Title of Invention

A METHOD FOR THE PRODUCTION OF MANAGANITE SPINELS AND PEROVKSITES

Abstract Abstract: A method for the production of manganese spinals of general formula AxMn3-x04 (A is transition metal ions, Co, Ni, Cu, etc.) and parasites of general formula A1.xBxMn03 (A is a rare earth element La, Pr etc. and B is alkaline earth metals Ca, Sr and Ba) wherein the starting material of general formula are: a. Spinals - Co (N03)2.6H20, MnS04.H20, KMn04 b. Parasites - La203, SrCI2.6H20, CaC03, BaCI2.2H20, KMn04, MnS04.H20 Wherein the above inorganic salts are purified by dissolving them in deionizer water and the corresponding acid is added till the salt is precipitated by common ion effect leaving all the impurities in the strongly acidic solution.
Full Text

This invention relates to a field of Metallurgy. Further the invention relates to the production of magnetic compounds this invention relates to a wet-chemical redox reaction method of production of manganite compound of general formulae AxMn3-x04 where A = Co, Cu, Ni etc and AX B-|.X Mn03 (A is a rare-earth element e.g. La, Ce, Pr, Nd and B is a divalent cation e.g. Ca, Sr, Ba).
AxMn3_xO4 has the spinel structure, whereas A-|.xBxMn03 is of perovskite structure. The prepared compounds are (i) spinels - CoxMn3.x04 (x = 0.6, 0.8, 1.2, 2) (ii) perovskites - (La, Ca)Mn03, (La, Sr)Mn03 and (La, Ba)Mn03. Cobalt manganite spinels find applications as NTC thermistors and semiconductor magnetic sensors. There is considerable interest in the perovskite manganite compounds because of its colossal magnetoresistance (CMR) property. These CMR compounds find applications as magnetic sensors, in memory applications and prototype disc drives employing CMR read-head technology.
Manganite spinels and perovskites exhibit interesting and technologically important electrical and magnetic properties. The exciting electronic and magnetic properties originate due to the valence fluctuations of Mn ions. Here we introduce a novel way of preparing manganite spinels and perovskites wherein the Mn ions in different oxidation states can be achieved.
The objective of this invention is to develop a low temperature wet-chemical process to prepare manganite spinels and perovskites involving redox reactions and therefore the area of technology is that of materials processing. In this invention, manganite spinels and perovskites are prepared by a co-precipitation technique involving the redox reaction between Mn(VII) and Mn(ll) salts in nitric acid medium, yielding Mn(IV) oxide or its derivatives substituted with other transition metal ions or rare-earth ions or alkaline earth metals.
The aqueous solutions of transition metals (Co, Ni, Cu etc) or rare-earth metals ( La, Ce, Pr, Nd ) and alkaline earth metals are mixed with manganese (II) sulphate and KMnCU in the desired ratio and the pH is maintained around 1 to 2 by adding concentrated nitric acid. This results in the precipitation of hydrated Mn(IV) oxide. Due to larger porosity and high surface area, hydrated Mn02 adsorbs larger quantities of other metal ions. Raising the pH to 7 by adding ammonium carbonate or sodium carbonate results in the complete co-precipitation of transition metals or rare-earth metals and alkaline earth metals. Precipitate is filtered, washed with deionised water and dried at 100° C. The washed precipitate is calcined at elevated temperature around 850° C for 6 to 8 h, yielding phase pure spinels or perovskites.
Manganites are normally prepared through ceramic route, which involves solid - solid reactions at high temperatures. Some wet-chemical methods are also

employed to prepare manganites, but none of these methods give defined stoichiometry with large oxygen content or high concentration of Mn^ions.
The aforesaid route has the following disadvantage. Through ceramic route, quality samples are obtained only after repeated grinding and firing at elevated temperatures. Samples prepared at high temperatures consume a lot of time and have low concentration of Mn^ions, which reduces the conductivity of the sample.
It is the primary object of the invention to invent a novel manganite compound.
It is another object of the invention to develop a low temperature wet-chemical process to prepare manganite spinels and perovskites involving redox reaction and thereof me area of technology is that of materials processing.
It is another object of the invention to invent and develop manganite compounds which find application as magnetic sensors, in memory application and prototype disc drives employing CMR read-head technology.
A further object of the invention will be clear from the following description.
This invention thus provides a method for the production of manganite spinels of general formula AxMn3.x04 (A= transition metal ions, Co, Ni, Cu etc) and perovskites of the general formula Ai.xBxMnO3(A=rare earths elements, La, Ce, Pr etc and B = alkaline earths metals, Ca, Sr or Ba) which incorporates high oxidation states of manganese, particularly Mn(IV) by a redox reaction involving Mn(II) and Mn(VII) salts in presence of nitric acid or nitrate ions as the source of active(nascent)oxygen.

Wherein the above inorganic salts are purified by dissolving them in deionised water and the corresponding acid is added till the salt is precipitated by common ion effect leaving all the impurities in the strongly acidic solution.
This description is with reference to the drawings accompanying this specification.
Fig.l X-ray diffraction pattern of CoxMn3-x04 calcined at 850 °C for x= 0.8 and 2.
Fig.2 X-ray diffraction pattern of Lao.75Cao.25MnO3 and Lao.667Cao.333MnO3 sintered at 1400°C.
Fig.3 X-ray diffraction patterns of Lao.gsSro.isMnOs sintered at 1250 and 1400°C.
Fig.4 X-ray diffraction pattern of Lao.7sBao75Mn03 sintered at 1250°C.


Manganite compounds, both spinels and perovskites can be prepared through a wet chemical method, which involves a redox reaction between Mn(VII), and Mn(ll) salts. The present method preserves the higher oxidation states of Mn ions and a large concentration of Mn4+ ions. This increases the conductivity of the manganites and exhibit very sharp metal-insulator (M-l) transitions. Sharp M-l transitions leads to large magnetoresistance value even at lower magnetic field strength (75% at 0.5 T) which can be used for magnetic sensor applications. In case of spinels large concentration of Mn4+ ions increases the mobility of holes and increases the B (Resistivity p = p0e(B/T)) value, which can be used for thermistor applications. A few compounds prepared through the above method are mentioned below.
Example 1:
Manganese Oxide: Mn02.xH20 (10 600 ml of 0.5 M MnS04.H20 solution is mixed with 1000 ml of deionised water and the pH is maintained between 1 to 2 by adding appropriate volume (~ 10 ml) of concentrated HN03. 800 ml of 0.25 M KMn04 is added to the above solution to precipitate hydrated Mn02. The precipitate of hydrated Mn02 is black in colour and this porous black precipitate of MnC>2 hydrate is formed only in acidic medium. The precipitate is filtered, washed with deionised water and dried at 100° C for 12 h.


Acid medium helps to preserve the specific intermediate oxidation number, in this case Mn4+.
Black precipitate of Mn02 is obtained only in acidic medium (pH between 1 to 2). The precipitate obtained in the basic medium is brown in colour and it is hydroxides of Mn(lll)/Mn(ll) plus other metals. Therefore in this method acidic medium containing nitric acid or nitrate ions is essential to get the black precipitate.
The expected quantity of MnO2 powder from the above preparation is about 223.5 g. We have obtained 223.1 g of Mn02 experimentally. This indicates that through this new method, complete precipitation is taking place, yielding the expected result.
Formation of higher Oxidation states of Mn ions
When spinel and perovskites phases are prepared through this method, larger proportion of Mn ions in the Mn4+ state is formed leading to high electrical conductivity and the desired magnetic properties. This is verified using iodometric titrations. The iodometric titration results are used for deriving the formulae of spinels and perovskites.

600 ml of 0.5 M Co(N03)2.6H20 solution is taken with 1440 ml of 0.5 M MnS04.H20 solution. 12 ml of concentrated HN03 ( pH is maintained between 1 to 2) is added to the above solution and heated to 60 - 70° C. 1920 ml of 0.25 M KMnCU solution is added to precipitate MnO2.. The Mn02 precipitate is allowed to settle down and the pH is raised to 7 by adding 6000 ml of 2 M ammonium carbonate or 6000 ml of 2 M sodium carbonate to complete the precipitation of cobalt ions. The precipitates are filtered, washed with deionised water and dried at 100° C followed by calcination at 850° C for 6 to 8 hours.
The X-ray diffraction patterns of the calcined powder at 850° C are shown in Fig. 1. Samples with x= 0.6 and 0.8 show tetragonally distorted spinel structure. For x > 2, it crystallizes in the cubic spinel structure.



300 ml of 0.5 M Co(N03)2.6H20 is mixed with 150 ml of 1 M NiS04 solution and 1440 ml of 0.5 M MnS04.H20. The pH is maintained between 1 to 2 by adding appropriate volume of concentrated nitric acid and heated to 60 - 70° C. 1920 ml of 0.25 M KMn04 is added to the mixed aqueous solutions to precipitate hydrated Mn02. The pH is increased to 7 by adding 6000 ml of 2M ammonium carbonate. The precipitates are filtered, washed with deionised water and dried at 100° C. The dried powder is heated at 850° C to obtain spinel phases.
Example 4: Cuo.3Coo.4Mn2.3O4
400 ml of 0.5 M Co(N03)2.6H20 is mixed with 150 ml of 1 M CuCI2.2H20 solution and 1380 ml of 0.5 M MnS04.H20. 10 ml of concentrated HN03 is added to maintain the pH between 1 to 2 and heated to 60 - 70° C. 1840 ml of 0.25 M KMn04 is added to the mixed aqueous solutions to precipitate hydrated Mn02. The Mn02 precipitate is allowed to settle down and the pH is increased to 7 by adding 6000 ml of 2M ammonium carbonate. The precipitates are filtered, washed with deionised water and dried at 100° C. The dried powder is heated at 850° C to obtain spinel phases. The Ni and Cu substituted samples exhibit low resistivity in comparison to cobalt manganite spinel phases.
Example 5: Perovskites
La0.75Cao.25Mn03
80 g of La203 is dissolved in 120 ml of concentrated HNO3 and it is mixed with 17 g of CaC03 dissolved in 80 ml of concentrated HN03. The above solution is mixed with 1000 ml of deionised water. 800 ml of MnS04.5H20 is added to the aqueous solutions of La and Ca and the pH is maintained around 1 to 2 by adding appropriate volume of concentrated HN03. The mixed aqueous

solution is heated to 60 - 70° C and 1070 ml of 0.25 M KMn04 is added to precipitate Mn(IV) oxide. The pH is raised to 7 by adding 6000 to 6500 ml of 2 M ammonium carbonate or 7000 ml of sodium carbonate to precipitate La and Ca ions. The precipitate is filtered and washed with deionised water and dried at 100° C. The dried powder is then heated at 850° C for 6 to 8 hours to obtain phase pure perovskites.
Fig.2 shows the X-ray patterns of Lai.xCaxMn03 (x=0.25 & 0.333) at 1400° C. They exhibit a cubic perovskite structure (a=3.881 A)

70 g of La203 is dissolved in 100 ml of concentrated HNO3. The resulting solution is mixed with 20 g of SrCI2.6H20 dissolved in 500 ml of deionised water. 600 ml of MnS04.H20 is added to the above solution and the pH is maintained around 1 to 2 by adding 10 ml of concentrated HN03. The mixed aqueous solution is heated to 60 - 70° C and 800 ml of 0.25 M KMn04 is added to precipitate hydrated Mn02. The pH is then increased to 7 by adding 6000 ml of 2 M ammonium carbonate to complete the precipitation of La and Sr ions. The precipitates are filtered and washed with deionised water and dried at 100° C. The dried powder is heated at elevated temperature, 850° C for 6 to 8 hours.
Fig.3 shows the x-ray pattern of La0.85Sro.i5Mn03. It exhibits a rhombohedral phase when sintered at 1250 and 1400° C.


60 g of La2O3 is dissolved in 100 ml of concentrated HN03 and it is mixed with 30 g of purified BaCl2.2H20 dissolved in 500 ml of deionised water. 600 ml of MnS04.H20 is added to the above solution and the pH is maintained around 1 to 2 by adding 15 ml of concentrated HN03. The mixed aqueous solution is heated to 60 - 70° C and 800 ml of 0.25 M KMn04 is added to precipitate hydrated Mn02. The pH is then increased to 7 by adding 6000 ml of 2 M ammonium carbonate to complete the precipitation of La and Ba ions. The precipitates are filtered and washed with deionised water and dried at 100° C. The dried powder is heated at elevated temperature, 850° C for 6 to 8 hours.
Fig.4 shows the x-ray pattern of Lao.75Bao.25Mn03 at different temperature of sintering. It exhibits an orthorhombic phase when sintered at 1200° C. This method gives spinel phases useful for NTC thermistors with high B values and large a > 8.5 % IK. It also increases the stability of thermistors due to high oxygen content.
In the case of spinels, the increased amount of Mn4+ enhances the conductivity and low temperature magnetization. Near the magnetic transition the cobalt manganite spinels exhibit the shift from NTC to PTC behaviour and large magnetoresistance. Magnetoresistance coefficient maximizes around 0.8 at 1 Tesla. In perovskites also a high oxygen content is preserved and maximizes the MR value. Lao.667Ca0.333Mn03 exhibit MR value of 75% at 0.5 T.
Salient features of the invention is as follows:
1) A method for the production of manganite spinels of general formula
AxMn3.x04 ( A is transition metal ions, Co, Ni, Cu etc) and perovskites of
general formula Ai.xBxMn03 ( A is a rare earth element La, Pr etc and B is
alkaline earth metals Ca, Srand Ba).
2) A method as claimed in claim 1 wherein the starting material of general
formula
(a) Spinels - Co(N03)2.6H20, MnS04.H20, KMn04

(b) Perovskites - La203, SrCI2.6H20, CaC03, BaCI2.2H20 , KMn04, MnS04.H20.
3) A method as claimed in claim 2 wherein the above inorganic salts are purified by dissolving them in deionised water and the corresponding acid is added till the salt is precipitated by common ion effect leaving all the impurities in the strongly acidic solution.
4) A method as claimed in claim 1 wherein the calcination is carried out at 850°C.
5) Another salient feature of invention the solutions are

(a) Spinels - CoxMn3-x04
(b) Perovskites- (La,Ca)Mn03, (La,Sr)Mn03 and (La,Ba)Mn03
6) A method for the production of manganite spinels of general formula
AxMn3.x04 where A is a transition metal ion and manganite perovskites of
general formula Ai-xBxMn03 where A is a rare earth element and B is a
divalent ion, substantially described here with reference to examples.
It is to be noted that the aforesaid description is intended to explain the salient features of the invention and it is not intended to limit the scope of the invention.
It is to be further noted that within the scope of the invention various modifications are permissible. The scope of the invention is defined in the above descriptions.


Claim:
1. A method for the production of manganite spinels of general formula AxMn3.x04
(A= transition metal ions, Co, Ni, Cu etc) and perovskites of the general formula
A1.xBxMn03 (A=rare earths elements, La, Ce, Pr etc and B=alkaline earths metals,
Ca, Sr or Ba) which incorporates high oxidation states of manganese, particularly
Mn(IV) by a redox reaction involving Mn(II) and Mn(VII) salts in presence of
nitric acid or nitrate ions as the source of active(nascent)oxygen and purifying the
reaction mixture followed by calcination.
2. The method as claimed in Claim 1, wherein the starting materials are of the
general formula
(a) Spinels -Co(N03)6H20, MnS04 H20, KMn04
(b) Perovskites- La2, SrCl26H20, KMn04, MnS04, H20.
3. The method as claimed in Claim 1, wherein the said inorganic salts are purified
by dissolving in deionised water and precipitated by common ion effect by adding
the corresponding acid so that the impurities are left behind in the acidic solution.
4. The method as claimed in Claim 3, wherein the precipitated inorganic salts is
calcined to remove nitric acid or nitrate or alkali ion impurities.
5. The method as claimed in Claim 4, wherein the calcination is carried out around
the 850°C for 6 to 8 hour.
6. The method as claimed in any one of Claims 1 to 5, wherein the compounds
obtained are:
(a) Spinels -CoxMn3-x04 (X= 0.6,0.8,1.2, 2)
(b) Perovksites - (La, Ca) Mn03, (La, Sr)Mn03, and (La, Ba)Mn03,
7. A method for the production of manganite spinels and perovksites involving the
redox reaction substantially as herein described and illustrated by the examples.


Documents:

170-mas-1999 abstract duplicate.pdf

170-mas-1999 abstract.pdf

170-mas-1999 claims duplicate.pdf

170-mas-1999 claims.pdf

170-mas-1999 correspondence others.pdf

170-mas-1999 correspondence po.pdf

170-mas-1999 description (complete) duplicate.pdf

170-mas-1999 description (complete).pdf

170-mas-1999 description (provisional).pdf

170-mas-1999 drawings duplicate.pdf

170-mas-1999 drawings.pdf

170-mas-1999 form-1.pdf

170-mas-1999 form-13.pdf

170-mas-1999 form-19.pdf

170-mas-1999 form-26.pdf

170-mas-1999 form-5.pdf


Patent Number 196442
Indian Patent Application Number 170/MAS/1999
PG Journal Number 30/2009
Publication Date 24-Jul-2009
Grant Date
Date of Filing 11-Feb-1999
Name of Patentee THE REGISTRAR, INDIAN INSTITUTE OF SCIENCE,
Applicant Address BANGALORE - 560 012.
Inventors:
# Inventor's Name Inventor's Address
1 MR, THUNDYIL RAMAN NARAYANAN KUTTY, MATERIALS RESEARCH CENTRE, INDIAN INSTITUTE OF SCIENCE, BANGALORE - 560 012.
2 MR. JOHN PHILIP MATERIALS RESEARCH CENTRE, INDIAN INSTITUTE OF SCIENCE, BANGALORE - 560 012.
PCT International Classification Number H017/06
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA