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Synthesis of magnesium titanate nanocrystallites from a cheap and water-soluble single source precursor
Inorganica Chimica Acta 363 (2010) 827–829
Contents lists available at ScienceDirect
Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica
Note
Synthesis of magnesium titanate nanocrystallites from a cheap and water-soluble single source precursor Yuan-Fu Deng *, Shi-Di Tang, Liang-Qiang Lao, Shu-Zhong Zhan Department of Chemistry, College of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, PR China
a r t i c l e
i n f o
Article history: Received 25 October 2009 Received in revised form 12 November 2009 Accepted 13 November 2009 Available online 20 November 2009 Keywords: Single source precursor MgTiO3 Nitrilotriacetatoperoxotitanate Crystal structure
a b s t r a c t Pure nanocrystallite magnesium titanate (MgTiO3) was conveniently synthesized by thermal decomposition of a cheap and water-soluble heterobimetallic single source precursor [Mg(H2O)5]2[Ti2(O2)2O(NC6H6O6)2]7H2O at low temperature. This single source precursor was obtained in high yield and in a crystalline form from the quaternary system of MgO–Ti(OC4H9)4–H2O2–H3nta (H3nta = nitrilotriacetic acid) at pH 4.0. It was characterized by elemental analysis, IR spectrum, NMR, thermal gravimetric analysis and X-ray single-crystal diffraction. The morphology, microstructure, and crystallinity of the resulting MgTiO3 materials have been characterized by transmission electron microscopy and X-ray diffraction. The TEM image of the resulting MgTiO3 powders only consists of the nano-scale crystallites with the crystalline size of 30–100 nm. Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction Magnesium titanate (MgTiO3) is a promising low-loss dielectric [1] materials with high quality factor (Q above 20 000 at 8 GHz) and intermediate dielectric constant (er = 17). This dielectric is widely used in many microwave applications such as multilayer capacitors [2], band-pass filters [3], antennas for communication [4], direct broadcasting satellite and global positioning system [5]. In addition, MgTiO3 could also be used for optical communication in planar light-wave circuits (PLC) as a buffer layer for sapphire and LiNbO3 [6]. Generally, the choice of the synthetic procedure has a direct influence on the formation and the properties of MgTiO3. Nanostructure materials exhibiting particular properties [7–9] due to the extremely low crystallite sizes are still difficult to obtain. New and simple routes toward this material are therefore of great interest. Attempts to replace standard ceramic methods to monophasic and pure MgTiO3 (which is difficult to obtain pure MgTiO3 because of its narrow range of phase stability) by alternative syntheses are abundant. Such as chemical co-precipitation method [9,10], metal– organic chemical vapor deposition [11,12] and sol–gel process [5,13–18]. Generally, the sol–gel method for preparation of mixed-metal oxides has many advantages including low processing temperature, together with high purity and homogeneity of the final products. However, the synthesis of pure phase MgTiO3 using this method was greatly constrained by the formation of additional phases [16,17]. The low solubility of magnesium alkox* Corresponding author. Tel.: +86 020 87112053. E-mail address: [email protected] (Y.-F. Deng). 0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2009.11.020
ides is believed as the primary impediment for sol–gel synthesis of this mixed-metal oxide, which has to be addressed by suitable modifications at the precursor level [5,15]. Despite the popularity of the sol–gel method for preparation of MgTiO3, it also presents several drawbacks such as the precursors used in this method are usually moisture sensitive and expensive and the stoichiometry of the final oxide are difficultly controlled because of using multiple sources. Therefore, it is still a challenge to find some novel route to synthesis of MgTiO3 with a high purity and a narrow size distribution using cheap raw materials. As an alternative route, thermal decomposition based on a molecular heterobimetallic magnesium–titanium compound should be a major advantage. Following our previous work directed toward the design of heterobimetallic complexes for mixed-metal oxide systems [19–22], we found that the nitrilotriacetatoperoxotitanate anion was synthesized conveniently and very stable in aqueous solution [22]. Herein, we present a new water-soluble molecular heterobimetallic magnesium nitrilotriacetatoperoxotitanate compound [Mg(H2O)5]2[Ti(O2)2O(NC6H6O6)2]7H2O (1), which acts as a single source precursor to prepare pure MgTiO3 nano-powders via thermal decomposition at low temperature.
2. Experimental 2.1. Preparation of the single source precursor [Mg(H2O)5]2[Ti2(O2)2O(NC6H6O6)2]7H2O (1) In a typical synthesis of compound 1: H3nta (9.05 g, 50 mol) was suspended in 200 mL of deionized water, to the suspension
828
Y.-F. Deng et al. / Inorganica Chimica Acta 363 (2010) 827–829
Fig. 1. ORTEP plot of complex 1 at the 30% probability level, the hydrogen atoms were omitted for clarity.
was added slowly with 17.0 mL Ti(OC4H9)4 with stirring 2 h, then 25 mL of 30% hydrogen peroxide was added to the above mixture at room temperature with stirring, after that, the mixture was filtered, and the filtrate was added to 2.0 g (50 mol) MgO slowly, finally, the resulting solution was kept at 4 °C for three days. Yellow crystals were collected and washed with deionized water two times and dried in vacuum to give compound 1 (22.70 g, 78% yield). Compound 1 can dissolve in water and its aqueous solution is very stable over a broad range of pH values (1–10). Elemental Anal. Calc. for C12H46O34N2Mg2Ti2: C, 15.79; H, 5.08; N, 3.14. Found: C, 15.89; H, 5.11; N, 3.09%. IR (KBr, cm 1): 1614 vs; 1402 s; (O–O), 872 m; (Ti–O2) 594 m, 534 m. 1H NMR (500 MHz, D2O): d, 4.25 (d, 2H, l2-CH2COO ) 3.64 (s, 2H, CH2COO ), 3.58 (d, 2H, CH2COO ); 13C NMR (D2O) d, 183.1 (l2-CO2); 182.3 (CO2); 68.0 (l2-CH2COO ); 67.7 (CH2COO ). Detail crystal data and physical measurements were listed in the supporting information. 3. Results and discussion 3.1. X-ray structural analysis Fig. 1 presents the crystal structure of the individual magnesium nitrilotriacetatoperoxotitanate compound determined from single-crystal X-ray diffraction data, which consists of the two mononuclear nitrilotriacetatoperoxotitanate fragments interlinked through the bridging oxygen atom (O7). The salient feature of the nitrilotriacetato ligand in this compound is its tetradentate nature as a whole molecule. As a result, the nitrogen atom (N1) and the three oxygen atoms (O1, O3 and O5) from C2, C4, and C6 carboxylato groups built up three five-membered chelated rings (Ti1-O1– C2–C1–N1, Ti1-O3–C4–C3–N1, and Ti1-O5–C6–C5–N1, respectively), providing the maximum stability of the complex. In addition, one peroxo group coordinates side-onto one titanium atom, which is similar to that of the other nitrilotriacetatoperoxotitanate compounds [22]. In the crystal structure, the [Mg(H2O)5]2[Ti(O2)2O(NC6H6O6)2] units form three dimensional structure via their hydrogen-bonds, which are formed from the oxygen atom of the carboxylato and water molecules. Similar to the compound of ammonium citratoperoxotitanate complex [23], the coordinated peroxo group (O8–O9) in complex 1 may play two important roles: (i) they retard further polymerization of the dimeric anion by occupying the free sites in the equatorial pentagonal plane that can also be active sites for nucleophilic attack and hydrolysis; (ii) they provide negative charge to the complex, thus making possible coordination of two [Mg(H2O)5]2+ cations. As shown in Fig. 1, the two magnesium ions in 1 are both hexa-coordination, surrounding by five water molecules and an oxygen atom (O2) from one of the l2-coordinated carboxylate group of the nta3 ligand, respectively.
3.2. NMR studies The 13C NMR spectrum of complex 1 has two sets of resonances. The peaks at 183.1 and 182.3 ppm were attributed to the carbons of the l2-coordinated carboxylate group and two non-bridged carboxylate groups, respectively. Similarly, the peaks at 68.0 and 67.7 ppm were attributed the carbons of l2-coordinated methylene and non-bridged methylene groups, respectively. This observation is in agreement with the conclusion derived from the Xray crystal structure. 3.3. Thermal decomposition process The thermal decomposition of complex 1 has been studied by TG–DTA and XRD. This compound can be cleanly converted into the desired heterobimetallic oxide (MgTiO3) by heating in air. TG analysis of the thermal decomposition of the compound reveals that it decompose in three basic steps to produce the final bimetallic oxide on heating in air (Fig. 2). The initial mass loss from the sample is likely caused by the elimination of lattice and coordination water molecules and peroxo groups from the sample, with an endothermic peak and a weak exothermic peak at 114 and 220 °C, respectively. The subsequent thermal decomposition of 1 is in the range 300–500 °C with an abrupt mass loss, which was assigned to the combustion of organic ligand. There is a strong exothermic peak at 397 °C in this step. The last decomposition of complex 1
DTA mV
TG % 100
o
114.7 C
2
90 80
1
70 o
727.7 C
60
0
50 o
40
220.1 C
30 20
-1
o
397.3 C 150
300
450
600
750
o Temperature ( C) Fig. 2. TG–DTA data for 1 with heating rate of 10 °C/min.
900
Y.-F. Deng et al. / Inorganica Chimica Acta 363 (2010) 827–829
*
#
MgTiO3 became stronger and stronger, and simultaneously, pure MgTiO3 was obtained when the temperature was at 700 °C.
MgTi2O5
* MgTiO3
*
o 700 C
*
*
*
3.5. Morphology observation
* *
*
** *
*
*
*
* ** * * *
o 650 C o 600 C #
10
20
#
40
50
2θ (
The transmission electron images of MgTiO3 well-dispersed particles calcined at 700 °C for 2 h are shown in Fig. 4, which indicate that MgTiO3 powders only consisted of the nano-scale crystallites with the crystalline size of 30–100 nm and a tetragonal flake-like shape. 4. Conclusions
#
30
829
60
70
80
o
)
Fig. 3. X-ray powder diffraction patterns of the samples obtained from the calcined complex 1 at different temperature for 2 h.
In summary, we successfully isolated and characterized a new heterobimetallic magnesium–titanium compound, which can convert into stoichiometric MgTiO3 via thermal decomposition in air as a single source precursor. The described titanium compound is highly stable toward hydrolysis and therefore has potential applications in cheap and convenient syntheses of a variety of MgTiO3-based materials for industrially important products through aqueous precursors. Acknowledgements We thank the National Science Foundation of China (No. B5080320). We also thank the ‘‘SRP” of South China University of Technology for financial support. Appendix A. Supplementary material CCDC 747026 contains the supplementary crystallographic data for compound 1. These data can be obtained free of charge from The Cambridge Crystallographic Data Center via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.ica. 2009.11.020. References
Fig. 4. TEM image of MgTiO3 obtained from the thermal decomposition of complex 1 at 700 °C for 2 h.
[1] [2] [3] [4] [5] [6] [7]
is in the range of 500–750 °C with a small mass loss, which was assigned to some residue oxidation reactions and the formation of MgTiO3 phase. The decomposition ends at about 700 °C, leaving a residue of 26.23% of the initial mass, slightly less than 26.51% calculated for complete conversion of the molecular precursor to the corresponding bimetallic mixed-oxide (MgTiO3).
[8] [9] [10] [11] [12] [13] [14]
3.4. Powder X-ray diffraction studies of the crystal phases of samples
[15] [16] [17] [18]
To investigate the crystal phases evolved in each decomposition step of complex 1, all samples characterized by XRD here were calcined (600–800 °C) in air for 2 h. As shown in Fig. 3, when the temperature at 600 °C, solid phase of MgTiO3 (JCPDS, 00-006-0494) was generated, with a small amount of other impurities. With the calcination temperature increasing, the peak intensities of
[19] [20] [21] [22] [23]
K. Wakino, Ferroelectrics 91 (1989) 69. J. Bernard, D. Houivet, J. Eur. Ceram. Soc. 4 (2004) 1877. C.L. Huang, C.M. Tsai, A. Yang, A. Hsu, Microwave Opt. Lett. 44 (2005) 421. W.W. Cho, K. Kakimoto, H. Ohsato, Mater. Sci. Eng. B 121 (2005) 48. K.P. Surendran, A.Y. Wu, P.M. Vilarinho, V.M. Ferreira, Chem. Mater. 20 (2008) 4260–4267, and references therein. Y.H. Choi, J. Lee, Thin Solid Films 385 (2001) 43. T. Lopez, J. Hernandez-Ventura, D.H. Aguilar, P. Quintana, J. Nanosci. Nanotechnol. 8 (2008) 6608. G. Parthasarathy, Mater. Lett. 61 (2007) 4329. H.M. Cheng, B. Xu, J.M. Ma, J. Mater. Sci. Lett. 16 (1997) 1570. G. Parthasarathy, S.V. Manorama, Bull. Mater. Sci. 30 (2007) 19. J.M. Zeng, H. Wang, S.G. Song, J. Cryst. Growth 178 (1997) 355. G.A. Seisenbaeva, S. Gohil, V.G. Kessler, Inorg. Chem. Commun. 7 (2004) 18. S. Komarneni, I.R. Abothu, A.V.P. Rao, J. Sol–Gel Sci. Technol. 19 (1999) 263. T. Lopez, J. Hernandez, R. Gomez, X. Bokhimi, J.L. Boldu, E. Munoz, O. Novaro, A. Garcia-Ruiz, Langmuir 15 (1999) 5689. I.R. Abothu, A.V.P. Rao, S. Komarneni, Mater. Lett. 38 (1999) 186. X. Bokhimi, J.L. Boldú, E. Mun´oz, O. Novaro, Chem. Mater. 11 (1999) 2716. Y.M. Miao, Q.L. Zhang, H. Yang, H.P. Wang, Mater. Sci. Eng. B 128 (2006) 103. H.M. Kang, L.Q. Wang, D.F. Xue, K.Y. Li, C.H. Liu, J. Alloys Compd. 460 (2008) 160. Y.F. Deng, Z.H. Zhou, Inorg. Chem. Commun. 11 (2008) 1064. Y.F. Deng, Z.H. Zhou, H.L. Wan, Inorg. Chem. 43 (2004) 6266. Y.F. Deng, H.L. Zhang, Q.M. Hong, W.Z. Weng, H.L. Wan, Z.H. Zhou, J. Solid State Chem. 180 (2007) 3152. Z.H. Zhou, Q.M. Hong, Y.F. Deng, Acta Chim. Sinica 62 (2004) 2379. M. Kakihana, M. Tada, M. Shiro, V. Petrykin, M. Osda, Y. Nakamura, Inorg. Chem. 40 (2001) 891.
Contents lists available at ScienceDirect
Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica
Note
Synthesis of magnesium titanate nanocrystallites from a cheap and water-soluble single source precursor Yuan-Fu Deng *, Shi-Di Tang, Liang-Qiang Lao, Shu-Zhong Zhan Department of Chemistry, College of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, PR China
a r t i c l e
i n f o
Article history: Received 25 October 2009 Received in revised form 12 November 2009 Accepted 13 November 2009 Available online 20 November 2009 Keywords: Single source precursor MgTiO3 Nitrilotriacetatoperoxotitanate Crystal structure
a b s t r a c t Pure nanocrystallite magnesium titanate (MgTiO3) was conveniently synthesized by thermal decomposition of a cheap and water-soluble heterobimetallic single source precursor [Mg(H2O)5]2[Ti2(O2)2O(NC6H6O6)2]7H2O at low temperature. This single source precursor was obtained in high yield and in a crystalline form from the quaternary system of MgO–Ti(OC4H9)4–H2O2–H3nta (H3nta = nitrilotriacetic acid) at pH 4.0. It was characterized by elemental analysis, IR spectrum, NMR, thermal gravimetric analysis and X-ray single-crystal diffraction. The morphology, microstructure, and crystallinity of the resulting MgTiO3 materials have been characterized by transmission electron microscopy and X-ray diffraction. The TEM image of the resulting MgTiO3 powders only consists of the nano-scale crystallites with the crystalline size of 30–100 nm. Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction Magnesium titanate (MgTiO3) is a promising low-loss dielectric [1] materials with high quality factor (Q above 20 000 at 8 GHz) and intermediate dielectric constant (er = 17). This dielectric is widely used in many microwave applications such as multilayer capacitors [2], band-pass filters [3], antennas for communication [4], direct broadcasting satellite and global positioning system [5]. In addition, MgTiO3 could also be used for optical communication in planar light-wave circuits (PLC) as a buffer layer for sapphire and LiNbO3 [6]. Generally, the choice of the synthetic procedure has a direct influence on the formation and the properties of MgTiO3. Nanostructure materials exhibiting particular properties [7–9] due to the extremely low crystallite sizes are still difficult to obtain. New and simple routes toward this material are therefore of great interest. Attempts to replace standard ceramic methods to monophasic and pure MgTiO3 (which is difficult to obtain pure MgTiO3 because of its narrow range of phase stability) by alternative syntheses are abundant. Such as chemical co-precipitation method [9,10], metal– organic chemical vapor deposition [11,12] and sol–gel process [5,13–18]. Generally, the sol–gel method for preparation of mixed-metal oxides has many advantages including low processing temperature, together with high purity and homogeneity of the final products. However, the synthesis of pure phase MgTiO3 using this method was greatly constrained by the formation of additional phases [16,17]. The low solubility of magnesium alkox* Corresponding author. Tel.: +86 020 87112053. E-mail address: [email protected] (Y.-F. Deng). 0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2009.11.020
ides is believed as the primary impediment for sol–gel synthesis of this mixed-metal oxide, which has to be addressed by suitable modifications at the precursor level [5,15]. Despite the popularity of the sol–gel method for preparation of MgTiO3, it also presents several drawbacks such as the precursors used in this method are usually moisture sensitive and expensive and the stoichiometry of the final oxide are difficultly controlled because of using multiple sources. Therefore, it is still a challenge to find some novel route to synthesis of MgTiO3 with a high purity and a narrow size distribution using cheap raw materials. As an alternative route, thermal decomposition based on a molecular heterobimetallic magnesium–titanium compound should be a major advantage. Following our previous work directed toward the design of heterobimetallic complexes for mixed-metal oxide systems [19–22], we found that the nitrilotriacetatoperoxotitanate anion was synthesized conveniently and very stable in aqueous solution [22]. Herein, we present a new water-soluble molecular heterobimetallic magnesium nitrilotriacetatoperoxotitanate compound [Mg(H2O)5]2[Ti(O2)2O(NC6H6O6)2]7H2O (1), which acts as a single source precursor to prepare pure MgTiO3 nano-powders via thermal decomposition at low temperature.
2. Experimental 2.1. Preparation of the single source precursor [Mg(H2O)5]2[Ti2(O2)2O(NC6H6O6)2]7H2O (1) In a typical synthesis of compound 1: H3nta (9.05 g, 50 mol) was suspended in 200 mL of deionized water, to the suspension
828
Y.-F. Deng et al. / Inorganica Chimica Acta 363 (2010) 827–829
Fig. 1. ORTEP plot of complex 1 at the 30% probability level, the hydrogen atoms were omitted for clarity.
was added slowly with 17.0 mL Ti(OC4H9)4 with stirring 2 h, then 25 mL of 30% hydrogen peroxide was added to the above mixture at room temperature with stirring, after that, the mixture was filtered, and the filtrate was added to 2.0 g (50 mol) MgO slowly, finally, the resulting solution was kept at 4 °C for three days. Yellow crystals were collected and washed with deionized water two times and dried in vacuum to give compound 1 (22.70 g, 78% yield). Compound 1 can dissolve in water and its aqueous solution is very stable over a broad range of pH values (1–10). Elemental Anal. Calc. for C12H46O34N2Mg2Ti2: C, 15.79; H, 5.08; N, 3.14. Found: C, 15.89; H, 5.11; N, 3.09%. IR (KBr, cm 1): 1614 vs; 1402 s; (O–O), 872 m; (Ti–O2) 594 m, 534 m. 1H NMR (500 MHz, D2O): d, 4.25 (d, 2H, l2-CH2COO ) 3.64 (s, 2H, CH2COO ), 3.58 (d, 2H, CH2COO ); 13C NMR (D2O) d, 183.1 (l2-CO2); 182.3 (CO2); 68.0 (l2-CH2COO ); 67.7 (CH2COO ). Detail crystal data and physical measurements were listed in the supporting information. 3. Results and discussion 3.1. X-ray structural analysis Fig. 1 presents the crystal structure of the individual magnesium nitrilotriacetatoperoxotitanate compound determined from single-crystal X-ray diffraction data, which consists of the two mononuclear nitrilotriacetatoperoxotitanate fragments interlinked through the bridging oxygen atom (O7). The salient feature of the nitrilotriacetato ligand in this compound is its tetradentate nature as a whole molecule. As a result, the nitrogen atom (N1) and the three oxygen atoms (O1, O3 and O5) from C2, C4, and C6 carboxylato groups built up three five-membered chelated rings (Ti1-O1– C2–C1–N1, Ti1-O3–C4–C3–N1, and Ti1-O5–C6–C5–N1, respectively), providing the maximum stability of the complex. In addition, one peroxo group coordinates side-onto one titanium atom, which is similar to that of the other nitrilotriacetatoperoxotitanate compounds [22]. In the crystal structure, the [Mg(H2O)5]2[Ti(O2)2O(NC6H6O6)2] units form three dimensional structure via their hydrogen-bonds, which are formed from the oxygen atom of the carboxylato and water molecules. Similar to the compound of ammonium citratoperoxotitanate complex [23], the coordinated peroxo group (O8–O9) in complex 1 may play two important roles: (i) they retard further polymerization of the dimeric anion by occupying the free sites in the equatorial pentagonal plane that can also be active sites for nucleophilic attack and hydrolysis; (ii) they provide negative charge to the complex, thus making possible coordination of two [Mg(H2O)5]2+ cations. As shown in Fig. 1, the two magnesium ions in 1 are both hexa-coordination, surrounding by five water molecules and an oxygen atom (O2) from one of the l2-coordinated carboxylate group of the nta3 ligand, respectively.
3.2. NMR studies The 13C NMR spectrum of complex 1 has two sets of resonances. The peaks at 183.1 and 182.3 ppm were attributed to the carbons of the l2-coordinated carboxylate group and two non-bridged carboxylate groups, respectively. Similarly, the peaks at 68.0 and 67.7 ppm were attributed the carbons of l2-coordinated methylene and non-bridged methylene groups, respectively. This observation is in agreement with the conclusion derived from the Xray crystal structure. 3.3. Thermal decomposition process The thermal decomposition of complex 1 has been studied by TG–DTA and XRD. This compound can be cleanly converted into the desired heterobimetallic oxide (MgTiO3) by heating in air. TG analysis of the thermal decomposition of the compound reveals that it decompose in three basic steps to produce the final bimetallic oxide on heating in air (Fig. 2). The initial mass loss from the sample is likely caused by the elimination of lattice and coordination water molecules and peroxo groups from the sample, with an endothermic peak and a weak exothermic peak at 114 and 220 °C, respectively. The subsequent thermal decomposition of 1 is in the range 300–500 °C with an abrupt mass loss, which was assigned to the combustion of organic ligand. There is a strong exothermic peak at 397 °C in this step. The last decomposition of complex 1
DTA mV
TG % 100
o
114.7 C
2
90 80
1
70 o
727.7 C
60
0
50 o
40
220.1 C
30 20
-1
o
397.3 C 150
300
450
600
750
o Temperature ( C) Fig. 2. TG–DTA data for 1 with heating rate of 10 °C/min.
900
Y.-F. Deng et al. / Inorganica Chimica Acta 363 (2010) 827–829
*
#
MgTiO3 became stronger and stronger, and simultaneously, pure MgTiO3 was obtained when the temperature was at 700 °C.
MgTi2O5
* MgTiO3
*
o 700 C
*
*
*
3.5. Morphology observation
* *
*
** *
*
*
*
* ** * * *
o 650 C o 600 C #
10
20
#
40
50
2θ (
The transmission electron images of MgTiO3 well-dispersed particles calcined at 700 °C for 2 h are shown in Fig. 4, which indicate that MgTiO3 powders only consisted of the nano-scale crystallites with the crystalline size of 30–100 nm and a tetragonal flake-like shape. 4. Conclusions
#
30
829
60
70
80
o
)
Fig. 3. X-ray powder diffraction patterns of the samples obtained from the calcined complex 1 at different temperature for 2 h.
In summary, we successfully isolated and characterized a new heterobimetallic magnesium–titanium compound, which can convert into stoichiometric MgTiO3 via thermal decomposition in air as a single source precursor. The described titanium compound is highly stable toward hydrolysis and therefore has potential applications in cheap and convenient syntheses of a variety of MgTiO3-based materials for industrially important products through aqueous precursors. Acknowledgements We thank the National Science Foundation of China (No. B5080320). We also thank the ‘‘SRP” of South China University of Technology for financial support. Appendix A. Supplementary material CCDC 747026 contains the supplementary crystallographic data for compound 1. These data can be obtained free of charge from The Cambridge Crystallographic Data Center via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.ica. 2009.11.020. References
Fig. 4. TEM image of MgTiO3 obtained from the thermal decomposition of complex 1 at 700 °C for 2 h.
[1] [2] [3] [4] [5] [6] [7]
is in the range of 500–750 °C with a small mass loss, which was assigned to some residue oxidation reactions and the formation of MgTiO3 phase. The decomposition ends at about 700 °C, leaving a residue of 26.23% of the initial mass, slightly less than 26.51% calculated for complete conversion of the molecular precursor to the corresponding bimetallic mixed-oxide (MgTiO3).
[8] [9] [10] [11] [12] [13] [14]
3.4. Powder X-ray diffraction studies of the crystal phases of samples
[15] [16] [17] [18]
To investigate the crystal phases evolved in each decomposition step of complex 1, all samples characterized by XRD here were calcined (600–800 °C) in air for 2 h. As shown in Fig. 3, when the temperature at 600 °C, solid phase of MgTiO3 (JCPDS, 00-006-0494) was generated, with a small amount of other impurities. With the calcination temperature increasing, the peak intensities of
[19] [20] [21] [22] [23]
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