Direct synthesis of ultrafine tetragonal BaTiO3 nanoparticles at room temperature
© Qi et al; licensee Springer. 2011
Received: 23 April 2011
Accepted: 23 July 2011
Published: 23 July 2011
A large quantity of ultrafine tetragonal barium titanate (BaTiO3) nanoparticles is directly synthesized at room temperature. The crystalline form and grain size are checked by both X-ray diffraction and transmission electron microscopy. The results revealed that the perovskite nanoparticles as fine as 7 nm have been synthesized. The phase transition of the as-prepared nanoparticles is investigated by the temperature-dependent Raman spectrum and shows the similar tendency to that of bulk BaTiO3 materials. It is confirmed that the nanoparticles have tetragonal phase at room temperature.
KeywordsBaTiO3 nanoparticle room temperature
Barium titanate (BaTiO3) is widely used for electronic devices in the technological ceramic industry because of its ferroelectric, thermoelectric, and piezoelectric properties when it assumes the tetragonal structure . As such, it can be widely used in capacitors, positive temperature coefficient resistors, dynamic random access memories, electromechanics, and nonlinear optics [2, 3]. For the existence of the size effect of ferroelectricity and the potential application of bottom-up assembled novel nanostructures, the synthesis of ultrafine BaTiO3 nanoparticles is theoretically and technologically important . Many novel synthesis techniques have been developed for this important material.
The hydrothermal method is one of the most popular approaches to the perovskite nanostructures directly from solution, but the synthesis processes are often conducted at elevated temperatures (typically 100°C to 280°C) and/or under relatively high pressures to improve the crystallinity of the products [5, 6]. To avoid high pressure during synthesis, the thermal decompositions of a metal-organic precursor were developed to prepare the nanostructures of BaTiO3, SrTiO3, BaZrO3, and their solid-state solution at around 200°C [4, 7–9], but the metal-organic precursors are often expensive. Much effort was done to decrease the synthesis temperature in order to obtain the fine particles with less agglomeration. Direct synthesis from solution (DSS) was developed to prepare perovskite nanoparticles with the particle size of 20 nm to approximately 70 nm, which was operated at 50°C to approximately 100°C and normal pressure [10–12] conveniently by dripping titanium or zirconium alkoxide solution into strong alkaline (i.e., barium hydroxide) solution, but much finer grain size is difficult to obtain and the production efficiency for industry is limited by the low solubility of alkaline earth hydroxides. Recently, barium titanate nanoparticles have been synthesized at room temperature with peptide nanorings as templates , or using biosynthesis method . However, it is difficult to enlarge the production scale, the process cannot be controlled facilely, and also the cost of biosynthesis is very high. Above all aqueous systems, cubic phase of BaTiO3 are synthesized mostly [6–13]. To obtain the tetragonal phase which has ferroelectricity, annealing at high temperature is necessary and thus grain growth and aggregation are inevitable. To further simplify the process, lower the processing temperature, improve the synthesis efficiency, and acquire much finer grain size and tetragonal phase are important and still rather challenging technically.
In this study, a method is developed to prepare ultrafine tetragonal barium titanate nanoparticles at room temperature. The quantity of the product can be easily enlarged, and the cost is low.
The method is evolved from DSS and is carried out in an enclosed system. The spontaneous reaction of alkali to environmental CO2 is avoided, and the content of barium carbonate is suppressed in the final products. The reagents anhydrous Ba(OH)2 and tetrabutyl titanate [Ti(OC4H9)4] are adopted as starting raw materials to prepare ultrafine BaTiO3 nanoparticles. The titanium solution is obtained by dissolving 34.0 g of Ti(OC4H9)4 into 50.0 ml butanol. The alkali slurry is prepared by ball milling of the mixture of 17.1 g Ba(OH)2 and 3.60 g H2O in 100 ml butanol for 4 h. The cubage of the milling jar is 250 ml. The titanium solution is added into the alkali slurry in the jar and resealed for another 18-h milling at the rate of 200 rpm; after that, homogenous white slurry is obtained. The white slurry is air-dried, and BaTiO3 nanoparticles are synthesized. All of the procedures are carried at room temperature.
The samples are characterized at room temperature by X-ray diffraction (XRD) on a Philips Diffractometer (model: X'Pert-Pro MPD; Philips, Eindhoven, The Netherland) using CuKα radiation (40 kV, 30 mA). The microstructures of the as-prepared powders are observed by transmission electron microscopy (TEM) on a JEOL TEM (model: JSM2010; JEOL Ltd., Tokyo, Japan). The Raman spectra are recorded on an HR800 (Horiba Jobin Yvon, Chilly Mazarin, France) particle analyzer using the laser exciting line of 637, 488, and 325 nm. The rate of measured temperature rise is 15°C/min.
Results and discussion
A large quantity (23.0 g) of barium titanate nanoparticles is directly synthesized at room temperature. Because ball milling is used as a means of blending, the solubility of barium hydroxide is not a limit during synthesis and thus the synthesis efficiency is improved distinctly. For example, a large quantity of solvents has to be used in a conventional solution method since the solubility of barium hydroxide is low (i.e., 20°C, 3.9 g/100 ml water). In our method, only small quantity of dispersant is needed and the batch of product can be enlarged easily.
The peak around 310 cm-1 appears below the Curie point and vanishes above the Curie point in BaTiO3 ceramics , suggesting that the peak at 311 cm-1 (E(3TO) + E(2LO) + B1) in our sample which vanished above 125°C is an intrinsic peak for tetragonal BaTiO3. The peaks at 532, 259, and 186 cm-1 are assigned to the fundamental TO mode of A1 symmetry while comprising the main difference in Raman spectra among tetragonal and orthorhombic phases of BaTiO3. The sharp peak at 186 cm-1 (E(2TO) + E(1LO) + A1(1TO) + A1(1LO)) which vanishes above 5°C reveals that it is a feature of orthorhombic phase. A sharp peak 169 cm-1 which appears at very low temperature and vanishes at -90°C shows that it is a characteristic wave band for rhombohedral phase. This peak has been documented in early references as ν3(TO)  or A1(TO) . Similar to the peak 169 cm-1, the peak 488 cm-1 has been documented as ν1(TO)  or E1(TO)  and only appears in rhombohedral phase but is rather weak. Although, both peaks at 169 cm-1 and 488 cm-1 appear rarely in recent references, our Raman spectra of 7-nm BaTiO3 nanoparticles agree well with early references which have been measured using bulk materials. Overall, the Raman spectroscopy clearly shows that the nanoparticles prepared from our method show the normal phase transition as bulk BaTiO3 materials and have tetragonal Raman behavior at room temperature even when the grain size is as small as 7 nm.
The ultrafine tetragonal BaTiO3 nanoparticles is synthesiezd in our system. The synthesis mechanism of BaTiO3 nanoparticles is believed to undergo two steps , hydrolysis of alkoxide to form titanium hydroxide and followed crystallization of BaTiO3 nanoparticles by adsorption of Ba2+. In our system, the water content is controlled and a suitable dispersent is chosen. Less water (include crystalline water) in the system causes less hydrogen interstitial introduced in the lattice, and thus, tetragonal phase can be achieved. The long alkanol chain of the dispersant, and also less water, depresses the interactions among the nanoparticles or/and dispersents, where ultrafine nanoparticles with less aggregation can be obtained. The more details of crystalline mechanism will be studied further. The ferroelectricity of the composite with the polymer and the ultrafine BaTiO3 nanoparticles will be done in the future.
A large quantity of tetragonal BaTiO3 nanoparticles as fine as 7 nm was directly synthesized at room temperature. The synthesis efficiency improved distinctly, and the batch processing could be scaled up easily because large quantity of solvents was not necessary in the method. Both XRD and TEM results revealed that the as-prepared nanoparticles had perfect crystallized perovskite phase with ultrafine grain size. Temperature-dependent Raman spectrum shows that the nanoparticles prepared from our method have the normal phase transition as bulk BaTiO3 materials and have tetragonal phase at room temperature even when the grain size is as small as 7 nm.
The work was supported by the National Science Foundation of China NSFC/RGC (NSFC grant no. 50831160522, grant no. N_PolyU 501/08) and the National Basic Research Program of China (973 Program) 2009CB623301. Support from the Hong Kong Innovation and Technology Fund (ITP 004/009NP) is also acknowledged.
- Hennings D, Klee M, Waser R: Advanced dielectrics: bulk ceramics and thin films. Adv Mater 1991, 3: 334–340. 10.1002/adma.19910030703View ArticleGoogle Scholar
- Cross LE: Dielectric, piezoelectric and ferroelectric components. Am Ceram Soc Bull 1984, 63: 586–590.Google Scholar
- Naumov II, Bellaiche L, Fu H: Unusual phase transitions in ferroelectric nanodisks and nanorods. Nature 2004, 432: 737–740. 10.1038/nature03107View ArticleGoogle Scholar
- Du HC, Wohlrab S, Weiß M, Kaskel S: Preparation of BaTiO 3 nanocrystals using a two-phase solvothermal method. J Mater Chem 2007, 17: 4605–4610. 10.1039/b708914gView ArticleGoogle Scholar
- Hernandez BA, Chang KS, Fisher ER, Dorhout PK: Sol-gel template synthesis and characterization of BaTiO 3 and PbTiO 3 nanotubes. Chem Mater 2002, 14: 480. 10.1021/cm010998cView ArticleGoogle Scholar
- Perez-Maqueda LA, Dianez MJ, Gotor FJ, Sayagues MJ, Real C, Criado JM: Synthesis of needle-like BaTiO 3 particles from the thermal decomposition of a citrate precursor under sample controlled reaction temperature conditions. J Mater Chem 2003, 13: 2234. 10.1039/b305828jView ArticleGoogle Scholar
- O'Brien S, Brus L, Murray CB: Synthesis and characterization of nanocrystals of barium titanate, toward a generalized synthesis of oxide nanoparticles. J Am Chem Soc 2001, 123: 12085–12086. 10.1021/ja011414aView ArticleGoogle Scholar
- Urban JJ, Yun WS, Gu Q, Park HK: Synthesis of single-crystalline perovskite nanowires composed of barium titanate and strontium titanate. J Am Chem Soc 2002, 124: 1186–1187. 10.1021/ja017694bView ArticleGoogle Scholar
- Niederberger M, Pinna N, Polleux J, Antonietti MR: A general soft chemistry route to perovskites and related materials: synthesis of BaTiO 3 , BaZrO 3 and LiNbO 3 nanoparticles. Angew Chem, Int Ed 2004, 43: 2270–2273. 10.1002/anie.200353300View ArticleGoogle Scholar
- Qi JQ, Li LT, Wang YL, Gui ZL: Preparation of nanoscaled BaTiO3 powders by DSS method near room temperature under normal pressure. J Crystal Growth 2004, 260: 551–556. 10.1016/j.jcrysgro.2003.08.059View ArticleGoogle Scholar
- Qi JQ, Wang Y, Chen WP, Li LT, Chan HLW: Direct large-scale synthesis of perovskite barium strontium titanate nano-particles from solutions. J Sol State Chem 2005, 178: 279–284. 10.1016/j.jssc.2004.12.003View ArticleGoogle Scholar
- Qi JQ, Sun L, Du P, Chen WP, Xu YG, Li LT: Stoichiometry of BaTiO 3 nanoparticles. J Nanopart Res 2010, 12: 2605–2609. 10.1007/s11051-009-9838-0View ArticleGoogle Scholar
- Nuraje N, Su K, Haboosheh A, Samson J, Manning EP, Yang NI, Matsui H: Room temperature-synthesis of ferroelectric barium titanate nanoparticles using peptide nano-rings as templates. Adv Mater 2006, 18: 807–811. 10.1002/adma.200501340View ArticleGoogle Scholar
- Bansal V, Poddar P, Ahmad A, Sastry M: Room-temperature biosynthesis of ferroelectric barium titanate nanoparticles. J Am Chem Soc 2006, 128: 11958–11963. 10.1021/ja063011mView ArticleGoogle Scholar
- Scherrer P: Bestimmung der Grösse und der inneren Struktur von Kolloidteilchen mittels Röntgenstrahlen. Nachr Ges Wiss Göttingen 1918, 26: 98–100.Google Scholar
- Kwei GH, Lawson AC, Billinge SJL, Cheong SW: Structures of the ferroelectric phases of barium titanate. J Phys Chem 1993, 97: 2368–2377. 10.1021/j100112a043View ArticleGoogle Scholar
- Shiratori Y, Pithan C, Dornseiffer J, Waser R: Raman scattering studies on nanocrystalline BaTiO 3 . Part I - isolated particles and aggregates. J Raman Spectrosc 2007, 38: 1288–1299. 10.1002/jrs.1764View ArticleGoogle Scholar
- Moreira ML, Mambrini GP, Volanti DP, Leite ER, Orlandi MO, Pizani PS, Mastelaro VR, Paiva-Santos CO, Longo E, Varela JA: Hydrothermal microwave: a new route to obtain photoluminescent crystalline BaTiO 3 nanoparticles. Chem Mater 2008, 20: 5381–5387. 10.1021/cm801638dView ArticleGoogle Scholar
- Pontes FM, Escote MT, Escudeiro CC, Leite ER, Longo E, Chiquito AJ, Pizani PS, Varela JA: Characterization of BaTi 1 - x Zr x O 3 thin films obtained by a soft chemical spin-coating technique. J Appl Phys 2004, 96: 4386–4391. 10.1063/1.1775048View ArticleGoogle Scholar
- Hayashi T, Oji N, Maiwa H: Film thickness dependence of dielectric properties of BaTiO 3 Thin films prepared by sol-gel method. Jpn J Appl Phys 1994, 33: 5277–5280. 10.1143/JJAP.33.5277View ArticleGoogle Scholar
- Joshi UA, Yoon S, Baik S, Lee JS: Surfactant-free hydrothermal synthesis of highly tetragonal barium titanate nanowires: a structural investigation. J Phys Chem B 2006, 110: 12249–12256. 10.1021/jp0600110View ArticleGoogle Scholar
- Perry CH, Hall DB: Temperature dependence of the Raman spectrum of BaTiO 3 . Phys Rev Lett 1965, 15: 700–702. 10.1103/PhysRevLett.15.700View ArticleGoogle Scholar
- Pinkzuk A, Taylor W, Burstein E: The Raman spectrum of BaTiO 3 . Sol Stat Comm 1967, 5: 429–433. 10.1016/0038-1098(67)90791-0View ArticleGoogle Scholar
- Testino A, Buscaglia V, Buscaglia MT, Viviani M, Nanni P: Kinetic modeling of aqueous and hydrothermal synthesis of barium titanate (BaTiO 3 ). Chem Mater 2005, 17: 5346–5356. 10.1021/cm051119fView ArticleGoogle Scholar
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