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Preparation and characterization of nano-sized Sr0.7Ca0.3TiO3 crystallines by low temperature aqueous synthesis method
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Materials Letters 62 (2008) 2157 – 2160 www.elsevier.com/locate/matlet
Preparation and characterization of nano-sized Sr0.7Ca0.3TiO3 crystallines by low temperature aqueous synthesis method Ping He, Hua-Rong Cheng, Yuan Le, Jian-Feng Chen ⁎ Sin-China Nano Technology Center, Key Lab for Nanomaterials, Ministry of Education, Beijing University of Chemical Technology, Beijing 100029, PR China Received 18 January 2007; accepted 19 November 2007 Available online 23 November 2007
Abstract Nano-sized calcium strontium titanate (Sr0.7Ca0.3TiO3) particles were prepared by low temperature aqueous synthesis method at temperature as low as 90 °C and under ambient pressure. To improve the morphology and crystallinity of the particles, the hydrothermal treatment was used. The lattice structure, particle size, particle morphology, and hydroxyl defects of Sr0.7Ca0.3TiO3 particles were investigated by using XRD, TEM, FESEM, TG and FT-IR measurements. The as-prepared particles with size about 100 nm were single cubic phase crystallines which consist of aggregates of small rounded nanocrystals about 10 nm in diameter. However, in as-prepared crystallines, a hydroxyl group was detected as a lattice defect. After the hydrothermal treatment, the hydroxyl groups in Sr0.7Ca0.3TiO3 nanoparticles were partially released from the perovskite lattice. The morphology and crystallinity of the hydrothermally treated particles were observably improved. © 2007 Elsevier B.V. All rights reserved. Keywords: Nanomaterials; Perovskites; Calcium strontium titanate; Crystallinity; Hydroxyl defect
1. Introduction There are many materials of type ABO3 that have the so-called perovskites structure [1]. This class of compounds can undergo a wide range of structural phase transition, which can strongly affect their physical and chemical properties. Strontium titanate (SrTiO3) is an incipient ferroelectric (or quantum paraelectric) [2] in which a ferroelectric phase can be induced at a low temperature by isotopic substitution or substitutional impurities as well as by an external stress [3–5]. Moreover, Ca-substitute strontium titanate, SrxCa1 − xTiO3 (SCT), permits much flexibility to investigate the relationship between the microwave dielectric relaxation process and the dynamics properties of nanometer polar regions in incipient and relaxor ferroelectric materials. Therefore, solid-solution oxides of calcium strontium titanate (SrxCa1 − xTiO3) with high dielectric constants and dielectric properties of a small temperature coefficient have attracted a great deal of attention for practical use as capacitor dielectrics [6]. SCT is conventionally obtained by solid-state synthesis with strontium carbonate (SrCO3), calcium carbonate (CaCO3) and ⁎ Corresponding author. Tel.: +86 10 64446466; fax: +86 10 64434784. E-mail address: [email protected] (J.-F. Chen). 0167-577X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2007.11.040
titania (TiO2) at temperature higher than 1300 °C [7–10]. However, SCT powders prepared by this method consist of nonuniform, submicrometer-sized coarse particles. The control of particle size distribution is not always easy and the grinding operations to reduce the dimension of the particles induce chemical contamination. Therefore, a new and simple preparation method to obtain a high quality of small SCT particles is of significance in both fundamental and applied study. In recent years an increasing interest has been focused on the low temperature aqueous synthesis (LTAS) [11] of BaTiO3 in aqueous medium using solution of inorganic or organo-metallic compounds at temperature b100 °C, because of their low cost and its attractive processing such as single-step process and high-yield of the product. However, the method usually introduced some impurities such as hydroxyl groups and the particle morphology was inferior. To the best of our knowledge, there is no report on the preparation and properties investigate of SCT via LTAS method. Herein, for the first time we describe a LTAS-based approach to synthesize nano-sized calcium strontium titanate under ambient pressure and at temperature as low as 90 °C. To improve the morphology and crystallinity of particles and release the hydroxyl defects, the hydrothermal treatment was followed.
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Moreover, the prepared SCT nanoparticles were characterized using various methods.
220 °C for 3 h. Then, the hydrothermal-treated precipitate was washed, filtered, and finally dried at 105 °C for 12 h. The as-synthesized powders were characterized by different techniques. Phase identification was conducted by using X-ray diffraction (XRD, XRD-6000) with Cu Kα radiation (λ = 0.15408 nm). The FT-IR spectra were taken with fourier transform infrared (FT-IR, Nicolet 8700) using the KBr method after drying the samples at 105 °C over night. Thermogravimetric analysis was conducted on thermogravimetry (TG, STA429) in air. Particle size and morphological characterization were performed via transmission electron microscope (TEM, Hitachi H-800) and field-emission scanning electron microscope (FESEM, JOEL-4700). The chemical composition were analyzed by an Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES, IRIS Intrepid II XSP) after the sample was dissolved in concentrated HCl acid and diluted with de-ionized water. The specific surface areas (SBET) were measured by a gas adsorption analyzer (ASAP-2010M).
2. Experimental
3. Results and discussion
All analytic reagents (i.e. SrCl2·6H2O, CaCl2, TiCl4, NaOH, HCl acid) were used without further purification. A 1.0 L of batch stirred tank was used and nano-sized Sr0.7Ca0.3TiO3 (SC0.3T) powders were prepared from SrCl2, CaCl2 and TiCl4 precursors in a strong alkaline NaOH solution (6.0 mol·L− 1) at 90 °C under ambient pressure. The total concentration of mixed chlorides in feed solution was kept at 1.0 mol·L− 1, and the initial ratio of [Sr2++ Ca2+]/[Ti4+] in the mixed chlorides solution was 1.6, while the molar ratio [Ca2+]/[Sr2+] was 9/7. The volume ratio between mixed chlorides solution and NaOH solution was equal to 1.0. The fully mixed solution of chlorides and NaOH solution were respectively heated to given temperatures and then simultaneously and continuously added into the reactor. At an encountering of the above two solutions, an instantaneous formation of white precipitate was observed. The entire precipitation process lasted only 10 min. Then, the precipitate was washed, filtered, and finally dried at 105 °C for 12 h. For the hydrothermal treatment, the precipitate suspension was introduced into Teflon-lined pressure vessel and kept at
Fig. 1 shows the room temperature XRD patterns of the SC0.3T samples with or without hydrothermal treatment. All peaks for the two samples can be identified as the perovskite SCT single-phase, indicating the polycrystalline nature of powders with (110) plane as the major peak. It is notable that the diffraction peaks corresponding to SrTiO3, CaTiO3 and TiO2 are absent. The diffraction peaks become sharper and their intensities increase after the hydrothermal treatment, which implies the crystallinity of the SC0.3T particles was increased. The ionic radius of Ca2+ is smaller than that of Sr2+ [12]. Therefore, the lattice constant a reduces when Ca substitute Sr in the cubic (Ca,Sr) TiO3 solid solution. The lattice constant calculated from pattern (a) is a = 3.912 Å, which is larger than the lattice constant of cubic SrTiO3 (a = 3.905 Å, JCPDS no. 73-0661). It is most probably due to the effect of hydroxyl defects incorporated into the perovskite lattice which can be revealed from TG curves and FT-IR spectra illustrated in Fig. 2(a) and (b). These defects could increase the lattice strains between the ions of perovskite structure, and hence the cell parameter of SCT sample is expanded. However, the lattice constant becomes a = 3.895 Å after the hydrothermal treatment, which is smaller than the value of cubic SrTiO3. It indicated that hydroxyl defects were partially released after the hydrothermal treatment and the crystallinity of the SC0.3 T solid
Fig. 1. Room temperature X-ray diffraction patterns of Sr0.7Ca0.3TiO3 nanoparticles (a, obtained from the LTAS route; b, after the hydrothermal treatment).
Fig. 2. (a) TG curves and (b) FT-IR spectra of Sr0.7Ca0.3TiO3 powders [(1), obtained from the LTAS route; (2), after the hydrothermal treatment].
