Title of Invention

A PROCESS FOR MANUFACTURING MAGNETOELECTRIC BISMUTH FERRITE

Abstract In the present invention a process for manufacturing phase pure nano-sized magneto-electric bismuth ferrite, which involves synthesis of magneto-electric bismuth ferrite by soft chemical technique is described. The process of the invention is based on the formation of hetero-metallic poly-nuclear complexes where reacting metal atoms come in close proximity to provide nanosized bismuth ferrite at a low temperature. In this invention bismuth ferrite synthesis through solutions of some specific salts leads to the formation of an amorphous structure at around 200 °C which shows well-formed phase-pure (perovskite) nano-sized (15-25 nm) bismuth ferrite at a temperature in the range of 350° to 450°C. In the prior art, solid state route requires calcination temperature of 700 to 800°C and co-precipitation needs 550 to 750°C to get phase pure bismuth ferrite. The process of the present invention for manufacturing magneto-electric bismuth ferrite, involving synthesis is a novel cost effective process and such nano-sized bismuth ferrite powder may have a potential application as a lead free piezoelectric material for actuators, magneto-electric sensors and spintronics.
Full Text This invention relates to a process for manufacturing magneto-electric bismuth ferrite. This invention particularly relates to a process for manufacturing nano-sized magneto-electric bismuth ferrite. This invention more particularly relates to a process for manufacturing nano-sized magneto-electric bismuth ferrite by soft chemical technique. This invention still more particularly relates to a process for manufacturing nano-sized magneto-electric bismuth ferrite by soft chemical technique at a low temperature.
The nano-sized magneto-electric bismuth ferrite will find diverse industrial applications such as for information storage, spintronics and sensors and actuators.
BiFeO3 with perovskite structure is one of the very few magneto-electronics (ferroelectro-magnet / seignetomagnet) systems where there is a coexistence of interrelated electric and magnetic dipole structures within a certain temperature range. BiFeO3 is ferroelectric (Tc~1103K) and anti-ferromagnetic (Tn~643K). Though BiFeO3 was discovered in 1960, its applications were hampered due to current leakage problems arising out of non-stoichiometry. Recently, there is a renewed interest in BiFeO3 because of its possible novel applications.
The following references may be pertinent in this context:
i) Russian patent no.; RU2189954,titled: radio-absorbing material, pertaining to electronic engineering technology. The invention relates to a radio-absorbing material comprising 0.10-0.70 mole parts of bismuth ferrite and 0.90-0.30 mole parts of lanthanum manganite. The invention can be used for making material exhibiting high dielectric loss in the microwave range of the radio-absorbing material, providing enhanced absorption of microwave radiation.
ii) J.D. Bucci, B.K Robertson & W.J. James, J. Appl. Cryst. 5, 187 (1972).
iii) F. Kubel & H. Schmid, Acta Cryst. 46, 698 (1990).
iv) V.R. Palkar and R. Pinto, Pramana, Journal of Physics, 58 (5,6) 1003(2002).
v) Y.P. Wang, L Zohu, M.F Zhang, X.Y. Chen, J.M. Liu & Z.G. Liu, Appl. Phys. Lett. 84(10)1731(2004).
In the hitherto known prior art so far, primarily two techniques have been tried to synthesize phase pure BiFeO3, namely the solid state route and simultaneous precipitation / co-precipitation followed by calcinations.
In the solid state route, reference may be drawn to G.D. Achenbach, W. J. James and R. Gerson, J. Am. Ceram. Soc. 8, 437(1967) and V.R. Palkar and R. Pinto, Pramana, Journal of Physics, 58 (5,6) 1003 (2002), wherein Bi2O3 and Fe2O3 are reacted at a temperature in the range of 800° to 830°C and unreacted Bi2O3 / Bi2Fe4O9 phases are removed by washing in HNO3. The disadvantage of this process lies in the necessity of leaching the unwanted phase using an acid and effectively providing coarser powder and also the reproducibility of the process is quite poor.
The other technique is to take recourse to simultaneous precipitation / coprecipitation. Reference may be made to S. Shetty, V.R Palkar & R. Pinto, Pramana; Journal of Phys., 58(5,6), 1027 (2002), wherein solutions of bismuth and iron nitrates are treated with ammonium hydroxide to get hydroxide precipitate. The precipitate needs calcination at a temperature in the range of 550 to 750°C to get phase pure BiFeO3. They claimed to have got XRD particle size of around 23 nm by calcination at 550°C. The drawback of the process lies in getting the desired reproducibility because experiments performed to reproduce the results yielded powders of particle size (XRD) of around 50 mm when calcined at 550°C.
It is clear from the hitherto known prior art, as referred above, that there is a definite need to provide a process for manufacturing magneto-electric bismuth ferrite, which obviates the drawbacks of the hitherto known prior art.
The main object of the present invention is to provide a process for manufacturing magneto-electric bismuth ferrite, which obviates the above said drawbacks of the hitherto known prior art.
Another object of the present invention is to provide a process for manufacturing nano-sized bismuth ferrite.
Still another object of the present invention is to provide a process for manufacturing nano-sized bismuth ferrite by soft chemical technique.
Yet another object of the present invention is to provide a process for manufacturing nano-sized magneto-electric bismuth ferrite by soft chemical technique at a low temperature.
Still another object of the present invention is to provide a simple and cost effective process for manufacturing nano-sized bismuth ferrite by soft chemical technique at a low temperature.
A further object of the present invention is to provide a process for manufacturing both phase pure as well as nano-sized bismuth ferrite at a low temperature.
The prior art method of producing bismuth ferrite by solid state reaction of Bi2O3 and Fe2O3 results in the formation of multiphase samples. The other prior art method of co-precipitation followed by calcinations suffers from impurity phases and lack of reproducibility. In the present invention a process for manufacturing phase pure nano-sized magneto-electric bismuth ferrite, which involves synthesis of magneto-electric bismuth ferrite by soft chemical technique is described. The process of the invention is based on the formation of hetero-metallic poly-nuclear complexes where reacting metal atoms come in close proximity to provide nanosized bismuth ferrite at a low temperature. In this invention bismuth ferrite synthesis through solutions of some specific salts leads to the formation of an amorphous structure at around 200 °C which shows well-formed phase-pure (perovskite) nano-sized (15-25 nm) bismuth ferrite at a temperature in the range of 350° to 450°C. In the prior art, solid state route requires calcination temperature of 700 to 800°C and co-precipitation needs 550 to 750°C to get phase pure bismuth ferrite. The process of the present invention for manufacturing magneto-electric bismuth ferrite, involving synthesis is a novel cost effective process and such nano-sized bismuth ferrite powder may have a potential application as a lead free piezoelectric material for actuators, magneto-electric sensors and spintronics.
Accordingly, the present invention provides a process for manufacturing magneto-electric bismuth ferrite, which comprises; i) preparing nitrates of bismuth and iron by reacting 0.1 M solution of Bi(NO3)3.5 H2O and 0.1M solution of Fe(NO3)3 9H2O in 2N HNO3 or by reacting bismuth and iron metal with nitric acid to obtain acidic solution of respective salts, ii) mixing the said acidic solutions in equal proportion to obtain a mixed solution, iii) adding organic acid having either two carboxylate or at least two carboxylate and two hydroxyl groups within the same molecule in 1:1 molar ratio with the said mixed solution to obtain a complex solution, iv) evaporating the complex solution under constant stirring to dryness to obtain a fluffy mass, and v) followed by calcining the said fluffy mass at a temperature in the range of 350° to 400°C for a period in the range of 1 to 2 hours to obtain desired product.
In an embodiment of the present invention bismuth and iron nitrates are prepared by reacting suitable bismuth and iron salts or metallic bismuth and iron with nitric acid.
