Novel hydroxide precursors for low temperature synthesis of selected ternary oxides

Article abstract of DOI:10.1016/j.materresbull.2007.07.006

A novel method of using hydroxide precursors to reduce the synthesis temperature for few selected ternary oxides has been presented here. This technique is very useful and advantageous when the ternary oxides contain an alkaline earth element. The selected compositions for this method are BaCeO₃ (BC), BaBiO₃ (BB), La_0.7Sr_0.3CoO₃ (LSCO) and BaBi₂Nb₂O₉ (BBN). Commercially purchased strontium (or barium) hydroxide and freshly prepared lanthanum, cobalt, bismuth and niobium hydroxides were mixed thoroughly in stoichiometric ratio and heated at different temperatures ranging from 100 to 700 °C for 10 h for corresponding compositions. The sequence of the reaction and evolution of the product phase were studied by the X-ray diffraction (XRD) studies. The phase purity and lattice parameters were also determined by XRD investigations. All the product phases in each case were formed at relatively low temperature than when they were prepared by co-precipitation or solid state method. The morphology and average particle size of these powders were investigated by scanning electron microscopy (SEM).

Full text of DOI:10.1016/j.materresbull.2007.07.006

Materials Research Bulletin 43 (2008) 1842–1849
www.elsevier.com/locate/matresbu
Novel hydroxide precursors for low temperature synthesis of
selected ternary oxides
H. Muthurajan a, N. Koteswara Rao b, U.N. Gupta b, Sivaram Pradhan b,
R.K. Jha b, H.H. Kumar a, S.A. Mirji c, V. Ravi c,
*
a Armament Research & Development Establishment, Pune 411021, India
b Catalysis Division, National Chemical Laboratory, Pune 411008, India
c Physical and Materials Chemistry Division, National Chemical Laboratory, Pune 411008, India
Received 13 May 2007; received in revised form 25 June 2007; accepted 3 July 2007
Available online 10 July 2007
Abstract
A novel method of using hydroxide precursors to reduce the synthesis temperature for few selected ternary oxides has been
presented here. This technique is very useful and advantageous when the ternary oxides contain an alkaline earth element. The
selected compositions for this method are BaCeO3 (BC), BaBiO3 (BB), La0.7Sr0.3CoO3 (LSCO) and BaBi2Nb2O9 (BBN).
Commercially purchased strontium (or barium) hydroxide and freshly prepared lanthanum, cobalt, bismuth and niobium
hydroxides were mixed thoroughly in stoichiometric ratio and heated at different temperatures ranging from 100 to 700 8C
for 10 h for corresponding compositions. The sequence of the reaction and evolution of the product phase were studied by the X-ray
diffraction (XRD) studies. The phase purity and lattice parameters were also determined by XRD investigations. All the product
phases in each case were formed at relatively low temperature than when they were prepared by co-precipitation or solid state
method. The morphology and average particle size of these powders were investigated by scanning electron microscopy (SEM).
# 2007 Elsevier Ltd. All rights reserved.
Keywords: A. Ceramics; A. Oxides; B. Chemical synthesis; C. X-ray diffraction; C. Electron microscopy
1. Introduction
The ABO3-type, BaBiO3 attracts special attention because it shows a metal–semiconductor transition and
superconductivity in the metallic phase [1–11]. Pure BaBiO3 also has potential application as a positive temperature
coefficient (PTC) thermistor, whereas doped BaBiO3 compounds show a negative temperature coefficient (NTC)
effect over a wide temperature range and have prospective applications in electronics for the suppression of in-rush
current, for temperature measurement and control, and for compensation for other circuit elements. Li-substituted
BaBiO3 acts as a catalyst action for the partial oxidation of methane. The compound, BaCeO3 has been reported to
have high ionic conductivity between 600 and 800 8C and considered as one of the best candidates to replace the YSZ
electrolyte materials for solid oxide fuel cell (SOFC).
Perovskite type oxides comprised of a rare earth ion and d-transition metal ion such as LaFeO3, LaMnO3 and
LaCoO3 are being increasingly applied as electronic and magnetic materials. A considerable attention has been
* Corresponding author. Tel.: +91 20 25902539.
E-mail address: r.venkat@ncl.res.in (V. Ravi).
0025-5408/$ – see front matter # 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.materresbull.2007.07.006