P. He et al. / Materials Letters 62 (2008) 2157–2160
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Fig. 3. TEM and FE-SEM images of Sr0.7Ca0.3TiO3 nanoparticles (a and b, obtained from the LTAS route; c and d, after the hydrothermal treatment).
solution was enhanced. This shrinkage of the unit cell also provides the evidence for the lattice substitution of the smaller Ca ions in the SCT solid solution, as compared with the larger Sr ions. To investigate the presence of lattice hydroxyl groups we carried out TG-DSC and FT-IR spectroscopy analysis. The TG curves of the asprepared SC0.3T with or without hydrothermal treatment are shown in Fig. 2(a). The total weight loss of the SC0.3T sample without hydrothermal treatment was 7.26 wt.%, while the total weight loss for the SC0.3T with hydrothermal treatment was 3.23 wt.%. The weight loss of the hydrothermal-treated SC0.3T sample was less than a half of that without treatment, which indicated that the incorporation of –OH groups in the lattice can be released by hydrothermal treatment [13]. As shown in Fig. 2(b), absorption around 3440 cm− 1 and 1630 cm− 1 are assigned to the –OH stretching and bending vibration [14], respectively, which may result from lattice hydroxyls and naturally absorbed surface water. The intensities of the peaks were reduced after the hydrothermal treatment, which implies the partial release of lattice hydroxyl groups. As impurities, the presence of carbonate groups was also detected in as-prepared SC0.3T powders, which was significantly removed by the hydrothermal treatment. The microstructures of the two samples are shown in Fig. 3. It can be seen that the sample before hydrothermal treatment mainly consists of as-spheral crystalline nanoparticles with mean size about 100 nm. In particular, the SC0.3T sample without hydrothermal treatment is somewhat “knobbly” around the edges (Fig. 3a). It is apparent from Fig. 3(b) that the particles consist of aggregates of small rounded nanocrystals about 10 nm in diameter, which make the edges somewhat “knobbly”. After the hydrothermal treatment, the edges of the particles become smooth and clear. As shown in Figs. 3 and 1, the morphology and crystallinity of hydrothermal-treated particles were observably improved, compared with the sample before hydrothermal treatment. The particle size of the hydrothermal-treated sample is about 100 nm and becomes more uniform. The specific surface areas of the SC0.3T samples with or without hydrothermal treatment are 20.97 m2·g− 1 and 8.57 m2·g− 1, respectively. The hydrothermal treatment led to the decrease of surface area
which resulted from the elimination of “knobbly” edges and slight increase of particle size. According to the ICP-AES analysis, the atomic ratio of the Sr, Ca and Ti in the SC0.3T nanoparticles was 0.3066: 0.6933: 1, which was in good consistence with the chemical formula of Sr0.7Ca0.3TiO3. However, the molar ratio of Ca/Sr in starting feed solution must be higher than 3/7 for the purpose of good compositional control.
4. Conclusions Nano-sized SC0.3T powders synthesized from the conventional raw materials via a single-step process are proposed. The process is quite fast and only requires a temperature as low as 90 °C under ambient pressure. Before hydrothermal treatment, the as-prepared SC0.3T powders exhibit a single cubic phase and are as-spheral crystalline nanoparticles with mean size about 100 nm. FE-SEM images revealed that the particles consist of aggregates of small rounded nanocrystals about 10 nm in diameter, which makes the edges of particles somewhat “knobbly”. In as-prepared SC0.3T crystallites, hydroxyl groups were detected as lattice defects. However, after the hydrothermal treatment, the hydroxyl groups in SC0.3T nanoparticles were partially released from the perovskite lattice. The morphology and crystallinity of the hydrothermal-treated particles were remarkably improved. Acknowledgement This work was partially supported by the NSF of China (grant no. 20325621). References [1] Z.X. Chen, Y. Chen, Y.S. Jiang, J. Phys. Chem. B 106 (2002) 9986.
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[2] K.A. Müller, H. Burkard, Phys. Rev. B 19 (1979) 3593. [3] M. Itoh, R. Wang, Y. Inaguma, T. Yamaguchi, Y.J. Shan, T. Nakamura, Phys. Rev. Lett. 82 (1999) 3540. [4] J.G. Bednorz, K.A. Müller, Phys. Rev. Lett. 52 (1984) 2289. [5] J.H. Haeni, P. Irvin, W. Chang, R. Uecker, P. Reiche, Y.L. Li, S. Choudhury, W. Tian, M.E. Hawley, B. Craigo, A.K. Tagantsev, X.Q. Pan, S.K. Streiffer, L.Q. Chen, S.W. Kirchoefer, J. Levy, D.G. Schlom, Nature 430 (2004) 758. [6] M. Yoshimura, O. Asai, W.S. Cho, M. Yashima, Y. Suzuki, M. Kakihana, J. Alloy. Compd. 265 (1998) 13. [7] M.H. Lente, J. de Los, S. Guerra, J.A. Eiras, T. Mazon, M.B.R. Andreeta, A.C. Hernandes, J. Eur. Ceram. Soc. 25 (2005) 2563.
[8] R. Ranjan, D. Pandey, J. Phys.: Condens. Matter. 13 (2001) 4239. [9] R. Ranjan, D. Pandey, W. Schuddinck, O. Richard, P. De Meulenaere, J. Van Landuyt, G. Van Tendeloo, J. Solid State Chem. 162 (2001) 20. [10] M. Daraktchiev, R.J. Harrison, E.H. Mountstevens, S.A.T. Redfern, Mater. Sci. Eng. A (in press). [11] S. Wadaa, T. Tsurumia, H. Chikamorib, T. Nomab, T. Suzuki, J. Crystal Growth 229 (2001) 433. [12] Y.B. Mao, S.S. Wong, Adv. Mater. 17 (2005) 2194. [13] T. Yan, X.L. Liu, N.R. Wang, J.F. Chen, J. Crystal Growth 218 (2005) 669. [14] L. Qia, B.I. Lee, P. Badheka, L.Q. Wang, P. Gilmour, W.D. Samuels, G.J. Exarhos, Mater. Lett. 59 (2005) 2794.
Materials Letters 62 (2008) 2157 – 2160 www.elsevier.com/locate/matlet
Preparation and characterization of nano-sized Sr0.7Ca0.3TiO3 crystallines by low temperature aqueous synthesis method Ping He, Hua-Rong Cheng, Yuan Le, Jian-Feng Chen ⁎ Sin-China Nano Technology Center, Key Lab for Nanomaterials, Ministry of Education, Beijing University of Chemical Technology, Beijing 100029, PR China Received 18 January 2007; accepted 19 November 2007 Available online 23 November 2007
Abstract Nano-sized calcium strontium titanate (Sr0.7Ca0.3TiO3) particles were prepared by low temperature aqueous synthesis method at temperature as low as 90 °C and under ambient pressure. To improve the morphology and crystallinity of the particles, the hydrothermal treatment was used. The lattice structure, particle size, particle morphology, and hydroxyl defects of Sr0.7Ca0.3TiO3 particles were investigated by using XRD, TEM, FESEM, TG and FT-IR measurements. The as-prepared particles with size about 100 nm were single cubic phase crystallines which consist of aggregates of small rounded nanocrystals about 10 nm in diameter. However, in as-prepared crystallines, a hydroxyl group was detected as a lattice defect. After the hydrothermal treatment, the hydroxyl groups in Sr0.7Ca0.3TiO3 nanoparticles were partially released from the perovskite lattice. The morphology and crystallinity of the hydrothermally treated particles were observably improved. © 2007 Elsevier B.V. All rights reserved. Keywords: Nanomaterials; Perovskites; Calcium strontium titanate; Crystallinity; Hydroxyl defect
1. Introduction There are many materials of type ABO3 that have the so-called perovskites structure [1]. This class of compounds can undergo a wide range of structural phase transition, which can strongly affect their physical and chemical properties. Strontium titanate (SrTiO3) is an incipient ferroelectric (or quantum paraelectric) [2] in which a ferroelectric phase can be induced at a low temperature by isotopic substitution or substitutional impurities as well as by an external stress [3–5]. Moreover, Ca-substitute strontium titanate, SrxCa1 − xTiO3 (SCT), permits much flexibility to investigate the relationship between the microwave dielectric relaxation process and the dynamics properties of nanometer polar regions in incipient and relaxor ferroelectric materials. Therefore, solid-solution oxides of calcium strontium titanate (SrxCa1 − xTiO3) with high dielectric constants and dielectric properties of a small temperature coefficient have attracted a great deal of attention for practical use as capacitor dielectrics [6]. SCT is conventionally obtained by solid-state synthesis with strontium carbonate (SrCO3), calcium carbonate (CaCO3) and ⁎ Corresponding author. Tel.: +86 10 64446466; fax: +86 10 64434784. E-mail address: [email protected] (J.-F. Chen). 0167-577X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2007.11.040
titania (TiO2) at temperature higher than 1300 °C [7–10]. However, SCT powders prepared by this method consist of nonuniform, submicrometer-sized coarse particles. The control of particle size distribution is not always easy and the grinding operations to reduce the dimension of the particles induce chemical contamination. Therefore, a new and simple preparation method to obtain a high quality of small SCT particles is of significance in both fundamental and applied study. In recent years an increasing interest has been focused on the low temperature aqueous synthesis (LTAS) [11] of BaTiO3 in aqueous medium using solution of inorganic or organo-metallic compounds at temperature b100 °C, because of their low cost and its attractive processing such as single-step process and high-yield of the product. However, the method usually introduced some impurities such as hydroxyl groups and the particle morphology was inferior. To the best of our knowledge, there is no report on the preparation and properties investigate of SCT via LTAS method. Herein, for the first time we describe a LTAS-based approach to synthesize nano-sized calcium strontium titanate under ambient pressure and at temperature as low as 90 °C. To improve the morphology and crystallinity of particles and release the hydroxyl defects, the hydrothermal treatment was followed.
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P. He et al. / Materials Letters 62 (2008) 2157–2160
Moreover, the prepared SCT nanoparticles were characterized using various methods.
220 °C for 3 h. Then, the hydrothermal-treated precipitate was washed, filtered, and finally dried at 105 °C for 12 h. The as-synthesized powders were characterized by different techniques. Phase identification was conducted by using X-ray diffraction (XRD, XRD-6000) with Cu Kα radiation (λ = 0.15408 nm). The FT-IR spectra were taken with fourier transform infrared (FT-IR, Nicolet 8700) using the KBr method after drying the samples at 105 °C over night. Thermogravimetric analysis was conducted on thermogravimetry (TG, STA429) in air. Particle size and morphological characterization were performed via transmission electron microscope (TEM, Hitachi H-800) and field-emission scanning electron microscope (FESEM, JOEL-4700). The chemical composition were analyzed by an Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES, IRIS Intrepid II XSP) after the sample was dissolved in concentrated HCl acid and diluted with de-ionized water. The specific surface areas (SBET) were measured by a gas adsorption analyzer (ASAP-2010M).
