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Materials Chemistry and Physics 127 (2011) 21–23

Contents lists available at ScienceDirect

Materials Chemistry and Physics

journa l homepage: www.e lsev ier .com/ locate /matchemphys

aterials science communication

iquid–solid reaction synthesis of SrTiO3 submicron-sized particles

iaohua Liu, Haixin Bai ∗

ollege of sciences, Henan Agricultural University, Zhengzhou, Henan 450002, China

r t i c l e i n f o

rticle history:eceived 29 June 2010eceived in revised form

a b s t r a c t

A low temperature (600 ◦C) liquid–solid reaction method was proposed for the synthesis of SrTiO3

submicron-sized particles from submicron-sized TiO2 powder and different amounts of excess Sr(NO3)2

(which has a melting point of about 570 ◦C)). The characterization results from X-ray diffraction and field

3 November 2010ccepted 24 January 2011

eywords:eramicsxides

emission scanning electron microscopy revealed that the resultant products were phase-pure perovskitestructure SrTiO3 submicron-sized particles with diameters of about 30–108 nm. X-ray photoelectronspectroscopy analysis disclosed that the resultant products had surface compositions slightly deviatedfrom the stoichiometry of SrTiO3. UV–vis absorption spectra of the as-synthesized SrTiO3 submicron-sizedparticles showed a wide absorption peak centered at around 3.5 or 3.4 eV.

conditions and even improved properties of the resultant prod-uct.

Herein, we report the scalable synthesis of SrTiO3 submicron-sized particles via the liquid–solid reaction between common

hemical synthesisptical properties

. Introduction

SrTiO3 is an indirect band gap semiconductor with a direct bandap of about 3.4 eV [1–3]. It has a lot of excellent physical andhemical properties, such as high thermal and chemical stabil-ty, low coefficient of thermal expansion, large nonlinear opticaloefficients, quantum paraelectricity and large dielectric constant,tc. which enable its wide uses in catalysis, sensor, optical andlectronic devices [1–18]. It is widely accepted that the practi-al performances of SrTiO3 are strongly influenced by its particleize, crystal defects and surface properties, etc. which ultimatelyepend on its preparation methods and preparation conditions1–18]. Generally speaking, phase-pure SrTiO3 particles with sto-chiometric composition and nano/submicron size can meet theasic requirements for most of their intended purposes.

Solid phase reaction method is one of the most practicaleans in synthesizing SrTiO3 powders [4–7]. However, in the

onventional solid phase processes, SrTiO3 powders were usuallyroduced through the reaction between the mechanically mixedrCO3 or SrO and TiO2 powders at temperatures above 1000 ◦C4–7]. It is a pity that the coarse particles yielded this way oftenave some unwanted characteristics, such as large size (usuallyicron-sized), broad size distribution, hard agglomeration, and

ven impure phases, etc. Therefore, it is highly desirable to exploren alternative cost-effective method for large-scale production ofhase-pure, stoichiometric and nano/submicron-sized SrTiO3 par-icles at a reaction temperature as low as possible.

∗ Corresponding author. Tel.: +86 371 63554844.E-mail address: haixinbai-08@sohu.com (H. Bai).

254-0584/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.matchemphys.2011.01.056

© 2011 Elsevier B.V. All rights reserved.

As a source material for strontium, Sr(NO3)2 possesses a melt-ing point of about 570 ◦C [19]. So, when Sr(NO3) is adopted asa reactant, it will emerge in a liquid state and behave just as aliquid reactant at 600 ◦C, which can enormously increase the inter-face and contact surface areas with the other solid reactants andaccelerate the reaction rate, leading to the lowered reaction tem-perature and even the improved properties of the resultant product.Furthermore, because nano/submicron-sized powders with largesurface area and high surface energy have highly reactive activity,the use of them as reactants may also result in milder preparation

Fig. 1. FESEM image of the reactant TiO2 powder.

22 X. Liu, H. Bai / Materials Chemistry and Physics 127 (2011) 21–23

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ig. 2. XRD patterns of the products synthesized using (a) 8 or (b) 5 mmol Sr(NO3)2,ith (h k l) indexations following JCPDS card no. 73-661.

nd cost-effective Sr(NO3)2 and submicron-sized TiO2 powderst 600 ◦C, which is much lower than the reaction temperaturesenerally above 1000 ◦C used in the conventional solid phaseeaction methods [4–7]. The structure, composition and opticalbsorption property of the as-synthesized SrTiO3 submicron-

ized crystals are characterized by X-ray diffraction (XRD),eld emission scanning electron microscopy (FESEM), X-rayhotoelectron spectroscopy (XPS), and UV–vis absorption spec-ra.

Fig. 3. FESEM images of the SrTiO3 products synthesized using (a) 8 or (b) 5 mmolSr(NO3)2.

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Fig. 4. XPS spectra of Sr 3d, Ti 2p and O1s of the products synthesized using (a) 8 or (b) 5 mmol Sr(NO3)2.

X. Liu, H. Bai / Materials Chemistry a

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Wavelength (nm)

ig. 5. UV–vis absorption spectra of the SrTiO3 submicron-sized particles synthe-ized using (a) 8 or (b) 5 mmol Sr(NO3)2.

. Materials and methods

TiO2 powder in the mixed phases of about 80 mass% anatase and 20 mass% rutileith the particle size of about 80–250 nm (whose FESEM image is shown in Fig. 1)ere purchased directly from Shanghai Academe of Fine Chemicals, and the other

eagents used were analytically pure.The powders of 4 mmol TiO2 and 5 or 8 mmol Sr(NO3)2 were mixed and ground

omogenously in a carnelian mortar, then transferred to a corundum crucible. Therucible was heated in a Muffle furnace at 600 ◦C for 10 h, then allowed to cool tooom temperature naturally. The residue solid was washed thoroughly with 1 mol/lNO3 aqueous solution and deionized water to remove the impurities, and finallyried in air at 80 ◦C.

The obtained products were characterized by XRD (German Bruker AXS D8DVANCE X-ray diffractometer), FESEM (Japan Hitachi S-4800 field emission scan-ing electron microscopy), XPS (American Thermo-VG Scientific ESCALAB 250 XPSystem with Al K� radiation as the exciting source, where the binding energiesere calibrated by referencing the C 1s peak (284.6 eV) to reduce the sample charge

ffect), and UV–vis absorption spectra (Japan Shimadzu UV-2550 spectrophotome-er, the samples were ultrasonically dispersed in distilled water).

. Results and discussion

The XRD patterns of the products synthesized using 8 andmmol Sr(NO3)2 are shown in Fig. 2(a) and (b), respectively. Bothroducts displayed the characteristic XRD peaks of cubic perovskitetructure SrTiO3 [JCPDS card no. 73-661], without any visible XRDeaks stemmed from the possible impurities such as TiO2, Sr2TiO4,rO2, or SrCO3, etc., indicating the synthesis of phase-pure SrTiO3owders.

The FESEM images of the SrTiO3 powders synthesized using 8nd 5 mmol Sr(NO3)2 are shown in Fig. 3(a) and (b), respectively. Asan be seen, both products comprised individual submicron-sizedarticles with diameters in the range of about 30–108 nm, as wells larger aggregates of these submicron-sized particles.

The compositions of the as-synthesized SrTiO3 submicron-sizedarticles were further determined by XPS. The survey XPS spec-ra of both samples (not shown) revealed the presence of only Sr,i and O components, except unavoidable carbon from adsorbedaseous molecules [20]. The binding energies of Sr 3d5/2, Ti 2p3/2nd O 1s were observed at around 132.63/132.77, 458.65/458.47

nd 530.06/529.69 eV (Fig. 4), respectively, which agreed with theiterature values for SrTiO3 [18,20]. Besides, quantification of theeak areas of the Sr 3d, Ti 2p and O 1s cores disclosed that theurface compositions of the products in Fig. 4(a) and (b) wererTi1.08O2.95 and SrTi1.03O2.90, respectively, which were slightly rich

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nd Physics 127 (2011) 21–23 23

in Ti and deficient in O, as compared with the stoichiometry ofSrTiO3.

The UV–vis absorption spectra of the SrTiO3 submicron-sizedparticles synthesized using 8 and 5 mmol Sr(NO3)2 are shown inFig. 5(a) and (b), respectively. As can be seen, either of our productsdisplayed a wide absorption peak centered at about 3.5 (352 nm,Fig. 5(a)) or 3.4 eV (360 nm, Fig. 5(b)), which fell within the reportedband gap range of SrTiO3 nanoparticles [7–10]. In addition, there isalso an absorption tail at lower energies for both the products. Thewide wavelength response suggested the as-synthesized SrTiO3submicron-sized particles may be used as a kind of photocatalystor photoelectric material.

4. Conclusions

Phase-pure cubic perovskite structure SrTiO3 submicron-sizedparticles were synthesized through the liquid–solid reactionbetween submicron-sized TiO2 powders and different amounts ofexcess Sr(NO3)2 in air at 600 ◦C for 10 h, coupled with a subsequentwashing process. The proposed method is simple, cost-effectiveand suitable for scale up production of multifunctional SrTiO3submicron-sized particles.

Acknowledgements

This work was supported by the National Natural Science Foun-dation of China with the grant no. 20735003, the Open Fund(no. SKLEAC2010011) of State Key Laboratory of ElectroanalyticalChemistry in China, the Projects (Nos. 30700348 and 30700349)Sponsored by the Scientific Research Foundation for the Doctors inHenan Agricultural University of China, as well as the Scientific andTechnological Key Project (no. 102102310335) of Henan Province.

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