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Hydrothermal synthesis and characterization of orthorhombic yttrium aluminum perovskites (YAP)
Materials Chemistry and Physics 112 (2008) 723–725
Contents lists available at ScienceDirect
Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Materials science communication
Hydrothermal synthesis and characterization of orthorhombic yttrium aluminum perovskites (YAP) B. Basavalingu a,∗ , H.N. Girish a , K. Byrappa a , Kohei Soga b a
Department of Studies in Geology, University of Mysore, Manasagangotri, Mysore 570006, India Department of Material Science and Technology, Tokyo University of Science, 2641 Yamazaki, 278-8510 Noda, Chiba, Japan b
a r t i c l e
i n f o
Article history: Received 9 February 2008 Received in revised form 13 May 2008 Accepted 15 June 2008 Keywords: YAP Hydrothermal Supercritical fluid
a b s t r a c t Yttrium aluminum perovskite (YAP) is a promising high temperature ceramic material, known for its structural, mechanical and optical properties. YAP’s also known as an ideal host material for solid-state lasers and phosphors. Polycrystals of yttrium aluminum perovskites were synthesized for the first time by employing hydrothermal supercritical fluid technique, in the pressure–temperature range of 100–200 MPa and 650–750 ◦ C. The synthesized YAP’s were characterized using powder XRD, SEM and EDAX studies. The X-ray diffraction pattern matches well with the reported orthorhombic YAP pattern (JCPDS-70.1677). © 2008 Elsevier B.V. All rights reserved.
1. Introduction The yttrium aluminum perovskite, YAlO3 (YAP) is a metastable form in the Y2 O3 –Al2 O3 system, which is formed together with stable oxide phases such as cubic Y3 Al5 O12 (YAG) and monoclinic Y4 Al2 O9 (YAM) [1,2]. YAG is very well known as phosphors and laser host material, widely used in display devices [3] like televisions, projection TV’s, field emissions, etc. The orthorhombic form of YAP’s are considered as the ideal replacement in many respects to YAG [4]. YAP’s are known for mechanical, optical and electrical properties, and they have low dielectric constant, suitable for microwave or high frequency applications. YAP’s have three kinetically favored forms viz., hexagonal, orthorhombic and cubic, known as YAlO3 -I, YAlO3 -II, YAlO3 -III, respectively [5]. The YAP’s crystallizes in the orthorhombically distorted perovskite structure, which lies between perovskite and ilmenite structure [1]. They offer several advantages over YAGs in laser properties and doping it with some of the active transition and rare earth elements will significantly alter the laser emissions, since it provides ideal distribution coefficients for dopants [6]. These oxides were commonly fabricated by solid-state reactions. Such type of preparation needs extensive mechanical mixing of high purity oxides and firing at temperatures around 1200 ◦ C. This process of prolonged heating generally does not produce pure phases and it invariably consists
∗ Corresponding author. E-mail address: [email protected] (B. Basavalingu). 0254-0584/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2008.06.049
of metastable phases [7,8]. Since the YAP’s melts incongruently and is metastable, hence its preparation by melt technique is rather difficult. However, small crystals of YAP’s have been prepared by other high temperature techniques such as flux [9] and hollow cathode floating zone [10] methods. But, these high temperature processes of preparation consume lot of energy and lead to certain thermally induced strains in the resultant products, thus affecting their quality. For several optical applications, ultra fine materials are required [11] and by conventional high temperature techniques it is difficult to get fine powders. Because, of the above said reasons, sol–gel technique has been attempted by several workers [12–14] for the preparation of YAP’s. Even these wet chemical methods could not produce single phase because of the preferential formation of other phases, such as YAG and YAM. Hence, the present authors have explored the hydrothermal route for the preparation of YAPs. Here the authors report the first ever successful synthesis of orthorhombic YAP crystals employing hydrothermal technique under the influence of supercritical water/carbon dioxide. 2. Experimental technique Hydrothermal synthesis of yttrium aluminum perovskite’s were carried out using the externally heated (Tuttle–Roy test tube type) pressure vessels. The starting charges used are the co-precipitated gels of the yttrium and aluminum. The coprecipitated gels were preferred instead of mixed oxides of yttrium and aluminum, because the gels are known to serve as more reactive starting materials. The coprecipitated gel was prepared by following the method described by Hamilton and Henderson (1954) [15] for the preparation of silicate minerals. Thus the gels were prepared by neutralizing the nitrate solutions of yttrium and aluminum of known concentrations, taken in appropriate quantity to prepare a targeted amount YAlO3
724
B. Basavalingu et al. / Materials Chemistry and Physics 112 (2008) 723–725
Fig. 2. XRD patterns of products obtained in the runs bg-61 & bg-47 compared with reported pattern of PDF 701677.
