Title of Invention	"A PROCESS OF PREPARING FERRO-ELECTRIC MATERIAL "
Abstract	The present invention relates to a process of preparing ferro-electric material of general formula PbxBao.4LayBi2Nb2O6 where x = 0.4-0.6, y = 0.01-0.03 and z = 0.01 to 0.03 comprising doping PbBaNb2O6 with Bi and La in place of lead only, barium site is left undisturbed leading to tightly packed structure resulting in improved piezoelectric properties.

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This invention relates to a process of preparing ferro-electric material with strong piezoelectric properties. BACKGROUND Tungston bronze lead barium niobate exhibits a morphotrophic phase boundary for a barium concentration of 0.4. EC Subba Rao reported extensive work on substituted lead metaniobate. Hot pressed lead barium lanthanum niobate (PBLN) was studied by Nagata, Okazaki et al. Neurogoankar also prepared lanthanum doped lead barium niobate and he could achieve a maximum d33 of 230-270µc/cm2. Neurogoankar prepared hot pressed lead barium niobate and lead barium lanthanum niobate ceramics and reported a d33 value of 236 jo.c/cm2 for PBN : 60 and 275 µc/cm2 for PBLN : 60/6. Neurogoanker substituted lanthanum in place of both lead and barium by adopting the formula (PbxBa1-x)1. 3y/2 LayNb2O6. In the above work a dopent La was substituted both in lead and barium sites. Poling of these ceramics causes problem due to a decrease in resistance at high temperature. It is the object of this invention to prepare a ferro-electric material with strong piezo electric properties. To achieve the said objective, this invention provides a process of preparing ferro-electric material of general formula Pbx.3y/2_3z/2 Bai.xLayBizNb2O6 where x = 0.4-0.6, y = 0.01-0.03 and z = 0.01 to 0.03 comprising doping PbBaNb2O6 with Bi and La in place of lead only, barium site is left undisturbed leading to tightly packed structure resulting in improved piezoelectric properties. A process of preparing ferro-electric material of general formula Pbx_3y/2-3z/2 Ba1-xLayBi,Nb2O6 where x = 0.4-0.6, y = 0.01-0.03 and z = 0.01 to 0.03 comprising doping which is carried out by: calcining the analytical reagent grade oxides of Pb, Ba, Bi, La and Nb in predetermined proportion at 800-900°C for 2-6 hours with 4-6% excess of lead oxide to compensate for PbO evaporation during firing, cooling the resultant product and grinding it and mixing it with a binder to form pellets. polishing such as herein described the said discs, sintering the said pellets in presence of air at 1250-1280°C for 1-1 1/2 hrs. to form sintered discs, applying silver paste to the said discs on both sides and firing, poling the said silver discs by corona discharge at 120-130°C with an electric field of 35-46 KV/cm. for 25?35 min. to get the required product. The said analytical reagent grade oxides are dry ground for 2 hours before calcining. The analytical reagent grade oxides are calcined at 800°C for 6 hours and the pellets were sintered in air at 1280°C for 1 hour to form the said discs. The binder used is polyvinyl alcohol. i> The grinding of the product is carried out in presence of an alcohol, preferably methanol. The said discs were poled by corona discharge at 125°C with an electric field of 40 KV/cm for 30 min. The invention will now be described with reference to the following example: EXAMPLE Taking the analytical reagent grade oxides of Pb, Ba, La, Bi and Nb in the proportion of one tenth of their molecular weights. Adding 5% excess of PbO in the said mixture. Calcining the said oxides mixtures at 800° C for 2 hours. Cooling the resultant product and grinding it and mixing it with Polyvinyl Alcohol to form pellets. The said pellets were sintered in presence of air at 1250°C for one hour to form sintered discs. The said discs were polished and silver paste is applied on both sides of the discs. Poling the said silver discs by Corona discharge at 125°C with an electric field of 40KV/cm for 30 minutes to get the required piezoelectric materials, as given in table 1. It may be seen that Pbo.54Bao.4Lao.o2Bio.o2Nb2O6 (AU I) or Pb0.525Bao.4Lao.o2Bio.o3Nb2O6 (AU 2) have high values of d33. The said materials yield very high d33 values of the order of 364 µc/cm2 and 303 µc/cm2 respectively along with high kp values of the order of 0.35 and low mechanical Q. Dielectric measurements were performed with an HP 4192 LF impedance analyzer at 1kHz frequency. Coupling factors were measured by the resonance method using the impedance analyzer. The planar coupling factor, kp, was calculated from the resonance and anti-resonance frequencies of a thin disc following the procedures described by Mason3. The thickness coupling factor was calculated from the ratio of the overtone frequency f2 to the fundamental frequency fl of the series-mode resonance. The d33 values were measured with a Sensor 0643 piezo-d-meter. TABLE 1 (Table Removed) TABLE 2 (Table Removed) DISCUSSION: Dielectric constants, kp, kt, d33 and Qm are given in Table II. Room temperature dielectric constant is very high for composition II, III and IV, which is lanthanum and zirconium, substituted compositions of lead barium niobate. Curie temperature dielectric constant and kp is high for samples VI, VII and VIII. kt exhibits a high value for compositions II and V. La addition leads to a dramatic increase in the dielectric constant. Room temperature dielectric constant increases up to sample IV. In sample VI and VIII dielectric constant at Curie temperature attains high value. Sample VII exhibits the lowest value of mechanical Q among the samples investigated, kp attains a maximum value of 0.39 for composition VII. In table III we compared our values with commercial samples marketed as modified Lead metaniobate. As can be seen while kp is negligible in commercial samples our samples exhibits reasonably high values of kp and k, for VI and VII and VIII. Qm has increased in our samples when compared to commercial samples. Dielectric constant is very high for our samples. Samples VI and VII and VIII exhibit high d33 while Qm is low only for sample VII. TABLE III Comparative Statement Of Our Values With Commercial Samples Of Some International Companies (Table Removed) TABLE IV: Comparative statement of our d33 values with the highest d33 values achieved by some investigators: (Table Removed) TABLE V: Ferro-electric and Piezo-electric properties of AU(I) and AU)II) (Table Removed) It may be seen from the tables that d33 values are of the order of 364µc/cm2 and 303 respectively, in case of our invention along with high kp values of the order of 0.39 and low mechanical Q values. CONCLUSION: Lead barium lanthanum niobate (sample VIII) has high room temperature dielectric constant, Curie temperature dielectric constant, kp, and kt. d33 is maximum in this sample. Qm value of 117 is higher than commercial samples. AU (I) and AU (II) exhibit high kp and d33 values. AU (II) has lowest Qm value among investigates samples. When compared with commercial lead metaniobate samples, due to addition of lanthanum our d33 values are much higher than modified lead metaniobate values. In conclusion, it can be said that the Lead barium niobate family has potentially important compositions and may surpass PZT (lead zirconium titanate) for particular applications such as undersea ultrasonic transducers. References: 1. R. Neurgaonkar, J.R. Oliver, J.G. Nelson, and L.E. Cross,, Mat. Res. Bull. Vol. 26, pp. 771-777, 1991 2. R. Neurgaonkar, J.R. Oliver, W.K. Cory and L.E. Cross, Mat. Res. Bull. Vol. 18, pp. 735-741. 1983 We claim: 1. A process of preparing ferro-electric material of general formula Pbx-3y/2. 3z/2 Ba1-xLayBizNb2O6 where x = 0.4-0.6, y = 0.01-0.03 and z = 0.01 to 0.03 comprising doping, which is carried out by: calcining the analytical reagent grade oxides of Pb, Ba, Bi, La and Nb in predetermined proportion at 800-900°C for 2-6 hours with 4-6% excess of lead oxide to compensate for PbO evaporation during firing, cooling the resultant product and grinding it and mixing it with a binder to form pellets, polishing such as herein described the said discs, sintering the said pellets in presence of air at 1250-1280°C for 1-l!/2 hrs. to form sintered discs, applying silver paste to the said discs on both sides and firing, poling the said silver discs by corona discharge at 120-130°C with an electric field of 35-46 KV/cm. for 25-35 min. to get the required product. 2. A process as claimed in claim 1 wherein the said analytical reagent grade oxides are dry ground for 4-6 hours before calcining. 3. A process as claimed in claim 1 wherein the analytical reagent grade oxides are calcined at 800°C for 6 hours and the pellets were sintered in air at 1280°C for 1 hour to form the said discs. 4. A process as claimed in claim 1 wherein the binder used is polyvinyl alcohol. 5. A process as claimed in claim 1 wherein grinding of the product is carried out in presence of an alcohol, preferably methanol. 6. A process as claimed in claim 1 wherein the said discs were poled by corona discharge at 125°C with an electric field of 40 KV/cm for 30 min. 7. A process as claimed in claim 1 wherein the ferroelectric material produced is Pb0.54Ba0.4La0.02Bi0.02Nb2O6 or Pb0.525Ba0.4La0.02Bi0.03Nb2O6 8. A process of preparing ferroelectric material of general formula PbxBa0.4LayBi2Nb2O6 where x = 0.4-0.6, y = 0.01-0.03 and z = 0.01 to 0.03 substantially as herein described with reference to the foregoing example.

Documents:

833-del-1999-abstract.pdf

833-del-1999-assignment.pdf

833-del-1999-claims.pdf

833-del-1999-correspondence-others.pdf

833-del-1999-correspondence-po.pdf

833-del-1999-description (complete).pdf

833-del-1999-form-1.pdf

833-del-1999-form-13.pdf

833-del-1999-form-19.pdf

833-del-1999-form-2.pdf

833-del-1999-form-3.pdf

833-del-1999-gpa.pdf

833-del-1999-pa.pdf

833-del-1999-petition-others.pdf