H. Muthurajan et al. / Materials Research Bulletin 43 (2008) 1842–1849
1843
focused on the La0.7Sr0.3CoO3 (LSCO) due to its excellent properties such as high electronic conductivity, magnetic
susceptibility, large negative magnetoresistance, magnetohydrodynamic (MHD) generators, catalytic activity, cathode
material with maximum electrochemical activity, extremely fast response thermocouple applications and low
resistivity [12–27]. The low resistivity of these materials can be exploited for use as electrodes in several situations and
the good catalytic activity for oxygen reduction in SOFCs for potential electric power generation because of the
simplicity of system design in SOFC.
Recently, bismuth-based compounds with the Aurivillius type structure have attracted much attention because of
their low operating voltage, fast switching speed, negligible fatigue after up to 1012 switching cycles, excellent
retention characteristics and low leakage current density on Pt electrodes for integrated device applications in
nonvolatile ferroelectric random access memories (FRAM) [28–32]. The Aurivillius family of compounds is
represented by a formula (Bi2O2 (AnBnÀ1O3n+1) where A (=Sr, Ba, Ca) is a larger cation in 12-fold coordination and B
(=Nb, Ta) a small cation in 6-fold environment.
Both traditional solid state and wet-chemical methods (co-precipitation and sol–gel) are used for the preparation of
these compounds. In all these techniques, the temperature for the formation of product is >700 8C. The solid state
method requires high temperatures. And this leads to poor compositional homogeneity and high sintering temperature.
The co-precipitation method also yields these powders only above 800 8C due to the fact that alkaline earth metal (Ba,
Sr, Ca) carbonate or oxalate will decompose only at higher temperatures (T > 800 8C) and hence this method also does
not produce this compound at low temperatures. Here we communicate a simple procedure to prepare all the above
compounds at relatively low temperature. This method is not reported in the literature. This technique has been already
used for the preparation of LiNbO3, KNbO3 and NaNbO3 and reported by us [33,34]. The method is easily amenable
for large-scale production and relatively economical.
2. Experimental
All the reagents used in this work were of AR grade (Loba cheme, India). To prepare BaCeO3 and BaBiO3, reagent
grade barium hydroxide (Ba(OH)2Á8H2O), cerium nitrate (Ce(NO)3Á6H2O), bismuth nitrate and sodium hydroxide
were used as the starting materials. Fresh cerium hydroxide and bismuth hydroxide were prepared under basic
conditions by adding an excess amount of sodium hydroxide to cerous (or bismuth) nitrate solution. The hydrated
individual hydroxide precipitates was filtered, washed free of anions by distilled water and oven dried overnight at
100 8C. Required quantity of Ce(OH)2 or Bi(OH)3 and Ba(OH)2 were mixed thoroughly and heated at different
temperatures ranging from 100 to 700 8C for 10 h.
To prepare La0.65Sr0.35CoO3, lanthanum oxide (La2O3), strontium hydroxide (Sr(OH)2Á8H2O), cobalt nitrate
(Co(NO3)2Á4H2O) and sodium hydroxide (NaOH) were used as starting materials. The required quantity of La2O3 was
dissolved in minimum amount of hydrochloric acid and aqueous sodium hydroxide is added to it dropwise to
precipitate lanthanum as hydroxide. Similarly, cobalt was precipitated as hydroxide under basic conditions. The
addition of NaOH was continued until pH ꢀ 11 to ensure completion of the precipitation. Then all the hydroxides were
mixed thoroughly in stoichiometric ratio in an agate and mortar for more than 1 h with the aid of acetone and heated at
different temperatures ranging from 100 to 700 8C for 10 h.
To prepare BaBi2Nb2O9, niobium(V) oxide, bismuth(III) nitrate, barium hydroxide and sodium hydroxide were
used as starting materials. First, commercial Nb2O5 was dissolved in minimum amount of HF after heating on a hot
water bath maintained around 90 8C for 10 h. Then niobium hydroxide was produced by the addition of aqueous
sodium hydroxide to the niobium fluoride solution. Bismuth hydroxide was precipitated by adding excess aqueous
NaOH to 0.1 M solution of bismuth nitrate solution under basic conditions. Then commercial barium hydroxide
(should be cautiously handled because of carbonate formation), freshly prepared dry bismuth and niobium hydroxides
were mixed thoroughly in stoichiometric ratio and heated at 450 8C for 10 h.
The sequence of the reaction and evolution of the product phase as a function of calcination temperature were
monitored by the X-ray diffraction (XRD) investigations. The phase purity and lattice parameters were also
determined by the X-ray diffraction studies. For lattice parameter and interplanar distance (d) calculation, the
samples were scanned in the 2u range of 10–808 in the step scan mode. Silicon was used as an internal standard. A
least squares method was employed to determine the lattice parameters. The scanning electron microscope (SEM)
images were observed using a Leica Cambridge 440 microscope. All the powders were dispersed in amyl acetate for
SEM studies.

1844
H. Muthurajan et al. / Materials Research Bulletin 43 (2008) 1842–1849
3. Results and discussion
Fig. 1 shows the XRD pattern of BaCeO3 precursor powder heated at different temperatures ranging from 100 to
350 8C. It is observed that at temperatures ꢀ100 8C, the product phase was formed but with some intermediate phases.
These peaks were authentically not indexed to any known compound but few peaks were for barium carbonate. All the
extra peaks were vanished when these powders were calcined at 350 8C. This is the lowest temperature reported so far
for the formation of BaCeO3 in the literature. The conventional method forms this phase only at T > 900 8C. The
BaCeO3 is orthorhombic and all the d-lines pattern match with reported values (JCPDS: 22-0074). The calculated
˚
˚
˚
˚
lattice parameters by least squares fit are a = 8.779 A, b = 6.214 A and c = 6.236 A (SD 0.003 A). When the sample
was heated at 500 8C, no change in the XRD (not shown) was found indicating stability of the compound. Fig. 2 shows
the XRD patterns of BaBiO3 precursor powder heated at different temperatures. It is observed that at temperatures
Fig. 1. The XRD of BaCeO3 precursor heated at (a) 100 8C, (b) 300 8C and (c) 350 8C.
Fig. 2. The XRD of BaBiO3 precursor powders heated at (a) 100 8C, (b) 200 8C and (c) 300 8C. The symbol ‘B1’ indicate Bi2O3 and
‘B2’ = Ba(OH)2Á8H2O.

H. Muthurajan et al. / Materials Research Bulletin 43 (2008) 1842–1849
1845
Fig. 3. The XRD of BaBiO3 precursor powders heated at (a) 400 8C and (b) 550 8C.
<400 8C, bismuth oxide (JCPDS; 273-50) (marked ‘B1’) and barium hydroxide (JCPDS: 26-0155) (marked ‘B2’)
peaks are seen in XRDs. However, at the calcination temperature ꢀ550 8C, the product phase was found to be formed
(Fig. 3). This is the lowest temperature reported so far for the formation of BaBiO3 in the literature. The crystal
structure of BaBiO3 is monoclinic and all the d-lines pattern match with reported values (JCPDS: 35-1020). The
˚
˚
˚
calculated lattice parameters by least squares fit are a = 6.182 A, b = 6.136 A, c = 8.669 A and b = 908 17 (SD
˚
0.003 A). When the sample was heated at 700 8C, no change in the XRD (not shown) was found indicating stability of
the compound.
Fig. 4 shows the XRD pattern recorded for the LSCO samples heated at different temperatures ranging from 200 to
400 8C for 10 h. At 400 8C, in addition to lanthanum oxide (JCPDS: 43-1003) and cobalt oxide peaks (JCPDS: 42-
1467), there are few more strong lines, which could not be indexed authentically and they may correspond to
intermediate phases formed during calcination. At 500 8C, XRD shows (Fig. 5) the d-lines pattern similar to that
Fig. 4. The XRD of La0.65Sr0.35CoO3 precursor powders heated at (a) 200 8C, (b) 300 8C and (c) 400 8C for 10 h. The symbol ‘L’ indicates La2O3,
C = Co3O4.

