Pyroelectric materials

This paper presents a review of pyroelectric materials. The physics of pyroelectric materials is described. Various pyroelectric materials are compared for their efficiency in the detection of radiation. Current trends in pyroelectric material technology are highlighted.     

Low-temperature pyroelectric properties of Li<Subscript>2</Subscript>SO<Subscript>4</Subscript>

The pyroelectric properties of lithium sulfate have been studied theoretically on the hypothesis of a pseudosymmetry of the structure of its polar phase. Analytical expressions are proposed for the temperature dependences of its pyroelectric polarization and pyroelectric coefficient at low temperatures and near the polymorphic transformation. The pyroelectric and piezoelectric coefficients of a polar crystal are shown to be in direct proportion.     

TGS和GTGS热释电晶体的热力学模型模拟曲线

通过热力学推导,建立了零电场下热释电晶体的极化与温度的方程。由热释电系数的定义,对热释电晶体的极化方程对温度求导,得出由热力学模型建立的热释电方程。并对热释电晶体硫酸三甘氨酸（TGS）和掺胍TGS（GLTGS）的实验曲线进行了模拟,该理论基本符合。     

Frequency response of multilayer pyroelectric sensors

The pyroelectric response of the multilayer system consisting of the front surroundings, the pyroelectric element, the intermediate layer, and the back surroundings is calculated. The general expression and simple relations are obtained between main geometric and thermophysical parameters of the system under consideration and characteristics of the pyroelectric response in a large variety of configurations of pyroelectric sensors, such as detectors with the pyroelectric element in a gas, detectors without air gap as well as detectors with air gap between the element and the substrate, and detectors in immersion systems, etc. In particular, it is shown that, for the detectors with air gap, the wide flat part of the frequency response appears with any properties of substrate if the double thermal resistance of the air gap exceed that of the pyroelectric element, whereas for the detectors without air gap it appears only if the substrate has relatively large complex thermal conductivity.     

Pyroelectric response to step radiation signals in thin ferroelectric films on a substrate

We describe theoretical and experimental investigations of thermal transient phenomena in pyroelectric films on a substrate, on which a rectangular laser light is projected. The transient distribution of pyroelectric films is calculated as a function of time, space, substrate and film thickness, and is discussed for the case of pyroelectric current. A critical film thickness d_cr was found for which the pyroelectric current reaches an extreme value.     

Polarization processes in pyroelectric Langmuir-Blodgett films

We report on an investigation into the origins of the pyroelectric effect in some alternate layer Langmuir-Blodgett (LB) films. The pyroelectric coefficient is measured as a function of temperature and of the thermal expansion coefficient of the substrate on which the film is deposited; these experiments enable a partial separation of the primary and secondary pyroelectric effects. The results indicate that thermal expansion of the substrate tends to reduce the total pyroelectric coefficient through a piezoelectrically induced effect. At low temperatures, the film behaves like a “free crystal”, and the pyroelectric coefficient shows a power law dependence on temperature. However, at temperatures above 240 K, the substrate- induced effect becomes dominant. The results are used to deduce methods by which the pyroelectric response of the LB film devices might be improved.     

Ferroelectric emission studies for electron emission lithography applications

Ferroelectric switching emission, dielectric switching emission, and pyroelectric emission were studied by patterning images on electron resist for electron emission lithography applications. It was observed that the pyroelectric emission is most acceptable for a high throughput 1:1 electron projection lithography application. A 1:1 electron projection lithography was demonstrated by patterning images with line widths of 30 /spl mu/m and using pyroelectric emission. A degradation of the pyroelectric emission property of the material was observed during repeated heating cycles below the phase-transition temperature of the ferroelectric material. Annealing excursions above the phase transition temperature prevented the degradation of the pyroelectric emitter.     

