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CERAMICS INTERNATIONAL
Ceramics International 40 (2014) 12899–12903 www.elsevier.com/locate/ceramint
Polymer-derived yttria stabilized bismuth oxide nanocrystalline ceramics Arda Aytimura,n, İbrahim Uslub, Şenol Durmuşoğluc, Ahmet Akdemirc a
Department of Advanced Technologies, Gazi University, Teknikokullar, Ankara 06500, Turkey b Department of Chemistry Teaching, Gazi University, Teknikokullar, Ankara 06500, Turkey c Department of Mechanical Engineering, Selcuk University, Kampüs, Konya 42075, Turkey
Received 13 February 2014; received in revised form 23 April 2014; accepted 23 April 2014 Available online 2 May 2014
Abstract Boron doped and undoped Bi2O3–Y2O3 nanofibers were synthesized by the electrospinning method. The nanofibers were then calcined to obtain nanocrystalline ceramics. The synthesized nanofibers and nanocrystalline ceramics were characterized using XRD, FT-IR, SEM and XPS. According to the XRD results the undoped Bi2O3–Y2O3 nanocrystalline ceramic has a face-centered cubic structure. The XPS results show that nanocrystalline ceramics were pure Bi2O3, and there were no peaks related to either bivalent or tetravalent or pentavalent states in Bi2O3. The XPS results also show that the crystallinity of the boron doped nanocrystalline ceramic was decreased because of the network former property of the boron. The average fiber diameters for electrospun boron doped and undoped PVA/Bi–Y acetate nanofibers were calculated as 179 nm and 96 nm, respectively. The SEM micrographs of the nanocrystalline ceramics show that the undoped Bi2O3–Y2O3 ceramic has needle-like crystalline structure. However, the crystallinity of the boron doped Bi2O3–Y2O3 ceramic decreased because of boron doping. & 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Keywords: A. Calcination; A. Precursors: organic; B. Nanocomposites; D. Y2O3
1. Introduction Bismuth oxide and its composites have been studied for various applications because of the excellent properties of bismuth oxide. Armelao et al. mentioned that bismuth oxide (Bi2O3) has at least four main crystalline forms usually indicated as α, β, γ and δ each showing different chemical and physical properties [1]. The high oxygen-ion conducting δ-phase has a (defect) fluorite structure and transforms to β-phase at about 650 1C and γ-phase at about 640 1C. Both β and γ phase have very low oxygen-ion conducting properties with respect to δ-phase. Defect-fluorite structure δ-phase contains a very large concentration of oxygen vacancies where three quarters of the tetrahedral interstices are randomly occupied by oxide ion. High oxide ion conduction of δ-phase is provided by oxide ion vacancies and interstitial oxide ions. The conductive characteristics of Bi2O3 are not retained over long periods of time and n
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http://dx.doi.org/10.1016/j.ceramint.2014.04.149 0272-8842/& 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
also its strength tends to diminish because of a large volume change during phase transformations [2]. The stability is the principal requirement for any realistic device based on Bi2O3 solid electrolytes such as solid oxide fuel cell (SOFC) applications [3]. Similar to stabilization of zirconia, yttria or some other oxides (Yb2O3, Er2O3, Y2O3, Dy2O3, and Gd2O3) have also been used in stabilization of defect-fluorite structure δ-phase Bi2O3 [4,5]. After stabilization the final ceramic bismuth yttrium oxides can keep fluorite-type δ-phase structure even at room temperature. In this study, polymer-derived boron containing Bi2O3– Y2O3 nanocrystalline ceramics were prepared using electrospinning technique. This technique is cost effective and a functional technique to produce nanofibers, polymer derived nanocrystalline ceramics and nanocomposites [6–8]. Tunc et al. referred to advantages of polymer derived nanocrystalline ceramics prepared by electrospinning in their paper. Tunc et al. said that the main advantages of such polymer-derived ceramics are the applicability of polymer-processing techniques, the homogeneity of the precursors on a molecular level,
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and the low processing temperatures when compared to conventional powder sintering methods [9–12]. Boron oxide (B2O3) was used in this study as a dopant because of its properties. Aytimur et al. [13] described the boron oxide and its properties. Aytimur et al. mentioned that B2O3 is almost always found as the amorphous form. It is an excellent network former and very effective sintering aid [14–19].
