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A coprecipitation technique to prepare NiNb2O6
Materials Letters 61 (2007) 2354 – 2355 www.elsevier.com/locate/matlet
A coprecipitation technique to prepare NiNb2O6 V. Samuel c , A.B. Gaikwad b , A.D. Jadhav a , N. Natarajan a , V. Ravi a,⁎ a
Physical and Materials Chemistry Division, National Chemical Laboratory, Pune 411008, India b Center for Materials Characterization, National Chemical Laboratory, Pune 411008, India c Catalysis division, National Chemical Laboratory, Pune 411008, India Received 10 April 2006; accepted 6 September 2006 Available online 25 September 2006
Abstract A mixture of ammonium carbonate and ammonium hydroxide was used to coprecipitate nickel and niobium ions as nickel carbonate and niobium hydroxide under basic conditions. This precursor yielded NiNb2O6 (NN) ceramics on calcining at 700 °C (at a temperature lower than 800 °C which is necessary for the formation of NiNb2O6 when prepared by the traditional solid state method). The average particle size and morphology of these powders were investigated by transmission electron microscope (TEM). © 2006 Elsevier B.V. All rights reserved. Keywords: Oxides; Chemical synthesis; X-ray methods; Electronic materials; Electron microscopy
1. Introduction ANb2O6 (A = Ba, Sr, Ca) compounds with columbite (orthorhombic) or trirutile (tetragonal) -type structure find wide applications in electro-optic, pyroelectric and photo-refractive applications [1–3]. On the contrary, there are not much investigations on transition metal niobates, e.g, NiNb2O6 and CoNb2O6. The NiNb2O6 ceramics has a potential application as photocatalyst for water splitting and prospective use for efficient H2 production from photocatalytically under visible light irradiation [4–7]. The band gap of NiNb2O6 was estimated to be 2.2 eV. NiNb2O6 was also reported [8] as a useful precursor material for the preparation of Pb(Ni,Nb)O3 perovskites by the columbite method to avoid pyrochlore formation. Traditional solid state method for the preparation of NN leads to poor compositional homogeneity and high sintering temperatures. The properties of ceramics are greatly affected by the characteristics of the powder, such as particle size, morphology, purity and chemical compositions. Using chemical methods, e.g. coprecipitation, sol–gel, hydrothermal and colloid emulsion technique has been confirmed to
⁎ Corresponding author. Tel.: +91 20 25902295; fax: +91 20 25893044. E-mail address: [email protected] (V. Ravi). 0167-577X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2006.09.010
efficiently control the morphology and chemical composition of the prepared powder. Here we communicate a simple coprecipitation procedure to prepare NiNb2O6 powders from water soluble salts. The limitation of coprecipitation process is that cations should have similar solubility. This method of preparation of NN is not reported in the literature. 2. Experimental For preparing NiNb2O6, niobium(V) oxide, nickel nitrate and ammonium carbonate and ammonium hydroxide were used as the starting materials (Loba Cheme, AR grade). Required quantity of Nb2O5 was dissolved in HF acid (40%) after heating in a hot water bath for 4 h. To this NbF5 solution, the stoichiometric amount of Ni(NO)3·9H2O was added and mixed thoroughly. An aqueous mixture of ammonium carbonate and ammonium hydroxide was added dropwise to precipitate niobium and nickel as hydroxide and carbonate, respectively. The pH was maintained at around 9 to ensure completion of the reaction. Then, the precipitated precursor powder was filtered and oven dried, then calcined at different temperatures from 400 to 800 °C for 6 h. XRD (Philips PW 1710 Diffractometer) and TEM were used to characterize the powders. For lattice parameter and interplanar distance (d) calculation, the samples were scanned in the 2θ range of 10–80° for a period of 5 s in the
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Fig. 3. TEM picture of NiNb2O6 powders (prepared by coprecipitation) calcined at 700 °C for 6 h. Fig. 1. XRD of NN precipitate powders calcined at (a) 300 °C, (b) 500 °C, (c) 700° for 6 h (‘1’ indicates NiCO3, ‘2’ indicates Ni2O3 and ‘3’ indicates Nb2O5 peaks).