PZT和PT陶瓷的热释电效应与晶格参数的关系

测量了锆钛酸铅（PZT和钛酸铅（PT）陶瓷材料的热释电效应，利用X射线衍射测量了陶瓷材料在不同温度下晶格结构变化，研究了PZT和PT陶瓷材料的热释电效应与晶格参数之间的相互关系，实验表明，陶瓷材料的热释电系数的大小与晶格参数随温度变化的情形有关，c轴与c／a比随温度变化大的材料，其热释电系数较高．     

Bicell Pyroelectric Optical Detector Made from a Single LiNbO(3) Domain-Reversed Electret

Using electric-field poling at room temperature, we selectively reversed the direction of the spontaneous polarization in a 200-mum-thick, z-cut LiNbO(3) electret to produce a bicell pyroelectric detector. The detector required only a single set of electrodes, one electrode on the front surface and one on the back surface. Microphonic noise that is typical of monocell pyroelectric detectors is reduced in the present device. Our spatial uniformity data indicate that the optical response of one half of the bicell detector area was equal to and opposite the other half within 1.2%. The microphonic suppression of the bicell pyroelectric detector was less than -36 dB from 10 to 50 Hz and less than -118 dB at 35 Hz of that of a reference monocell pyroelectric detector. The substrate thickness is significantly greater than those of other domain-engineered pyroelectric detector designs and allows us to build practical, large-area detectors for radiometric applications.     

PZT和PT陶瓷的热释电效应与晶格参数的关系

测量了锆钛酸铅（ＰＺＴ）和钛酸铅（ＰＴ）陶瓷材料的热释电效应，利用Ｘ射线衍射测量了陶瓷材料在不同温度下晶格结构变化，研究了ＰＺＴ和ＰＴ陶瓷材料的热释电效应与晶格参数之间的相互关系，实验表明，陶瓷材料的热释电系数的大小与晶格参数随温度变化的情形有关，ｃ轴与ｃ／ａ比随温度变化大的材料，其热释电系数较高。     

PCLT/P(VDF-TrFE) 0–3 nanocomposite thin films for pyroelectric applications

 Nanocrystalline calcium and lanthanum modified lead titanate (PCLT) powder was prepared by a sol-gel process followed by annealing at 850°C. 0–3 nanocomposite thin films of PCLT powder dispersed in a vinylidene fluoride /trifluoroethylene (P(VDF-TrFE)) copolymer matrix were fabricated on glass substrates using the spin-coating technique. The permittivity, pyroelectric coefficient, specific heat and pyroelectric figures-of-merit were measured as functions of the volume fraction (φ) of ceramic for φ up to 0.16. Single-element pyroelectric sensors with PCLT/P(VDF-TrFE) nanocomposites as the sensing elements were fabricated and characterized. The voltage and current responsivities R_v and R_i of the sensors were measured as functions of frequency and found to agree well with the calculated values. Since the pyroelectric coefficients of PCLT and P(VDF-TrFE) have like signs while the piezoelectric coefficients have opposite signs, the poled composite has high pyroelectric but low piezoelectric activity, thereby reducing the vibration-induced electrical noise in pyroelectric sensor applications. Received: 21 July 1998 / Reviewed and accepted: 22 October 1998     

Novel pyroelectric sensor materials

Ceramic compositions of barium strontium titanium oxide (BSTO) have been formulated for applications as pyroelectric sensor materials. The material has been fabricated in tape-cast and thin film forms. In general, the materials demonstrated high pyroelectric coefficients (p) accompanied with low dielectric constant and low dissipation factor. The compositions of the tape-cast and thin film specimens examined in this paper include a well-known commercially adopted Ba_0.64Sr_0.36TiO₃ as well as a composition suggested in the literature, and a patented composition with the addition of MgO to BSTO is investigated. Doping BSTO with MgO has been shown to reduce the dielectric constant and loss tangent (over a very wide frequency range from 100 Hz-10 GHz) of the material and thereby increase the pyroelectric figure of merit. This article will discuss the processing, material characterization, pyroelectric coefficient, and pyroelectric figure-of-merit of the above mentioned BSTO compositions.     

Infrared responsivity of a pyroelectric detector with a single-wall carbon nanotube coating

The performance of a 10 mm diameter pyroelectric detector coated with a single-wall carbon nanotube (SWCNT) was evaluated in the 0.8 to 20 microm wavelength range. The relative spectral responsivity of this detector exhibits significant fluctuations over the wavelength range examined. This is consistent with independent absorbance measurements, which show that SWCNTs exhibit selective absorption bands in the visible and near-infrared. The performance of the detector in terms of noise equivalent power and detectivity in wavelength regions of high coating absorptivity was comparable with gold-black-coated pyroelectric detectors based on 50 microm thick LiTaO(3) crystals. The response of this detector was shown to be nonlinear for DC equivalent photocurrents >10(-9) A, and its spatial uniformity of response was comparable with other pyroelectric detectors utilizing gold-black coatings. The nonuniform spectral responsivity exhibited by the SWCNT-coated detector is expected to severely restrict the use of SWCNTs as black coatings for thermal detectors. However, the deposition of SWCNT coatings on a pyroelectric crystal followed by the study of the prominence of the spectral features in the relative spectral responsivity of the resultant pyroelectric detectors is shown to provide an effective method for quantifying the impurity content in SWCNT samples.     

Optically Governed Dynamic Surface Charge Redistribution of Hybrid Plasmo‐Pyroelectric Nanosystems

Though plasmonic effect is making some headway in the energy harvesting realm, its fundamental charge transfer mechanism to a large extent is attributed to the hot‐carrier generation at the contact interface. Herein this work attempts to elucidate the physical origin of light induced plasmo‐pyroelectric enhancement based on charge density manipulation on surface state in the vicinity of the metal–ferroelectric contact interface. More importantly, by tuning the band bending, it is shown that the charge density on the surface state of a hybrid plasmo‐pyroelectric (BaTiO₃‐Ag) nanosystem can be manipulated and largely increased under the resonant blue light illumination (363 nm). It is also demonstrated that owing to this effect, the spatial pyroelectric activity of a hybrid plasmo‐pyroelectric nanosystem governs 46% enhancement in pyroelectric coefficient. This research highlights the optically regulated charge density in plasmo‐pyroelectric nanosystems, which could pave a new avenue for energy harvesting/conversion devices with distinguished advantages in wireless, photonic‐controlled, localized, and dynamic stimulation.     

Dielectric and pyroelectric properties of triglycerol-gelatin films

The dielectric and pyroelectric properties of triglycerol-gelatin thick films were studied as a function of temperature and frequency. The films exhibited a strong dispersion in the dielectric permittivity accompanied by a high dielectric loss near room temperature. The pyroelectric current measured by the static Byer-Roundy method is heavily dominated by the thermally stimulated currents. Measurements performed on prepoled samples using the dynamic technique of A.G. Chynoweth (1956) clearly proved the presence of a true, reversible pyroelectric response in the examined films. The value of the pyroelectric coefficient of the films was found to be comparable to that of polyvinylidene fluoride (PVDF)     

复合相变陶瓷材料的FRL-FRH相变研究

制备了低温铁电菱方相（ＦＲＬ）－高温铁电菱方相（ＦＲＨ）相变复合陶瓷材料，利用计算横模拟了复合陶瓷材料的相变行为，结果表明，在复相陶瓷材料中，存在着离子扩散，离子扩散对于宏观热释电效应的影响取决地相关材料的相变特性，计算机模拟的方法可以有效地用于分析复合的离子扩散情形，为新型功能材料的设计与研究提供帮助。     

Pyroelectric nanogenerators for harvesting thermoelectric energy

Harvesting thermoelectric energy mainly relies on the Seebeck effect that utilizes a temperature difference between two ends of the device for driving the diffusion of charge carriers. However, in an environment that the temperature is spatially uniform without a gradient, the pyroelectric effect has to be the choice, which is based on the spontaneous polarization in certain anisotropic solids due to a time-dependent temperature variation. Using this effect, we experimentally demonstrate the first application of pyroelectric ZnO nanowire arrays for converting heat energy into electricity. The coupling of the pyroelectric and semiconducting properties in ZnO creates a polarization electric field and charge separation along the ZnO nanowire as a result of the time-dependent change in temperature. The fabricated nanogenerator has a good stability, and the characteristic coefficient of heat flow conversion into electricity is estimated to be ～0.05-0.08 Vm(2)/W. Our study has the potential of using pyroelectric nanowires to convert wasted energy into electricity for powering nanodevices.     

钽酸锂薄膜材料及其热释电红外传感器应用研究进展

介绍了钽酸锂薄膜材料及其热释电红外传感器应用研究概况;简要阐述了热释电红外传感器的工作原理;着重分析了钽酸锂薄膜材料的新制备技术,以及在热释电红外传感器应用方面的研究现状;指出了钽酸锂薄膜材料及其热释电红外传感器应用研究发展前景.