Pyroelectric Constant Research Articles

Ferroelectric behavior in paracrystalline poly(vinyl trifluoroacetate)

Abstract Dielectric behavior in paracrystalline poly(vinyl trifluoroacetate) was investigated from the viewpoint of ferroelectricity. This polymer has a large CF3 dipole moment (2.3 Debye) and structural defects due to the atactic sequence in its chain conformation. It is possible to rotate the dipoles in paracrystals with defects under high electric field. The dielectric behavior was measured from 20 to 200 °C. A large dielectric constant and dielectric relaxation strength (Δε = 17 at 110 °C) were observed in the α-relaxation region. Corona poling on the samples was carried out at DC field 80 MV/m and 80 °C. Ferroelectric D–E hysteresis loop was observed under high electric field, and the remanent polarization and coercive field at 40 °C were 15 mC/m2 and 155 MV/m, respectively. Pyroelectric response and thermally stimulated current were measured from the current through the electrode irradiated by a pulsed semiconductor laser. A pyroelectric constant of about 6 μC/m2K was observed, which was stable up to near the poling temperature. The ferroelectricity in poly(vinyltrifluoroacetate) stems from the rotation of molecular chains in its paracrystals and orientation of the CF2 dipoles. Poly(vinyltrifluoroacetate) dielectrics can be used for capacitors with high power density, artificial skins, muscles and other flexible electronics.

Analysis of a sandwiched piezoelectric semiconducting thermoelectric structure

In this paper, we analyze the piezo-thermoelectric responses of an integrated n-type piezoelectric semiconducting (PS) thermoelectric (TE) film and substrate membrane structure. Equations governing the behavior of the laminated PSTE structure are first derived based on the phenomenological theories of thermoelectricity and piezoelectric semiconductors. Closed form solutions of stress, deformation, electric displacement and electric field are obtained under a steady state thermal gradient and fixed grip end conditions. A parametric study for a zinc oxide (ZnO) PSTE film sandwiched between zirconia (ZrO2) substrate membranes show that both tensile and compressive stresses develop in the ZnO film and all field variables are dramatically influenced by the pyroelectric constant.

Effective polarization of ferroelectric materials by using a triboelectric nanogenerator to scavenge wind energy

Effective polarization of ferroelectric materials can be achieved by utilizing a conventional high-voltage polarization equipment with a high voltage but a large volume. Here, we report that the polarization of a ferroelectric BaTiO3 material can be realized by using a triboelectric nanogenerator (TENG) to scavenge ambient wind energy, where the TENG is ideal for providing a higher voltage, a smaller current, and especially a smaller volume. Both the output voltage and current signals of TENG can be adjustable by controlling different wind speeds, where the TENG can deliver an output voltage pulse (<10 ms in period) of about 1000 V and an output current pulse of smaller than 100 µA under a wind speed of about 14 m/s. A piezoelectric constant of larger than 150 pC/N and a pyroelectric constant of larger than 14 nC/cm2 K were achieved by using a TENG to polarize the ferroelectric BaTiO3 material. A handheld TENG can be also utilized to polarize the ferroelectric material, demonstrating the possibility of obtaining small-scale high-voltage polarization equipments.

Enhanced pyroelectric property of PMN–PT/P[VDF–TrFE] thick film by optimizing poling temperature

Lead magnesium niobate–lead titanate (PMN–PT) ceramic powder and Poly[VinyliDeneFluoride-co-TriFluoroEthylene] (P[VDF–TrFE]) have been used to fabricate 0–3 composites thick films on ITO substrates by tape casting. The phase structure and grain size of PMN–PT were analyzed by XRD and SEM. The distribution of ceramic powder in polymer matrix was characterized by SEM. In order to find out the optimal poling temperature, dielectric-temperature spectrums of the composite films were measured to calculate the electric field applied to the ceramic phase (Ec). Finally, PMN–PT/P[VDF–TrFE] composite films were polarized by one-step polarization under optimized polarization temperature and their pyroelectric constant were compared with these of samples poled using conventional two-step polarization method. The results showed that the pyroelectric coefficient increases to 58.6 μC m−2 K−1 at a ceramic mass fraction of 55% at the optimized polarizing temperature 110 °C.

Signature of multiferroicity and pyroelectricity close to room temperature in BaFe12O19 hexaferrite

In this paper, we have reported the signature of multiferroicity and pyroelectricity in BaFe12O19 hexaferrite close to room temperature. The BaFe12O19 hexaferrite samples are synthesized by co-precipitation method at different sintering temperature ranging from 800 to 1200°C and study their structural, ferroelectric, magnetic, magnetoelectric and pyroelectric properties. X-ray Diffraction patterns show the pure phase formation for all samples. Morphological changes are examined through the scanning electron microscope. The maximum ferroelectric polarization (0.66μC/cm2) is observed for the sample sintered at 1200°C, however maximum magnetic polarization 74emu/g is observed for sample sintered at 1000°C. Magneto-electric coupling measurements are also performed through dynamic method and average magneto-electric coupling coefficient (~ 7.05 × 10−7mV/cmOe2) is observed at room temperature for the sample sintered at 1200°C. Furthermore, maximum pyroelectric constant (147 × 10−13C/cm2°C) is observed at 75°C for BaFe12O19 samples sintered at 1200°C. The observation of both multiferroicity and pyroelectricity close to room temperature in BaFe12O19 hexaferrite is interesting and useful for multifunctional devices.

Pb(ZrTi)0.98Mn0.02O3 weight ratio effects on the properties of Pb(ZrTi)0.98Mn0.02O3/P(VDF-TrFE) composite film and infrared detectors

The effect of Pb(ZrTi)0.98Mn0.02O3 (PZTM) weight ratio on the properties of PZTM/P(VDF-TrFE) pyroelectric composites and devices was reported in this paper. Infrared devices were fabricated using PZTM/P(VDF-TrFE) composite films with different weight ratio. The pyroelectric coefficient, the dielectric properties and the infrared absorptivity of the composite materials have been measured. It was found that the pyroelectric constant of the composite decreased as PZTM weight increased. In contrast, the dielectric permittivity increased as PZTM weight increased. Especially, the composite with 0.41 PZTM weight ratio showed the smallest dielectric loss and largest infrared absorptivity. The properties of the detectors fabricated using the composite materials with different PZTM weight ratio have been further tested. It was found that the infrared irradiation absorptivity showed great impact on the performance of the devices other than the pyroelectric coefficient and dielectric permittivity.

Improved pyroelectric performance for thin film lead zirconate titanate (PZT) capacitors with IrO2 electrodes

A four orders-of-magnitude reduction in high temperature leakage current was realized through the use of IrO2 top electrodes in thin film lead zirconate titanate capacitors which has been shown to directly impact the performance of future energy conversion applications. Pyroelectric energy conversion is enhanced near the material Curie temperature, but elevated leakage current in this temperature range hinders current applications. Conductivity experiments varying temperature, composition, and applied bias showed that oxygen vacancy hopping dominates the leakage current in the thin film capacitors above 200 °C. IrO2 top electrodes allow for a reduction in vacancy concentration by allowing for oxygen to be reintroduced during a post-processing annealing step for the thin film. The power lost to leakage current through the pyroelectric conversion cycle is explored. Improvements in remnant polarization and pyroelectric constant are also realized.

Preparation of High β-Phrase Poly(Vinylidene Fluoride) Thin Film by Doping Hydrated Magnesium Nitrate

In this study, the high β-phrase poly(vinylidene fluoride) (PVDF) thin film was spin-coated from a solution that contained microscale hydrated magnesium nitrate. Fourier transform infrared spectroscopy (FT-IR) was used to study influence of the hydrated magnesium nitrate on crystallization behavior of PVDF thin films. As indicated, the presence of hydrated magnesium nitrate promotes the formation of β crystal phase, the desired ferroelectric phrase, in PVDF films. Further, the surface topography, the relative permittivity, as well as its pyroelectric constant and leakage current of PVDF thin films were characterized. At room temperature, in the range of 1Hz∼106Hz, the relative permittivity constant and the dielectric loss of PVDF thin films with different hydrated magnesium nitrate concentrations exhibited similar curve trend, the dielectric properties of PVDF films weren't changed by doping hydrated magnesium nitrate. However, the pyroelectric constant was improved by doping hydrated magnesium nitrate because of the high β phrase. This reveals that the PVDF thin films with high figures of merit (Fv and Fd) could be applied in pyroelectric detector.

Hot plate annealing at a low temperature of a thin ferroelectric P(VDF-TrFE) film with an improved crystalline structure for sensors and actuators.

Ferroelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymer 70/30 thin films are prepared by spin coating. The crystalline structure of these films is investigated by varying the annealing temperature from the ferroelectric phase to the paraelectric phase. A hot plate was used to produce a direct and an efficient annealing effect on the thin film. The dielectric, ferroelectric and pyroelectric properties of the P(VDF-TrFE) thin films are measured as a function of different annealing temperatures (80 to 140 °C). It was found that an annealing temperature of 100 °C (slightly above the Curie temperature, Tc) has induced a highly crystalline β phase with a rod-like crystal structure, as examined by X-ray. Such a crystal structure yields a high remanent polarization, Pr = 94 mC/m2, and pyroelectric constant, p = 24 μC/m2K. A higher annealing temperature exhibits an elongated needle-like crystal domain, resulting in a decrease in the crystalline structure and the functional electrical properties. This study revealed that highly crystalline P(VDF-TrFE) thin films could be induced at 100 °C by annealing the thin film with a simple and cheap method.

A Novel Sol-Gel Method of Preparation of the LiTaO3 Thin Film and Its Property Research

The dielectric constant and the dielectric loss of the LiTaO3 thin film derived through the experimental method which is called the Sol-Gel method, as well as its pyroelectric constant and ferroelectric hysteresis loop are explored in the manuscript. In comparison, the dielectric constant and the dielectric loss of the annealed LiTaO3 thin film derived from Pt(111)/SiO2/Si(100) substrate are superior to which are derived from Fluorine-doped tin oxide substrate. The relationships among ferroelectric hysteresis loop and pyroelectric constant as well as temperature are measured. In room temperature, the dielectric constant of LiTaO3 film is 45 at a frequency of 10 kHz, the dielectric loss is lower 0.006 than dielectric constant, The remanent polarization is 10.71 μC·cm−2. The pyroelectric coefficient is 1.43×10−8 C·cm−2·K−1 at 62 oC. This proves that the LiTaO3 thin films with high figures of merit (FV = 0.56×10−10 C·cm·J−1, FD = 0.51×10–8 C·cm·J−1) can be used widely in thermal detectors.

Pyroelectric Properties of Highly Ordered Pb(Sc0.5Ta0.5)O3 Ceramics by a Two-Step Sintering Technique

Dense Pb(Sc0.5Ta0.5)O3 (PST) ceramics were fabricated by a two-step sintering technique. X-ray diffraction analysis showed that the order of degree is 0.91 and micrograph indicated that the grain size is 1–3 μm. Under dc bias of 700 V/mm, the detective figure of merit reaches over 70 × 10−5 Pa−1/2, where the pyroelectric coefficient, dielectric constant, and dielectric loss are 650 × 10−8 C·(cm2·K)−1, 6600, and 0.019, respectively. Such superior pyroelectric properties and fine grain size give it a particular advantage in application for uncooled focal plane array detectors.

Pyroelectric surface charge in hydroxyapatite ceramics

Surface charge of pyroelectric nature is measured in poled hydroxyapatite ceramics. The average pyroelectric constant can range from 0.1 to 40 nC cm−2 K−1 at temperatures of 300–500 °C, while at 27–60 °C the value ranges from 15 to 64 nC cm−2 K−1. The higher temperature values are comparable to conventional pyroelectric ceramics such as LiTaO3 or PZT. The lower temperature values are four orders higher than those observed in bone and tendon.

Ferroelectric behavior and structural change of poly(trimethylene terephthalate) induced by external electric field

AbstractThe ferroelectric behavior and structural change induced by the external electric field were observed for poly(trimethylene terephthalate) (PTT), which has nonpolar crystalline structure with carbonyl groups aligned antiparallel to each other. The displacement‐electric field hysteresis curves of PTT films showed hysteresis above 140 °C, which indicated the polarization reversal of PTT. The pyroelectric constant and thermally stimulated depolarization current suggest the depolarization of the polar structure of PTT induced by the external electric field above 150 °C. An endothermic peak caused by the depolarization was also observed in the differential scanning calorimetry for the PTT film poled at 30 MV/m. The change of the crystalline structure and the orientation of carbonyl groups induced by the electric filed were investigated by X‐ray diffraction patterns and infrared spectra. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1991–1996, 2009

Characterization of the Dielectric and Pyroelectric Properties of Ferroelectric Material

Ferroelectrics are suitable for the realization of sensors because their characteristics depend on modifying quantities such as temperature, electric fields, and pressure. The dependence of the dielectric and pyroelectric constant of ferroelectric materials on temperature is large and close to the Curie temperature, and this behavior can be exploited for the realization of capacitive sensors with high sensitivity in such a range of temperature. In this paper, a convenient solution for the investigation of the dielectric and pyroelectric coefficients of a ferroelectric device is discussed, along with a characterization tool developed to measure them. The architecture adopted was developed to study the aforementioned material properties up to the Curie temperature. A general-purpose data acquisition card and instruments usually available in research and educational laboratories were used, thus guaranteeing the low-cost feature, easy reproducibility, and flexibility.

High Piezoelectric Activity in Nonpoled Thin Films Prepared by Vapor Deposition Polymerization

The piezoelectric constant of 50 pm V-1 and pyroelectric constant of 20 µC m-2 K-1 were obtained for polyurea thin films (∼300 nm) prepared by vapor deposition polymerization from methane diisocyanate and diaminofluorene. The pyroelectric signal and the infrared spectrum indicate that the dipoles of urea groups in the polymer were highly oriented normal to the surface of the aluminum substrate to induce remanent polarization without a conventional poling process. The piezoelectricity observed for the film is due to the coupling effect of the remanent polarization and electrostriction. No ferroelectric polarization reversal was observed for the film up to 390 K.

Relaxer ferroelectrics as promising materials for IR detectors

The dielectric and pyroelectric properties of a typical relaxer ferroelectric, 0.9PbMg1/3Nb2/3O3-0.1PbTiO3 (PMN-PT), are studied experimentally. Based on the results obtained, the pyroelectric constant and figure of merit of the material when used in IR detectors are calculated. These parameters are presented as a function of temperature and external electric field. The current and voltage sensitivities and the detectivity of PMN-PT-based IR detectors are evaluated. They are compared with the same properties of pyroelectric detectors and dielectric bolometers that use traditional pyroelectric materials as the active element and also of other uncooled photodetectors.

Properties of Sol–Gel Derived (Polyvinylidene Fluoride/Lead Titanate) Pyroelectric Bilayer Thin Films

Ferroelectric polymer/ceramic bilayer thin films composed of polar β-phase polyvi-nylidene fluoride (PVDF) and 1-µm-thick polycrystalline lead titanate (PbTiO3) thin films were prepared, using a sol–gel method. The influence of various processing parameters on the characteristics of PVDF/PbTiO3 thin films was studied by varying the thickness of PVDF thin films (100–580 nm). The results show that the surface of the obtained PVDF film was smooth with less lower porosity above the PbTiO3 film, enabling a significant decrease in the leakage current of bilayer thin films. Although the coercive field (Ec), remanent polarization (Pr) and pyroelectric constant (p) of bilayer thin films decreased with the increase of PVDF thin film thickness, the deposition of PVDF thin films onto the PbTiO3 films caused the leakage current (J) measured at 40 kV/cm to decrease from 1.57 ×10-6 A/cm2 to 3.86 ×10-7 A/cm2 as well as the relative dielectric constant (εr) from 63 to 20. The figures of merit (FV and Fm) due to relative low-dielectric constant (εr) revealed that good infrared responses of bilayer thin films can be utilized in their application to detectors.

Preparation and Characterization of Ba1-xSrxTiO3 Based Thin Films for Pyroelectric Applications

ABSTRACTThe use of pyroelectric thin films in uncooled IR detectors has many advantages over the present IR detector technology, which requires extensive cooling for operation. These advantages include reduced weight, reduced footprint, reduced complexity, increased reliability, and decreased maintenance. Ba1-xSrxTiO3 (BST), based thin films are ideal candidates for use in these devices due to their tailorable materials properties. These properties include a high dielectric constant, low dielectric loss, high electrical resistivity, as well as a high pyroelectric constant. BST thin films were doped with Mg in varying amounts, from 0 to 20mol%. The thin films were deposited via metalorganic solution deposition (MOSD) on Pt/Ti/SiO2/Si substrates. Annealing temperatures ranged from 500 to 750 °C. The films were characterized for structural, microstructural, compositional, surface morphological, dielectric and insulating properties. Glancing angle x-ray diffraction (GAXRD) was used to determine crystallinity, phase formation and film orientation. Field emission scanning electron microscopy (FESEM) and cross sectional transmission electron microscopy (TEM) were employed to access surface morphology and microstructure. The Materials Detectivity Figure of Merit (FOM), D*, [D*=pi/(CV(ε0εrtanδ)1/2] was used to evaluate the film's detectivity response. Our results show that undoped Ba60Sr40TiO3, with a value D*= 0.08 (cm3/J)1/2, appears to out perform Pb based pyroelectric thin films, thus making it a viable candidate for IR pyroelectric detector applications.

Nonelectrical poling in ferroelectric polythioureas

A new poling method utilizing the cooperativity and strong hydrogen bonding force of thiourea groups is proposed in ferroelectric polythioureas [poly(octamethylene thiourea) and poly(nonamethyleno thiourea)]. The method, which is named "surface energy poling," takes advantage of the surface energy difference of the polar amorphous material to form remanent polarization. A polythiourea film sandwiched between a metal with higher surface energy and polytetrafluoroethylenes with lower surface energy was heated up to T/sub c/ [1.15/spl times/T/sub g/ (glass transition temperature)] and cooled slowly to room temperature. The resulting film showed a pyroelectric constant of 10 /spl mu//m/sup 2/K, giving evidence of remanent polarization. This method is similar to the orientation process in liquid crystal devices.

Dielectric and pyroelectric studies of an antiferroelectric liquid crystal

Polymorphism and polar properties of an antiferroelectric (R)-2-methylheptyloxycarbonylphenyl-4-[(4-decyloxy-3-fluoro)benzoyloxy]benzoate liquid crystal are studied. The phases are identified, and the phase transition points are determined. Dielectric constant, dielectric losses, and pyroelectric properties are studied for the orthogonal smectic SmA and tilted smectic, SmCα*, SmC*, SmCγ*, and SmCA* phases. The temperature dependence of spontaneous polarization is measured by the repolarization current technique and integration of the pyroelectric constant.