Compositions: ceramic – Ceramic compositions – Titanate – zirconate – stannate – niobate – or tantalate or...
Reexamination Certificate
2000-03-20
2003-03-18
Koslow, C. Melissa (Department: 1755)
Compositions: ceramic
Ceramic compositions
Titanate, zirconate, stannate, niobate, or tantalate or...
C501S137000, C423S598000
Reexamination Certificate
active
06534429
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a multi-component material having a wide range of compositions which is suitable for use in devices such as uncooled thermal imaging detectors. The invention also relates to a simple graphical means by which to provide a first order estimate of the desired composition of the multi-component material.
2. Discussion of the Prior Art
Thermal detectors and imagers which employ thermally sensitive materials may utilize ferroelectric and pyroelectric compounds such as barium strontium titanate. Each material has its characteristic Curie point, i.e., the transition temperature at which the material changes from being ferroelectric to paraelectric. This change is accompanied by a rapid change in the dielectric constant as the temperature reaches the Curie point. By selecting the proper amounts of related materials, a solid solution of the materials can be fabricated which has a room temperature (i.e., 25° C.) Curie point. With such a material, very small changes in thermal energy can be detected as the material goes through the transition point, as manifested by large changes in either the electronic capacitance or the dielectric constant. These dramatic changes in values constitute an electronic signal. When this material is made into an array of very small detectors, the resulting combined electronic signals from all of the detectors produce an electronic image of the thermal scene.
Multi-component materials such as BaSrTiO
3
have heretofore been employed in the imaging arrays of uncooled thermal detectors, which by design, operate at ambient or room temperature. Since BaSrTiO
3
is, however, relatively expensive, other multi-component materials may be employed which possess similar characteristics and operate in the same manner.
A detector material consisting of PbSrTiO
3
having a composition defined by the general formula Pb
(1−x)
Sr
x
TiO
3
is disclosed in U.S. Pat. No. 5,079,200, the disclosure of which is incorporated by reference herein. In one embodiment the material contains approximately 64-68% strontium titanate, which provides a detector material with a Curie point temperature and maximum sensitivity near standard or room temperature.
Thus, in order to reduce the expense associated with devices which employ BaSrTiO
3
, it is desirable to utilize alternative multi-component compositions which while operating in the same manner as BaSrTiO
3
, and also offer a broader range of potential compositions.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a multi-component material having a wide range of compositions which is suitable for use in devices such as uncooled thermal imaging detectors. It is a farther object of the invention to provide a graphical method which facilitates the preparation of a first order estimate of the composition of the multi-component material.
Accordingly, the present invention relates to a multi-component material represented by the general formula (I):
Ba
(1−x−y)
Pb
y
M
x
TiO
3
(I)
in which:
M is Sr or Cd;
x is the decimal fraction molar concentration of MTiO
3
, where x has a value equal to or greater than about 0.20 and less than or equal to about 0.75;
y is the decimal fraction molar concentration of PbTiO
3
, where y has a value greater than zero and less than or equal to about 0.40; and
x+y is less than 1.0.
The invention also relates to a graphical method of estimating the composition of the multi-component material represented by the general formula (I) comprising the steps of:
selecting a value of x;
locating a first point on a first graphical representation comprising a temperature axis (y-axis) representing Curie points in °C. and a concentration axis (x-axis) representing mole percentage of BaTiO
3
and MTiO
3
, the first point corresponding to the intersection of an abscissa representing x expressed as a mole percentage, with an ordinate representing a temperature (T) between about −40° C. to 60° C., with 25° C. (room temperature) being preferred;
locating a second point on the first graphical representation corresponding to the intersection of an abscissa representing 100% MTiO
3
with an ordinate representing a temperature of −220° C.;
drawing a straight line from the second point through the first point, and extending said line to intercept the temperature axis and line DE at a third point; where line DE now represents the decimal mole fraction of PbTiO
3
in the BaTiO
3
/PbTiO
3
system (See FIG.
1
-B);
and multiplying the decimal mole fraction of PbTiO
3
identified by the third point by a value equal to 1−x to determine the value of y.
Thus, by selecting a value of x within the allowed range for a desired temperature (preferably ambient or room temperature) operation, and then employing graphical means, the corresponding value of y can be determined, and a first order estimate of the desired composition of a 3-component titanate can be provided.
REFERENCES:
patent: 2467169 (1949-04-01), Wainer
patent: 5079200 (1992-01-01), Jackson
Jona and Shirane, Ferroelectric Crystals, International Series of Monographs on Solid State Physics, vol. #1, pp. 241 and 249 (1962).
Adams William V.
Biffoni U. John
Koslow C. Melissa
The United States of America as represented by the Secretary of
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