1846
H. Muthurajan et al. / Materials Research Bulletin 43 (2008) 1842–1849
Fig. 5. The XRD of La0.65Sr0.35CoO3 at 500 8C.
reported to LSCO (JCPDS Card No. 46-0704). This is the lowest temperature reported so far for the formation of
LSCO. All other wet chemical method requires temperature above 800 8C for the orthorhombic phase LSCO. The
˚
˚
˚
˚
calculated lattice parameters by least squares method are a = 7.73 A, b = 10.87 A and c = 11.58 A (SD 0.003 A). The
traditional solid state method forms LSCO only at 900 8C with some minor secondary phases. Fig. 6 shows the XRD of
BBN hydroxides precursor mixture heated at 450 8C. The formation of BBN phase is confirmed by X-ray diffraction
studies (Fig. 6) (JCPDS: 86-1191). This is the lowest temperature reported so far for the preparation of these
compounds. It is very advantageous to use this technique to prepare single phase compound in large scale without the
involvement of carbonates.
The average particle size and morphology of the calcined powders were examined by scanning electron
microscopy. Particle morphology of these calcined powders prepared by this technique were irregular in shape and
agglomerated, with an average primary particle size around 50 nm (Figs. 7–10). The particle size (calculated from
Scherrer’s formula (t = Kl/B cosuB), where t is the average size of the particles, assuming particles are spherical,
Fig. 6. The XRD of BBN powders heated at 450 8C.

H. Muthurajan et al. / Materials Research Bulletin 43 (2008) 1842–1849
1847
Fig. 7. The SEM micrograph of BaCeO3 powders.
Fig. 8. The SEM micrograph of BaBiO3 powders.
Fig. 9. The SEM micrograph La0.65Sr0.35MnO3 powders.

1848
H. Muthurajan et al. / Materials Research Bulletin 43 (2008) 1842–1849
Fig. 10. The SEM micrograph of BBN powders.
K = 0.9, l is the wavelength of X-ray radiation, B is the full width at half maximum of the diffracted peak and uB is the
angle of diffraction) were in the range of 40–60 nm for these powders.
4. Conclusions
A simple two-step process is described for the preparation of ultrafine powders of ternary oxides which have
alkaline earth element in their compositions. This process produces the final product relatively at low temperatures as
compared to all other methods. The sequence of reaction was monitored by gradually heating samples over a
temperature range and analyzing the XRD pattern at every stage. The average particle size and morphology of these
powders were investigated by SEM.
References
[1] F. Abbattista, M. Vallino, A. Delmastro, D. Mazza, S. Ronchetti, J. Solid State Chem. 117 (1995) 55.
[2] C. Chaillout, J.P. Remeika, A. Santoro, M. Marezio, Solid State Commun. 56 (1985) 829.
[3] F. Munakata, A. Nozaki, T. Kawano, H. Yamauchi, Solid State Commun. 83 (1992) 355.
[4] H.L. Lin, R.K. Chiang, C.L. Kuo, C.W. Chang, J. Non-Cryst. Solids 353 (2007) 1188.
[5] A.V. Kuzmin, V.P. Gorelov, B.T. Melekh, M. Glerup, F.W. Poulsen, Solid State Ionics 162/163 (2003) 13.
[6] M.M. Savosta, J. Englich, J. Kohout, V.D. Doroshev, V.A. Borodin, Yu.G. Pashkevich, A.G. Soldatov, S.N. Barilo, S.V. Shiryaev, Physica C
341–348 (2000) 943.
[7] Q. Zhou, B.J. Kennedy, Solid State Commun. 132 (2004) 389.
[8] H.W. Hsu, Y.H. Chang, G.J. Chen, K.J. Lin, Mater. Sci. Eng. B64 (1999) 180.
[9] C.-F. Kao, C.-L. Zheng, Solid State Ionics 120 (1999) 163.
[10] J.M. Liu, C.K. Ong, Appl. Phys. Lett. 73 (1998) 1047.
[11] C. Kwon, Y. Gim, Y. Fan, M.F. Hundley, J.M. Roper, P.N. Arendt, Q.X. Jia, Appl. Phys. Lett. 73 (1998) 695.
[12] N.C. Yeh, C.C. Fu, J.Y.T. Wei, R.P. Vasquez, J. Huynh, S.M. Maurer, G. Beach, D.A. Beam, J. Appl. Phys. 81 (1997) 5499.
[13] M. Itoh, I. Natori, S. Kubota, K. Motoya, J. Phys. Soc. Jpn. 63 (1994) 1486.
[14] F.M. Figueiredo, F.M.B. Marques, J.R. Frade, Solid State Ionics 111 (1998) 273.
[15] T.-Y. Yum, C.-L. Mak, K.-H. Wong, Appl. Surf. Sci. 252 (2006) 4829.
[16] N.X. Phuc, L.V. Bau, N.V. Khiem, L.H. Sona, D.N.H. Nam, Physica B 327 (2003) 177.
[17] I. Kojima, H. Adachi, I. Iasumori, Surf. Sci. 130 (1983) 50.
[18] T. Nakamura, M. Misono, Y. Yoneda, J. Catal. 83 (1983) 151.
[19] F.A.N. Petrov, V.A. Cherepanov, O. Kononchuk, L.Ya. Gavrilova, J. Solid State Chem. 87 (1990) 69.
[20] C.B. Alcock, R.C. Doshi, Y. Shen, Solid State Ionics 51 (1992) 281.
[21] D. Waller, L.G. Coccia, J.A. Kilner, I.W. Boyd, Solid State Ionics 134 (2000) 119.
[22] Y. Takeda, R. Kanno, M. Noda, Y. Tomida, O. Yamamoto, J. Electrochem. Soc. 134 (1987) 2656.
[23] M. Godickemeier, K. Sasaki, L.J. Gauckler, I. Riess, Solid State Ionics 86–88 (1996) 691.

