Pyroelectric properties of fine bartum titanate/70:30MOL% poly(vinylidene fluoride: Trifluoroethylene) thin-film composites

Abstract

The ferroelectric poling behaviour and pyroelectric properties of thin-film fine barium titanate / 70:30mol% poly(vinylidene fluoride:trifluoroethylene) composite materials have been studied. The poling time and electric field distribution were predicted using Maxwell-Wagner theory. The pyroelectric coefficient was determined as a function of poling temperature, electric field and time. Maximum activity was achieved by poling above the polymer Curie point and coercive electric field for a time greater than 60sec. A thin-film(1.3μm) composite containing 4%vol of fine barium titanate powder possessed a pyroelectric coefficient of 77μCm⁻²K⁻¹ at T=293K when poled at T=120°C, E=54V/μ, t=2hrs45min. Decay of pyroelectric activity was minimal over a period of 200hrs after poling, independent of poling time. Annealing of composites resulted in an increase in the relative permittivity due to a decrease in film thickness. This alters the composite structure from a 0–3 connectivity pattern towards a 1–3 connectivity pattern. Poling produces a reduction in the relative permittivity of the composites due to the decrease in relative permittivity of the polymer phase. The composites possess a large dielectric noise figure of merit, FD(1kHz,20°C)=160, which is double that of pure 70:30mol% p(VDF:TrFE) thin-films. These composites are therefore promising materials for use in an integrated thermal-imaging device.