- Email: [email protected]
Synthesis of strontium- and magnesium-doped lanthanum gallate by glycine-nitrate combustion method
CHINA PARTICUOLOGY Vol. 4, No. 1, 9-12, 2006
SYNTHESIS OF STRONTIUM- AND MAGNESIUM-DOPED LANTHANUM GALLATE BY GLYCINE-NITRATE COMBUSTION METHOD Ning Liu1, Yupeng Yuan1, Min Shi1,*, Yudong Xu1, P. Majewski2 and F. Aldinger2 1 Department of Materials Science and Engineering, Hefei University of Technology, Hefei 230009, P. R. China Max-Planck-Institut fűr Metallforschung, Pulvermetallurgisches Laboratorium, Heisenbergstr. 5, D-70569 Stuttgart, Germany *Author to whom correspondence should be addressed. E-mail: [email protected]
2
Abstract Sr- and Mg-doped lanthanum gallate powders with the composition of La0.85Sr0.15Ga0.85Mg0.15O2.85 were synthesized by a glycine-nitrate combustion method. Powders prepared under different fuel combustion conditions were investigated by XRD and TEM. The results show that, under slightly rich fuel condition, the product powders contain less impurity phases, and powders prepared by the glycine-nitrate combustion contain far less impurity phases and have smaller particle sizes than those prepared by solid-state reaction method or acrylamide polymerization technique. Keywords
glycine-nitrate combustion method, solid-state reaction method, acrylamide polymerization technique, phase constitution
1. Introduction As lanthanum gallate (LaGaO3) ceramics (denoted as LSGM) doped with strontium and magnesium are known to have superior oxygen-ion-conducting properties, they have become widely used as electrolytes for Solid Oxide Fuel Cells (SOFCs) (Ishihara et al., 1994; Feng & Goodenough, 1994). In general, LSGM powders are prepared by using the solid-state reaction method or the acrylamide polymerization technique (Huang et al., 1996; Tas et al., 2000; Tarancón et al., 2003). The conventional solid-state reaction method involves intimate mechanical mixing of the oxides of La, Sr, Ga and Mg and repeated grinding and heating cycles to achieve complete reaction between the reagents. Despite its simplicity, this method has the clear disadvantages of producing large grains, repeated thermal treatment and grinding, and the presence of many impurities such as LaSrGaO4, LaSrGa3O7, La3Ga5O12 and La4Ga2O9. The acrylamide polymerization technique, too, requires expensive metal alkoxide precursors and calls for great care in mixing the precursors to obtain LSGM powders with the desired stoichiometry. The new synthesis route involving glycine–nitrate combustion was developed by Chlik et al. (Stevenson et al., 1997; Cong et al., 2003; Sin & Sdier, 2000) and has now become an attractive synthesis method for preparing multiple component inorganic oxides. This method offers several distinct advantages: first, the homogeneous mixtures of several components at molecular or atomic levels can be achieved in solution, and ultra-fine powders can be obtained, and second, this synthesis process is time-saving and the final products contain less impurities. Research has focused on the sintering ability of the synthesized powder and the electrical conductivity of the sintered product. But work on the influence of combustion fuel condition on synthesized powders has not yet been reported. This paper investigated the effects of combustion
fuel condition on the constitution of the powder product, its morphology and particle size. Solid-state reaction and acrylamide polymerization were also used for comparison.
