Title of Invention	AN IMPROVED PROCESS FOR PREPARATION OF LEAD MAGNESIUM NIOBATE BASED HIGH PERMITTIVITY CERAMICS FOR MULTILAYER CAPACITORS
Abstract	The invention relates to an improved process (PMN) based high permithnity ceramics useful for the menufacture of multi layer capacitors. The ceromic has very high permittivity with dielectric constant (k) upto 25,000 based on PMN which find application in electronic industry. The improved process leads to pyrochlore free perovskites with how dissipation factor, high insulation resistance and high dielectric constants. The hiring temperature is also power than the reponted friring temperature in the prior art processes.

Title of Invention

AN IMPROVED PROCESS FOR PREPARATION OF LEAD MAGNESIUM NIOBATE BASED HIGH PERMITTIVITY CERAMICS FOR MULTILAYER CAPACITORS

Abstract

The invention relates to an improved process (PMN) based high permithnity ceramics useful for the menufacture of multi layer capacitors. The ceromic has very high permittivity with dielectric constant (k) upto 25,000 based on PMN which find application in electronic industry. The improved process leads to pyrochlore free perovskites with how dissipation factor, high insulation resistance and high dielectric constants. The hiring temperature is also power than the reponted friring temperature in the prior art processes.

Full Text	This invention relates to an improved process for preparation of lead magnesium niobate (PMN) based high permittivity ceramics useful for the manufacture of multi layer capacitors. The present invention relates to the preparation of very high permittivity ceramics with dielectric constant (k) upto 25,OOO based on PMN which find application in electronic industry for manufacturing multi layer ceramic capacitors. In conventional process, PMN based ceramics (ferroelectric relaxor materials) are prepared either by mixed oxide route wherein all the ingredient oxides are mixed together, calcined and sintered to get final product or by coulumbite precursor route wherein only magnesium oxide and niobium oxide are mixed and calcined initially to form magnesium niobate and then the remaining ingredients are supplemented. The latter route is often chosen to minimise formation of undesirable pyrochlore phase instead of perovskite phase. Presence of pyrochlore phase in the product leads to poor dielectric properties. However, both the above processes are not suitable for preparation of PMN based ceramics with pyrochlore free perovskite phase. As a result products prepared by these processes show inferior dielectric properties and cannot be used for very high permittivity applications. Further the product requires higher firing temperatures ( >1200°C) making it necessary to use expensive electrode materials such as palladium or palladium rich silver alloy. Other drawbacks of the conventional processes are that these lead to ceramics with high values of dissipation factor and temperature coefficient of capacitance. The main object of the present invention is to provide an improved process for the preparation of lead magnesium niobate based high permittivity ceramics useful for the manufacture of multi layer ceramic capacitors. The process leads to pyrochlore free perovskites with very high dielectric constants (15,000 to 25,000), low dissipation factor (0.01 to 0.03), high insulation resistance (1011 to 1212 ohm) and, low temperature coefficient of capacitance. The ceramics prepared by this process possess the above mentioned properties and are suitable for manufacturing ceramic capacitors with Electronics Industries Association CEIAD codes Z5V and Y5U. Another object of the invention is to reduce the firing temperature of the capacitor ceramics in the range 900 -1 10O°C by incorporating suitable process steps in the flowsheet so as to use either pure silver or silver rich palladium alloys instead of expensive palladium or palladium rich silver alloys which are being used for hither to known processes (Ref: American Ceramic Society Bulletin, Vol.6, No.4,P 704-711.(1987)). Accordingly the present invention provides an improved process for preparation of lead magnesium niobate based high permittivity ceramics useful for the manufacture of mul ti layer capacitors which comprises; i) calcining mixed magnesium oxide in the range of 2 to 10% by wt. and niobium pentoxide in the range of 10 to 30% by wt of final product at a temperature in the range of 850-1100°C for a period in the range of 10 to 30 hrs. to form magnesium niobate, ii) grinding the said magnesium niobate with three or more additives selected from lead oxide in the rage of 45 to 75% by wt; titanium dioxide in the range to 2 to 5% by wt; zirconium dioxide in the range of 1 to 4 % by wt., barium carbonate in the range of 0.5 to 3% by wt; strontium carbonate in the range of 1 to 7% by wt; and calcium carbonate in the range of 1 to 5% by wt., drying and calcining again at a temperature in the range of 750 to 900°C for a period of 2 to 8 hrs to form a precursor, iii) wet grinding the said precursor with three or more ingredient selected from zirconium dioxide in the range of 0.05 to 1.5% by wt; titanium dioxide in the range of 0.1-2% by wt; magnesium oxide in the range of 0.1 to 4% by wt; lead oxide in the range of 0.5-5% by wt; boric acid in the range of 0.2-4% by wt; calcium carbonate in the range of 0.5-2.5% by wt; manganese dioxide in the range of 0.2-2% by wt; lithium fluoride in the range of 0.3-b% by wt; in addition to polyvinyl alcohol in the range of 0.4 to 4% by wt to obtain milled slurry, iv) drying the said milled slurry to obtain lead magnesium niobate based high permittivity ceramics. According to a feature of the process of the present invention the weight percentage of ingredients in the basic composition is in the following ranges. MgO - 2-10% Nb2O5 - 10-30% PbO - 45-75% Ti02 - 2-5% ZrO2 - 1-4% BaCO3 ~ 0.5-3% SrCO3 - 1-7% CaCO - 1-5% 3 According to another feature of the present invention the additives over and above the basic composition are within the weight percentage 1 im its of the basic composition: and are in the range of: ZrO - 0.05-1 .5% •j TiO - 0.1-2% 2 MgO - 0.1-4% PbO - 0.5-5% H3 BO3 - 0.2-4% CaCO - 0.5-2.5% 3 MnO2 - 0.2-2% LiF - 0.3-6% Polyvinyl - 0.4-4 % alcohol The process of the present invention is described below i n detail. Magnesium oxide (2-10 wt%) and niobium oxide (10-30 wt%) are wet mixed in a pot mill. The said mixture is dried and calcined at 85O-1050°C for 10 to 30h to form magnesium niobate. The magnesium niobate thus formed is wet milled in a pot mill along with three or more ingredients chosen from lead oxide (45-75 wt%) , titanium dioxide (2-5 wt%) , zirconium oxide, barium carbonate (0.5-3 wt %) and strontium carbonate (1-7 wt%) and calcium carbonate (1-5 wr%). The said slurry is dried and recalcined at 750 to 90O°C for 2-8h to get a precursor. The precursor is again wet milled along with three or more ingredients chosen from zirconium oxide (0.05-1.5 wt%) , titanium dioxide (0.1-2 wt%) , magnesium oxide (0.1-4 wt%) , lead oxide (0.5-5 wfXo) , boric acid (0.2-4 wt%) , calcium carbonate ( O.5-2. 5 wt%) , manganese dioxide (O. 2-2 wt%), and lithium fluoride (0.3 -6 wt%) in addition to polyvinyl alcohol (0.4-4 wt%). The said milled slurry is dried to obtain PMN based high permittivity ceramics. The phase analysis of the final products and the intermediate products are carried out by XPD (A typical XRD pattern of the final product is given in Fig. 1) . The products thus obtained by the present process are evaluated by fabricating capacitors using them and studying their dielectric properties. The said capacitors are found to conform the specifications of Z5V type capacitors. The following examples are given to illustrate the process of the present invention and should not be construed to limit the scope of the invention. Example-1 Laboratory reagent grade magnesium oxide (4g) and niobium pentoxide (25g) are mixed, dried a.nd calcined in an alumina crucible at 1 100 deg. C for 20h to get magnesium niobate. The product thus formed is wet milled along with lead oxide, (70g) titanium dioxide (2.5g), barium carbonate (1g) and calcium carbonate (0.5g) in water medium using plastic pot and zirconia balls. The slurry is dried and again calcined at 800°C for a period of 3h. The material thus obtained constitutes the major ingredient for the final product. This is again wet nulled along with lead oxide (1.5g), boric acid (0.5g), magnesium oxide (0.5g) and polyvinyl alcohol ( 1g) and dried in an oven at 90°C to obtain a typical PMN-based high permittivity ceramics for manufacturing multi layer ceramic capacitors. A typical XRD pattern of the final product is given in Fig. 1 . Example -2 Magnesium niobate is first prepared by calcining a homogeneous mixture of magnesium oxide (4g) and niobium pent oxide (25g) at 1100°C for 20h. It is wet milled along with lead oxide (72g), titanium dioxide (2g), strontium carbonate CO. (0.75g) and calcium carbonate (0.5g) using water medium. The slurry is dried and calcined at 830 deg. C for a period of 3h. The calcined material is again wet milled along with additives namely lead oxide (1g), boric acid (0.3g), magnesium oxide (0.5g), manganese dioxide (0.2g), lithium fluoride (O. Ig) and polyvinyl alcohol (Ig) and dried in an oven at 9O deg. C to obtain PMN based high permittivity ceramics for manufacturing multilayer capacitors with very low dissipation factor. The main advantages of the process of the present invention are: 1) The process is a reliable method for preparation of PMN-based high permittivity ceramics with near total perovskite phase. Consequently the materials prepared by this process: have very high dielectric constants upto 25,OOO. 2) The composition and process parameters can be adjusted such that tailor-made dielectric materials conforming to EIA code Z5V and Y5U are possible. 3) Apart from achieving very high dielectric constant, the process gives rise to materials with low dissipation factor ( resistance (>l011 ohms} and low temperature coefficient of capacitance. 4) The process is suitable for preparation of high permittivity ceramics with low firing temperatures (900-1100°C) and as a result, less expensive internal electrode materials such as pure silver or silver rich palladium alloys can be used instead of palladium or palladium rich silver alloys. 5) The major objection to processing of lead compounds is their pollution hazards, especially PbO evolution above 900°C as vapour. Since the material prepared by the process of the present invention has a lower firing temperature, the process is more environmental friendly. We Claim: 1. An improved process for the preparation of lead magnesium niobate (PMN) based high permittivity ceramics useful for the manufacture of multi layer capacitors which comprises; i) calcining mixed magnesium oxide in the range of 2 to 10% by wt. and niobium pentoxide in the range of 10 to 30% by wt of final product at a temperature in the range of 850-1100°C for a period in the range of 10 to 30 hrs. to form magnesium niobate, ii) grinding the said magnesium niobate with three or more additives selected from lead oxide in the rage of 45 to 75% by wt; titanium dioxide in the range to 2 to 5% by wt; zirconium dioxide in the range of 1 to 4 % by wt., barium carbonate in the range of 0.5 to 3% by wt; strontium carbonate in the range of 1 to 7% by wt; and calcium carbonate hi the range of 1 to 5% by wt., drying and calcining again at a temperature in the range of 750 to 900°C for a period of 2 to 8 hrs to form a precursor, iii) wet grinding the said precursor with three or more ingredient selected from zirconium dioxide in the range of 0.05 to 1.5% by wt; titanium dioxide in the range of 0.1 -2% by wt; Magnesium oxide in the range of 0.1 to 4% by wt; Lead oxide in the range of 0.5-5% by wt; Boric acid in the range of 0.2-4% by wt; Calcium carbonate in the range of 0.5-2.5% by wt; Manganese dioxide in the range of 0.2-2% by wt; Lithium fluoride in the range of 0.3-b% by wt; in addition to poly vinyl alcohol in the range of 0.4 to 4% by wt to obtain milled slurry, iv) drying the said milled slurry to obtain lead magnesium niobate based high permittivity ceramics. 2. An improved process for preparation of lead magnesium niobate based high permittivity ceramics useful for the manufacture of multi layer capacitors substantially as herein described with reference to the examples.

Full Text

This invention relates to an improved process for preparation of lead magnesium niobate (PMN) based high permittivity ceramics useful for the manufacture of multi layer capacitors.
The present invention relates to the preparation of very high permittivity ceramics with dielectric constant (k) upto 25,OOO based on PMN which find application in electronic industry for manufacturing multi layer ceramic capacitors.
In conventional process, PMN based ceramics (ferroelectric relaxor materials) are prepared either by mixed oxide route wherein all the ingredient oxides are mixed together, calcined and sintered to get final product or by coulumbite precursor route wherein only magnesium oxide and niobium oxide are mixed and calcined initially to form magnesium niobate and then the remaining ingredients are supplemented. The latter route is often chosen to minimise formation of undesirable pyrochlore phase instead of perovskite phase. Presence of pyrochlore phase in the product leads to poor dielectric properties.
However, both the above processes are not suitable for preparation of PMN based ceramics with pyrochlore free perovskite phase. As a result products prepared by these processes show inferior dielectric properties and cannot be used for very high permittivity applications. Further the

product requires higher firing temperatures ( >1200°C) making it necessary to use expensive electrode materials such as palladium or palladium rich silver alloy. Other drawbacks of the conventional processes are that these lead to ceramics with high values of dissipation factor and temperature coefficient of capacitance.
The main object of the present invention is to provide an
improved process for the preparation of lead magnesium niobate
based high permittivity ceramics useful for the manufacture of multi
layer ceramic capacitors. The process leads to pyrochlore free
perovskites with very high dielectric constants (15,000 to 25,000), low
dissipation factor (0.01 to 0.03), high insulation resistance (1011 to 1212 ohm)
and, low temperature coefficient of capacitance. The ceramics
prepared by this process possess the above mentioned properties and are
suitable for manufacturing ceramic capacitors with Electronics
Industries Association CEIAD codes Z5V and Y5U. Another object of the
invention is to reduce the firing temperature of the capacitor
ceramics in the range 900 -1 10O°C by incorporating suitable process
steps in the flowsheet so as to use either pure silver or
silver rich palladium alloys instead of expensive palladium or
palladium rich silver alloys which are being used for hither to known processes (Ref: American Ceramic Society Bulletin, Vol.6, No.4,P 704-711.(1987)).

Accordingly the present invention provides an improved process for preparation of lead magnesium niobate based high permittivity ceramics
useful for the manufacture of mul ti layer capacitors which comprises;
i) calcining mixed magnesium oxide in the range of 2 to 10% by wt. and niobium pentoxide in the range of 10 to 30% by wt of final product at a temperature in the range of 850-1100°C for a period in the range of 10 to 30 hrs. to form magnesium niobate,
ii) grinding the said magnesium niobate with three or more additives selected from lead oxide in the rage of 45 to 75% by wt; titanium dioxide in the range to 2 to 5% by wt; zirconium dioxide in the range of 1 to 4 % by wt., barium carbonate in the range of 0.5 to 3% by wt; strontium carbonate in the range of 1 to 7% by wt; and calcium carbonate in the range of 1 to 5% by wt., drying and calcining again at a temperature in the range of 750 to 900°C for a period of 2 to 8 hrs to form a precursor,
iii) wet grinding the said precursor with three or more ingredient selected from zirconium dioxide in the range of 0.05 to 1.5% by wt;
titanium dioxide in the range of 0.1-2% by wt;
magnesium oxide in the range of 0.1 to 4% by wt;
lead oxide in the range of 0.5-5% by wt;
boric acid in the range of 0.2-4% by wt;
calcium carbonate in the range of 0.5-2.5% by wt;
manganese dioxide in the range of 0.2-2% by wt;
lithium fluoride in the range of 0.3-b% by wt; in addition to polyvinyl
alcohol in the range of 0.4 to 4% by wt to obtain milled slurry,
iv) drying the said milled slurry to obtain lead magnesium niobate based high permittivity ceramics.
According to a feature of the process of the present invention the weight percentage of ingredients in the basic composition is in the following ranges.
MgO - 2-10%
Nb2O5 - 10-30%
PbO - 45-75%
Ti02 - 2-5%
ZrO2 - 1-4%

BaCO3 ~ 0.5-3%
SrCO3 - 1-7%
CaCO - 1-5%
3
According to another feature of the present invention the additives
over and above the basic composition are within the weight percentage
1 im its of the basic composition: and are in the range of:
ZrO - 0.05-1 .5%
•j
TiO - 0.1-2%
2
MgO - 0.1-4%
PbO - 0.5-5%
H3 BO3 - 0.2-4%
CaCO - 0.5-2.5%
3
MnO2 - 0.2-2%
LiF - 0.3-6%
Polyvinyl - 0.4-4 % alcohol
The process of the present invention is described below i n detail. Magnesium oxide (2-10 wt%) and niobium oxide (10-30 wt%) are wet
mixed in a pot mill. The said mixture is dried and calcined at 85O-1050°C for 10 to 30h to form magnesium niobate. The magnesium niobate thus formed is wet milled in a pot mill along with three or more ingredients chosen from lead oxide (45-75 wt%) , titanium dioxide (2-5 wt%) , zirconium oxide, barium carbonate (0.5-3 wt %) and strontium carbonate

(1-7 wt%) and calcium carbonate (1-5 wr%). The said slurry is dried and recalcined at 750 to 90O°C for 2-8h to get a precursor. The precursor is again wet milled along with three or more ingredients chosen from zirconium oxide (0.05-1.5 wt%) , titanium dioxide (0.1-2 wt%) , magnesium oxide (0.1-4 wt%) , lead oxide (0.5-5 wfXo) , boric acid (0.2-4 wt%) , calcium carbonate ( O.5-2. 5 wt%) , manganese dioxide (O. 2-2 wt%), and lithium fluoride (0.3 -6 wt%) in addition to polyvinyl alcohol (0.4-4 wt%). The said milled slurry is dried to obtain PMN based high permittivity ceramics. The phase analysis of the final products and the intermediate products are carried out by XPD (A typical XRD pattern of the final product is given in Fig. 1) .
The products thus obtained by the present process are evaluated by fabricating capacitors using them and studying their dielectric properties. The said capacitors are found to conform the specifications of Z5V type capacitors.
The following examples are given to illustrate the process of the present invention and should not be construed to limit the scope of the invention.
Example-1
Laboratory reagent grade magnesium oxide (4g) and niobium pentoxide (25g) are mixed, dried a.nd calcined in an alumina crucible at 1 100 deg. C for 20h to get magnesium niobate. The product thus formed is wet milled along with lead oxide, (70g) titanium dioxide (2.5g), barium carbonate (1g) and calcium carbonate (0.5g) in water medium using plastic pot and zirconia balls. The slurry is dried and again calcined at 800°C for a period of 3h. The material thus obtained constitutes

the major ingredient for the final product. This is again wet nulled along with lead oxide (1.5g), boric acid (0.5g), magnesium oxide (0.5g) and polyvinyl alcohol ( 1g) and dried in an oven at 90°C to obtain a typical PMN-based high permittivity ceramics for manufacturing multi layer ceramic capacitors. A typical XRD pattern of the final product is given in Fig. 1 .
Example -2
Magnesium niobate is first prepared by calcining a homogeneous mixture of magnesium oxide (4g) and niobium pent oxide (25g) at 1100°C for 20h. It is wet milled along with lead oxide (72g), titanium dioxide (2g), strontium carbonate CO. (0.75g) and calcium carbonate (0.5g) using water medium. The slurry is dried and calcined at 830 deg. C for a period of 3h. The calcined material is again wet milled along with additives namely lead oxide (1g), boric acid (0.3g), magnesium oxide (0.5g), manganese dioxide (0.2g), lithium fluoride (O. Ig) and polyvinyl alcohol (Ig) and dried in an oven at 9O deg. C to obtain PMN based high permittivity ceramics for manufacturing multilayer capacitors with very
low dissipation factor.

The main advantages of the process of the present invention are:
1) The process is a reliable method for preparation of
PMN-based high permittivity ceramics with near total
perovskite phase. Consequently the materials prepared by
this process: have very high dielectric constants upto 25,OOO.
2) The composition and process parameters can be adjusted
such that tailor-made dielectric materials conforming to EIA
code Z5V and Y5U are possible.
3) Apart from achieving very high dielectric constant, the process gives
rise to materials with low dissipation factor ( resistance (>l011 ohms} and low temperature coefficient of capacitance.
4) The process is suitable for preparation of high
permittivity ceramics with low firing temperatures (900-1100°C) and
as a result, less expensive internal electrode materials such as pure silver or silver rich palladium alloys can be used instead of palladium or palladium rich silver alloys.
5) The major objection to processing of lead compounds is
their pollution hazards, especially PbO evolution above 900°C as
vapour. Since the material prepared by the process of the present
invention has a lower firing temperature, the process is more
environmental friendly.

We Claim:
1. An improved process for the preparation of lead magnesium niobate (PMN) based high permittivity ceramics useful for the manufacture of multi layer capacitors which comprises;
i) calcining mixed magnesium oxide in the range of 2 to 10% by wt. and
niobium pentoxide in the range of 10 to 30% by wt of final product at
a temperature in the range of 850-1100°C for a period in the range of
10 to 30 hrs. to form magnesium niobate, ii) grinding the said magnesium niobate with three or more additives
selected from lead oxide in the rage of 45 to 75% by wt; titanium
dioxide in the range to 2 to 5% by wt; zirconium dioxide in the range
of 1 to 4 % by wt., barium carbonate in the range of 0.5 to 3% by wt;
strontium carbonate in the range of 1 to 7% by wt; and calcium
carbonate hi the range of 1 to 5% by wt., drying and calcining again at
a temperature in the range of 750 to 900°C for a period of 2 to 8 hrs to
form a precursor, iii) wet grinding the said precursor with three or more ingredient selected
from
zirconium dioxide in the range of 0.05 to 1.5% by wt;
titanium dioxide in the range of 0.1 -2% by wt;
Magnesium oxide in the range of 0.1 to 4% by wt;
Lead oxide in the range of 0.5-5% by wt;
Boric acid in the range of 0.2-4% by wt;
Calcium carbonate in the range of 0.5-2.5% by wt;
Manganese dioxide in the range of 0.2-2% by wt;
Lithium fluoride in the range of 0.3-b% by wt; in addition to
poly vinyl alcohol in the range of 0.4 to 4% by wt to obtain milled
slurry,
iv) drying the said milled slurry to obtain lead magnesium niobate based high permittivity ceramics.
2. An improved process for preparation of lead magnesium niobate based high permittivity ceramics useful for the manufacture of multi layer capacitors substantially as herein described with reference to the examples.

Documents:

1798-del-1995-abstract.pdf

1798-del-1995-claims.pdf

1798-del-1995-correspondence-others.pdf

1798-del-1995-correspondence-po.pdf

1798-del-1995-description (complete).pdf

1798-del-1995-drawings.pdf

1798-del-1995-form-1.pdf

1798-del-1995-form-2.pdf

1798-del-1995-form-4.pdf

1798-del-1995-form-9.pdf

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Patent Number

192550

Indian Patent Application Number

1798/DEL/1995

PG Journal Number

18/2004

Publication Date

01-May-2004

Grant Date

09-Sep-2005

Date of Filing

29-Sep-1995

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI-110001, INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	UPENDRAN SYAMAPRASAD	RRL(CSIR), TRIVANDRUM
2	PARTHASARATHI MUKHERJEE	RRL(CSIR), TRIVANDRUM
3	SHEEJA NAIR AMBIKA RAVINDRANATH	RRL(CSIR), TRIVANDRUM
4	MADHAVAN SANKARA SARMA	RRL(CSIR), TRIVANDRUM
5	PERUMAL GURUSWAMY	RRL(CSIR), TRIVANDRUM
6	ALATHOOR DAMODARAN DAMODARAN	RRL(CSIR), TRIVANDRUM

PCT International Classification Number

B32B 18/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA