Analysis of Pyroelectric Figures of Merit by Using Off Polar Axis Cut Crystals

Abstract

Crystal cutting angles are critical for the pyroelectric device fabrication and performance optimization. In this report, we evaluated two pyroelectric figures of merit, p/ϵ and p/√ϵ, in all directions in space and suggested the crystallographic rotating angles having potential to maximize the effect. The polarization directions of the secondary pyroelectric effects are also evaluated for several crystal systems. It appears that the directions of the secondary pyroelectric effect, coupled through the piezoelectric, thermal expansion and elastic stiffness effect, follow those of the primary and thus the total pyroelectric effect in various crystallographic polar groups. Selected materials of interest with reported properties are examined and shown improvements of pyroelectric figure of merit p/ϵ by off polar axis cutting. The pyroelectric figures of merit of a specific material, TGS, are calculated with respect to its crystal orientation. The results show an appreciate improvement of pyroelectric figure of merit for the large area sensors applications. As for the point detectors (figure of merit, p/√ϵ), the pyroelectric figure of merit remains maximum along the polar axis, p₂. The results are discussed in view of designing various pyroelectric sensing and imaging devices for several crystallographic polar point group materials.

Keywords:

• Pyroelectrics
• ferroelectrics
• off axis pyroelectric coefficients
• figures of merit

Acknowledgments

This work has been supported by the National Science Foundation under grants DMR-0407462 and NIRT-0709293.