2. Experimental Ga (99.95% purity), La2O3 (>99.95% purity), Mg(NO3)2 (>99% purity) and Sr(NO3)2 (>99.5% purity) were used as the starting materials. A powder with the composition of La0.85Sr0.15Ga0.85Mg0.15O2.85 (denoted as LSGM) was synthesized by the glycine-nitrate combustion method. Appropriate amounts of Ga, La2O3, Mg(NO3)2 and Sr(NO3)2 were first dissolved in strong HNO3 to obtain corresponding nitrate solutions. According to the formula of LSGM, these nitrate solutions were then mixed together with water in a glass beaker, and glycine (as fuel and complexant) was added into the mixed nitrate solution at a molar ratio of nMe: nglycine =1:1.78. The glass beaker containing the above mixed glycine–nitrate solution was heated on a hot plate, to boil off sufficient water until the solution began to froth and catch fire at some instant. In this way, a homogeneous white powder product was eventually obtained in a matter of several minutes. By acrylamide polymerization or by solid-state reaction, the above process would take several hours or even days. The combustion gas consists of CO, CO2, H2O and N2, according to the following reaction: 85La(NO3)3(aq) + 15Sr(NO3)2(aq) + 85Ga(NO3)3(aq) 1
+ 15Mg(NO3)2(aq) + 356 4 C2H5NO2(aq) 1
= 100La0.85Sr0.15Ga0.85Mg0.15O2.85(s) + 178 8 CO(g) 5
1
3
+ 890 8 H2O(g) + 463 8 N2(g) + 534 8 CO2(g) ,
where, (aq), (s) and (g) mean liquid, solid and gas, respectively. For examining the effect of combustion fuel condition on the properties of the final powder, different combustion fuel conditions were designed by adding different amounts of glycine. For example, for rich fuel condition, twice the
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CHINA PARTICUOLOGY Vol. 4, No. 1, 2006
stoichiometric amount of glycine, i.e. nMe: nglycine =1:3.56 was used, while for lean fuel condition, half of the stoichiometric amount of glycine, i.e. nMe: nglycine =1:0.89 was used. For slightly rich fuel condition, a little more than stoichiometric amount of glycine, i.e. nMe: nglycine =1:2 was used. Synthesis of the LSGM powder, using the solid-state reaction and the acrylamide polymerization techniques, was carried out following the procedures described by Huang et al.(1998) and Sin and Sdier (2000), respectively. Room-temperature X-ray diffractometry (XRD) (D/MaxrB, Rigaku, Japan) was performed on the synthesized powders with Cu Kα radiation. The XRD diffraction patterns were collected at an angle of 20°−80° and at a 0.02° angle step. The particle size and morphology were examined by transmission electron microscope (TEM, H800, Hitachi, Japan). Test powders were prepared by suspending the powder in ethanol on a copper grid.
3. Results and Discussion 3.1 Phase analysis of XRD Figure 1 shows the remarkable dependence of phase constitution on fuel condition for powders prepared by the glyine-nitrate combustion method. Precalcined powders synthesized under stoichiometric combustion fuel conditions (pattern c) consists nearly all of LaSrGa3O7, which is
Relative density
-LSGM -LaSrGaO4 -LaSrGa3O7
2θ/°
XRD patterns of powders synthesized under different fuel conditions: (a) lean fuel, (b) slightly rich fuel, (c) stoichiometric fuel and (d) rich fuel. -LSGM -LaSrGaO4 + -LaSrGa3O7
Relative density
Fig. 1
2θ/°
Fig. 2
XRD patterns of powders synthesized under slightly rich fuel condition and followed by calcination for 6 h at different temperatures: (a)uncalcined, (b) 800°C, (c) 900°C, (d)1000°C, (e)1200°C, (f)1300°C.
evidently different from the results reported by Stevenson (1997), who showed approximately 89 wt% LaGaO3. The difference may be due to the different amounts of fuel added. Under lean (pattern a) and rich (pattern d) fuel conditions, nearly the same results were obtained, indicating essentially the absence of LaGaO3 in the synthesized powders. Surprisingly, for slightly rich fuel condition (pattern b) as much as 90 wt% LaGaO3 phase was produced, as shown in Fig. 1. The different phase constitutions may be attributed to the different thermodynamic surroundings, i.e., under lean or rich fuel conditions, the less or more than stoichiometric glycine decreases the flame temperature, so that less thermal energy is available to develop the stable crystalline LaGaO3 phase. For the slightly rich fuel condition, the formation of LaGaO3 phase may well be due to the higher flame temperature. The morphologies of the precursors are somewhat confusing: a thread-like white precursor for stoichiometric condition and a coral-like white powder for slightly rich fuel condition, the latter being the coarsened product due to sintering at the higher flame temperature. Figure 2 shows the phase evolution of powders in terms of XRD measurements synthesized under slightly rich fuel condition and followed by calcination for 6 h at the temperatures of 800°, 900°, 1000°, 1200° and 1300°C. It can be seen that LaGaO3 exists in the uncalcined powder and the phase constitution has not changed after calcinations at 800°C, indicating that the LaGaO3 phase formed during the burning process has not changed with calcination at the low temperature of 800°C. Many researchers have reported that the LaGaO3 phase formation temperature is about 1000°C, so the low heat treatment effect is not evident. When calcined at 1300°C for 6 h, small amounts of other thermodynamically stable phases, such as LaSrGaO4, LaSrGa3O7, LaSrGaO4, and LaSrGa3O7 appear to take the place of the single LaGaO3 phase, making the synthesis of a pure single phase LSGM difficult. With further increase of calcination temperature, the amounts of the impurity phases decrease, dwindling to traces at 1500°C. Previous works have concluded that, independent of preparation technique, calcination up to 1500℃ is mandatory to obtain the pure LaGaO3 phase (Gorelov et al., 2001). For comparison, the XRD patterns of the powders prepared by solid-state reaction and the acrylamide polymerization technique are shown respectively in Figs. 3a and 3b. Fig. 3a shows that, after twice thermal treatment (1200℃ for 24 h), the fraction of LaGaO3 in the synthesized powder prepared by solid-state reaction has increased remarkably, though there exist profuse impurity phases such as LaSrGaO4 and LaSrGa3O7. Fig. 3b shows the XRD of powders prepared by the acrylamide polymerization technique, indicating the considerable amounts of the impurity phases. Compared to Fig. 2, it can be seen that the powders synthesized by the glycine–nitrate combustion method contain far less impurity phases than those prepared by solid-state reaction or acrylamide polymerization technique.
Liu, Yuan, Shi, Xu, Majewski & Aldinger: Synthesis of Lanthanum Gallate by Combustion Method
11
3.2 TEM micrographs -LSGM -LaSrGaO4 + -LaSrGa3O7
Relative density
a
2θ/°
b
Relative density
-LSGM -LaSrGaO4 + -LaSrGa3O7
Figure 4 shows the TEM micrographs of powders produced under different combustion fuel conditions. The particle size obtained under slightly rich fuel condition is evidently larger than that obtained under rich or lean fuel conditions (under lean fuel condition, the particles agglomerate), validating the result that the powders prepared under slightly rich fuel condition has been partially sintered because of the higher flame temperature. The size of particles prepared under rich fuel condition is less than 50 nm. The morphologies of powders obtained under lean and stoichiometric conditions are similar, indicating that combustion under these two conditions took place under similar flame temperatures and thus resulted in similar products. b
a
2θ/°
Fig. 3 XRD patterns of powders synthesized by (a) solid-state reaction method: 1- single calcination at 1200°C for 24 h, 2- after second time calcination at 1200°C for 24 h; (b) acrylamide polymerization technique: 1- heat treatment at 1000°C for 6 h, 2- 1200°C for 6h, 3-1300°C for 6 h. a
b
Fig. 5
TEM images of LSGM powders prepared by different routes: (a) solid-state reaction, (b) acrylamide polymerization.
Figures 5a and 5b show respectively the morphologies of powders synthesized by solid-state reaction (two runs of calcination at 1200°C for 24 h) and acrylamide polymerization (calcined at 1300°C for 6 h). It can be seen that the glycine-nitrate method can produce relatively small particle size in comparison with solid-state reaction and acrylamide polymerization. c
Fig. 4
d
TEM micrographs of LSGM powders prepared by glycine -nitrate technology under different fuel conditions: (a) lean fuel, (b) stoichiometric fuel, (c) slightly rich fuel, (d) rich fuel.
4. Conclusion Sr- and Mg-doped lanthanum gallate powders were synthesized by a glycine-nitrate combustion method. The effect of combustion fuel condition on the phase constitution and morphology of the synthesized powders was studied through XRD and TEM. The results show that slightly rich fuel condition can produce powders having higher LaGaO3 content than those under lean, stoichiometric or rich fuel condition. The TEM images also verify the results. In contrast with the solid–state reaction method and acrylamide polymerization technique, the glycine-nitrate combustion method can produce powders with far less amounts of impurity phases, smaller particle size and is a convenient and time-saving route to synthesize the LSGM powders.
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CHINA PARTICUOLOGY Vol. 4, No. 1, 2006
Acknowledgements The authors wish to acknowledge the financial support of this research from the Scientific Research Foundation for Returned Overseas Chinese Scholars, State Education Ministry, China, the Scientific Research Foundation of Hefei University of Technology and the Max-Plank Society, Germany.
References Cong, L., He, T., Ji, Y., Guan, P., Huang, Y. & Su, W. (2003). Synthesis and characterization of IT-electrolyte with perovskite structure La0.8Sr0.2Ga0.85Mg0.15O3-δby glycine-nitrate combustion method. J. Alloys Compd., 348, 325−331. Feng, M. & Goodenough, J. B. (1994). A superior oxide-ion conductor. Eur. J. Solid Inorg. Chem., 31, 663−672. Gorelov, V. P., Bronin, D. I., Sokolova, J. V., Näfe, H. & Aldinger, F. (2001). The effect of doping and processing conditions on properties of La1-zSrzGa1-yMgyO3-δ. J. Eur. Ceram. Soc., 21, 2311−2317. Huang, K., Feng, M. & Goodenough, J. B. (1996). Sol-gel synthesis of a new oxide-ion conductor Sr- and Mg-doped LaGaO3 perovskite. J. Am. Ceram. Soc., 79, 1100−1104.
Huang, K., Tichy, R. S. & Goodenough, J. B. (1998). Superior Perovskite oxide-ion conductor; strontium- and magnesiumdoped LaGaO3: I, phase relationships and electrical properties. J. Am. Ceram. Soc., 81, 2565−2575. Ishihara, T., Matsuda, H. & Takita, Y. (1994). Doped LaGaO3 perovskite type oxide as a new oxide ionic conductor. J. Am. Chem. Soc., 116, 3801−3803. Sin, A. & Sdier, P. (2000). Gelation by acrylamide, a quasi-universal medium for the synthesis of fine oxide powders for electroceramic applications. Adv. Mater., 12, 649−652. Stevenson, J. W., Armstrong, T. R., McCready, D. E., Pederson, L. R. & Weber, W. J. (1997). Processing and electrical properties of alkaline earth-doped lanthanum gallate. J. Electrochem. Soc., 144, 3613−3620. Tarancón, A., Dezanneau, G., Arbiol, J., Peiró, F. & Morante, J. R. (2003). Synthesis of nanocrystalline materials for SOFC applications by acrylamide polymerization. J. Power Sources, 118, 256−264. Tas. C. A., Majewski, J. & Aldinger, F. (2000). Chemical preparation of pure and strontium- and/or magnesium-doped lanthanum gallate powders. J. Am. Ceram. Soc., 83, 2954−2960. Manuscript received January 4, 2005 and accepted December, 28, 2005.
SYNTHESIS OF STRONTIUM- AND MAGNESIUM-DOPED LANTHANUM GALLATE BY GLYCINE-NITRATE COMBUSTION METHOD Ning Liu1, Yupeng Yuan1, Min Shi1,*, Yudong Xu1, P. Majewski2 and F. Aldinger2 1 Department of Materials Science and Engineering, Hefei University of Technology, Hefei 230009, P. R. China Max-Planck-Institut fűr Metallforschung, Pulvermetallurgisches Laboratorium, Heisenbergstr. 5, D-70569 Stuttgart, Germany *Author to whom correspondence should be addressed. E-mail: [email protected]
2
Abstract Sr- and Mg-doped lanthanum gallate powders with the composition of La0.85Sr0.15Ga0.85Mg0.15O2.85 were synthesized by a glycine-nitrate combustion method. Powders prepared under different fuel combustion conditions were investigated by XRD and TEM. The results show that, under slightly rich fuel condition, the product powders contain less impurity phases, and powders prepared by the glycine-nitrate combustion contain far less impurity phases and have smaller particle sizes than those prepared by solid-state reaction method or acrylamide polymerization technique. Keywords
glycine-nitrate combustion method, solid-state reaction method, acrylamide polymerization technique, phase constitution
1. Introduction As lanthanum gallate (LaGaO3) ceramics (denoted as LSGM) doped with strontium and magnesium are known to have superior oxygen-ion-conducting properties, they have become widely used as electrolytes for Solid Oxide Fuel Cells (SOFCs) (Ishihara et al., 1994; Feng & Goodenough, 1994). In general, LSGM powders are prepared by using the solid-state reaction method or the acrylamide polymerization technique (Huang et al., 1996; Tas et al., 2000; Tarancón et al., 2003). The conventional solid-state reaction method involves intimate mechanical mixing of the oxides of La, Sr, Ga and Mg and repeated grinding and heating cycles to achieve complete reaction between the reagents. Despite its simplicity, this method has the clear disadvantages of producing large grains, repeated thermal treatment and grinding, and the presence of many impurities such as LaSrGaO4, LaSrGa3O7, La3Ga5O12 and La4Ga2O9. The acrylamide polymerization technique, too, requires expensive metal alkoxide precursors and calls for great care in mixing the precursors to obtain LSGM powders with the desired stoichiometry. The new synthesis route involving glycine–nitrate combustion was developed by Chlik et al. (Stevenson et al., 1997; Cong et al., 2003; Sin & Sdier, 2000) and has now become an attractive synthesis method for preparing multiple component inorganic oxides. This method offers several distinct advantages: first, the homogeneous mixtures of several components at molecular or atomic levels can be achieved in solution, and ultra-fine powders can be obtained, and second, this synthesis process is time-saving and the final products contain less impurities. Research has focused on the sintering ability of the synthesized powder and the electrical conductivity of the sintered product. But work on the influence of combustion fuel condition on synthesized powders has not yet been reported. This paper investigated the effects of combustion
fuel condition on the constitution of the powder product, its morphology and particle size. Solid-state reaction and acrylamide polymerization were also used for comparison.
2. Experimental Ga (99.95% purity), La2O3 (>99.95% purity), Mg(NO3)2 (>99% purity) and Sr(NO3)2 (>99.5% purity) were used as the starting materials. A powder with the composition of La0.85Sr0.15Ga0.85Mg0.15O2.85 (denoted as LSGM) was synthesized by the glycine-nitrate combustion method. Appropriate amounts of Ga, La2O3, Mg(NO3)2 and Sr(NO3)2 were first dissolved in strong HNO3 to obtain corresponding nitrate solutions. According to the formula of LSGM, these nitrate solutions were then mixed together with water in a glass beaker, and glycine (as fuel and complexant) was added into the mixed nitrate solution at a molar ratio of nMe: nglycine =1:1.78. The glass beaker containing the above mixed glycine–nitrate solution was heated on a hot plate, to boil off sufficient water until the solution began to froth and catch fire at some instant. In this way, a homogeneous white powder product was eventually obtained in a matter of several minutes. By acrylamide polymerization or by solid-state reaction, the above process would take several hours or even days. The combustion gas consists of CO, CO2, H2O and N2, according to the following reaction: 85La(NO3)3(aq) + 15Sr(NO3)2(aq) + 85Ga(NO3)3(aq) 1
+ 15Mg(NO3)2(aq) + 356 4 C2H5NO2(aq) 1
= 100La0.85Sr0.15Ga0.85Mg0.15O2.85(s) + 178 8 CO(g) 5
1
3
+ 890 8 H2O(g) + 463 8 N2(g) + 534 8 CO2(g) ,
where, (aq), (s) and (g) mean liquid, solid and gas, respectively. For examining the effect of combustion fuel condition on the properties of the final powder, different combustion fuel conditions were designed by adding different amounts of glycine. For example, for rich fuel condition, twice the
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CHINA PARTICUOLOGY Vol. 4, No. 1, 2006
stoichiometric amount of glycine, i.e. nMe: nglycine =1:3.56 was used, while for lean fuel condition, half of the stoichiometric amount of glycine, i.e. nMe: nglycine =1:0.89 was used. For slightly rich fuel condition, a little more than stoichiometric amount of glycine, i.e. nMe: nglycine =1:2 was used. Synthesis of the LSGM powder, using the solid-state reaction and the acrylamide polymerization techniques, was carried out following the procedures described by Huang et al.(1998) and Sin and Sdier (2000), respectively. Room-temperature X-ray diffractometry (XRD) (D/MaxrB, Rigaku, Japan) was performed on the synthesized powders with Cu Kα radiation. The XRD diffraction patterns were collected at an angle of 20°−80° and at a 0.02° angle step. The particle size and morphology were examined by transmission electron microscope (TEM, H800, Hitachi, Japan). Test powders were prepared by suspending the powder in ethanol on a copper grid.
3. Results and Discussion 3.1 Phase analysis of XRD Figure 1 shows the remarkable dependence of phase constitution on fuel condition for powders prepared by the glyine-nitrate combustion method. Precalcined powders synthesized under stoichiometric combustion fuel conditions (pattern c) consists nearly all of LaSrGa3O7, which is
Relative density
-LSGM -LaSrGaO4 -LaSrGa3O7
2θ/°
XRD patterns of powders synthesized under different fuel conditions: (a) lean fuel, (b) slightly rich fuel, (c) stoichiometric fuel and (d) rich fuel. -LSGM -LaSrGaO4 + -LaSrGa3O7
Relative density
Fig. 1
2θ/°
Fig. 2
XRD patterns of powders synthesized under slightly rich fuel condition and followed by calcination for 6 h at different temperatures: (a)uncalcined, (b) 800°C, (c) 900°C, (d)1000°C, (e)1200°C, (f)1300°C.
evidently different from the results reported by Stevenson (1997), who showed approximately 89 wt% LaGaO3. The difference may be due to the different amounts of fuel added. Under lean (pattern a) and rich (pattern d) fuel conditions, nearly the same results were obtained, indicating essentially the absence of LaGaO3 in the synthesized powders. Surprisingly, for slightly rich fuel condition (pattern b) as much as 90 wt% LaGaO3 phase was produced, as shown in Fig. 1. The different phase constitutions may be attributed to the different thermodynamic surroundings, i.e., under lean or rich fuel conditions, the less or more than stoichiometric glycine decreases the flame temperature, so that less thermal energy is available to develop the stable crystalline LaGaO3 phase. For the slightly rich fuel condition, the formation of LaGaO3 phase may well be due to the higher flame temperature. The morphologies of the precursors are somewhat confusing: a thread-like white precursor for stoichiometric condition and a coral-like white powder for slightly rich fuel condition, the latter being the coarsened product due to sintering at the higher flame temperature. Figure 2 shows the phase evolution of powders in terms of XRD measurements synthesized under slightly rich fuel condition and followed by calcination for 6 h at the temperatures of 800°, 900°, 1000°, 1200° and 1300°C. It can be seen that LaGaO3 exists in the uncalcined powder and the phase constitution has not changed after calcinations at 800°C, indicating that the LaGaO3 phase formed during the burning process has not changed with calcination at the low temperature of 800°C. Many researchers have reported that the LaGaO3 phase formation temperature is about 1000°C, so the low heat treatment effect is not evident. When calcined at 1300°C for 6 h, small amounts of other thermodynamically stable phases, such as LaSrGaO4, LaSrGa3O7, LaSrGaO4, and LaSrGa3O7 appear to take the place of the single LaGaO3 phase, making the synthesis of a pure single phase LSGM difficult. With further increase of calcination temperature, the amounts of the impurity phases decrease, dwindling to traces at 1500°C. Previous works have concluded that, independent of preparation technique, calcination up to 1500℃ is mandatory to obtain the pure LaGaO3 phase (Gorelov et al., 2001). For comparison, the XRD patterns of the powders prepared by solid-state reaction and the acrylamide polymerization technique are shown respectively in Figs. 3a and 3b. Fig. 3a shows that, after twice thermal treatment (1200℃ for 24 h), the fraction of LaGaO3 in the synthesized powder prepared by solid-state reaction has increased remarkably, though there exist profuse impurity phases such as LaSrGaO4 and LaSrGa3O7. Fig. 3b shows the XRD of powders prepared by the acrylamide polymerization technique, indicating the considerable amounts of the impurity phases. Compared to Fig. 2, it can be seen that the powders synthesized by the glycine–nitrate combustion method contain far less impurity phases than those prepared by solid-state reaction or acrylamide polymerization technique.
Liu, Yuan, Shi, Xu, Majewski & Aldinger: Synthesis of Lanthanum Gallate by Combustion Method
11
3.2 TEM micrographs -LSGM -LaSrGaO4 + -LaSrGa3O7
Relative density
a
2θ/°
b
Relative density
-LSGM -LaSrGaO4 + -LaSrGa3O7
Figure 4 shows the TEM micrographs of powders produced under different combustion fuel conditions. The particle size obtained under slightly rich fuel condition is evidently larger than that obtained under rich or lean fuel conditions (under lean fuel condition, the particles agglomerate), validating the result that the powders prepared under slightly rich fuel condition has been partially sintered because of the higher flame temperature. The size of particles prepared under rich fuel condition is less than 50 nm. The morphologies of powders obtained under lean and stoichiometric conditions are similar, indicating that combustion under these two conditions took place under similar flame temperatures and thus resulted in similar products. b
a
2θ/°
Fig. 3 XRD patterns of powders synthesized by (a) solid-state reaction method: 1- single calcination at 1200°C for 24 h, 2- after second time calcination at 1200°C for 24 h; (b) acrylamide polymerization technique: 1- heat treatment at 1000°C for 6 h, 2- 1200°C for 6h, 3-1300°C for 6 h. a
b
Fig. 5
TEM images of LSGM powders prepared by different routes: (a) solid-state reaction, (b) acrylamide polymerization.
Figures 5a and 5b show respectively the morphologies of powders synthesized by solid-state reaction (two runs of calcination at 1200°C for 24 h) and acrylamide polymerization (calcined at 1300°C for 6 h). It can be seen that the glycine-nitrate method can produce relatively small particle size in comparison with solid-state reaction and acrylamide polymerization. c
Fig. 4
d
TEM micrographs of LSGM powders prepared by glycine -nitrate technology under different fuel conditions: (a) lean fuel, (b) stoichiometric fuel, (c) slightly rich fuel, (d) rich fuel.
4. Conclusion Sr- and Mg-doped lanthanum gallate powders were synthesized by a glycine-nitrate combustion method. The effect of combustion fuel condition on the phase constitution and morphology of the synthesized powders was studied through XRD and TEM. The results show that slightly rich fuel condition can produce powders having higher LaGaO3 content than those under lean, stoichiometric or rich fuel condition. The TEM images also verify the results. In contrast with the solid–state reaction method and acrylamide polymerization technique, the glycine-nitrate combustion method can produce powders with far less amounts of impurity phases, smaller particle size and is a convenient and time-saving route to synthesize the LSGM powders.
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CHINA PARTICUOLOGY Vol. 4, No. 1, 2006
Acknowledgements The authors wish to acknowledge the financial support of this research from the Scientific Research Foundation for Returned Overseas Chinese Scholars, State Education Ministry, China, the Scientific Research Foundation of Hefei University of Technology and the Max-Plank Society, Germany.
References Cong, L., He, T., Ji, Y., Guan, P., Huang, Y. & Su, W. (2003). Synthesis and characterization of IT-electrolyte with perovskite structure La0.8Sr0.2Ga0.85Mg0.15O3-δby glycine-nitrate combustion method. J. Alloys Compd., 348, 325−331. Feng, M. & Goodenough, J. B. (1994). A superior oxide-ion conductor. Eur. J. Solid Inorg. Chem., 31, 663−672. Gorelov, V. P., Bronin, D. I., Sokolova, J. V., Näfe, H. & Aldinger, F. (2001). The effect of doping and processing conditions on properties of La1-zSrzGa1-yMgyO3-δ. J. Eur. Ceram. Soc., 21, 2311−2317. Huang, K., Feng, M. & Goodenough, J. B. (1996). Sol-gel synthesis of a new oxide-ion conductor Sr- and Mg-doped LaGaO3 perovskite. J. Am. Ceram. Soc., 79, 1100−1104.
Huang, K., Tichy, R. S. & Goodenough, J. B. (1998). Superior Perovskite oxide-ion conductor; strontium- and magnesiumdoped LaGaO3: I, phase relationships and electrical properties. J. Am. Ceram. Soc., 81, 2565−2575. Ishihara, T., Matsuda, H. & Takita, Y. (1994). Doped LaGaO3 perovskite type oxide as a new oxide ionic conductor. J. Am. Chem. Soc., 116, 3801−3803. Sin, A. & Sdier, P. (2000). Gelation by acrylamide, a quasi-universal medium for the synthesis of fine oxide powders for electroceramic applications. Adv. Mater., 12, 649−652. Stevenson, J. W., Armstrong, T. R., McCready, D. E., Pederson, L. R. & Weber, W. J. (1997). Processing and electrical properties of alkaline earth-doped lanthanum gallate. J. Electrochem. Soc., 144, 3613−3620. Tarancón, A., Dezanneau, G., Arbiol, J., Peiró, F. & Morante, J. R. (2003). Synthesis of nanocrystalline materials for SOFC applications by acrylamide polymerization. J. Power Sources, 118, 256−264. Tas. C. A., Majewski, J. & Aldinger, F. (2000). Chemical preparation of pure and strontium- and/or magnesium-doped lanthanum gallate powders. J. Am. Ceram. Soc., 83, 2954−2960. Manuscript received January 4, 2005 and accepted December, 28, 2005.