2. Experimental
3. Results and discussion
All analytic reagents (i.e. SrCl2·6H2O, CaCl2, TiCl4, NaOH, HCl acid) were used without further purification. A 1.0 L of batch stirred tank was used and nano-sized Sr0.7Ca0.3TiO3 (SC0.3T) powders were prepared from SrCl2, CaCl2 and TiCl4 precursors in a strong alkaline NaOH solution (6.0 mol·L− 1) at 90 °C under ambient pressure. The total concentration of mixed chlorides in feed solution was kept at 1.0 mol·L− 1, and the initial ratio of [Sr2++ Ca2+]/[Ti4+] in the mixed chlorides solution was 1.6, while the molar ratio [Ca2+]/[Sr2+] was 9/7. The volume ratio between mixed chlorides solution and NaOH solution was equal to 1.0. The fully mixed solution of chlorides and NaOH solution were respectively heated to given temperatures and then simultaneously and continuously added into the reactor. At an encountering of the above two solutions, an instantaneous formation of white precipitate was observed. The entire precipitation process lasted only 10 min. Then, the precipitate was washed, filtered, and finally dried at 105 °C for 12 h. For the hydrothermal treatment, the precipitate suspension was introduced into Teflon-lined pressure vessel and kept at
Fig. 1 shows the room temperature XRD patterns of the SC0.3T samples with or without hydrothermal treatment. All peaks for the two samples can be identified as the perovskite SCT single-phase, indicating the polycrystalline nature of powders with (110) plane as the major peak. It is notable that the diffraction peaks corresponding to SrTiO3, CaTiO3 and TiO2 are absent. The diffraction peaks become sharper and their intensities increase after the hydrothermal treatment, which implies the crystallinity of the SC0.3T particles was increased. The ionic radius of Ca2+ is smaller than that of Sr2+ [12]. Therefore, the lattice constant a reduces when Ca substitute Sr in the cubic (Ca,Sr) TiO3 solid solution. The lattice constant calculated from pattern (a) is a = 3.912 Å, which is larger than the lattice constant of cubic SrTiO3 (a = 3.905 Å, JCPDS no. 73-0661). It is most probably due to the effect of hydroxyl defects incorporated into the perovskite lattice which can be revealed from TG curves and FT-IR spectra illustrated in Fig. 2(a) and (b). These defects could increase the lattice strains between the ions of perovskite structure, and hence the cell parameter of SCT sample is expanded. However, the lattice constant becomes a = 3.895 Å after the hydrothermal treatment, which is smaller than the value of cubic SrTiO3. It indicated that hydroxyl defects were partially released after the hydrothermal treatment and the crystallinity of the SC0.3 T solid
Fig. 1. Room temperature X-ray diffraction patterns of Sr0.7Ca0.3TiO3 nanoparticles (a, obtained from the LTAS route; b, after the hydrothermal treatment).
Fig. 2. (a) TG curves and (b) FT-IR spectra of Sr0.7Ca0.3TiO3 powders [(1), obtained from the LTAS route; (2), after the hydrothermal treatment].
P. He et al. / Materials Letters 62 (2008) 2157–2160
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Fig. 3. TEM and FE-SEM images of Sr0.7Ca0.3TiO3 nanoparticles (a and b, obtained from the LTAS route; c and d, after the hydrothermal treatment).
solution was enhanced. This shrinkage of the unit cell also provides the evidence for the lattice substitution of the smaller Ca ions in the SCT solid solution, as compared with the larger Sr ions. To investigate the presence of lattice hydroxyl groups we carried out TG-DSC and FT-IR spectroscopy analysis. The TG curves of the asprepared SC0.3T with or without hydrothermal treatment are shown in Fig. 2(a). The total weight loss of the SC0.3T sample without hydrothermal treatment was 7.26 wt.%, while the total weight loss for the SC0.3T with hydrothermal treatment was 3.23 wt.%. The weight loss of the hydrothermal-treated SC0.3T sample was less than a half of that without treatment, which indicated that the incorporation of –OH groups in the lattice can be released by hydrothermal treatment [13]. As shown in Fig. 2(b), absorption around 3440 cm− 1 and 1630 cm− 1 are assigned to the –OH stretching and bending vibration [14], respectively, which may result from lattice hydroxyls and naturally absorbed surface water. The intensities of the peaks were reduced after the hydrothermal treatment, which implies the partial release of lattice hydroxyl groups. As impurities, the presence of carbonate groups was also detected in as-prepared SC0.3T powders, which was significantly removed by the hydrothermal treatment. The microstructures of the two samples are shown in Fig. 3. It can be seen that the sample before hydrothermal treatment mainly consists of as-spheral crystalline nanoparticles with mean size about 100 nm. In particular, the SC0.3T sample without hydrothermal treatment is somewhat “knobbly” around the edges (Fig. 3a). It is apparent from Fig. 3(b) that the particles consist of aggregates of small rounded nanocrystals about 10 nm in diameter, which make the edges somewhat “knobbly”. After the hydrothermal treatment, the edges of the particles become smooth and clear. As shown in Figs. 3 and 1, the morphology and crystallinity of hydrothermal-treated particles were observably improved, compared with the sample before hydrothermal treatment. The particle size of the hydrothermal-treated sample is about 100 nm and becomes more uniform. The specific surface areas of the SC0.3T samples with or without hydrothermal treatment are 20.97 m2·g− 1 and 8.57 m2·g− 1, respectively. The hydrothermal treatment led to the decrease of surface area
which resulted from the elimination of “knobbly” edges and slight increase of particle size. According to the ICP-AES analysis, the atomic ratio of the Sr, Ca and Ti in the SC0.3T nanoparticles was 0.3066: 0.6933: 1, which was in good consistence with the chemical formula of Sr0.7Ca0.3TiO3. However, the molar ratio of Ca/Sr in starting feed solution must be higher than 3/7 for the purpose of good compositional control.
4. Conclusions Nano-sized SC0.3T powders synthesized from the conventional raw materials via a single-step process are proposed. The process is quite fast and only requires a temperature as low as 90 °C under ambient pressure. Before hydrothermal treatment, the as-prepared SC0.3T powders exhibit a single cubic phase and are as-spheral crystalline nanoparticles with mean size about 100 nm. FE-SEM images revealed that the particles consist of aggregates of small rounded nanocrystals about 10 nm in diameter, which makes the edges of particles somewhat “knobbly”. In as-prepared SC0.3T crystallites, hydroxyl groups were detected as lattice defects. However, after the hydrothermal treatment, the hydroxyl groups in SC0.3T nanoparticles were partially released from the perovskite lattice. The morphology and crystallinity of the hydrothermal-treated particles were remarkably improved. Acknowledgement This work was partially supported by the NSF of China (grant no. 20325621). References [1] Z.X. Chen, Y. Chen, Y.S. Jiang, J. Phys. Chem. B 106 (2002) 9986.
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[2] K.A. Müller, H. Burkard, Phys. Rev. B 19 (1979) 3593. [3] M. Itoh, R. Wang, Y. Inaguma, T. Yamaguchi, Y.J. Shan, T. Nakamura, Phys. Rev. Lett. 82 (1999) 3540. [4] J.G. Bednorz, K.A. Müller, Phys. Rev. Lett. 52 (1984) 2289. [5] J.H. Haeni, P. Irvin, W. Chang, R. Uecker, P. Reiche, Y.L. Li, S. Choudhury, W. Tian, M.E. Hawley, B. Craigo, A.K. Tagantsev, X.Q. Pan, S.K. Streiffer, L.Q. Chen, S.W. Kirchoefer, J. Levy, D.G. Schlom, Nature 430 (2004) 758. [6] M. Yoshimura, O. Asai, W.S. Cho, M. Yashima, Y. Suzuki, M. Kakihana, J. Alloy. Compd. 265 (1998) 13. [7] M.H. Lente, J. de Los, S. Guerra, J.A. Eiras, T. Mazon, M.B.R. Andreeta, A.C. Hernandes, J. Eur. Ceram. Soc. 25 (2005) 2563.
[8] R. Ranjan, D. Pandey, J. Phys.: Condens. Matter. 13 (2001) 4239. [9] R. Ranjan, D. Pandey, W. Schuddinck, O. Richard, P. De Meulenaere, J. Van Landuyt, G. Van Tendeloo, J. Solid State Chem. 162 (2001) 20. [10] M. Daraktchiev, R.J. Harrison, E.H. Mountstevens, S.A.T. Redfern, Mater. Sci. Eng. A (in press). [11] S. Wadaa, T. Tsurumia, H. Chikamorib, T. Nomab, T. Suzuki, J. Crystal Growth 229 (2001) 433. [12] Y.B. Mao, S.S. Wong, Adv. Mater. 17 (2005) 2194. [13] T. Yan, X.L. Liu, N.R. Wang, J.F. Chen, J. Crystal Growth 218 (2005) 669. [14] L. Qia, B.I. Lee, P. Badheka, L.Q. Wang, P. Gilmour, W.D. Samuels, G.J. Exarhos, Mater. Lett. 59 (2005) 2794.