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Preparation of gadolinium gallium garnet polycrystalline material by coprecipitation method
November 2002
Materials Letters 56 (2002) 1098 – 1102 www.elsevier.com/locate/matlet
Preparation of gadolinium gallium garnet polycrystalline material by coprecipitation method Guangjun Zhao*, Tao Li, Xiaoming He, Jun Xu Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Tacheng Road 295, P.O. Box 800-216, Shanghai 201800, PR China Received 11 June 2001; accepted 9 August 2001
Abstract The gadolinium gallium garnet (Gd3Ga5O12, GGG) polycrystalline powder with pure phase has been prepared by coprecipitation method. The key factors for preparation of GGG powder by liquid-phase method were discussed in the paper. Compared with solid-state synthesis, the coprecipitation method possesses the merits of lower synthesis temperature and shorter sintering time. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Coprecipitation method; Gd3Ga5O12; GGG; Polycrystalline powder; Solid-state synthesis
1. Introduction Gadolinium gallium garnet (Gd3Ga5O12, GGG) single crystals are regarded as the ideal substrates for YIG and YIG-like magneto-optical epitaxial films, which are widely applied in the fields of optical isolators, optical waveguide and integrated optics [1 – 3]. Consequently, manufacture of high-quality and large-sized GGG single crystals has been paid much more attention at present. Because GGG single crystals are the congruent melt compounds [4], they are grown by the traditional Czochralski technique commonly. However, the serious decomposition and evaporation of Ga2O3 were frequently encountered during GGG single crystal
*
Corresponding author. Tel.: +86-21-59928755; fax: +86-2159928755. E-mail address: [email protected] (G. Zhao).
growth by Cz method, which makes it difficulty for growing high-quality GGG single crystals [5]. To decrease the evaporation of Ga2O3, the growth atmosphere of 2 vol.% O2+98 vol.% N2 was adopted by many authors [5,6]. Although little amount of oxygen will reduce the decomposition of Ga2O3 to some degree, it will oxidise the iridium crucible greatly as well, which gives rise to many iridium metal inclusions in the GGG single crystals. If the GGG polycrystalline materials without Ga2O3 in them are used as the starting charge for single crystal growth, and the pure neutral gas as the growth atmosphere, the largesized and high-quality GGG single crystals can be obtained by Czochralski technique [7]. As a result, it is very important to synthesize the GGG polycrystalline material with pure phase for high-quality single crystal growth. Hellstrom et al. [8] have reported the preparation of GGG polycrystalline material by means of solid-state reaction. To our knowledge, few literatures upon
0167-577X/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 5 7 7 X ( 0 2 ) 0 0 6 8 6 - 9
G. Zhao et al. / Materials Letters 56 (2002) 1098–1102
1099
detailed description of the liquid-phase method for preparation of GGG polycrystalline charge are reported. In this paper, the optimized procedures and conditions for preparation of GGG polycrystalline powder by coprecipitation method have been presented. The key factors for preparation of GGG polycrystalline materials by coprecipitation method were discussed. In addition, the comparisons between solid-state reaction method and liquid-phase method were also made in this letter.
2. Experimental After the high-purity Gd 2O 3 (z99.99%) and Ga2O3 (z99.999%) in the specific mole ratio [(a) stoichiometric ratio, e.g. Gd2O3/Ga2O3=3:5; (b) stoichiometric ratio with excess Ga2O3 1 wt.%; (c) stoichiometry with overweight Ga2O3 2 wt.%)] were weighted out respectively, they were separately dissolved into the HNO3 solutions with different concentrations (C1=5 mol/l, C2=0.5 mol/l). When they dissolved completely, the above solutions that have dissolved the Gd2O3 and Ga2O3 oxides were mixed. The fully mixed solution containing Gd3+ and Ga3+ cations was gradually dropped into the aqueous ammonia (pH=10) for titration. During the process of titration, the pH value of post-titration solution should be kept between 9 and 10. While titrating, the coprecipitate of Gd(OH)3 and Ga(OH)3 was being formed. After the coprecipitates were filtered, washed and dried, they were sintered in the furnace at 800 and 1000 jC for 15 h in the air. The optimized procedures for synthesis of GGG polycrystalline material by coprecipitation method are illustrated in Fig. 1. To make comparisons between the GGG polycrystalline materials prepared by liquid-phase method and by solid-state reaction method, the GGG samples 1 and 2 were synthesized using the solid-state reaction of parent oxides method. The synthesis conditions of samples 1 and 2 were in a 3:5 Gd2O3/Ga2O3 mole ratio (e.g. stoichiometric ratio) and they were sintered in the air at 800 and 1000 jC for 24 h, respectively. All the phase identifications of above GGG samples prepared by both liquid-phase method and by solid-state reaction method were examined by XRD
Fig. 1. Procedure diagram of synthesis of GGG polycrystalline material by liquid-phase coprecipitation method.
technique. The X-ray diffraction experiment was carried out using D/MAX-IIIC (RIKAKV) with CuKa radiation (k=0.154098 nm)and graphite monochromator. All the XRD patterns are shown in Figs. 2 and 3. (Figures can be seen in Sections 3.2 and 3.3.)
3. Results and discussion 3.1. The selectivity of pH value for coprecipitation Like Al(OH)3, the Ga(OH)3 hydroxide also displays basic and acidic functions, and it can be dissolved in the strong acid and basic solutions by the
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G. Zhao et al. / Materials Letters 56 (2002) 1098–1102
following chemical equations (a) and (b) at room temperature. For example, GaðOHÞ3 ðsÞ þ 3Hþ ¼ Ga3þ þ 3H2 O
ðaÞ
½Ga3þ Ksp1 K1 ¼ ¼ 3 ½Hþ Kw
ð1Þ
GaðOHÞ3 ðsÞ þ OH ¼ GaðOHÞ 4
ðbÞ
½GaðOHÞ 4 ¼ Kst Ksp1 ½OH
ð2Þ
K2 ¼
In the above formulae, K1 and K2 are the equilibrium constants of Eqs. (a) and (b), Ksp1(0.71035) is the solubility product of Ga(OH)3, Kst(1034.3) denotes stability constant of the Ga(OH)4 complex compound in the basic solution, and Kw(1014) means the ion product of water. Values of the above constants are those at room temperature (about 25 jC), and they are cited in the handbook of chemistry [9]. When the concentration of Ga3+ in the solution is less than 105 mol/l, for example, [Ga3+]<105 mol/l, it can be assumed that Ga3+ cation precipitates completely. According to Eq. (1), the lowest pH value for total precipitation of Ga3+ in acid solution is pH1, for example, pH1=log[H+]=105Kw3/Ksp1=4. Similarly, the highest pH value in alkali for precipitation can be deduced from Eq. (2), for example, pH2=14+log [OH]=14+105/(KstKsp1)=10. Consequently, the pH range for total precipitation of Ga3+ should be 4
ðcÞ
Ksp2 ¼ ½Gd3þ ½OH 3
ð3Þ
When Gd3+ cation precipitated completely, the concentration of Gd3+ should be less than 105mol/ l, for example, [Gd3+]=105 mol/l. Ksp2=2.11022 [Ksp2 is the solubility product of Gd(OH)3 at room temperature] [9]. Therefore, the pH value for total precipitation of Gd3+ cation should be pH>9.
Given the consideration about coprecipitation for Ga3+ and Gd3+ cations, the pH range for coprecipitation should be pH=9 – 10 in theory. 3.2. Optimized compositional proportion of Gd2O3 and Ga2O3 XRD patterns shown in Fig. 2 were those of GGG samples prepared by liquid-phase method, which were of different compositional proportion of Gd2O3 and Ga2O3. Sample a was 3:5 Gd2O3/Ga2O3 in mole ratio, sample b was of stoichiometric ratio and overweight Ga2O3 1 wt.%, and sample c was of stoichiometric ratio plus excess Ga2O3 2 wt.%. From the XRD patterns of a and b in the above Fig. 2, positions of diffraction peaks mostly agree with those of standard GGG; meanwhile, some positions are in accordance with those of Gd2O3. This result showed that samples a and b prepared by liquid-phase method possessed not only GGG phase, but also had the Gd2O3 phase. For sample c, positions of peaks agree exactly with those of standard GGG; furthermore, the peaks are also narrow and strong. These results indicated that the optimized compositional proportion should be in 3:5 Gd2O3/Ga2O3 mole ratio
Fig. 2. XRD patterns of GGG polycrystalline samples with different compositional proportion prepared by coprecipitation method; all samples were sintered at 1000 jC for 15 h. (a) Gd2O3/Ga2O3=3:5, (b) Ga2O3 overweight 1 wt.%, (c) Ga2O3 overweight 2 wt.%.
G. Zhao et al. / Materials Letters 56 (2002) 1098–1102
and overweight Ga2O3 2 wt.% for synthesis of GGG polycrystalline material by coprecipitation method. The Ga2O3 overweighting 2 wt.% in the liquidphase synthesis process may be explained by the following reasons. Firstly, due to the systematic discrepancies in the above calculations of pH value for Ga3+ total precipitation, the Ga3+ cation could not precipitate completely in the solution with pH=9 – 10 in practice. Secondly, because the titration in our experiment was dropping solution containing Ga3+ and Gd3+ cations into the basic solution of pH=10, it was possible that Ga(OH)3 hydroxide formed at the beginning of titration would be dissolved in the aqueous ammonia of pH=10. In addition, when coprecipitation sintered, Ga(OH)3 decomposed into Ga2O3 and it might evaporate in the air. However, the exact reason for loss of Ga2O3 in liquid-phase process will be investigated in the further experiment. Consequently, it is very necessary to adjust the compositional proportion of Gd2O3 and Ga2O3 for synthesis of GGG polycrystalline material with exact stoichiometric ratio. In our experiment, the optimized ratio of constitution was of stoichiometric ratio plus excess Ga2O3 2 wt.% in the given pH=9 – 10 solution. 3.3. The comparison with solid-state reaction method For comparison between GGG preparation by liquid-phase method and by solid-state method, samples 1 and 2 both in 3:5 Gd2O3/Ga2O3 mole ratio (stoichiomeric ratio) were sintered in air at 800 and 1000 jC for 24 h, respectively. Sample 3 with stoichiometric ratio plus excess Ga2O3 2 wt.% was sintered in the air at 800 jC for 15 h. The XRD patterns of samples 1 –3 are shown below Fig. 3. From Fig. 3, positions of diffraction peaks of samples 1 and 2 were different from those of the standard GGG totally, and it was composed of Gd2O3 and Ga2O3 phases. This means that GGG polycrystalline material did not synthesize at 800 –1000 jC even for 24 h by solid-state reaction method. In fact, using solid-state reaction method to prepare the GGG polycrystalline materials, high temperature (1350 – 1650 jC) and long time (at least 24 h) for Gd2O3 and Ga2O3 to react completely is very necessary [9]. However, for liquid-phase coprecipitation method, the GGG material with pure phase could be obtained in the lower sintered temperature (800 jC) and for
1101
Fig. 3. XRD patterns of GGG polycrystalline samples prepared by solid-state reaction (samples 1 and 2) and prepared by coprecipitation method (sample 3). (1) Gd2O3/Ga2O3=3:5, sintered at 800 jC for 24 h; (2) Gd2O3/Ga2O3=3:5, sintered at 1000 jC for 24 h; (3) Ga2O3 overweight 2 wt.% sintered at 800 jC for 15 h.
shorter time (15 h), because the coprecipitation increased the activity of GGG synthesis reaction. The XRD pattern of sample 3 in Fig. 3 agrees exactly with the pattern of the standard GGG, and sample 3 with the composition of Ga2O3 overweight 2 wt.% was sintered in air at 800 jC for 15 h. These results testified the above conclusion that liquid-phase synthesis method possesses the merits of lower synthesis temperature and shorter sintering time.