In another embodiment of the present invention, the acidic solution of respective salts is obtained by dissolving equimolar amounts of Bi(NO3)3.5 H2O and Fe(NO3)3 9H2O in 2N HNO3.
Fe(NO3)3.9H2O in 2N HNO3.
In still another embodiment of the present invention, the acidic solution of respective salts is obtained by preparing 0.1 M solution of Bi(NO3)3.5 H2O and 0.1M solution of Fe(NO3)3 9H2O in 2N HNO3.
In yet another embodiment of the present invention, the acidic solution of respective salts and organic acid are used in equal proportions.
In still yet another embodiment of the present invention, the organic acids used is such as having either two carboxylate or at least two carboxylate and two hydroxyl groups within the same molecule.
In a further embodiment of the present invention, the organic acids having either two carboxylate or at least two carboxylate and two hydroxyl groups within the same molecule are such as tartaric acid, oxalic acid and citric acid.
In a yet further embodiment of the present invention, 0.2 M organic acid is added in 1:1 molar ratio with the mixed solution to obtain a complex solution.
In a still further embodiment of the present invention, the evaporation of the complex solution under constant stirring to dryness to obtain a fluffy mass is effected by heating the complex solution at a temperature in the range of 95 to110°C till complete evaporation.
The principle behind the process of the present invention for manufacturing magneto-electric bismuth ferrite resides in the formation of hetero-metallic poly-nuclear complexes where reacting metal atoms come in close proximity. This occurs due to the presence of either two carboxylate or two carboxylate and two hydroxyl group with proper orientation to form a stable five or six membered poly-nuclear complex, which breaks on heating in presence of concentrated HNO3 leading to the formation of bismuth ferrite.
The novelty of the process of the present invention for manufacturing magneto-electric bismuth ferrite resides in obtaining phase pure nano-sized bismuth ferrite at low temperature. The novelty is realized by the non-obvious inventive step of forming an intermediate hetero-metallic poly-nuclear complex followed by soft solution. In this process, nano-sized phase pure bismuth ferrite (of size as low as 16 nm) are obtained at a temperature in the range of 350° to 450°C, whereas the prior art solid state route requires calcination at a temperature in the range of 700 to 800 °C and the prior art co-precipitation route requires calcination at a temperature in the range of 550 to 750 °C to get phase pure bismuth ferrite.
The non-obvious inventive steps of the present invention for manufacturing magneto-electric bismuth ferrite lie in:
a) Selecting the organic acids which can form hetero-metallic poly-nuclear complexes so as to provide nano-sized bismuth ferrite at a low temperature.
b) The process where the formation of hetero-metallic poly-nuclear complexes play a key role in the synthesis of nano-sized bismuth ferrite at a low temperature.
The process steps of the present invention for manufacturing magneto-electric bismuth ferrite, are as follows:
a) Preparing 0.1 M solution of Bi(NO3)3.5 H2O and 0.1M solution of Fe(NO3)3 9H2O in 2N HNO3 to obtain acidic solution of respective salts by dissolving bismuth and iron as nitrate (equimolar amounts of Bi(NO3)3 and Fe(NO3)3 in 2N HNO3 solution). The bismuth and iron nitrates may be prepared by reacting suitable bismuth and iron salts or metallic bismuth and iron with nitric acid.
b) Mixing acidic Bi(NO3)3.5 H2O solution with acidic Fe(NO3)3 9H2O solution in equal amounts to obtain a mixed solution.
c) Adding 0.2M organic acid, such as tartaric, oxalic or citric acid in 1:1 molar ratio with the mixed solution to obtain a complex solution.
d) Heating the complex solution at a temperature in the range of 95 to110 °C till complete evaporation to obtain a fluffy mass.
e) Calcining the fluffy mass at a temperature in the range of 350 to 450 °C for a period in the range of 1 to 2 hours.
The following examples are given by the way of illustration of the process of the present invention for manufacturing magneto-electric bismuth ferrite in actual practice and should not be construed to limit the scope of the present invention.
Example-1
4.85g (0.1M) Bi(NO3)3.5H2O and 4.04g (0.1 M) Fe(NO3)3.9H2O were dissolved separately in 100 mL of 2N HNO3 solution and then mixed together. 3.0018 g (0.2M) tartaric acid, dissolved in 100mL of water, was added to the above metal nitrate solution. The resultant mixture was heated to boiling with constant stirring until all the liquid evaporated out from the solution. The resultant light weight fluffy mass was calcined at 400 °C. XRD study confirmed the presence of phase pure bismuth ferrite of particle size around 15 to 25 nm.
Example-2
4.85g (0.1M) Bi(NO3)3.5H2O and 4.04g (0.1 M) Fe(NO3)3.9H2O were dissolved separately in 100mL of 2N HNO3 solution and then mixed together. 2.521 g (0.2M) oxalic acid, dissolved in 100mL of water, was added to the above metal nitrate solution. The resultant mixture was heated to boiling with constant stirring until all the liquid evaporated out
from the solution. The resultant light weight fluffy mass was calcined at 400 °C. XRD study confirmed the presence of phase pure bismuth ferrite of particle size around 15 to 25 nm.
Example-3
4.66g (0.1M) Bi2O3 is converted to BiONO3 by the action of concentrated nitric acid and the resultant solution was diluted to 100mL to make it 2N with respect to HNO3. 4.04 g (0.1M) Fe(NO3)3, dissolved separately in 100 mL of 2N HNO3, was added to the above solution. 3.0018 g (0.2M) tartaric acid dissolved in 100mL of water was added to the above metal nitrate solution. The resultant mixture was heated to boiling with constant stirring until all the liquid evaporated out from the solution. The resultant light weight fluffy mass was calcined at 400 °C. XRD study confirmed the presence of phase pure bismuth ferrite of particle size around 15 to25 nm.
Example-4
0.556 g of iron powder was converted to Fe(NO3)3 by the action of concentrated nitric acid and the resultant solution was diluted to 100mL to make it 2N with respect to HNO3. 4.85 g (0.1 M) Bi(NO3)3.5 H2O, dissolved separately in 100 mL of 2N HNO3, was added to the above solution. 2.521g (0.2 M) oxalic acid dissolved in 100mL of water was added to the above metal nitrate solution. The resultant mixture was heated to boiling with constant stirring until all the liquid evaporated out from the solution. The resultant light weight fluffy mass was calcined at 400 °C. XRD study confirmed the presence of phase pure bismuth ferrite of particle size around 15 to 25 nm.
Example-5
1.60g (0.1M) Fe2O3 was converted to FeCI3 by the action of hydrochloric acid. This FeCI3 was then converted to Fe(OH)3 by the action of
ammonium hydroxide. The precipitated Fe(OH)3 was then converted to Fe(NO3)3 by the action of nitric acid. It was then estimated for iron. 4.85 g (0.1M) Bi(NO3)3.5H2O dissolved separately in 100 mL of 2N HNO3 was added to the above solution. 2.521 g (0.2 M) oxalic acid, dissolved in 100mL of water, was added to the above metal nitrate solution. The resultant mixture was heated to boiling with constant stirring until all the liquid evaporated out from the solution. The resultant light weight fluffy mass was calcined at 400 °C. XRD study confirms the presence of phase pure bismuth ferrite of particle size around 15 to 25 nm.
Example-6
4.85g (0.1M) Bi(NO3)3.5H2O and 4.04g (0.1M) Fe(NO3)3.9H2O were dissolved separately in 100mL of 2N HNO3 solution and then mixed together. 4.2028g (0.2M) citric acid, dissolved in 100mL of water, was added to the above metal nitrate solution. The resultant mixture was heated to boiling with constant stirring until all the liquid evaporated out from the solution. The resultant light weight fluffy mass was calcined at 400 °C. XRD study confirmed the presence of phase pure bismuth ferrite of particle size around 15 to 25 nm.
The main advantages of the process of the present invention for manufacturing magneto-electric bismuth ferrite are as follows:
1) The process is simple and cost-effective.
2) Using this process phase pure as well as nanosized bismuth ferrite can be obtained at a temperature as low as 400 °C.
3) The yield is of the order of 92 %.









We claim :
1. A process for manufacturing magneto-electric bismuth ferrite, which comprises; i) preparing nitrates of bismuth and iron by reacting 0.1 M solution of Bi(NO3)3-5 H2O and 0.1M solution of Fe(NO3)3.9H2O in 2N HNO3 or by reacting bismuth and iron metal with nitric acid to obtain acidic solution of respective salts, ii) mixing the said acidic solutions in equal proportion to obtain a mixed solution, iii) adding organic acid having either two carboxylate or at least two carboxylate and two hydroxyl groups within the same molecule in 1:1 molar ratio with the said mixed solution to obtain a complex solution, iv) evaporating the complex solution under constant stirring to dryness to obtain a fluffy mass, and v) followed by calcining the said fluffy mass at a temperature in the range of 350° to 400°C for a period in the range of 1 to 2 hours to obtain desired product.
2. A process as claimed in claim 1, wherein the organic acids having either two carboxylate or at least two carboxylate and two hydroxyl groups within the same molecule are selected from tartaric acid, oxalic acid and citric acid.
3. A process as claimed in claim 1, wherein in step iii) 0.2 M organic acid is added to obtain a complex solution.
4. A process as claimed in claim 1, wherein in step iv), evaporation of the complex solution under constant stirring to dryness to obtain a fluffy mass is effected by heating the complex solution at a temperature in the range of 95 to110°C till complete evaporation.
5. A process for manufacturing magneto-electric bismuth ferrite, substantially as herein described with reference to the examples.

Documents:

2273-DEL-2004-Abstract-(03-03-2011).pdf

2273-del-2004-abstract.pdf

2273-del-2004-claims (03-03-2011).pdf

2273-del-2004-claims.pdf

2273-DEL-2004-Correspondence-Others-(03-03-2011).pdf

2273-DEL-2004-Correspondence-Others-(09-03-2011).pdf

2273-del-2004-correspondence-others.pdf

2273-del-2004-desacription (complete).pdf

2273-DEL-2004-Description (Complete)-(03-03-2011).pdf

2273-del-2004-form-1.pdf

2273-del-2004-form-18.pdf

2273-del-2004-form-2.pdf

2273-DEL-2004-Form-3-(03-03-2011).pdf

2273-del-2004-form-3.pdf

2273-del-2004-form-5.pdf


Patent Number 247636
Indian Patent Application Number 2273/DEL/2004
PG Journal Number 18/2011
Publication Date 06-May-2011
Grant Date 28-Apr-2011
Date of Filing 16-Nov-2004
Name of Patentee COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH
Applicant Address RAFI MARG, NEW DELHI-110 001,INDIA
Inventors:
# Inventor's Name Inventor's Address
1 SUSHMITA GHOSH CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, KOLKATA 700 032, INDIA
2 SUBRATA DASGUPTA CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, KOLKATA 700 032, INDIA
3 AMARNATH SEN CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, KOLKATA 700 032, INDIA
4 HIMADRI SEKHAR CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, KOLKATA 700 032, INDIA
PCT International Classification Number C04B 35/32
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA