Pyroelectric effect in ultrathin layers of achiral mesogenic composites

Abstract

The pyroelectric properties of the solid mixtures of achiral liquid crystalline polymers with their monomers were studied. The composites were fabricated in a thin film form (less than 1 μm) by spin-coating technique. The maximum value of the current responsivity being 0.67 μA/W has been obtained for optimum monomer/polymer ratio of 33%:67% by weight. The pyroelectric voltage was measured in the frequency range from 10 Hz up to 250 kHz. The figure of merit for the composite at room temperature is about 0.8 nC/cm2 K, which is more than twice higher than that of polyvinylidene fluoride with trifluroethylene 70%:30%.

Pyroelectric current measurements on PbZr0.2Ti0.8O3 epitaxial layers

“…35 The pyroelectric response is essentially unchanged up to 1 MHz, which is consistent with other frequency-dependent measurements reported in the literature. 36,37 The observed reduction in the pyroelectric coefficient magnitude near 1 MHz heating frequency can be attributed to capacitive effects not included in the modeling. While there may be thermomechanical-induced strains in the pyroelectric layer, any currents generated by these strains are small relative to the pyroelectric currents observed here.…”

Longitudinal and transverse pyroelectric effects in a chiral ferroelectric liquid crystal

“…The pyro electric voltage in this case was measured across the load resistor R load = 1 MΩ, R load > R in , where R in is the input resistance of the synchronous detector. An anal ogous dependence for the well known organic pyro electric guanidine nitrate [19] is shown for comparison (curve 2). In the case of guanidine, the modulus of the pyroelectric current was measured; i.e., the synchro nous detector was used in the current measuring regime.…”

Passive Amplification Effect in Thin Pyroelectric Films

“…The methods of the preparation of the pyroelectric cells based on pyroelectric materials: tetraaminobiphenyl, mixtures of achiral liquid crystal ferroelectric polymers and their monomers (Pm6R8 þ 33%m6R8) and ferroelectric copolymer (P(VDF-TrFE) 70:30% have been described elsewhere [1,2,10,11]. Thick aluminum layers evaporated onto the pyroelectric material were used as front electrodes.…”

“…In Figure 5 the frequency mode ffiffiffi ffi x p is obtained allowing calculating the pyroelectric coefficients. Since the pyroelectric coefficient for TAD is known, c TAD ¼ 50 mC=m 2 R [11], it is possible to calculate the pyroelectric coefficients [13,14], h TAD ¼ 1.5 mm; 2 -Glassy liquid crystalline achiral antiferroelectric mixture of polymer with its monomer [1,2], h LC ¼ 0.6 mm; 3 -Ferroelectric copolymer P(VDF-TrFE) 70:30%, h cjp ¼ 12.5 mm [1,2,14].…”

“…The pyroelectric effect is an example of a thermoelectric phenomenon which involves the generation of a current or voltage at a change of temperature [1,2]. In pyroelectric detectors, as a rule, energy of quanta of detected radiation is insufficient for excitation of an electronic subsystem of a crystal and radiant energy is used to increase the oscillatory energy of system of atoms through temperature and spontaneous polarization changes [3].…”