4. Conclusion Using coprecipitation method, the GGG polycrystalline materials were successfully prepared in our lab. The optimized synthesis conditions by liquid-phase method were presented as follows. The compositional proportion was 3:5 Gd2O3/Ga2O3 mole ratio plus excess Ga2O3 2 wt.%, the pH range for coprecipitation of Gd3+ and Ga3+ cations was pH=9 –10, the synthesis temperature and time for preparation of GGG polycrystalline materials were 800 jC and 15 h, respectively. Compared with solid-state reaction method, the coprecipitation method has advantages of lower syn-
1102
G. Zhao et al. / Materials Letters 56 (2002) 1098–1102
thesis temperature and shorter sintering time. At the same time, the GGG polycrystalline powder with exact stoichiometric ratio and pure phase can be obtained by coprecipitation method.
References [1] K. Shiraishi, Appl. Opt. 24 (1985) 951. [2] C.L. Wang, C.S. Tsai, J. Lightwave Technol. 15 (1997) 7908.
[3] [4] [5] [6]
N. Sugimoto, et al., J. Lightwave Technol. 14 (1996) 2537. J. Nicolas, et al., J. Solid State Chem. 52 (1984) 101. C.D. Brandle, et al., J. Cryst. Growth 12 (1972) 195. S.E. Stokowski, et al., IEEE J. Quantum Electron. 24 (1988) 934. [7] G.J. Zhao, et al., Proceedings of ICCG-13, 2001, in press. [8] E.E. Hellstrom, et al., J. Am. Ceram. Soc. 72 (1989) 1376. [9] A. John, Lange’s Handbook of Chemistry, 11th edn., McGrawHill, New York, 1973.
Materials Letters 56 (2002) 1098 – 1102 www.elsevier.com/locate/matlet
Preparation of gadolinium gallium garnet polycrystalline material by coprecipitation method Guangjun Zhao*, Tao Li, Xiaoming He, Jun Xu Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Tacheng Road 295, P.O. Box 800-216, Shanghai 201800, PR China Received 11 June 2001; accepted 9 August 2001
Abstract The gadolinium gallium garnet (Gd3Ga5O12, GGG) polycrystalline powder with pure phase has been prepared by coprecipitation method. The key factors for preparation of GGG powder by liquid-phase method were discussed in the paper. Compared with solid-state synthesis, the coprecipitation method possesses the merits of lower synthesis temperature and shorter sintering time. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Coprecipitation method; Gd3Ga5O12; GGG; Polycrystalline powder; Solid-state synthesis
1. Introduction Gadolinium gallium garnet (Gd3Ga5O12, GGG) single crystals are regarded as the ideal substrates for YIG and YIG-like magneto-optical epitaxial films, which are widely applied in the fields of optical isolators, optical waveguide and integrated optics [1 – 3]. Consequently, manufacture of high-quality and large-sized GGG single crystals has been paid much more attention at present. Because GGG single crystals are the congruent melt compounds [4], they are grown by the traditional Czochralski technique commonly. However, the serious decomposition and evaporation of Ga2O3 were frequently encountered during GGG single crystal
*
Corresponding author. Tel.: +86-21-59928755; fax: +86-2159928755. E-mail address: [email protected] (G. Zhao).
