Narottam P. Bansal

Glenn Research Center, Cleveland, Ohio

Zhimin Zhong

QSS Group, Inc., Cleveland, Ohio

Combustion Synthesis of Sm0.5Sr0.5CoO3-x and

La0.6Sr0.4CoO3-x Nanopowders for Solid Oxide

Fuel Cell Cathodes

NASA/TM—2005-213897

August 2005
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Narottam P. Bansal

Glenn Research Center, Cleveland, Ohio

Zhimin Zhong

QSS Group, Inc., Cleveland, Ohio

Combustion Synthesis of Sm0.5Sr0.5CoO3-x and

La0.6Sr0.4CoO3-x Nanopowders for Solid Oxide

Fuel Cell Cathodes

NASA/TM—2005-213897

August 2005

National Aeronautics and

Space Administration

Glenn Research Center

Prepared for the

Sixth Pacific Rim Conference on Ceramic and Glass Technology

sponsored by the American Ceramic Society

Maui, Hawaii, September 11–16, 2005
Acknowledgments

Thanks are due to Ralph Garlick for x-ray diffraction analysis. This work was supported by

the Low Emissions Alternative Power (LEAP) Project of the Vehicle Systems Program

at NASA Glenn Research Center.

Available from

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7121 Standard Drive

Hanover, MD 21076

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Available electronically at http://gltrs.grc.nasa.gov

This work was sponsored by the Low Emissions Alternative

Power Project of the Vehicle Systems Program at the

NASA Glenn Research Center.
NASA/TM—2005-213897 1 

Combustion Synthesis of Sm0.5Sr0.5CoO3-x and La0.6Sr0.4CoO3-x

Nanopowders for Solid Oxide Fuel Cell Cathodes

Narottam P. Bansal 

National Aeronautics and Space Administration, 

Glenn Research Center 

Cleveland, Ohio 44135 

Zhimin Zhong 

QSS Group, Inc. 

Cleveland, Ohio 44135 

Abstract 

 Nanopowders of Sm0.5Sr0.5CoO3-x (SSC) and La0.6Sr0.4CoO3-x (LSC) compositions, which are 

being investigated as cathode materials for intermediate temperature solid oxide fuel cells, were 

synthesized by a solution-combustion method using metal nitrates and glycine as fuel. 

Development of crystalline phases in the as-synthesized powders after heat treatments at various 

temperatures was monitored by x-ray diffraction. Perovskite phase in LSC formed more readily 

than in SSC. Single phase perovskites were obtained after heat treatment of the combustion 

synthesized LSC and SSC powders at 1000 and 1200 °C, respectively. The as-synthesized 

powders had an average particle size of ~12 nm as determined from x-ray line broadening 

analysis using the Scherrer equation. Average grain size of the powders increased with increase 

in calcination temperature. Morphological analysis of the powders calcined at various 

temperatures was done by scanning electron microscopy. 

1. Introduction 

 Solid oxide fuel cells (SOFC) are being considered (ref. 1) as the premium power generation 

devices in the future as they have demonstrated high energy conversion efficiency, high power 

density, extremely low pollution, in addition to flexibility in using hydrocarbon fuel. A major 

obstacle for commercial applications of SOFC still is high cost, both in terms of materials and 

processing. Intermediate Temperature Solid Oxide Fuel Cell (IT-SOFC) operated between 500 to 

800 °C, which allows utilization of available and inexpensive interconnects and sealing 

materials, can significantly reduce the cost of SOFC. The IT-SOFC also will have better 

reliability and portability. To keep up with the performance of traditional SOFC that operates 

between 900 to 1000 °C, new materials with improved performance have to be used (refs. 2 

and 3). To enhance the oxygen ion conductivity of the electrolyte at the reduced temperature, La1-

xSrxGa1-yMgyOz (LSGM), scandium stabilized zirconia or lanthanum (gadolinium, samarium) 

doped ceria can be used to replace the yttrium stabilized zirconia. Similarly, cathode materials with 

higher performance at the lower temperature such as Sm0.5Sr0.5CoO3-x (SSC), La0.6Sr0.4CoO3-x

(LSC), La0.8Sr0.2Co0.2Fe0.8O3-x (LSCF) will be used to substitute La1-ySryMnO3-x (LSM), the 

performance of which decreases rapidly when the operating temperature is below 800 °C. 
NASA/TM—2005-213897 2 

 The primary objective of this study was to synthesize fine powders of SSC and LSC 

compositions for applications as SOFC cathodes. A number of approaches such as, solid state 

reaction, sol-gel, hydrothermal, spray-drying, freeze-drying, co-precipitation, and solution 

combustion have been used for ceramic powders processing. The solution-combustion method is 

particularly useful in the production of ultrafine ceramic powders of complex oxide compositions 

in a relatively short time. This approach has been utilized (refs. 4 to 10) for the synthesis of 

various oxide powders such as ferrites, chromites, manganites, Ni-YSZ cermet, zirconates, doped 

ceria, hexa-aluminates, pyrochlores, oxide phosphors, spinels, etc. An amino acid such as glycine 

is commonly used as the fuel in the combustion process. However, urea, citric acid, 

oxylydihydrazide, and sucrose have also been recently utilized (refs. 6 and 10) as complexing 

agents and fuel in the combustion synthesis. 

 In the present study, SSC and LSC cathode powders were synthesized using the glycinenitrate solution-combustion technique (refs. 4 to 6) because of its high energy efficiency, fast 

heating rates, short reaction times, and high reaction temperatures. This process is also unique as 

all the reactants are mixed in solution at the molecular level resulting in homogeneous reaction 

products and faster reaction rates. Development of crystalline phases in the powders, on heat 

treatments at various temperatures, was followed by powder x-ray diffraction. Morphology of the 

powders was characterized by scanning electron microscopy (SEM). 

2. Experimental Methods 

2.1 Powder Synthesis

 The starting materials used in the synthesis were metal nitrates Sm(NO3)3.6H2O (99.9 percent 

purity), La(NO3)3.6H2O (99.9 percent purity), Sr(NO3)2 (98 percent purity), Co(NO3)2.6H2O 

(97.7 percent purity) and glycine (NH2CH2COOH, 99.5 percent purity), all from Alfa Aesar. A 

flow chart showing the various steps involved in the synthesis of powders by the solutioncombustion process is shown in figure 1. Metal nitrates are employed both as metal precursors 

and oxidizing agents. Stoichiometric amounts of the metal nitrates, to yield 10 g of the final SSC 

or LSC oxide powder, were dissolved in deionized water. A calculated amount of the amino acid 

glycine (0.7 mole per mole of NO3

-

) was also dissolved in deionized water. The glycine solution 

was slowly added to the metal nitrate aqueous solution under constant stirring. Glycine acts as a 

complexing agent for metal cations of varying sizes as it has a carboxylic group at one end and 

an amino group at the other end. The complexation process increases the solubility of metal ions 

and helps to maintain homogeneity by preventing their selective precipitation. The resulting clear 

and transparent red colored solution was heated on a hot plate until concentrated to about 

2 mole/liter on metal nitrate basis. While the solution was still hot, it was added dropwise to a 

2 liter glass beaker that was preheated between 300 to 400 °C. The water in the solution quickly 

evaporated, the resulting viscous liquid swelled, auto-ignited and initiated a highly exothermic 

self-contained combustion process, converting the precursor materials into fine powder of the 

complex oxides. Glycine acts as a fuel during the combustion reaction, being oxidized by the 

nitrate ions. Oxygen from air does not play an important role during the combustion process. The 

overall combustion reactions can be represented as: 
NASA/TM—2005-213897 3 

0.6 La(NO3)3 + 0.4 Sr(NO3)2 + Co(NO3)2 + 3.2 H2NCH2COOH + (1.8 - x/2) O2 →

 La0.6Sr0.4CoO3-x + 6.4 CO2 + 8 H2O + 3.9 N2 (1) 

0.5 Sm(NO3)3 + 0.5 Sr(NO3)2 + Co(NO3)2 + 3.2 H2NCH2COOH + (1.95 - x/2) O2 →

 Sm0.5Sr0.5CoO3-x + 6.4 CO2 + 8 H2O + 3.85 N2 (2)

indicating the formation of CO2, N2, and H2O as the gaseous products. The evolution of gases 

during the combustion process helps in the formation of fine ceramic powder by limiting the 

inter-particle contact. The resulting black powder contained some carbon residue and was further 

calcined to convert to the desired product. Small portions (~1 g) of this powder were heat treated 

in air at various temperatures between 700 and 1300 °C for 2 h to study the development of 

crystalline phases. 

2.2 Characterization 

 Thermal gravimetric analysis (TGA) of the powders was carried out using a Perkin-Elmer 

Thermogravimetric Analyzer 7 system which was interfaced with computerized data acquisition 

and analysis system at a heating rate of 10 °C/min. Air at 40 ml/min was used as a purge gas. 
NASA/TM—2005-213897 4 

X-ray diffraction (XRD) analysis was carried out on powders heat treated at various 

temperatures for crystalline phase identification and crystallite size determination. Powder XRD 

patterns were recorded at room temperature using a step scan procedure (0.02°/2θ step, time per 

step 0.5 or 1 s) in the 2θ range 10 to 70° on a Philips ADP-3600 automated diffractometer 

equipped with a crystal monochromator employing Cu Kα radiation. Microstructural analysis 

was carried out using a JEOL JSM-840A scanning electron microscope (SEM). Prior to analysis, 

a thin layer of Pt or carbon was evaporated onto the SEM specimens for electrical conductivity. 

3. Results and Discussion 

3.1 Thermogravimetric Analysis 

 Figure 2 shows the TGA curves recorded at a heating rate of 10 °C/min in air from room 

temperature to 1200 °C for the as-synthesized LSC and SSC powders using the solutioncombustion method. For both precursors, about 6 percent weight loss was observed between 600 

to 850 °C that was likely due to loss of carbon residue by oxidation and also from decomposition 

of SrCO3. For SSC, there was additional 1 percent weight loss between 850 to 1000 °C for which 

there is no simple explanation based on the x-ray diffraction results of figure 4. 
NASA/TM—2005-213897 5 

3.2 Phase Formation and Microstructure

 Both the LSC and SSC as-synthesized powders were calcined in air for 2 h at various 

temperatures between 700 to 1300 °C to investigate the evolution of crystalline phases. X-ray 

diffraction patterns for these heat treated LSC and SSC powders are shown in figures 3 and 4, 

respectively and the results are summarized in table 1. The as-prepared LSC powder shows weak 

crystallinity of the perovskite phase. SrCO3 phase was also observed in the as-synthesized 

powder and after calcination at 700 °C. An unknown peak at 32° (probably Sr3Co2O6.13, 83-375) 

appeared for the powder calcined at 800 and 900 °C. Formation of the perovskite phase, 

La0.6Sr0.4CoO3-x, is completed above 1000 °C as observed by XRD results in figure 3. The 

as-prepared SSC powder showed the presence of Sm2O3, Co3O4, and SrCO3 phases. The desired 

Sm0.5Sr0.5CoO3-x perovskite phase emerged as the major phase after the powder was calcined at 

700 °C. Secondary phases such as Sr3Co2O6.13 remained even after the powder was heat treated 

at 1100 °C. Perovskite phase-pure Sm0.5Sr0.5CoO3-x powder was obtained on heat treatment at 1200 °C 

for 2 h. Earlier investigation (ref. 7) of synthesis of SSC by solid-state reaction method indicated 

that the perovskite phase was formed after calcination at 1200 °C for 6 h. The products calcined 

at this temperature will have low porosity and non-ideal microstructure as cathode materials. 
NASA/TM—2005-213897 6 

