Compositions – Piezoelectric
Reexamination Certificate
2000-06-02
2002-02-19
Koslow, C. Melissa (Department: 1755)
Compositions
Piezoelectric
C501S134000, C501S135000, C264S618000, C264S438000
Reexamination Certificate
active
06348160
ABSTRACT:
This application claims the benefits of and priority to Indian Patent Application No. 833/Del/99, filed Jun. 3, 1999, which status is pending, and is hereby incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to compositions having niobate anions and a combination of lead, barium, lanthanum, and bismuth cations. These compositions are part of the Tungsten Bronze class of ferroelectric ceramic materials, and may have very high piezoelectric charge coefficients, d
33
, and high dielectric constants. The invention also relates to processes of preparing the compositions, and ferroelectric ceramic materials and articles comprising the composition.
2. Background Art
When barium is partly substituted for lead in lead metaniobate, there is morphotrophic phase boundary at barium concentrations of about 0.4. In fact Francombe has shown (
Acta Cryst.
13, 131-40 (1960)) that for barium concentration of 0.375 to 0.475, a mixed phase of tetragonal and orthorhombic structure occur. Subbarao et al. reported extensive work on substituted lead metaniobate, (
J. chem. Phys.
32, 1846-51 (1960)). Pioneering work on hot pressed lead barium lanthanum niobate (PBLN) was done by Nagata, Okazaki et al. In this ceramic, grains are needle shaped and oriented parallel to c-axis.
Baxter and Hellicar (
J. Am Ceram Soc.
43, 578-83 (1960)) prepared lead barium niobates and studied their electrical properties. They found that the structure of Pb
x
Ba
(1−x)
Nb
2
O
6
is orthorhombic for Barium content in the range 0-0.4 and the Curie temperature decreases for the same range of composition. With further increases of barium content, the structure become tetragonal and Curie temperature again rises. Mechanical Q
m
is 5 and 8 for barium contents between about 0 and 0.4, and as barium content increases, there is a sharp increase of Q
m
to 1000. There is a morphotrophic phase boundary between the orthorhombic and tetragonal structures at barium concentrations of about 0.4.
Substitution of barium for lead in PbNb
2
O
6
decreases the orthorhombic distortion and then induces a tetragonal structure with polar axis along ‘c’ rather than orthorhombic ‘b’ (See Francombe,
Acta Cryst.
13,131-40 (1960); Lewis and Thomas,
Proc. Internet. Conf. Solid State Phys. Electronics Telecommun.,
Brussels 4, Pt. 2, 883-90 (1958, Publ. 1960); Isupov, and Kosiakov,
Zh. Tekh. Fiz.
28, 2175-85 and
Soviet Phys.—Tech. Phys.
3, 2002-10 (1958); Goodman, G,. Am.Ceram. Soc. Bull. 34, No. 4, Program 11 (1955); U.S. Pat. Nos. 2,805,165; and 2,729,757). The substitution of substantial amounts of barium in lead niobate, PbNb
2.
O
6
, causes remarkable change in ferro-electric properties. Greatly enhanced dielectric and piezoelectric properties are observed, as the barium content approaches 0.4.
During 1983, Nagata et al. studied the electric properties of hot-pressed (Pb
x
Ba
1−x
)
1-3y/2
La
y
Nb
2
O
6
, (see Japanese Journal of Applied Physics, Vol. 22 Supplement 22-2, pp 123-125 (1983); and Japanese Journal of Applied Physics, Vol. 24 Supplement 24-3, pp 100-102 (1985)). They found that k
t
increases on tetragonal side up to x/y=60/4 and the maximum value of k
t
is 0.4. In the orthorhombic x/y=80/4 side k
t
decreases, the value of Q is 6, 12 and is low. Further, in the orthorhombic side, when x/y=65/4 and 70/4 remnant polarization P
r
attains maximum value of 10.
Nagata et al, in 1985 prepared PBLN by molten salt synthesis and found the maximum value of k
t
=0.36 and lowest Q
m
=30 and they concluded that the needle shaped PBLN prepared by molten salt synthesis become smaller in size and shorter in length with increase in and Lanthanum substitution. They concluded that with introduction of Lanthanum grain orientation fades as length to diameter ratio of grains decreases.
Neurogoankar et.al. studied hot pressed samples of Pb
0.6
Ba
0.4
Nb
2
O
6
with or without Lanthanum (See Mat. Res.Bull. Vol. 26, pp. 771-777, 1991). It was found that the value of P
s
(spontaneous polarization)=is 10.9 &mgr;c/cm
2
in PBN: 60/6 and 23.6 &mgr;c/cm
2
in PBN. They reported d
33
values of 275×10
−12
C/N in PBLN 60/6 and 236×10
−12
C/N in PBN 60.
In all previous works, whenever a dopant was substituted, it was substituted both in lead and barium sites. Poling of these ceramics caused problems due to a decrease of resistance at high temperature. SUMMARY OF THE INVENTION
The object of this invention is to prepare compositions and/or ceramic materials having strong piezoelectric and/or ferroelectric properties of the tungsten bronze type class of ceramic materials, which can be poled easily.
To achieve the said objective, in one embodiment the invention relates to compositions having Nb
2
O
6
2−
anions (niobate anions) in combination with lead, barium, lanthanum, and bismuth cations.
In a preferred embodiment, the invention relates to compositions of the general formula Pb
(x−3y/2−3z/2)
Ba
(1−x)
La
y
Bi
z
Nb
2
O
6
, wherein x is preferably from about 0.4 to about 0.6, y is preferably from about 0.01 to about 0.03 and z is preferably from about 0.01 to about 0.03.
The above-described compositions may be easily poled, to provide piezoelectric and/or ferroelectric ceramic materials, that preferably have high piezoelectric charge coefficients, i.e. high d
33
values and/or high dielectric constants.
The instant invention further relates to processes for preparing ferroelectric ceramic materials of general formula Pb
(x−3y/2−3z/2)
Ba
(1−x)
La
y
Bi
z
Nb
2
O
6
, wherein x is preferably from about 0.4 to about 0.6, y is preferably from about 0.01 to about 0.03 and z is preferably from about 0.01 to about 0.03, and articles comprising the ferroelectric materials.
DETAILED DESCRIPTION OF THE INVENTION
In one embodiment, the invention relates to compositions having Nb
2
O
6
2−
anions (niobate anions) in combination with lead, barium, lanthanum, and bismuth cations.
In a preferred embodiment, the invention relates to compositions of the general formula Pb
(x−3y/2−3z/2)
Ba
(1−x)
La
y
Bi
z
Nb
2
O
6
, wherein x is preferably from about 0.4 to about 0.6, y is preferably from about 0.01 to about 0.03 and z is preferably from about 0.01 to about 0.03. In more preferred embodiments, x is about 0.6, y is about 0.02, and z is about 0.02. In other more preferred embodiments, x is about 0.6, y is about 0.02, and z is about 0.03. Preferred compositions of the invention also include Pb
0.54
Ba
0.4
La
0.02
Bi
0.02
Nb
2
O
6
and Pb
0.525
Ba
0.4
La
0.2
Bi
0.03
Nb
2
O
6
.
The compositions of the invention may be poled, to provide piezoelectric and/or ferroelectric ceramic materials. Alternatively, the compositions may be formed into articles, then poled, to provide piezoelectric and/or ferroceramic articles. The ferroelectric ceramic materials and/or articles of the invention may be formed into articles that are surprisingly easily poled, i.e. the microscopic domains of the material and/or article may be re-oriented in a desired direction, preferably by applying a d.c. electric field to the material. The ferroelectric ceramic materials and/or articles exhibit unexpectedly high piezoelectric charge coefficients, i.e. high d
33
values, that may be greater than about 300 pc/N.
The invention also provides processes for preparing the piezoelectric and/or ferroelectric ceramic materials and/or articles. The articles are useful as components of ultra-sonic transducers.
In one embodiment, the processes for preparing Pb
(x−3y/2−3z/2)
Ba
(1−x)
La
y
Bi
z
Nb
2
O
6
comprise doping Pb
x
Ba
(1−x)
Nb
2
O
6
with Bi and La in place of lead only, wherein the barium sites are left undisturbed, leading to tightly packed structure resulting in an improved piezoelectric material with high d
33
value.
In preferred embodiments of processes of the invention, the ferroelectric ceramic materials of the invention are prepared by calcining oxides or carbonates of Pb and
Bhanumathi Akella
Umakantham Kodidasu
Venkata Narasimhacharya Vakkalanka
Department of Science & Technology
Koslow C. Melissa
Needle & Rosenberg P.C.
LandOfFree
Ferroelectric ceramic material with strong piezoelectric... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Ferroelectric ceramic material with strong piezoelectric..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ferroelectric ceramic material with strong piezoelectric... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2942564