Table 2 Table showing the EDAX analysis of the YAlO3 crystal in atomic percentage
Fig. 1. Schematic diagram showing the steps of preparation of co-precipitated gel.
gel. Fig. 1 shows schematic flow chart of different steps involved in the preparation of co-precipitated gel. The precipitate thus obtained is then fired above 600 ◦ C until the constancy in weight as well as the predetermined amount is achieved. If there is a weight deviation of more than 0.5% such gels were discarded. The starting charge comprising the co-precipitated gel and water/organic solvent were enclosed in platinum/gold capsules (4 mm dia., 40 mm length, having a wall thickness of 0.1 mm) were sealed by arc welding. The capsules were checked for any leakage after sealing and then placed in the autoclaves. The temperature and pressure were monitored constantly until they equilibrated with the set value. The duration of all the runs was 60–80 h. The runs were quenched with air blast followed by dipping the autoclave in to cold-water bath. The capsules were opened and the products were recovered carefully, washed, dried and subjected to XRD, SEM and EDAX studies for further characterization.
3. Results and discussion The experimental details and the resultant products are tabulated in Table 1. The experiments using the mixed oxides or individual gels taken in stoichiometric proportions as starting material did not yield the desired product but, by using coprecipitated gel as starting material a homogenous phase of YAP was formed. It is evident from the results that the stable region for the formation of orthorhombic YAP crystals was at temperatures above 650 ◦ C and pressures in the range of 100–150 MPa in both water and carbon dioxide environment inside the capsule. Indicating that the super critical water or carbon dioxide environment inside the capsule has similar effect on the formation
O
Al
Y
Total
32.47 at.%
27.97 at.%
39.57 at.%
100 at.%
of YAP phase. Further, YAP phase formation is more temperature dependent rather than the pressure. At temperatures less than 650 ◦ C the run products were mixture of respective oxide phases, with the dominance of corundum phase. The crystalline products obtained were confirmed by X-ray powder diffraction technique and further characterization was carried out using FTIR, and SEM supported with EDAX analysis. The X-ray diffraction studies of the precursor material, i.e. the co-precipitated gel (even after firing in air above 600 ◦ C) used as starting charge confirm that it was amorphous. The experimental run products of bg-61 and bg-47 were subjected to XRD studies, which confirmed that the product obtained are crystalline and belongs to orthorhombic YAlO3 phase (Fig. 2). The XRD patterns match well with that of the reported YAlO3 phase of PDF = 701677. The refined cell parameters ao = 5.330, bo = 7.375, co = 5.180 were obtained using CHECKCELL. The morphology and the particle size of the crystals obtained in the above mentioned runs are analyzed using the SEM (Fig. 3). The selected area on the crystals was also subjected to EDAX analysis and the atomic wt% is tabulated in Table 2. Morphological study supported with compositional analysis again confirms that the crystals obtained were orthorhombic and posses nominal phase stoichiometry. Thus, proving the supercritical fluids generated inside the autoclave has great influence in not only stabilizing YAP phase at low temperature but, also in achieving
Table 1 Experimental details and run products obtained for hydrothermal synthesis of YAP phase Run no.
Starting charge
Temp. (◦ C)
Pressure (MPa)
Duration (h)
Run products
Bg-26 Bg-27 Bg-34 Bg-36 Bg-39 Bg-40 Bg-40 Bg-43 Bg-47 Bg-54 Bg-56 Bg-61
Y2 O3 + Al2 O3 + H2 O Y2 O3 + Al2 O3 + HCOOH Y2 O3 + Al isopropoxide + H2 O Gels of Y2 O3 + Al2 O3 + H2 O YAlO3 -co-precipitated gel + H2 O YAlO3 -co-precipitated gel + H2 O YAlO3 -co-precipitated gel + H2 O YAlO3 -co-precipitated gel + HCOOH YAlO3 -co-precipitated gel + H2 O YAlO3 -co-precipitated gel + HCOOH YAlO3 -co-precipitated gel + H2 O YAlO3 -co-precipitated gel + HCOOH
550 600 600 650 400 500 600 700 700 600 650 650
150 180 200 180 190 175 180 200 220 150 160 200
90 82 75 100 92 120 98 120 102 72 96 86
Y2 O3 + white powder Y2 O3 + white powder Y2 O3 + Al2 O3 Y2 O3 + Al2 O3 Y2 O3 + white powder Y2 O3 + white powder Y2 O3 + Al2 O3 YAlO3 YAlO3 Y2 O3 + white powder YAlO3 YAlO3
B. Basavalingu et al. / Materials Chemistry and Physics 112 (2008) 723–725
725
Fig. 3. Photomicrographs of SEM images of YAlO3 crystals along with EDAX results.
the high degree of compositional and morphological homogeneity. 4. Conclusions The YAP crystals synthesis under hydrothermal condition is sensitive to the nature of the starting materials used and the synthesis temperature. The single phase of YAP has been difficult to synthesize so far due to the need of controlled stoichiometric composition. Crystallization of YAP occurs at many low temperatures when compared to temperatures required for solid-state reactions or sol gel techniques. In this paper, we have clearly demonstrated the synthesis of YAP crystals employing hydrothermal technique, under the influence of supercritical fluid, which is a boost for further investigations to the synthesis of similar oxides with several transition metal and rare earth elements as dopants for specialized application such as lasers and phosphors.
References [1] I. Warshaw, R. Roy, J. Am. Ceram. Soc. 42 (1959) 434. [2] S. Mathur, H. Shen, R. Rapalaviciute, A. Kareiva, N. Donia, J. Mater. Chem. 14 (2004) 3259–3265. [3] I.F. Elder, M.J.P. Payne, Optics Comm. 148 (1998) 265–269. [4] K. Gowda, J. Mater. Sci., Lett. 5 (1986) 1029–1032. [5] J. Marchal, T. John, R. Baranwal, T. Hinklin, R.R. Laine, Chem. Mater. 16 (2004) 822. [6] M. Harada, A. Ue, M. Inoue, X. Guo, K. Sakurai, J. Mater. Sci. Lett. 20 (2001) 741–742. [7] Ya Zhydachevskii, A. Durygin, V. Drozd, A. Suchocki, D. Sugak, J. Wrobel, J. Phys.: Condens. Matter 20 (2008) 095204. [8] J.R. Lo, T.Y. Tseng, Mater. Chem. Phys. 56 (1998) 56–62. [9] J.P. Remeika, J. Am. Chem. Soc. 78 (1956) 4259. [10] W. Class, J. Cryst. Growth 3/4 (1968) 241. [11] D.R. Messier, G.E. Gazza, Am. Ceram. Soc. Bull. 51 (1972) 692. [12] R.P. Rao, J. Electrochem. Soc. 143 (1996) 189. [13] V.S. Krylov, I.L. Belova, R.L. Magunov, V.D. Kozlov, V. Kalinichenko, N.P. Krot’ko, Inorg. Mater. 9 (1973) 1233. [14] M. Stockenhuber, H. Mayer, J.A. Lercher, J. Am. Ceram. Soc. 76 (1993) 1185. [15] D.L. Hamilton, C.M.B. Henderson, Text Book on Silicate Synthesis, 1958, p. 532.
Contents lists available at ScienceDirect
Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Materials science communication
Hydrothermal synthesis and characterization of orthorhombic yttrium aluminum perovskites (YAP) B. Basavalingu a,∗ , H.N. Girish a , K. Byrappa a , Kohei Soga b a
Department of Studies in Geology, University of Mysore, Manasagangotri, Mysore 570006, India Department of Material Science and Technology, Tokyo University of Science, 2641 Yamazaki, 278-8510 Noda, Chiba, Japan b
a r t i c l e
i n f o
Article history: Received 9 February 2008 Received in revised form 13 May 2008 Accepted 15 June 2008 Keywords: YAP Hydrothermal Supercritical fluid
a b s t r a c t Yttrium aluminum perovskite (YAP) is a promising high temperature ceramic material, known for its structural, mechanical and optical properties. YAP’s also known as an ideal host material for solid-state lasers and phosphors. Polycrystals of yttrium aluminum perovskites were synthesized for the first time by employing hydrothermal supercritical fluid technique, in the pressure–temperature range of 100–200 MPa and 650–750 ◦ C. The synthesized YAP’s were characterized using powder XRD, SEM and EDAX studies. The X-ray diffraction pattern matches well with the reported orthorhombic YAP pattern (JCPDS-70.1677). © 2008 Elsevier B.V. All rights reserved.
1. Introduction The yttrium aluminum perovskite, YAlO3 (YAP) is a metastable form in the Y2 O3 –Al2 O3 system, which is formed together with stable oxide phases such as cubic Y3 Al5 O12 (YAG) and monoclinic Y4 Al2 O9 (YAM) [1,2]. YAG is very well known as phosphors and laser host material, widely used in display devices [3] like televisions, projection TV’s, field emissions, etc. The orthorhombic form of YAP’s are considered as the ideal replacement in many respects to YAG [4]. YAP’s are known for mechanical, optical and electrical properties, and they have low dielectric constant, suitable for microwave or high frequency applications. YAP’s have three kinetically favored forms viz., hexagonal, orthorhombic and cubic, known as YAlO3 -I, YAlO3 -II, YAlO3 -III, respectively [5]. The YAP’s crystallizes in the orthorhombically distorted perovskite structure, which lies between perovskite and ilmenite structure [1]. They offer several advantages over YAGs in laser properties and doping it with some of the active transition and rare earth elements will significantly alter the laser emissions, since it provides ideal distribution coefficients for dopants [6]. These oxides were commonly fabricated by solid-state reactions. Such type of preparation needs extensive mechanical mixing of high purity oxides and firing at temperatures around 1200 ◦ C. This process of prolonged heating generally does not produce pure phases and it invariably consists
∗ Corresponding author. E-mail address: [email protected] (B. Basavalingu). 0254-0584/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2008.06.049
of metastable phases [7,8]. Since the YAP’s melts incongruently and is metastable, hence its preparation by melt technique is rather difficult. However, small crystals of YAP’s have been prepared by other high temperature techniques such as flux [9] and hollow cathode floating zone [10] methods. But, these high temperature processes of preparation consume lot of energy and lead to certain thermally induced strains in the resultant products, thus affecting their quality. For several optical applications, ultra fine materials are required [11] and by conventional high temperature techniques it is difficult to get fine powders. Because, of the above said reasons, sol–gel technique has been attempted by several workers [12–14] for the preparation of YAP’s. Even these wet chemical methods could not produce single phase because of the preferential formation of other phases, such as YAG and YAM. Hence, the present authors have explored the hydrothermal route for the preparation of YAPs. Here the authors report the first ever successful synthesis of orthorhombic YAP crystals employing hydrothermal technique under the influence of supercritical water/carbon dioxide. 2. Experimental technique Hydrothermal synthesis of yttrium aluminum perovskite’s were carried out using the externally heated (Tuttle–Roy test tube type) pressure vessels. The starting charges used are the co-precipitated gels of the yttrium and aluminum. The coprecipitated gels were preferred instead of mixed oxides of yttrium and aluminum, because the gels are known to serve as more reactive starting materials. The coprecipitated gel was prepared by following the method described by Hamilton and Henderson (1954) [15] for the preparation of silicate minerals. Thus the gels were prepared by neutralizing the nitrate solutions of yttrium and aluminum of known concentrations, taken in appropriate quantity to prepare a targeted amount YAlO3
724
B. Basavalingu et al. / Materials Chemistry and Physics 112 (2008) 723–725
Fig. 2. XRD patterns of products obtained in the runs bg-61 & bg-47 compared with reported pattern of PDF 701677.
Table 2 Table showing the EDAX analysis of the YAlO3 crystal in atomic percentage
Fig. 1. Schematic diagram showing the steps of preparation of co-precipitated gel.
gel. Fig. 1 shows schematic flow chart of different steps involved in the preparation of co-precipitated gel. The precipitate thus obtained is then fired above 600 ◦ C until the constancy in weight as well as the predetermined amount is achieved. If there is a weight deviation of more than 0.5% such gels were discarded. The starting charge comprising the co-precipitated gel and water/organic solvent were enclosed in platinum/gold capsules (4 mm dia., 40 mm length, having a wall thickness of 0.1 mm) were sealed by arc welding. The capsules were checked for any leakage after sealing and then placed in the autoclaves. The temperature and pressure were monitored constantly until they equilibrated with the set value. The duration of all the runs was 60–80 h. The runs were quenched with air blast followed by dipping the autoclave in to cold-water bath. The capsules were opened and the products were recovered carefully, washed, dried and subjected to XRD, SEM and EDAX studies for further characterization.
3. Results and discussion The experimental details and the resultant products are tabulated in Table 1. The experiments using the mixed oxides or individual gels taken in stoichiometric proportions as starting material did not yield the desired product but, by using coprecipitated gel as starting material a homogenous phase of YAP was formed. It is evident from the results that the stable region for the formation of orthorhombic YAP crystals was at temperatures above 650 ◦ C and pressures in the range of 100–150 MPa in both water and carbon dioxide environment inside the capsule. Indicating that the super critical water or carbon dioxide environment inside the capsule has similar effect on the formation
O
Al
Y
Total
32.47 at.%
27.97 at.%
39.57 at.%
100 at.%
of YAP phase. Further, YAP phase formation is more temperature dependent rather than the pressure. At temperatures less than 650 ◦ C the run products were mixture of respective oxide phases, with the dominance of corundum phase. The crystalline products obtained were confirmed by X-ray powder diffraction technique and further characterization was carried out using FTIR, and SEM supported with EDAX analysis. The X-ray diffraction studies of the precursor material, i.e. the co-precipitated gel (even after firing in air above 600 ◦ C) used as starting charge confirm that it was amorphous. The experimental run products of bg-61 and bg-47 were subjected to XRD studies, which confirmed that the product obtained are crystalline and belongs to orthorhombic YAlO3 phase (Fig. 2). The XRD patterns match well with that of the reported YAlO3 phase of PDF = 701677. The refined cell parameters ao = 5.330, bo = 7.375, co = 5.180 were obtained using CHECKCELL. The morphology and the particle size of the crystals obtained in the above mentioned runs are analyzed using the SEM (Fig. 3). The selected area on the crystals was also subjected to EDAX analysis and the atomic wt% is tabulated in Table 2. Morphological study supported with compositional analysis again confirms that the crystals obtained were orthorhombic and posses nominal phase stoichiometry. Thus, proving the supercritical fluids generated inside the autoclave has great influence in not only stabilizing YAP phase at low temperature but, also in achieving
Table 1 Experimental details and run products obtained for hydrothermal synthesis of YAP phase Run no.
Starting charge
Temp. (◦ C)
Pressure (MPa)
Duration (h)
Run products
Bg-26 Bg-27 Bg-34 Bg-36 Bg-39 Bg-40 Bg-40 Bg-43 Bg-47 Bg-54 Bg-56 Bg-61
Y2 O3 + Al2 O3 + H2 O Y2 O3 + Al2 O3 + HCOOH Y2 O3 + Al isopropoxide + H2 O Gels of Y2 O3 + Al2 O3 + H2 O YAlO3 -co-precipitated gel + H2 O YAlO3 -co-precipitated gel + H2 O YAlO3 -co-precipitated gel + H2 O YAlO3 -co-precipitated gel + HCOOH YAlO3 -co-precipitated gel + H2 O YAlO3 -co-precipitated gel + HCOOH YAlO3 -co-precipitated gel + H2 O YAlO3 -co-precipitated gel + HCOOH
550 600 600 650 400 500 600 700 700 600 650 650
150 180 200 180 190 175 180 200 220 150 160 200
90 82 75 100 92 120 98 120 102 72 96 86
Y2 O3 + white powder Y2 O3 + white powder Y2 O3 + Al2 O3 Y2 O3 + Al2 O3 Y2 O3 + white powder Y2 O3 + white powder Y2 O3 + Al2 O3 YAlO3 YAlO3 Y2 O3 + white powder YAlO3 YAlO3
B. Basavalingu et al. / Materials Chemistry and Physics 112 (2008) 723–725
725
Fig. 3. Photomicrographs of SEM images of YAlO3 crystals along with EDAX results.
the high degree of compositional and morphological homogeneity. 4. Conclusions The YAP crystals synthesis under hydrothermal condition is sensitive to the nature of the starting materials used and the synthesis temperature. The single phase of YAP has been difficult to synthesize so far due to the need of controlled stoichiometric composition. Crystallization of YAP occurs at many low temperatures when compared to temperatures required for solid-state reactions or sol gel techniques. In this paper, we have clearly demonstrated the synthesis of YAP crystals employing hydrothermal technique, under the influence of supercritical fluid, which is a boost for further investigations to the synthesis of similar oxides with several transition metal and rare earth elements as dopants for specialized application such as lasers and phosphors.
References [1] I. Warshaw, R. Roy, J. Am. Ceram. Soc. 42 (1959) 434. [2] S. Mathur, H. Shen, R. Rapalaviciute, A. Kareiva, N. Donia, J. Mater. Chem. 14 (2004) 3259–3265. [3] I.F. Elder, M.J.P. Payne, Optics Comm. 148 (1998) 265–269. [4] K. Gowda, J. Mater. Sci., Lett. 5 (1986) 1029–1032. [5] J. Marchal, T. John, R. Baranwal, T. Hinklin, R.R. Laine, Chem. Mater. 16 (2004) 822. [6] M. Harada, A. Ue, M. Inoue, X. Guo, K. Sakurai, J. Mater. Sci. Lett. 20 (2001) 741–742. [7] Ya Zhydachevskii, A. Durygin, V. Drozd, A. Suchocki, D. Sugak, J. Wrobel, J. Phys.: Condens. Matter 20 (2008) 095204. [8] J.R. Lo, T.Y. Tseng, Mater. Chem. Phys. 56 (1998) 56–62. [9] J.P. Remeika, J. Am. Chem. Soc. 78 (1956) 4259. [10] W. Class, J. Cryst. Growth 3/4 (1968) 241. [11] D.R. Messier, G.E. Gazza, Am. Ceram. Soc. Bull. 51 (1972) 692. [12] R.P. Rao, J. Electrochem. Soc. 143 (1996) 189. [13] V.S. Krylov, I.L. Belova, R.L. Magunov, V.D. Kozlov, V. Kalinichenko, N.P. Krot’ko, Inorg. Mater. 9 (1973) 1233. [14] M. Stockenhuber, H. Mayer, J.A. Lercher, J. Am. Ceram. Soc. 76 (1993) 1185. [15] D.L. Hamilton, C.M.B. Henderson, Text Book on Silicate Synthesis, 1958, p. 532.