TABLE 1.—X-RAY DIFFRACTION ANALYSIS OF Sm0.5Sr0.5CoO3-X AND La0.6Sr0.4CoO3-X POWDERS MADE BY 

SOLUTION-COMBUSTION SYNTHESIS AFTER HEAT TREATMENTS AT VARIOUS TEMPERATURES IN AIR 

System Heat treatment 

Temperature, 

°C 

Time, 

h 

Crystalline phasesa

 Average grain 

size,b

nm 

As synthesized -- La0.6Sr0.4CoO3-x, SrCO3 12 

700 2 La0.6Sr0.4CoO3-x, SrCO3 15 

800 2 La0.6Sr0.4CoO3-x, low intensity peak at 32° 2θ 17 

900 2 La0.6Sr0.4CoO3-x, low intensity peak at 32° 2θ 28 

1000 2 La0.6Sr0.4CoO3-x 37 

1100 2 La0.6Sr0.4CoO3-x 50 

1200 2 La0.6Sr0.4CoO3-x

La0.6Sr0.4CoO3-x

1300 2 La0.6Sr0.4CoO3-x

As synthesized -- Sm2O3, Co3O4, SrCO3 --- 

700 2 Sm0.5Sr0.5CoO3-x, SrCO3, Co3O4 15 

800 2 Sm0.5Sr0.5CoO3-x, Sr3Co2O6.13, Co3O4 15 

900 2 Sm0.5Sr0.5CoO3-x, Sr3Co2O6.13 25 

1000 2 Sm0.5Sr0.5CoO3-x, Sr3Co2O6.13, low intensity peak at 32 ̊ 2θ 38 

1100 2 Sm0.5Sr0.5CoO3-x, Sr3Co2O6.13, low intensity peak at 32 ̊ 2θ 41 

1200 2 Sm0.5Sr0.5CoO3-x 

Sm0.5Sr0.5CoO3-x

1300 2 Sm0.5Sr0.5CoO3-x

a

Phases in decreasing order of peak intensity

b

Calculated from Scherrer formula using FWHM of XRD peak in 47 to 48° range of 2θ.
NASA/TM—2005-213897 7 

 The SEM micrographs of La0.6Sr0.4CoO3-x and Sm0.5Sr0.5CoO3-x powders made by solutioncombustion synthesis after heat treatments at different temperatures for 2 h in air are presented in 

Figures 5 and 6, respectively. The as prepared powders were highly porous and particles were 

linked together in agglomerates of different shapes and sizes. Substantial particle growth was 

observed upon calcination for 2 h at 1000 °C or higher temperatures. The particle size of samples 

calcined at 1000 °C increased but the structure remained highly porous, which resembled the 

typical cathode structure for SOFC. Therefore, LSC and SSC powders should be sintered around 

1000 °C for fabrication of cathode structures. After calcination at 1200 °C, LSC became dense 

and lost porosity. SSC powder sintered into a dense pellet following heat treatment at 1200 °C. 
NASA/TM—2005-213897 8 

3.3. Particle Size Analysis 

 After each heat treatment of the as synthesized LSC and SSC powders, the average particle 

size was evaluated from X-ray line broadening analysis using the Scherrer equation (ref. 11): 

 t = 0.9 λ/(B cos θB) (3) 

where t is the average particle size, λ the wave length of Cu Kα radiation, B is the width (in 

radian) of the XRD diffraction peak at half its maximum intensity, and θB the Bragg diffraction 

angle of the line. Correction for the line broadening by the instrument was applied using a large 

particle size silicon standard and the relationship 
NASA/TM—2005-213897 9 

B2 = B2

M - B2S (4) 

where BM and BS are the measured widths, at half maximum intensity, of the lines from the 

sample and the standard, respectively. Values of average grain sizes of the as synthesized SSC 

and LSC powders and of those after heat treatments at various temperatures are given in table 1. 

The as synthesized powders had an average grain size of about 10 to 12 nm. A number of factors 

are responsible for the nanosize of the resulting powders. Before the reaction, all the reactants 

are uniformly mixed in solution at atomic or molecular level. So, during combustion, the 

nucleation process can occur through the rearrangement and short-distance diffusion of nearby 

atoms and molecules. Also, large volume of the gases evolved during the combustion reactions 

(1) and (2) limit the inter-particle contact. Moreover, the combustion process occurs at such a 

fast rate that sufficient energy and time are not available for long-distance diffusion or migration 

of the atoms or molecules which would result in growth of crystallites. Consequently, the initial 

nanosize of the powders is retained after the combustion reaction. 

 The X-ray line broadening method can be used only for the size determination of small 

crystallites (~100 nm). The values obtained are not the true particle size, but the average size of 

coherently diffracting domains; the latter being usually much smaller than the actual size of the 

particles. The crystallite size of the as-synthesized powder depends (refs. 8 and 9) on the glycine 

to nitrate ratio used during the combustion synthesis. Powder made using a fuel-deficient system 

has the highest surface area. The powder surface area decreases as the glycine to nitrate ratio is 

increased. This has been attributed to an increase in the flame temperature during combustion 

which helps in the growth of crystal size. The average grain size of the SSC and LSC powders 

increased (table 1) with the increase in calcination temperature, as expected. 

4. Summary and Conclusions 

 Nanopowders of Sm0.5Sr0.5CoO3-x (SSC) and La0.6Sr0.4CoO3-x (LSC) cathode materials for solid 

oxide fuel cells have been synthesized by the glycine-nitrate solution-combustion method. 

Formation of crystalline phases in both the powders started at relatively low temperatures. 

However, the as-synthesized powders had to be calcined at or above 1000 °C to yield phase pure 

perovskite products. The high temperature calcination caused significant reduction in surface 

area, coarsening of the powders, and sintering which is not favorable for forming the cathode 

structures for SOFC. The investigations of electrochemical activity of these materials and 

co-sintering with fuel cell electrolytes are being investigated and will be presented in the future. 