step scan mode. Silicon was used as an internal standard. Least squares method was employed to determine the lattice parameters. The TEM picture was recorded with JEOL model 1200 EX instrument at the accelerating voltage of 100 kV. The fine powders were dispersed in amyl acetate on a carbon coated TEM copper grid. For comparison, NiNb2O6 samples were also prepared by the ceramic method. The corresponding oxides or carbonates are taken in stoichiometric ratio and mixed, ground several times and heated at 800 °C for 24 h. 3. Results and discussion Fig. 1 shows the XRD pattern of the NiNb2O6 precursor powder calcined at different temperatures. At 300 °C, The XRD indicates the presence of NiCO3 (JCPDS 12-771) and probably niobium oxide may be in amorphous state. When heated at 500 °C, NiCO3 decomposes into
Ni2O3 (JCPDS 14-481). At 700 °C, phase pure NiNb2O6 was only found. This is the lowest temperature reported for the formation NN in the literature. The crystal structure of NiNb2O6 is orthorhombic and all the d-lines match with reported values (JCPDS: 31-906). The calculated lattice parameters by least squares fit are a = 14.023 Å, b = 5.67 Å and c = 5.02 Å. Conventional solid state method also forms the NiNb2O6 phase after prolonged heating (24 h) at 800 °C (Fig. 2). Few extra lines in XRD at lower temperature calcination may arise from unknown impurities present or intermediate phase formed. The particle size and morphology of the calcined powders were examined by transmission electron microscopy. The particle morphology of the calcined powder (700 °C for 6 h) prepared by coprecipitation technique was irregular polygon in shape and agglomerated, with an average primary particle size around 80 nm (Fig. 3). The average crystallite size calculated from Scherrer's formula (t = Kλ / BcosθB) where t is the average size of the particles, assuming particles are spherical, K = 0.9, λ is the wavelength of X-ray radiation, B is the full width at half maximum of the diffracted peak and θB is the angle of diffraction is 75 nm.
4. Conclusions A simple coprecipitation process was used for the preparation of ultrafine powders of NiNb2O6. For comparison, NN samples are also prepared by traditional solid state method. The observed results show that the formation of NN phase by coprecipitation occurs at comparatively lower temperature than that by ceramic method. References
Fig. 2. XRD of NN powders (solid state route) calcined at (a) 400 °C and (b) 800 °C, 6 h (the symbol ‘⁎’ indicates Nb2O5 and ‘+’ indicates NiCO3 peaks).
[1] S.P. Gaikwad, V. Samuel, R. Pasricha, V. Ravi, Mater. Lett. 58 (2004) 3699. [2] N. Natarajan, V. Samuel, R. Pasricha, V. Ravi, Mater. Sci. Eng., B, SolidState Mater. Adv. Technol. 117 (2005) 169. [3] V. Ravi, Mater. Charact. 55 (2005) 92. [4] R. Pasricha, V. Ravi, Mater. Chem. Phys. 94 (2005) 34. [5] J. Ye, Z. Zou, A. Matsushita, Int. J. Hydrogen energy 28 (6) (2003) 651. [6] L. Guochang, L.P. Bicelli, G. Razzini, R.R. Borremei, Mater. Chem. Phys. 23 (1989) 477. [7] L. Guochang, L.P. Bicelli, G. Razzini, L. Guffre, Sol. Energy Mater. 21 (1991) 335. [8] C.H. Lu, W.J. Hwang, Ceram. Int. 22 (1996) 373.
A coprecipitation technique to prepare NiNb2O6 V. Samuel c , A.B. Gaikwad b , A.D. Jadhav a , N. Natarajan a , V. Ravi a,⁎ a
Physical and Materials Chemistry Division, National Chemical Laboratory, Pune 411008, India b Center for Materials Characterization, National Chemical Laboratory, Pune 411008, India c Catalysis division, National Chemical Laboratory, Pune 411008, India Received 10 April 2006; accepted 6 September 2006 Available online 25 September 2006
Abstract A mixture of ammonium carbonate and ammonium hydroxide was used to coprecipitate nickel and niobium ions as nickel carbonate and niobium hydroxide under basic conditions. This precursor yielded NiNb2O6 (NN) ceramics on calcining at 700 °C (at a temperature lower than 800 °C which is necessary for the formation of NiNb2O6 when prepared by the traditional solid state method). The average particle size and morphology of these powders were investigated by transmission electron microscope (TEM). © 2006 Elsevier B.V. All rights reserved. Keywords: Oxides; Chemical synthesis; X-ray methods; Electronic materials; Electron microscopy
1. Introduction ANb2O6 (A = Ba, Sr, Ca) compounds with columbite (orthorhombic) or trirutile (tetragonal) -type structure find wide applications in electro-optic, pyroelectric and photo-refractive applications [1–3]. On the contrary, there are not much investigations on transition metal niobates, e.g, NiNb2O6 and CoNb2O6. The NiNb2O6 ceramics has a potential application as photocatalyst for water splitting and prospective use for efficient H2 production from photocatalytically under visible light irradiation [4–7]. The band gap of NiNb2O6 was estimated to be 2.2 eV. NiNb2O6 was also reported [8] as a useful precursor material for the preparation of Pb(Ni,Nb)O3 perovskites by the columbite method to avoid pyrochlore formation. Traditional solid state method for the preparation of NN leads to poor compositional homogeneity and high sintering temperatures. The properties of ceramics are greatly affected by the characteristics of the powder, such as particle size, morphology, purity and chemical compositions. Using chemical methods, e.g. coprecipitation, sol–gel, hydrothermal and colloid emulsion technique has been confirmed to
