Reactivity of binary mixtures of La(III) oxide and Cu(II) oxalate or nitrate and synthesis of La(III) cuprate

Article abstract of DOI:10.1023/A:1010195619121

Reactivity of mixtures of La(III) oxide and Cu(II) oxalate/nitrate in hydrated as well as anhydrous state was studied using TG, DTA and XRD. Cu(II) oxide formed in the endothermic decomposition of mixture containing hydrated Cu(II) nitrate and La(III) oxi

Full text of DOI:10.1023/A:1010195619121

Journal of Thermal Analysis and Calorimetry, Vol. 62 (2000) 285–294
REACTIVITY OF BINARY MIXTURES OF La(III)
OXIDE AND Cu(II) OXALATE OR NITRATE AND
SYNTHESIS OF La(III) CUPRATE
1
L. Bapat , G. N. Natu , J. Kher and M. Bhide
2
1
1
1
Department of Chemistry, N. Wadia College, Pune 411 001
Department of Chemistry, University of Pune, Pune 411 007, India
Received February 10, 1999; in revised form December 30, 1999)
2
(
Abstract
Reactivity of mixtures of La(III) oxide and Cu(II) oxalate/nitrate in hydrated as well as anhydrous
state was studied using TG, DTA and XRD.
Cu(II) oxide formed in the endothermic decomposition of mixture containing hydrated Cu(II)
nitrate and La(III) oxide could not form La
composition of mixture containing hydrated/anhydrous Cu(II) oxalate and La(III) oxide reacts with
La(III) oxide and develops the phases CuLaO and La CuO
2 4
CuO while Cu(II) oxide formed in the exothermic de-
3
2
4
.
2 4
The maximum reactivity with respect to the formation of La CuO phase was observed in mix-
ture containing anhydrous Cu(II) oxalate.
Keywords: reactivity of La
CuC O or Cu(NO )
2 3 2 4 2 3
O , synthesis of La CuO , thermal decomposition of La O and
2
4
3 2
Introduction
La(III) cuprate containing excess oxygen [1, 2] or alkaline earth metal ions substi-
tuted at sites of La(III) ions [3–5] exhibits superconductivity at temperatures below
3
8 K. The superconducting ceramics are synthesized adopting different thermal pro-
cedures, (i) by firing and sintering corresponding oxides [6, 7] and (ii) by decompos-
ing the mixtures of hydroxides, nitrates, carbonates, formates, citrates or oxalates of
the corresponding cations, in appropriate proportions and sintering the oxide prod-
ucts at ~1273 K [1, 8, 9]. In these processes, attempts have been made to make a mix-
ture of oxides in situ so that at lower sintering temperature the required compound
can be formed in the single phase.
In the present work the synthesis of La(III) cuprate (La CuO phase) is at-
2
4
tempted by decomposing mixtures of La(III) oxide and Cu(II) oxalate/nitrate in hy-
drated as well as anhydrous state, at various temperatures in air and under reduced
pressure. As Cu(II) nitrate/oxalate decomposes to Cu(II) oxide around 823 K [10–15]
a homogeneous mixture of La(III) oxide and Cu(II) oxide will be formed and it is ex-
1
418–2874/2000/ $ 5.00
2000 Akadémiai Kiadó, Budapest
Akadémiai Kiadó, Budapest
©
Kluwer Academic Publishers, Dordrecht