H. Muthurajan et al. / Materials Research Bulletin 43 (2008) 1842–1849
1849
[24] T. Kawada, K. Masuda, J. Suzuki, A. Kaimai, K. Kawamura, Y. Nigara, J. Mizusaki, H. Yugami, H. Arashi, N. Sakai, H. Yokokawa, Solid State
Ionics 121 (1999) 271.
[25] S.N. Kale, R. Rajagopal, J. Mona, D.P. Londhe, R.S. Joshee, T.C. Jagdale, C. Satyanarayana, V. Ravi, Mater. Lett. 62 (2008) 191.
[26] A. Daundkar, S.N. Kale, S.P. Gokhale, V. Ravi, Mater. Lett. 60 (2006) 1212.
[27] V. Ravi, S.D. Kulkarni, V. Samuel, S.N. Kale, J. Mona, R. Rajagopal, A. Daundkar, P.S. Lahoti, R.S. Joshee, Ceram. Int. 33 (2007) 1129.
[28] S.P. Gaikwad, H.S. Potdar, V. Samuel, V. Ravi, Ceram. Int. 31 (2005) 379.
[29] S.P. Gaikwad, R. Pasricha, V. Ravi, Mater. Sci. Eng. B 117 (2005) 159.
[30] V. Samuel, A.B. Gaikwad, A.D. Jadhav, S.A. Mirji, V. Ravi, Mater. Lett. 61 (2007) 765.
[31] S.P. Gaikwad, R. Pasricha, V. Ravi, Ceram. Int. 31 (2005) 773.
[32] S.P. Gaikwad, S.R. Dhage, H.S. Potdar, V. Samuel, V. Ravi, J. Electroceramics 14 (2005) 83.
[33] H. Muthurajan, H.H. Kumar, N. Natarajan, V. Ravi, Ceram. Int. 34 (2008) 669.
[34] H. Muthurajan, H.H. Kumar, V. Samuel, U.N. Gupta, V. Ravi, Ceram. Int. 34 (2008) 671.