Pyroelectric characteristics of modified barium titanate ceramics
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M. D. Hill and J. F. Kelly Ceramic Division, Electronic Materials Group, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (Received 30 January 1992; accepted 10 August 1992)
BaZrO 3 and BaHfO3 modified polycrystalline BaTiO3 are candidate materials for transverse mode and pyroelectric charge coupled device (CCD) arrays. Addition of 3—4% barium zirconate and barium hafnate to barium titanate alters the temperature of phase transformations and with it, dielectric and pyroelectric properties. These additions create a temperature range close to room temperature where the pyroelectric coefficient is extremely high relative to the dielectric permittivity. These materials show a very high figure of merit for dielectric bolometer applications that is competitive with existing materials, while being relatively easy to prepare.
I. INTRODUCTION This work is the continuation of our current efforts to develop new pyroelectric materials for infrared detectors. The major disadvantages of pyroelectric thermal detectors are their low peak detectivities, in the range of 108 to 109 cm Hz1/2 W" 1 , and their limited bandwidths of operation.1 To have high detectivities (and good performance) pyroelectric materials must have their Curie temperature (Tc) close to the operating temperature.2-3 This results in high values of both permittivity and pyroelectric coefficient, which are advantageous in fine pitch, high resolution, imaging arrays. Stable operation at the Curie temperature can be achieved by applying a dc bias field as in dielectric bolometers.4'5 It is well known that ferroelectric perovskite ceramics such as lanthanum substituted lead zirconate titanate (PLZT), barium strontium titanate (BST), and lead titanate (PbTiO3) are good infrared detector materials. Barium titanate (BaTiO3) ceramics are interesting in that they possess the perovskite structure and their physical properties are readily modified by the inclusion of selected dopants into either of the cation sublattices.6'7 It was shown earlier8"10 that substitutions of Zr 4+ and Hf4+ on the Ti 4+ site significantly influence the dielectric and structural characteristics of BaTiO3. These additions are found to increase the temperature of the orthorhombic-to-tetragonal transition, while lowering the Curie temperature. Chynoweth11 measured the pyroelectric effect in pure BaTiO3 single crystals and confirmed that a first order transition occurs at the Curie temperature. Similar behavior was observed in polycrystalline BaTiO3 ceramics.12'13 Berlincourt14 studied the pyroelectric effect in several BaTiO 3 based compositions, but the poling conditions were not clearly specified. The pyro3296 http://journals.cambridge.org
electric properties of BaTiO3 polycrystalline ceramics are very much dependent on the poling conditions.15'16 Therefore, it is important that all BaTiO3-based compositions are poled under identical conditions so that an objective comparison of the pyroelectric properties can be made. The present paper describes the physical propert
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