⁎ Corresponding author. Tel.: +91 20 25902295; fax: +91 20 25893044. E-mail address: [email protected] (V. Ravi). 0167-577X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2006.09.010
efficiently control the morphology and chemical composition of the prepared powder. Here we communicate a simple coprecipitation procedure to prepare NiNb2O6 powders from water soluble salts. The limitation of coprecipitation process is that cations should have similar solubility. This method of preparation of NN is not reported in the literature. 2. Experimental For preparing NiNb2O6, niobium(V) oxide, nickel nitrate and ammonium carbonate and ammonium hydroxide were used as the starting materials (Loba Cheme, AR grade). Required quantity of Nb2O5 was dissolved in HF acid (40%) after heating in a hot water bath for 4 h. To this NbF5 solution, the stoichiometric amount of Ni(NO)3·9H2O was added and mixed thoroughly. An aqueous mixture of ammonium carbonate and ammonium hydroxide was added dropwise to precipitate niobium and nickel as hydroxide and carbonate, respectively. The pH was maintained at around 9 to ensure completion of the reaction. Then, the precipitated precursor powder was filtered and oven dried, then calcined at different temperatures from 400 to 800 °C for 6 h. XRD (Philips PW 1710 Diffractometer) and TEM were used to characterize the powders. For lattice parameter and interplanar distance (d) calculation, the samples were scanned in the 2θ range of 10–80° for a period of 5 s in the
V. Samuel et al. / Materials Letters 61 (2007) 2354–2355
2355
Fig. 3. TEM picture of NiNb2O6 powders (prepared by coprecipitation) calcined at 700 °C for 6 h. Fig. 1. XRD of NN precipitate powders calcined at (a) 300 °C, (b) 500 °C, (c) 700° for 6 h (‘1’ indicates NiCO3, ‘2’ indicates Ni2O3 and ‘3’ indicates Nb2O5 peaks).
step scan mode. Silicon was used as an internal standard. Least squares method was employed to determine the lattice parameters. The TEM picture was recorded with JEOL model 1200 EX instrument at the accelerating voltage of 100 kV. The fine powders were dispersed in amyl acetate on a carbon coated TEM copper grid. For comparison, NiNb2O6 samples were also prepared by the ceramic method. The corresponding oxides or carbonates are taken in stoichiometric ratio and mixed, ground several times and heated at 800 °C for 24 h. 3. Results and discussion Fig. 1 shows the XRD pattern of the NiNb2O6 precursor powder calcined at different temperatures. At 300 °C, The XRD indicates the presence of NiCO3 (JCPDS 12-771) and probably niobium oxide may be in amorphous state. When heated at 500 °C, NiCO3 decomposes into
Ni2O3 (JCPDS 14-481). At 700 °C, phase pure NiNb2O6 was only found. This is the lowest temperature reported for the formation NN in the literature. The crystal structure of NiNb2O6 is orthorhombic and all the d-lines match with reported values (JCPDS: 31-906). The calculated lattice parameters by least squares fit are a = 14.023 Å, b = 5.67 Å and c = 5.02 Å. Conventional solid state method also forms the NiNb2O6 phase after prolonged heating (24 h) at 800 °C (Fig. 2). Few extra lines in XRD at lower temperature calcination may arise from unknown impurities present or intermediate phase formed. The particle size and morphology of the calcined powders were examined by transmission electron microscopy. The particle morphology of the calcined powder (700 °C for 6 h) prepared by coprecipitation technique was irregular polygon in shape and agglomerated, with an average primary particle size around 80 nm (Fig. 3). The average crystallite size calculated from Scherrer's formula (t = Kλ / BcosθB) where t is the average size of the particles, assuming particles are spherical, K = 0.9, λ is the wavelength of X-ray radiation, B is the full width at half maximum of the diffracted peak and θB is the angle of diffraction is 75 nm.
4. Conclusions A simple coprecipitation process was used for the preparation of ultrafine powders of NiNb2O6. For comparison, NN samples are also prepared by traditional solid state method. The observed results show that the formation of NN phase by coprecipitation occurs at comparatively lower temperature than that by ceramic method. References
Fig. 2. XRD of NN powders (solid state route) calcined at (a) 400 °C and (b) 800 °C, 6 h (the symbol ‘⁎’ indicates Nb2O5 and ‘+’ indicates NiCO3 peaks).
[1] S.P. Gaikwad, V. Samuel, R. Pasricha, V. Ravi, Mater. Lett. 58 (2004) 3699. [2] N. Natarajan, V. Samuel, R. Pasricha, V. Ravi, Mater. Sci. Eng., B, SolidState Mater. Adv. Technol. 117 (2005) 169. [3] V. Ravi, Mater. Charact. 55 (2005) 92. [4] R. Pasricha, V. Ravi, Mater. Chem. Phys. 94 (2005) 34. [5] J. Ye, Z. Zou, A. Matsushita, Int. J. Hydrogen energy 28 (6) (2003) 651. [6] L. Guochang, L.P. Bicelli, G. Razzini, R.R. Borremei, Mater. Chem. Phys. 23 (1989) 477. [7] L. Guochang, L.P. Bicelli, G. Razzini, L. Guffre, Sol. Energy Mater. 21 (1991) 335. [8] C.H. Lu, W.J. Hwang, Ceram. Int. 22 (1996) 373.