growth by Cz method, which makes it difficulty for growing high-quality GGG single crystals [5]. To decrease the evaporation of Ga2O3, the growth atmosphere of 2 vol.% O2+98 vol.% N2 was adopted by many authors [5,6]. Although little amount of oxygen will reduce the decomposition of Ga2O3 to some degree, it will oxidise the iridium crucible greatly as well, which gives rise to many iridium metal inclusions in the GGG single crystals. If the GGG polycrystalline materials without Ga2O3 in them are used as the starting charge for single crystal growth, and the pure neutral gas as the growth atmosphere, the largesized and high-quality GGG single crystals can be obtained by Czochralski technique [7]. As a result, it is very important to synthesize the GGG polycrystalline material with pure phase for high-quality single crystal growth. Hellstrom et al. [8] have reported the preparation of GGG polycrystalline material by means of solid-state reaction. To our knowledge, few literatures upon
0167-577X/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 5 7 7 X ( 0 2 ) 0 0 6 8 6 - 9
G. Zhao et al. / Materials Letters 56 (2002) 1098–1102
1099
detailed description of the liquid-phase method for preparation of GGG polycrystalline charge are reported. In this paper, the optimized procedures and conditions for preparation of GGG polycrystalline powder by coprecipitation method have been presented. The key factors for preparation of GGG polycrystalline materials by coprecipitation method were discussed. In addition, the comparisons between solid-state reaction method and liquid-phase method were also made in this letter.
2. Experimental After the high-purity Gd 2O 3 (z99.99%) and Ga2O3 (z99.999%) in the specific mole ratio [(a) stoichiometric ratio, e.g. Gd2O3/Ga2O3=3:5; (b) stoichiometric ratio with excess Ga2O3 1 wt.%; (c) stoichiometry with overweight Ga2O3 2 wt.%)] were weighted out respectively, they were separately dissolved into the HNO3 solutions with different concentrations (C1=5 mol/l, C2=0.5 mol/l). When they dissolved completely, the above solutions that have dissolved the Gd2O3 and Ga2O3 oxides were mixed. The fully mixed solution containing Gd3+ and Ga3+ cations was gradually dropped into the aqueous ammonia (pH=10) for titration. During the process of titration, the pH value of post-titration solution should be kept between 9 and 10. While titrating, the coprecipitate of Gd(OH)3 and Ga(OH)3 was being formed. After the coprecipitates were filtered, washed and dried, they were sintered in the furnace at 800 and 1000 jC for 15 h in the air. The optimized procedures for synthesis of GGG polycrystalline material by coprecipitation method are illustrated in Fig. 1. To make comparisons between the GGG polycrystalline materials prepared by liquid-phase method and by solid-state reaction method, the GGG samples 1 and 2 were synthesized using the solid-state reaction of parent oxides method. The synthesis conditions of samples 1 and 2 were in a 3:5 Gd2O3/Ga2O3 mole ratio (e.g. stoichiometric ratio) and they were sintered in the air at 800 and 1000 jC for 24 h, respectively. All the phase identifications of above GGG samples prepared by both liquid-phase method and by solid-state reaction method were examined by XRD
Fig. 1. Procedure diagram of synthesis of GGG polycrystalline material by liquid-phase coprecipitation method.
technique. The X-ray diffraction experiment was carried out using D/MAX-IIIC (RIKAKV) with CuKa radiation (k=0.154098 nm)and graphite monochromator. All the XRD patterns are shown in Figs. 2 and 3. (Figures can be seen in Sections 3.2 and 3.3.)
3. Results and discussion 3.1. The selectivity of pH value for coprecipitation Like Al(OH)3, the Ga(OH)3 hydroxide also displays basic and acidic functions, and it can be dissolved in the strong acid and basic solutions by the
1100
G. Zhao et al. / Materials Letters 56 (2002) 1098–1102
following chemical equations (a) and (b) at room temperature. For example, GaðOHÞ3 ðsÞ þ 3Hþ ¼ Ga3þ þ 3H2 O
ðaÞ
½Ga3þ Ksp1 K1 ¼ ¼ 3 ½Hþ Kw
ð1Þ
GaðOHÞ3 ðsÞ þ OH ¼ GaðOHÞ 4
ðbÞ
½GaðOHÞ 4 ¼ Kst Ksp1 ½OH
ð2Þ
K2 ¼
In the above formulae, K1 and K2 are the equilibrium constants of Eqs. (a) and (b), Ksp1(0.71035) is the solubility product of Ga(OH)3, Kst(1034.3) denotes stability constant of the Ga(OH)4 complex compound in the basic solution, and Kw(1014) means the ion product of water. Values of the above constants are those at room temperature (about 25 jC), and they are cited in the handbook of chemistry [9]. When the concentration of Ga3+ in the solution is less than 105 mol/l, for example, [Ga3+]<105 mol/l, it can be assumed that Ga3+ cation precipitates completely. According to Eq. (1), the lowest pH value for total precipitation of Ga3+ in acid solution is pH1, for example, pH1=log[H+]=105Kw3/Ksp1=4. Similarly, the highest pH value in alkali for precipitation can be deduced from Eq. (2), for example, pH2=14+log [OH]=14+105/(KstKsp1)=10. Consequently, the pH range for total precipitation of Ga3+ should be 4
ðcÞ
Ksp2 ¼ ½Gd3þ ½OH 3
ð3Þ
When Gd3+ cation precipitated completely, the concentration of Gd3+ should be less than 105mol/ l, for example, [Gd3+]=105 mol/l. Ksp2=2.11022 [Ksp2 is the solubility product of Gd(OH)3 at room temperature] [9]. Therefore, the pH value for total precipitation of Gd3+ cation should be pH>9.
Given the consideration about coprecipitation for Ga3+ and Gd3+ cations, the pH range for coprecipitation should be pH=9 – 10 in theory. 3.2. Optimized compositional proportion of Gd2O3 and Ga2O3 XRD patterns shown in Fig. 2 were those of GGG samples prepared by liquid-phase method, which were of different compositional proportion of Gd2O3 and Ga2O3. Sample a was 3:5 Gd2O3/Ga2O3 in mole ratio, sample b was of stoichiometric ratio and overweight Ga2O3 1 wt.%, and sample c was of stoichiometric ratio plus excess Ga2O3 2 wt.%. From the XRD patterns of a and b in the above Fig. 2, positions of diffraction peaks mostly agree with those of standard GGG; meanwhile, some positions are in accordance with those of Gd2O3. This result showed that samples a and b prepared by liquid-phase method possessed not only GGG phase, but also had the Gd2O3 phase. For sample c, positions of peaks agree exactly with those of standard GGG; furthermore, the peaks are also narrow and strong. These results indicated that the optimized compositional proportion should be in 3:5 Gd2O3/Ga2O3 mole ratio
Fig. 2. XRD patterns of GGG polycrystalline samples with different compositional proportion prepared by coprecipitation method; all samples were sintered at 1000 jC for 15 h. (a) Gd2O3/Ga2O3=3:5, (b) Ga2O3 overweight 1 wt.%, (c) Ga2O3 overweight 2 wt.%.
G. Zhao et al. / Materials Letters 56 (2002) 1098–1102
and overweight Ga2O3 2 wt.% for synthesis of GGG polycrystalline material by coprecipitation method. The Ga2O3 overweighting 2 wt.% in the liquidphase synthesis process may be explained by the following reasons. Firstly, due to the systematic discrepancies in the above calculations of pH value for Ga3+ total precipitation, the Ga3+ cation could not precipitate completely in the solution with pH=9 – 10 in practice. Secondly, because the titration in our experiment was dropping solution containing Ga3+ and Gd3+ cations into the basic solution of pH=10, it was possible that Ga(OH)3 hydroxide formed at the beginning of titration would be dissolved in the aqueous ammonia of pH=10. In addition, when coprecipitation sintered, Ga(OH)3 decomposed into Ga2O3 and it might evaporate in the air. However, the exact reason for loss of Ga2O3 in liquid-phase process will be investigated in the further experiment. Consequently, it is very necessary to adjust the compositional proportion of Gd2O3 and Ga2O3 for synthesis of GGG polycrystalline material with exact stoichiometric ratio. In our experiment, the optimized ratio of constitution was of stoichiometric ratio plus excess Ga2O3 2 wt.% in the given pH=9 – 10 solution. 3.3. The comparison with solid-state reaction method For comparison between GGG preparation by liquid-phase method and by solid-state method, samples 1 and 2 both in 3:5 Gd2O3/Ga2O3 mole ratio (stoichiomeric ratio) were sintered in air at 800 and 1000 jC for 24 h, respectively. Sample 3 with stoichiometric ratio plus excess Ga2O3 2 wt.% was sintered in the air at 800 jC for 15 h. The XRD patterns of samples 1 –3 are shown below Fig. 3. From Fig. 3, positions of diffraction peaks of samples 1 and 2 were different from those of the standard GGG totally, and it was composed of Gd2O3 and Ga2O3 phases. This means that GGG polycrystalline material did not synthesize at 800 –1000 jC even for 24 h by solid-state reaction method. In fact, using solid-state reaction method to prepare the GGG polycrystalline materials, high temperature (1350 – 1650 jC) and long time (at least 24 h) for Gd2O3 and Ga2O3 to react completely is very necessary [9]. However, for liquid-phase coprecipitation method, the GGG material with pure phase could be obtained in the lower sintered temperature (800 jC) and for
1101
Fig. 3. XRD patterns of GGG polycrystalline samples prepared by solid-state reaction (samples 1 and 2) and prepared by coprecipitation method (sample 3). (1) Gd2O3/Ga2O3=3:5, sintered at 800 jC for 24 h; (2) Gd2O3/Ga2O3=3:5, sintered at 1000 jC for 24 h; (3) Ga2O3 overweight 2 wt.% sintered at 800 jC for 15 h.
shorter time (15 h), because the coprecipitation increased the activity of GGG synthesis reaction. The XRD pattern of sample 3 in Fig. 3 agrees exactly with the pattern of the standard GGG, and sample 3 with the composition of Ga2O3 overweight 2 wt.% was sintered in air at 800 jC for 15 h. These results testified the above conclusion that liquid-phase synthesis method possesses the merits of lower synthesis temperature and shorter sintering time.
4. Conclusion Using coprecipitation method, the GGG polycrystalline materials were successfully prepared in our lab. The optimized synthesis conditions by liquid-phase method were presented as follows. The compositional proportion was 3:5 Gd2O3/Ga2O3 mole ratio plus excess Ga2O3 2 wt.%, the pH range for coprecipitation of Gd3+ and Ga3+ cations was pH=9 –10, the synthesis temperature and time for preparation of GGG polycrystalline materials were 800 jC and 15 h, respectively. Compared with solid-state reaction method, the coprecipitation method has advantages of lower syn-
1102
G. Zhao et al. / Materials Letters 56 (2002) 1098–1102
thesis temperature and shorter sintering time. At the same time, the GGG polycrystalline powder with exact stoichiometric ratio and pure phase can be obtained by coprecipitation method.
References [1] K. Shiraishi, Appl. Opt. 24 (1985) 951. [2] C.L. Wang, C.S. Tsai, J. Lightwave Technol. 15 (1997) 7908.
[3] [4] [5] [6]
N. Sugimoto, et al., J. Lightwave Technol. 14 (1996) 2537. J. Nicolas, et al., J. Solid State Chem. 52 (1984) 101. C.D. Brandle, et al., J. Cryst. Growth 12 (1972) 195. S.E. Stokowski, et al., IEEE J. Quantum Electron. 24 (1988) 934. [7] G.J. Zhao, et al., Proceedings of ICCG-13, 2001, in press. [8] E.E. Hellstrom, et al., J. Am. Ceram. Soc. 72 (1989) 1376. [9] A. John, Lange’s Handbook of Chemistry, 11th edn., McGrawHill, New York, 1973.