, R.J.M. Konings, J. Nucl. Mater. 152 (1988) 301.
[2] T. Yamashita, Report, JAERI 1310, 1988.
[3] P.J. Galy, G. Meunier, Acta Crystallogr. B 27 (1971) 608.
[4] J. Wroblewska, A. Erb, J. Dobrowolski, W. Freundilich, Ann. Chim.
France 4 (1979) 353.
[5] K. Krishnan, G.A. Rama Rao, K.D. Singh Mudher, V. Venugopal, J.
Nucl. Mater. 254 (1998) 49.
[6] K. Krishnan, G.A. Rama Rao, K.D. Singh Mudher, V. Venugopal, J.
Alloys Compd. 288 (1999) 96.
Fig. 2. Temperature dependence of partial pressures of TeO2(g) over
LaCrTeO6(s) and LaCrO3(s).
[7] K. Krishnan, G.A. Rama Rao, K.D. Singh Mudher, V. Venugopal, J.
Alloys Compd. 307 (2000) 114.
from the relation:
ꢀfG◦(LaCrTeO6(s))
[8] K. Krishnan, G.A. Rama Rao, K.D. Singh Mudher, V. Venugopal, J.
Nucl. Mater. 230 (1996) 61.
[9] H.M. Kaspar, Mater. Res. Bull. 4 (1969) 33.
[10] V.K. Wadhawan, LATPAR, Neutron Physics Division, BARC, Private
communication.
[11] K. Krishnan, G.A. Rama Rao, K.D. Singh Mudher, V. Venugopal, J.
Alloys Compd. 316 (2001) 264.
[12] M.S. Samant, S.R. Bhardwaj, A.S. Kerkar, S.N. Tripathi, S.R. Dharwad-
kar, J. Nucl. Mater. 211 (1994) 181.
= ꢀfG◦(LaCrO3(s)) + ꢀfG◦(TeO2(l)) + 0.5RT ln p(O2(g))
+ RT ln(p(TeO2)/p◦(TeO2))
(11)
Using the values of p◦(TeO2) from our earlier studies [12], the
Gibbs free energy formation data of TeO2(l) from the literature
[13] the Gibbs free energy formation of LaCrTeO6(s) was cal-
culated and the data are given in Table 4, which is represented
by the relation:
[13] E.H.P. Cordfunke, R.J.M. Konings (Eds.), Thermochemical Data for
Reactor Materials and Fission Products, North-Holland, Amsterdam,
1990.
ꢀfG◦(LaCrTeO6(s)) 12 kJ/mol
= −612.0 + 0.3488T (1106–1210 K)
(12)