References 

 1. N.Q. Minh, Ceramic Fuel Cells, J. Am. Ceram. Soc., 76 [3], 563–588 (1993). 

 2. D. Stover, H.P. Buchkremer, and S. Uhlenbruck, Processing and Properties of the Ceramic 

Conductive Multilayer Device SOFC, Ceram. Int., 30(7), 1107–1113 (2004). 

 3. Y. Liu, S. Zha, and M. Liu, Adv. Mater., 16(3), 256–260 (2004). 

 4. S.-J. Kim, W. Lee, W.-J. Lee, S.D. Park, J.S. Song, and E.G. Lee, Preparation of 

Nanocrystalline Nickel Oxide-Yttria-Stabilized Zirconia Composite Powder by Solution 

Combustion with Ignition of Glycine Fuel, J. Mater. Res., 16 [12], 3621–3627 (2001). 
NASA/TM—2005-213897 10 

 5. L.A. Chick, L.R. Pederson, G.D. Maupin, J.L. Bates, L.E. Thomas, and G. J. Exarhos, GlycineNitrate Combustion Synthesis of Oxide Ceramic Powders, Mater. Lett., 10, 6–12 (1990). 

 6. M. Marinsek, K. Zupan, and J. Maeek, Ni-YSZ Cermet Anodes Prepared by Citrate/Nitrate 

Combustion Synthesis, J. Power Sources, 106, 178–188 (2002). 

 7. T. Ishihara, M. Honda, T. Shibayama, H. Minami, H. Nishiguchi, and Y. Takita, Intermediate 

Temperature SOFCs Using a New LaGaO3 Based Oxide Ion Conductor. I. Doped SmCoO3 as a 

New Cathode Material, J. Electrochem. Soc., 145(9), 3177-3183 (1998). 

 8. R.D. Purohit, S. Saha, and A.K., Tyagi, Nanocrystalline Thoria Powders via Glycine-Nitrate 

Combustion, J. Nuclear Mater., 288 [1], 7–10 (2001). 

 9. T. Ye, Z. Guiwen, Z. Weiping, and X. Shangda, Combustion Synthesis and Photoluminescence 

of Nanocrystalline Y2O3: Eu Phosphors, Mater. Res. Bull., 32, 501 (1997). 

10. K. Prabhakaran, J. Joseph, N.M. Gokhale, S.C. Sharma, and R. Lal, Sucrose Combustion 

Synthesis of LaxSr(1-x)MnO3 (x ≤0.2) Powders, Ceram. Int., 31 [2], 327–331 (2005). 

11. B.D. Cullity, Elements of X-Ray Diffraction, 2nd Edition, Addison-Wesley, Reading, MA, 

p. 284 (1978). 
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16

Combustion Synthesis of Sm0.5Sr0.5CoO3-x and La0.6Sr0.4CoO3-x Nanopowders

for Solid Oxide Fuel Cell Cathodes

Narottam P. Bansal and Zhimin Zhong

Solid oxide fuel cells; Cathodes; Powder processing; Nanomaterials

Unclassified -Unlimited

Subject Categories: 44, 23, and 27

Prepared for the Sixth Pacific Rim Conference on Ceramic and Glass Technology sponsored by the American Ceramic

Society, Maui, Hawaii, September 11–16, 2005. Narottam P. Bansal, NASA Glenn Research Center; and Zhimin Zhong,

QSS Group, Inc., 21000 Brookpark Road, Cleveland, Ohio 44135. Responsible person, Narottam P. Bansal, organization

code RMC, 216–433–3855.

Nanopowders of Sm0.5Sr0.5CoO3-x (SSC) and La0.6Sr0.4CoO3-x (LSC) compositions, which are being investigated as

cathode materials for intermediate temperature solid oxide fuel cells, were synthesized by a solution-combustion method

using metal nitrates and glycine as fuel. Development of crystalline phases in the as-synthesized powders after heat

treatments at various temperatures was monitored by x-ray diffraction. Perovskite phase in LSC formed more readily

than in SSC. Single phase perovskites were obtained after heat treatment of the combustion synthesized LSC and SSC

powders at 1000 and 1200 °C, respectively. The as-synthesized powders had an average particle size of ~12 nm as

determined from x-ray line broadening analysis using the Scherrer equation. Average grain size of the powders increased

with increase in calcination temperature. Morphological analysis of the powders calcined at various temperatures was

done by scanning electron microscopy.