2. Experimental section In the experiments, poly(vinyl alcohol) (PVA) (average Mw 85,000–124,000; Sigma-Aldrich), bismuth(III) acetate (SigmaAldrich), yttrium(III) acetate (Sigma-Aldrich) and boric acid (Merck) were used. Ultrapure deionized water was used as a solvent. An aqueous PVA solution (8%) was first prepared by dissolving the PVA powder in ultrapure deionized water. In the experiments, two hybrid polymer solutions were prepared. As a typical procedure, proper amounts of the metal acetate salts and boric acid powder were dissolved in ultrapure deionized water (see Table 1). Metal acetate and boric acid solutions were added to the proper amount of the PVA solution to prepare electrospinning solutions. Obtained electrospinning solutions were poured into syringes, the needle (18 gauge) being connected to the positive terminal of a high-voltage supply (Gamma High Voltage Research) able to generate DC voltages up to 40 kV. Solutions were delivered to the needle by a syringe pump (New Era Pump Systems Inc., USA). The distance between the tip of the needle and the aluminum collector was fixed at 18 cm. The following operative parameters were chosen: flow rate 0.5 ml/h and applied voltage 20 kV. Electrospun nanofibers were dried in vacuum for 12 h at 80 1C. Nanofibers were calcined at 850 1C in the furnace at atmospheric conditions. Major steps of nanocrystalline ceramic material preparation were given in Fig. 1. The pH and conductivity of the solutions were measured by using Wissenschaftlich-Technische-Werkstätten (WTW) and 315i/SET apparatus. The viscosity of the hybrid polymer solutions was measured with AND SV-10 viscometer. The surface tension of the complex hybrid polymer solutions was measured by using KRUSS model manual measuring system. Fiber morphology, average fiber diameter and distribution were determined by scanning electron microscopy (JEOL JSM 7000F Field Emission) on samples sputtered with gold and observed at an accelerating voltage of 10 kV. Fiber diameter was measured by image processing software, ImageJ (Image Pro-Express, Version 5.0.1.26, Media Cybernetics Inc.). ImageJ is a public domain Java image processing program [20]. The crystal structures of the
calcined powders were investigated by means of X-ray diffraction (XRD) (Ultima-IV XRD (Rigaku, Tokyo, Japan) with Cu Kα radiation at 40 kV and 30 mA). 3. Results and discussion The morphology of the fibers depends on the properties of the electrospinning solution. Therefore, the pH, viscosity, conductivity and surface tension of the PVA/Bi–Y acetate solutions were measured before the electrospinning experiment. Measured values were given in Table 2. The solution viscosity is one of the prime parameter affecting the fiber diameter. A higher viscosity results in a large fiber diameter. Moreover, the viscosity has a meaningful effect on whether the electrospinning jet breaks up into small droplets or whether the resulting electrospun fibers contain beads [21,22]. The conductivity of the polymer solution is important to initiate the electrospinning process. Furthermore, the conductivity of the electrospinning solution is a considerable parameter influencing the diameter of electrospun nanofibers as well as viscosity. An increase in the electrical conductivity of the solution causes a decrease in the diameter of the electrospun nanofibers [21]. Fig. 2 exhibits the FT-IR spectra of the precursor electrospun nanofibers and the calcined nanocrystalline undoped and boron doped ceramics. It is seen that both the undoped and boron doped PVA/Bi–Y acetate nanofibers have approximately the same IR spectrum because of the presence of poly(vinyl alcohol). The broad band around 3200 cm 1 and around 1550 cm 1 correspond to the stretching vibration and deformation vibration of hydroxyl (–OH) groups, respectively. The existence of these bands indicate the existence of adsorbed water on the surface of the electrospun nanofibers. The band corresponds to the
Fig. 1. Major steps of the nanocrystalline ceramic preparation.
Table 1 Amounts of poly(vinyl alcohol), metal acetates and boric acid in the electrospinning solutions. Solution
Bismuth acetate powder (g)
Yttrium acetate powder (g)
Boric acid powder (g)
PVA solution (g)
PVA/undoped Bi–Y acetate (solution-1) PVA/boron doped Bi–Y acetate (solution-2)
1.00 1.00
0.2297 0.2297
– 0.25
125 125
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Table 2 The pH, electrical conductivity, surface tension and viscosity values of the metal acetates containing polymer solutions. Polymer solution
Electrical conductivity (mS/cm)
Viscosity (Pa s)
pH
Surface tension (mN/m)
PVA/undoped Bi–Y acetate (solution-1) PVA/boron doped Bi–Y acetate (solution-2)
1.324 1.309
0.154 0.178
3.30 3.21
46 51
Fig. 3. X-ray diffraction patterns of the undoped and boron doped yttria stabilized bismuth oxide nanocrystalline ceramic powders. Fig. 2. Fourier transform infrared (FT-IR) spectra of the nanofibers and the undoped and boron doped yttria stabilized bismuth oxide nanocrystalline ceramic powders.
stretching C–H vibration of alkyl groups observed at 2964 cm 1. Bands of the stretching C–H vibration, the stretching vibration and deformation vibration of hydroxyl (–OH) groups were not observed in the IR spectrum of nanocrystalline ceramics after calcination as seen from Fig. 2. This can be interpreted as all water and carbon contents were removed from nanocrystalline ceramics. The band of Bi–O–Bi vibration corresponds to bismuth oxide observed at 840 cm 1 in the IR spectra of both undoped and boron doped nanocrystalline ceramics [23]. The band observed at 710 cm 1 originates due to the bending vibration of B–O–B in [BO3] triangles and the infrared band at 1372 cm 1 assigned to B–O– stretching vibration for the boron doped nanocrystalline ceramic powder [24–26]. The X-ray diffraction (XRD) patterns of the undoped and boron doped nanocrystalline ceramics are shown in Fig. 3. The face-centered cubic structure (δ-phase bismuth oxide), which has main peak (111) and other peaks (200), (220), (311), (222) clearly appeared for undoped powders [27]. However, the peak intensity decreased because of boron doping. This result was interpreted by Aytimur et al. [13] as boron atoms behave as network formers and the incorporation of B2O3 atoms into the yttria stabilized bismuth oxide prevents the nucleus formation and the crystallinity, and turns the structure into a more amorphous glassy form [28]. Bismuth(III) orthoborate (BiBO3) was formed by boron doping. Honma et al. [29] synthesized and characterized this structure in their study. Fig. 4 shows the Bi4f core-level XPS spectra of the undoped and boron doped yttria stabilized bismuth oxide nanocrystalline
Fig. 4. XPS spectra of the undoped and boron doped yttria stabilized bismuth oxide nanocrystalline ceramic powders.
ceramic powders. For both the samples, no spurious peaks were found and the Bi4f spectra consist of two multiple-split peaks, which also have a slight asymmetry towards higher binding energy which indicates that there is a tendency of increase of the average valence of bismuth ions towards a higher value. This result indicated that the nanocrystalline ceramic powder samples were pure Bi2O3, and there were nopeaks related to either bivalent or tetravalent or pentavalent states in bismuth oxide. Shoulders of the Bi4f7/2 peaks were not observed. It can be observed from the Fig. 4 that binding energy shifts to a higher value for Bi4f7/2 for the undoped samples which is mainly due to the increase in the crystallinity of the undoped nanocrystalline
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Fig. 5. SEM micrographs of the: (a) undoped and (b) boron doped PVA/Bi–Y acetate nanofibers.
Fig. 6. The SEM micrographs of the: (a) undoped and (b) boron doped yttria stabilized bismuth oxide nanocrystalline ceramic powders.
ceramic with respect to the boron doped ones [30]. The energy position of the main peaks and the spin-orbit splitting value (calculated as 5.3 eV) are in good agreement with the previously reported literature [1,3,31–37]. The SEM micrographs of the electrospun undoped and boron doped nanofibers were given in Fig. 5(a) and (b). It could be seen that the surface of the boron doped PVA/Bi–Y acetate nanofibers was uniform, smooth and linear with respect to the undoped PVA/Bi–Y acetate nanofibers. The boron doped nanofiber mats have also no beadings. The average fiber diameters for the electrospun undoped and boron doped PVA/Bi–Y acetate nanofibers were calculated using ImageJ software as 179 nm and 96 nm, respectively. Fifty different parts of the nanofibers were randomly selected and diameters of these parts were calculated. Then average of the diameters was calculated. In Fig. 6(a) and (b), the undoped and boron doped yttria stabilized bismuth oxide nanocrystalline ceramic powders are shown. Fig. 6(a) exhibits the SEM micrograph of the undoped yttria stabilized bismuth oxide nanocrystalline ceramic powder. It can be seen from the SEM micrograph that after calcination needle-like crystalline structures were formed. As seen from Fig. 6(b) the microstructure of the boron doped yttria stabilized bismuth oxide nanocrystalline ceramic was changed because of boron doping. The glassy structure can be easily seen form the SEM micrograph of the boron doped yttria stabilized bismuth oxide nanocrystalline ceramic. This result confirms the XRD results. The glassy structure was detected from the XRD pattern of the boron doped yttria stabilized bismuth oxide. These results
indicate that adding excessive amount of boron as a dopant affected the structure of ceramic and turned it into the glassy structure instead of nanocrystalline structure.
4. Conclusion A cost effective and functional method was described to produce the undoped and boron doped yttria stabilized bismuth oxide nanofibers and nanocrystalline ceramics in this paper. Obtained undoped and boron doped yttria stabilized bismuth oxide nanofibers and nanocrystalline ceramic materials were characterized by the FT-IR, XRD, XPS and SEM techniques. The XRD results show that the undoped Bi2O3–Y2O3 nanocrystalline ceramic has a face-centered cubic structure; however, the boron doped sample has an amorphous structure. According to the XPS results the nanocrystalline ceramic powder samples were pure Bi2O3, and there were no peaks related to either bivalent or tetravalent or pentavalent states in Bi2O3. In addition, the XPS results show that the crystallinity of boron doped nanocrystalline ceramic was decreased because of its network former property. The SEM micrographs of the nanofibers exhibit that the boron doped nanofibers were linear, smooth and uniform with respect to the undoped fiber mats. The boron doped nanofiber mats have also no beadings. The average fiber diameters for the electrospun undoped and boron doped PVA/Bi–Y acetate nanofibers were calculated as 179 nm and 96 nm, respectively. The SEM micrographs of the ceramics show that the undoped Bi2O3–Y2O3 ceramic has a needle-like crystalline structure. However, the crystallinity of the
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boron doped Bi2O3–Y2O3 ceramic decreased because of boron doping. Acknowledgments Financial support received from the Scientific Research Coordination Center of Selcuk University (BAP) to conduct the study is gratefully acknowledged. References [1] L. Armelao, P. Colombo, M. Fabrizio, Synthesis of Bi2O3 and Bi4(SiO4)3 thin films by the sol–gel method, J. Sol–Gel Sci. Technol. 13 (1998) 213–217. [2] R. Kant, Studies of some bismuth based electrolytes for solid oxide fuel cells (Ph.D. Thesis), School of Physics and Materials Science, Thapar University, Patiala, India, 2008. [3] X.H. Wu, W. Qin, W.D. He, Thin bismuth oxide films prepared through the sol–gel method as photocatalyst, J. Mol. Catal. A-Chem. 261 (2007) 167–171. [4] P.J. Dordor, J. Tanaka, A. Watanabe, Electrical characterization of phasetransition in yttrium doped bismuth oxide, Bi1.55Y0.45O3, Solid State Ion. 25 (1987) 177–181. [5] M. Bosacka, The synthesis and selected properties of new double vanadates M2InV3O11, where M ¼Zn, Mg, Mater. Res. Bull. 41 (2006) 2181–2186. [6] I. Uslu, S.S. Cetin, A. Aytimur, S. Yuceyurt, M.O. Erdal, Synthesis and properties of boron doped NaxCo2O4 nanocrystalline ceramics, J. Inorg. Organomet. Polym. 22 (2012) 766–771. [7] S. Keskin, I. Uslu, T. Tunc, M. Ozturk, A. Aytimur, Preparation and characterization of neodymia doped PVA/Zr–Ce oxide nanocrystalline composites via electrospinning technique, Mater. Manuf. Process. 26 (2011) 1346–1351. [8] I. Uslu, A. Aytimur, Production and characterization of poly(vinyl alcohol)/poly(vinylpyrrolidone) iodine/poly(ethylene glycol) electrospun fibers with (hydroxypropyl)methyl cellulose and aloe vera as promising material for wound dressing, J. Appl. Polym. Sci. 124 (2012) 3520–3524. [9] T. Tunc, I. Uslu, S. Durmusoglu, S. Keskin, A. Aytimur, A. Akdemir, Preparation of gadolina stabilized bismuth oxide doped with boron via electrospinning technique, J. Inorg. Organomet. Polym. 22 (2012) 105–111. [10] M.A. Schiavon, I.V.P. Yoshida, Ceramic matrix composites derived from CrSi2-filled silicone polycyclic network, J. Mater. Sci. 39 (2004) 4507–4514. [11] I. Uslu, A. Aytimur, M.K. Ozturk, S. Kocyigit, Synthesis and characterization of neodymium doped ceria nanocrystalline ceramic structures, Ceram. Int. 38 (2012) 4943–4951. [12] A. Aytimur, I. Uslu, S. Kocyigit, F. Ozcan, Magnesia stabilized zirconia doped with boron, ceria and gadolinia, Ceram. Int. 38 (2012) 3851–3856. [13] A. Aytimur, S. Kocyigit, I. Uslu, S. Durmusoglu, A. Akdemir, Fabrication and characterization of bismuth oxide–holmia nanofibers and nanoceramics, Curr. Appl. Phys. 13 (2013) 581–586. [14] E.E. Horopanitis, G. Perentzis, A. Beck, L. Guczi, G. Peto, L. Papadimitriou, Correlation between structural and electrical properties of heavily lithiated boron oxide solid electrolytes, J. Non-Cryst. Solids 354 (2008) 374–379. [15] V.I. Kushnirenko, I.V. Markevich, A.V. Rusavsky, Influence of boric acid as a flux on the properties of ZnO ceramics, Radiat. Meas. 45 (2010) 468–471. [16] Z. Misirli, H. Erkalfa, O.T. Ozkan, Effect of B2O3 addition on the sintering of α-Al2O3, Ceram. Int. 22 (1996) 33–37.
12903
[17] D.Z. de Florio, R. Muccillo, Effect of boron oxide on the cubic-tomonoclinic phase transition in yttria-stabilized zirconia, Mater. Res. Bull. 39 (2004) 1539–1548. [18] R.A. Smith, Basic geology and chemistry of borate, Am. Ceram. Soc. Bull. 81 (2002) 61–64. [19] I. Uslu, T. Tunc, M.K. Ozturk, A. Aytimur, Synthesis and characterization of boron-doped hafnia electrospun nanofibers and nanocrystalline ceramics, Polym.-Plast. Technol. 51 (2012) 257–262. [20] 〈http://rsbweb.nih.gov/ij/docs/intro.html〉, 2014 (accessed 10.01.14). [21] D. Li, J.T. McCann, Y.N. Xia, Electrospinning: a simple and versatile technique for producing ceramic nanofibers and nanotubes, J. Am. Ceram. Soc. 89 (2006) 1861–1869. [22] S.L. Shenoy, W.D. Bates, H.L. Frisch, G.E. Wnek, Role of chain entanglements on fiber formation during electrospinning of polymer solutions: good solvent, non-specific polymer–polymer interaction limit, Polymer 46 (2005) 3372–3384. [23] R. Irmawati, M.N.N. Nasriah, Y.H. Taufiq-Yap, S.B.A. Hamid, Characterization of bismuth oxide catalysts prepared from bismuth trinitrate pentahydrate: influence of bismuth concentration, Catal. Today 93-5 (2004) 701–709. [24] M. Abid, M. Et-tabirou, M. Taibi, Structure and DC conductivity of lead sodium ultraphosphate glasses, Mat. Sci. Eng. B-Solid 97 (2003) 20–24. [25] E.I. Kamitsos, A.P. Patsis, M.A. Karakassides, G.D. Chryssikos, Infrared reflectance spectra of lithium borate glasses, J. Non-Cryst. Solids 126 (1990) 52–67. [26] A.K. Hassan, L. Borjesson, L.M. Torell, The boson peak in glass formers of increasing fragility, J. Non-Cryst. Solids 172 (1994) 154–160. [27] J.G. Lee, S.H. Kim, H.H. Yoon, Synthesis of yttria-doped bismuth oxide powder by carbonate coprecipitation for IT-SOFC electrolyte, J. Nanosci. Nanotechnol. 11 (2011) 820–823. [28] A. Tabata, J. Nakano, K. Mazaki, K. Fukaya, Film-thickness dependence of structural and electrical properties of boron-doped hydrogenated microcrystalline silicon prepared by radiofrequency magnetron sputtering, J. Non-Cryst. Solids 356 (2010) 1131–1134. [29] T. Honma, Y. Benino, T. Fujiwara, R. Sato, T. Komatsu, New optical nonlinear crystallized glasses and YAG laser-induced crystalline dot formation in rare-earth bismuth borate system, Opt. Mater. 20 (2002) 27–33. [30] L.Q. Jing, H.G. Fu, B.Q. Wang, B.F. Xin, S.D. Li, J.Z. Sun, Effects of Sn dopant on the photoinduced charge property and photocatalytic activity of TiO2 nanoparticles, Appl. Catal. B-Environ. 62 (2006) 282–291. [31] A. Gulino, S. LaDelfa, I. Fragala, R.G. Egdell, Low-temperature stabilization of tetragonal zirconia by bismuth, Chem. Mater. 8 (1996) 1287–1291. [32] M. Pal, P. Brahma, D. Chakravorty, B.R. Chakraborty, C. Anandan, S. Bera, Mixed valency character of bismuth in ferrite lattices, J. Mater. Sci. Lett. 16 (1997) 270–272. [33] Y. Fujimoto, New infrared luminescence from Bi-doped glasses, in: M. Grishin (Ed.), Advances in Solid-State Lasers: Development and Applications, Intech, Croatia, 2010, p. 630. [34] G.H. Hwang, W.K. Han, J.S. Park, S.G. Kang, An electrochemical sensor based on the reduction of screen-printed bismuth oxide for the determination of trace lead and cadmium, Sens. Actuators B-Chem. 135 (2008) 309–316. [35] C. Hinnen, C.N. Vanhuong, P. Marcus, A comparative X-ray photoemission-study of Bi2Sr2CaCu2O8 þ δ and Bi1.6Pb0.4Sr2CaCu2O8 þ δ, J. Electron. Spectrosc. 73 (1995) 293–304. [36] I.G. Casella, M. Contursi, Characterization of bismuth adatom-modified palladium electrodes – the electrocatalytic oxidation of aliphatic aldehydes in alkaline solutions, Electrochim. Acta 52 (2006) 649–657. [37] K. Uchida, A. Ayame, Dynamic XPS measurements on bismuth molybdate surfaces, Surf. Sci. 357 (1996) 170–175.