2
86
BAPAT et al.: REACTIVITY OF BINARY MIXTURES
pected that there will be reaction between two oxides to form La CuO phase at tem-
perature below 1273 K.
2
4
Experimental
Pure crystalline monohydrate Cu(II) oxalate was prepared by mixing aqueous solutions
of Cu(II) nitrate (Analar) and sodium oxalate (BDH). The following mixtures in 1:1 mo-
lar proportion were prepared by mechanical mixing of the appropriate quantities of dried
La(III) oxide (E-Merck) with: (A) hexahydrate Cu(II) nitrate, (B) monohydrate Cu(II)
oxalate and (C) anhydrous Cu(II) oxalate (prepared by degassing under vacuum at
4
23 K).
As hexahydrate Cu(II) nitrate decomposes to basic Cu(II) nitrate Cu(NO ) ·
3
2
2Cu(OH) [10–13] during dehydration process it was not possible to prepare a mix-
ture of pure anhydrous Cu(II) nitrate and La(III) oxide.
2
TG and DTA
TG and DTA traces of mixtures A and B were recorded in dry air at the heating rate
1
–
0 K min in the temperature range of 298 to 1273 K on MOM Derivatograph OD
1
type 102, using 200 mg mixture, α-Al O as a reference material and platinum cruci-
bles. Results are shown in Figs 1 and 3 and tabulated in Table 1.
2
3
–
1
Mixtures were heated at the rate 10 K min upto 673, 823, 923, 1023, 1173 or
223 K for 1 h (designated as 6Ht, 8Ht, 9Ht, 10Ht, 11Ht or 12Ht respectively) either in
1
–3
dry air or under reduced pressure (1.0⋅10 torr), rapidly cooled to room temperature and
their X-ray powder diffraction (XRD) patterns were recorded on Rigaku PR-511 using
Fig. 1 TG-DTA traces of the mixture A
J. Therm. Anal. Cal., 62, 2000

BAPAT et al.: REACTIVITY OF BINARY MIXTURES
287
Fig. 2 XRD pattern of the sample A-12Ht
Fig. 3 TG-DTA traces of the mixture B
CuK radiation which are shown in Figs 2 and 4–7. Sample A-6Ht and A-V-6Ht repre-
sent mixture A heated at 673 K for 1 h, in air and under reduced pressure respectively.
α
Results and discussion
TG and DTA traces of mixture A (Fig. 1 and Table 1) reveal the following reactions
(
Table 2) [10–15, 19]:
i) decomposition of hexahydrate Cu(II) nitrate to trihydrate and water (reaction
1)) and subsequent reaction of water with La(III) oxide (reaction (2)), resulting in the
(
(
formation of La(III) hydroxide, (ii) decomposition of trihydrate to anhydrous Cu(II)
nitrate and its further decomposition to Cu(II) oxide, oxygen and NO gases (reac-
2
tions (3) and (5)) and (iii) decomposition of La(III) hydroxide to La(III) oxide (reac-
tions (4) and (7)).
Around 853 K mixture A decomposes to oxides of Cu(II) and La(III). Except the
exothermic (exo-) reaction (2) all the rest of reactions are endothermic (endo-). As La(III)
J. Therm. Anal. Cal., 62, 2000

Table 1 Thermal analysis data of decomposition of binary mixtures of (A) Cu(NO
3
)
2
·6H
2
O+La
2
O
3
and (B) CuC
2
O
4
·H
2
O+La
2
O
3
TG
DTA
Composition of
mixture
*
Mass loss/%
obs. theor
Reactions
correlated
*
*
***
Tstep/K
mol
Composition
Anhydrous
Peakendo/K
Peakexo/K
~313
Cu(NO
La
3 2
)2·6H O+ Step-I
1
0.2
3.3
8.7
–3H
2
O
Cu(NO
La(OH)
3
)
2
,
~363
~453
(1), (2), (3)
2
O
3
298–533
Step-II
2
3
–H
–2HNO
2
O
2LaO(OH),
CuO
~573
~643
(4)
(5)
(6)
2
23.22
5
33–793
3
~
663
Step-III
93–1003
La
CuO
2
O
3
,
~753
broad
~823
broad
(7)
(7)
5
.11
5.8
2
–2H O
7
Total loss
38.61
37.72

Table 1 Continued
TG
DTA
Composition of
mixture
*
Mass loss/%
obs. theor.
Reactions
correlated
**
mol
***
Tstep/K
Composition
Anhydrous
Peakendo/K Peakexo/K
CuC
La
:1
2
O
4
·H
2
O
CuC
0.75La
0.5La(OH)
CuO
2 4
O ,
Step-I
03–533
+
2
O
3
1.22
0.91
–0.25H
2
O
2
O
3
,
~313
(8), (2)
3
1
3
0
.75La
2
O
2
CO
3
,
Step-II
33–593
–1.25CO
+0.5O
2
(10)
(9)
8
.58
7.88
5.35
0.5La(OH)
CuO
3
~568
5
2
Step-III
93–683
–0.5CO
2
–0.25H O
2
6
.1
0.25La
.75La
2
2
(OH)
O
3
4
CO
3
,
~673
803
~848
~883
(4), (11),
(12)
5
0
~
Step-IV
and
Step-V
–
–
0.25CO
0.5H
2
La O ,
2
CuO
3
4.9
4.04
(12), (13)
2
O
~
1043
7
8
93–893
93–1093
CuLaO
[20]
3
~
1143
Total loss
20.80
18.18
*
*
*
Mole proportion 1:1
Loss (–) and uptake (+) of species, mol
**
Composition at step end
*

Table 2 Reactions involved in the thermal decomposition of mixtures A, B and C
Reactions
References
[10]
Cu(NO
La +3H
Cu(NO ·3H
La(OH)
3
)
2
·6H
2
2
O
O
endothermic
exothermic
endothermic
endothermic
endothermic
Cu(NO
2La(OH)
Cu(NO
LaO(OH)+H
2CuO+4NO
4HNO
La +H
CuC +H
2CuO+4CO
3
)
2
·3H
2
O+3H
2
O
(1)
(2)
2
O
3
2
O
3
[19]
3
)
2
3
)
2
+3H
2
O
(3)
[12, 13]
[19]
3
2
O
(4)
2
4
2
Cu(NO
NO +O
LaO(OH)
3
)
2
2
+O
2
(5)
[11, 12]
2
2
+2H
2
O
3
(6)
endothermic
endothermic
exothermic
exothermic
2
O
3
2
O
(7)
[19]
CuC
CuC
La
La(OH)
2
O
4
H
2
O
2
O
4
2
O
(8)
2
2
O
4
+O
+CO
+LaO(OH)+CO
2
2
(9)
[14, 15]
[20]
2
O
3
2
La
2
La
2
La
2
La
2
La
2
O
2
CO
(OH) CO
+CO
CO +2H
3
(10)
(11)
(12)
(13)
(14)
3
2
4
3
[19]
La
La
2
2
O
2
CO
3
endothermic
endothermic
endothermic
O
O
3
2
2
[19]
(OH)
4
CO
3
3
2
O
[19]
CuO+La
2
O
3
CuO
4
[1, 23]

BAPAT et al.: REACTIVITY OF BINARY MIXTURES
291
lines of predominant phase of CuO. Therefore, oxides of Cu(II) and La(III) do not react.
The thermal analysis of mixture B (Fig. 3 and Table 1) reveals the following re-
actions (Table 2):
(
i) dehydration of Cu(II) oxalate (reaction (8)) and reaction of evolved water
with 0.25 moles of La(III) oxide to produce 0.5 moles of La(III) hydroxide (reaction
2)), (ii) at 568 K exothermic decomposition of Cu(II) oxalate to Cu(II) oxide and
CO gas (reaction (9)) and carbonation of the remaining 0.75 moles of La(III) oxide
(
2
(
reaction (10)) [17] to form 0.75 moles of La O CO phase, (iii) at ~673 K decompo-
2 2 3
sition of La(III) oxycarbonate to La(III) oxide (reaction (12)) and carbonation of
La(III) hydroxide to yield La (OH) CO compound (reactions (4) and (11)), (iv) at
2
4
3
1093 K complete decomposition of La (OH) CO in reactions (13) and (12) to La(III)
2 4 3
oxide and (v) around 1143 K reaction between oxides of Cu(II) and La(III) to develop
the phase CuLaO [21].
3
Fig. 4 XRD patterns of samples a – B-6Ht and b – B-11Ht
XRD pattern of B-6Ht sample (Fig. 4a) shows lines of CuO, Cu O, La O CO
and La(OH) phases while that of B-11Ht sample (Fig. 4b) reveals lines of CuLaO
2
2
2
3
3
3
phase along with phases of unreacted oxides and lines of CuLaO phase [22] with
weak intensities.
2
It is found that although CuO phase appears at ~568 K (reaction (9)) La(III) oxide is
not available free to react with it as during carbonation the phase of La(III) oxide is com-
pletely used up (reaction (10)) (Fig. 4a). On further heating at 1143 K both the oxides
partially react to develop the phase CuLaO (Fig. 4b) and probably the phase La CuO
3
2
4
will be developed at temperature greater than 1273 K. It appears that the presence of de-
composition products CO gas and water vapours (reactions (4), (8), (9), (12) and (13)) in
between the surfaces of both the oxide particles, hinders the formation of La CuO phase
2
2
4
(reaction (14)). If it is assumed that CO gas and water vapours are expelled out during
heating of mixture B under reduced pressure (1.0×10 torr) there will be predominant
2
–3
phase formation of La CuO . On the contrary XRD patterns of B-V-6Ht and B-V-11Ht
samples (Fig. 5a and b) show lines of La(OH) , La O CO and CuO phases and those of
weak intensities of La CuO [1, 23].
2
4
3
2
2
3
2
4
J. Therm. Anal. Cal., 62, 2000

2
92
BAPAT et al.: REACTIVITY OF BINARY MIXTURES
Fig. 5 XRD patterns of samples a – B-V-6Ht and b – B-V-11Ht
Fig. 6 XRD patterns of samples a – C-8Ht, b – C-9Ht and c – C-10Ht
As the XRD pattern of C-8Ht sample (Fig. 6a) shows lines of La O CO , CuO
and CuLaO phases it appears that there is carbonation of La(III) oxide with CO gas
2
2
3
2
2
evolved in the decomposition of anhydrous Cu(II) oxalate (reaction (9)) and hence at
823 K no reaction of Cu(II) oxide with La(III) oxide is observed. On further heating
~
oxycarbonate will decompose to La(III) oxide (reaction (12)) which will react with
Cu(II) oxide and develop the phase La CuO and indeed XRD pattern of C-9Ht sam-
ple (Fig. 6b) shows lines of well developed phase of La CuO and other compounds
2
4
2
4
viz. Cu O [14, 15] and La O while pattern of C-10Ht exhibits lines of single phase of
La CuO (Fig. 6c). It is observed that the temperature at which La CuO phase forms
2
2
3
2
4
2
4
in the previous sintering processes [6, 7] is shifted by 250 K towards lower tempera-
ture side in the case of mixture C, i.e. from 1273 to 1023 K.
In order to avoid carbonation, the mixture C was heated under reduced pressure
–
3
(
1.0×10 torr) and it was expected that the phase La CuO will form at ~823 K. On
2 4
J. Therm. Anal. Cal., 62, 2000

BAPAT et al.: REACTIVITY OF BINARY MIXTURES
293
Fig. 7 XRD patterns of samples a – C-V-10Ht and b – C-V-12Ht
the contrary the XRD pattern of C-V-10Ht sample (Fig. 7a) shows lines of predomi-
nant phase La O CO . Therefore, it can be visualized that the carbonation occurs im-
mediately after decomposition of Cu(II) oxalate to form La O CO phase which is not
2
2
3
2
2
3
decomposing upto ~1023 K. As the XRD pattern of C-V-12Ht sample (Fig. 7b)
shows lines of La CuO , CuLaO and Cu phases the thermal treatment of mixture C
under reduced pressure is not useful to obtain single phase of La CuO .
2
4
3
2
4
It was found that while cooling unreacted La(III) oxide reacts with residual
moisture and CO gas present in the reaction cell in all mixtures and forms La(III) hy-
2
droxide and La(III) oxycarbonate [19, 20] in trace amounts as seen in Figs 2, 4b, 5b,
6
c and 7b.
Considering all the results shown in Figs 1–7 and tabulated in Table 1 it can be
concluded that the mixture of anhydrous Cu(II) oxalate and dried La(II) oxide shows
highest reactivity with respect to the formation of La CuO phase.
2
4
*
* *
Authors are deeply thankful to the authorities of Department of Atomic Energy (DAE), Government
of India, for providing the funds for research project and to Professor A. V. Phadke, Department of
Geology, University of Pune, for valuable discussion.
References
1
C. N. R. Rao and J. Gopalakrishnan, ‘New directions in solid state chemistry’, Chapter 9, Cam-
bridge Solid State Science Series, Cambridge University Press, Cambridge, New York 1989,
pp. 476, 488, 489.
2
3
4
5
6
K. Sekizwa, Y. Takano, H. Takigami, S. Tasaki and T. Inaba, Jpn. J. Appl. Phys., 26 (1987) L840.
C. Politis, J. Geerk, M. Dietrich and B. Obst, Z. Phys. B-Condensed Matter, 64 (1986) 189.
R. J. Cava, R. B. Van Dover, B. Batlogg and E. A. Rietman, Phys. Rev. Lett., 58 (1987) 408.
H. Takagi, S. Uchida, K. Kitazawa and S. Tanaka, Jpn. J. App. Phys., 26 (1987) L123.
T. Arakwa, G. Adachi and J. Shiokawa, Nippon Kagaku Kaishi, 10 (1980) 1573.
J. Therm. Anal. Cal., 62, 2000

2
94
BAPAT et al.: REACTIVITY OF BINARY MIXTURES
7
8
9
J. C. Park, P. V. Huong, M. Rey-Lafon, J. C. Grenier, A. Wattiaux and M. Pouchard, Physica
C, 177 (1991) 487.
T. V. Ramakrishnan and C. N. R. Rao, ‘Superconductivity today’, Chapter 3, Wiley Eastern
Ltd., New Delhi 1992, pp. 47, 48.
V. F. Savchenko and Ya. S. Rubinchik, Izu. Akad. Nauk SSSR, Neorg. Mater., 13 (1977) 2038.
1
1
1
1
1
1
1
1
0 T. J. Taylor, D. Dollimore and G. A. Gamlen, Thermochim. Acta., 103 (1986) 333, 334 and 340.
1 S. Peltier and C. Duval, Compt. Rend., 226 (1948) 1727.
2 E. D. Pierron, J. A. Rashkin and J. F. Roth, J. Catal., 9 (1967) 38.
3 S. Gordon and C. Campbell, Anal. Chem., 27 (1955) 1102.
4 D. Broadbent, J. Dollimore, T. A. Evans and D. Dollimore, JCS Faraday Trans., 87 (1991) 161.
5 A. Coetzee, D. J. Eve and M. E. Brown, J. Thermal Anal., 39 (1993) pp. 953.
6 S. A. A. Mansour, J. Thermal Anal., 46 (1996) 263.
7 B. R. Carson, G. Kenessey, J. R. Allan and G. Liptay, J. Thermal Anal., 45 (1995) 369 and 46
(1996) 1577.
1
1
8 M. A. A. Elmasry, A. Gaber and E. M. H. Khater, J. Thermal Anal., 47 (1996) 757.
9 S. Bernal, F. J. Botana, R. Garcia and J. M. Rodriguez-Izquierdo, Thermochim. Acta, 66
(1983) 142, 143, 145.
2
0 O. A. Songina, ‘Rare Metals (Redkie Metally)’ Chapter 6, 3rd Ed. Israel Program for Scientific
Translations Ltd. Jerusalem, 1970 translated (to English) by J. Schmorak, Keter Press, Jerusa-
lem. 1970, p. 180.
2
2
2
2
2
2
1 A. Dwivedi, M. A. Rodriguez and A. N. Cormack, J. Am. Ceram. Soc., 75 (1993) 1993.
2 H. Haas and E. Kordes, Z. Kristallogr., 129 (1969) 259.
3 L. Lehvede and M. Daire, C. R. Acad. Sci. Ser. C, 276 (1973) 1011.
4 R. G. Rupard and P. K. Gallagher, Thermochim. Acta, 272 (1996) 11.
5 A. M. Mansour Donia and D. Dollimore, Thermochim. Acta, 290 (1997) 139.
6 A. M. Donia, Polyhedron, 16 (1999) 3013.
J. Therm. Anal. Cal., 62, 2000