Papers by Keyword: Pyroelectricity

Abstract: The removal of dyes and pathogens from contaminated water remains a significant challenge. In the present study, NaNbO₃ and NaNbO₃/Bi₂S₃ powders were prepared by a simple hydrothermal method, and then the noble metal Ag was successfully deposited on NaNbO₃/Bi₂S₃ by photoreduction to constitute the NaNbO₃/Bi₂S₃/Ag ternary nanorods heterostructure. With continuous visible light irradiation and controlled temperature variation (25-55 °C), the monomeric NaNbO₃ could degrade 73.3% of Rhodamine B (RhB) and inactivated 46% of Salmonella while the ternary complex NaNbO₃/Bi₂S₃/Ag showed a higher RhB degradation efficiency of 94.9% as well as an higher sterilization efficiency of 82%. In addition, after four replicate experiments, NaNbO₃/Bi₂S₃/Ag still had a high degradation efficiency. Compared with NaNbO₃ monomer, NaNbO₃/Bi₂S₃/Ag possessed stronger catalytic ability. The improvement of catalytic activity could be attributed to the efficient separation of pyroelectric and photocatalytic electrons and holes through the formation of NaNbO₃/Bi₂S₃/Ag heterostructural nanorod. Keywords: Ternary heterostructures; Nanocomposites; Pyroelectricity; RhB solution degradation; Salmonella sterilization

Abstract: X-ray emission using pyroelectric crystals is intermittent, and has low intensity and stability. One of the factors for low stability is related to creeping discharge, due to the accumulation of surface electric charges that change in response to the temperature. The time dependence of the net amount of electric charge was investigated by changing the cycle period of the crystal temperature. The stability of the X-ray emission is demonstrated to be strongly dependent on the temperature cycle period.

Abstract: The mechanism of pryoelectric-induced X-ray emission in LaTiO₃ crystals is discussed. It is suggested that electrons which contribute to the X-ray emission were generated around and close to the crystal and were emitted from the z surface. The poor reproducibility was found to be due to a creeping electrostatic discharge. It is speculated that one of the factors of the discharge is the accumulation of positive charges on the z surface.

Abstract: A three-dimensional pattern is helpful to improve the temperature variation rates in pyroelectric elements, using lateral temperature gradients induced on the sidewalls of the responsive elements. Creating a complex pattern with a deep trench structure for fitting various discharges of waste heat was imperative, and hard to fabricate, using the traditional methods of dry/wet etching and a dicing saw. A novel method using sandblast etching was successful in fabricating the complex pattern of the vortex-like electrode for improving the electrical output and enhancing the efficiency of the PZT pyroelectric harvesting converters.

Abstract: Pyroelectric sensors based on PVDF polymers have great potentialities in the practical areas because of their great merits in the high converting efficiency from caloric or kinetic energy to the electric signal, as well as light-weight and flexibility. This work emphasized on the simulation of the PVDF pyroelectric sensor on the circuit level. The presented equivalent circuit model was simulated with the combination of the whole testing circuit in the environment of Multisim, so the simulated data could be comparable with the measured ones. And the validity of this PVDF sensor’s Multisim model was testified by the comparison with experimental data. Moreover, thermoelectric energy conversion was discussed by the extracted parameters in the equivalent circuit.

Abstract: Trenching PZT material in a thicker PZT pyroelectric cell to improve the temperature variation rate was proposed in this study to enhance the efficiency of thermal energy-harvesting conversion by pyroelectricity. A thicker pyroelectric cell is beneficial in generating electricity pyroelectrically, but it opposes rapid temperature variations. Therefore, the PZT sheet was fabricated to produce deeper trenches to cause lateral temperature gradients induced by the trenched electrode, enhancing the temperature variation rate under homogeneous heat irradiation. When the trenched electrode type with an electrode width of 200 μm and a cutting depth of 150 μm was used to fabricate the PZT pyroelectric cell with a 200 μm thick PZT sheet, the temperature variation rate was improved by about 55%. Therefore, the trenched electrode design did indeed enhance the temperature variation rate and the efficiency of pyroelectric energy converters.

Abstract: Lead strontium zirconate titanate (Pb_0.92Sr_0.08)(Zr_0.65Ti_0.35)O₃ (PSZT) thin films were grown on Pt (111)/Ti/SiO₂/Si(100) substrates using a simple sol-gel method. X-ray diffraction studies confirmed that all the PSZT films undergone various thermal process show highly preferred (001)-orientation. On the surface image of the thin film, many clusters are found, which are composed by grains in size of 0.5-0.8 mm. Between the clusters, the nano-size grain is about 50-80 nm. The root mean square (RMS) roughness of the film surfaces is 5.1 nm. PSZT thin film exhibit excellent ferroelectric behavior, demonstrated by reproducible hystersis loops with high remnant polarization (P_r =49 μC cm^-2) and relative low coercive field (E_c=53.5 kV cm^-1). The pyroelectric coefficients (p) were measured, at 26 °C, the p=215 mC m^-2 K^-1 for PSZT films. The dielectric properties as well as phase transition behavior were characterized and a ferroelectric to paraelectric transition were found in the vicinity of 196 °C.

Abstract: Three and six LiTaO₃ single crystals are used to achieve continuous emission of high-intensity X-rays. Furthermore, the interaction between X-rays and the case of the X-ray source is used to generate electrons. X-rays were emitted continuously and fluctuations in the count rate were reduced when three or six crystals were used. Moreover, the X-ray intensity increased and the number of electrons generated by the above-mentioned interaction increased with increasing number of crystals.

Abstract: X-ray radiation using pyroelectric crystal is intermittent and the X-ray intensity is low and unstable compared with a conventional X-ray radiation method, such as X-ray tube. It is expected that the X-ray intensity becomes stable if electric field intensity and supply of electron are stable. In this study, to use X-ray radiation equipment as an electron source, tandem-type X-ray radiation equipment which is composed of two LiNbO3 single crystals polarized in a z-axis is proposed. When the temperature gradient for each crystal was the same, the X-ray intensity became approximately 6 times higher at a maximum. When the temperature gradient for each crystal was reversed, the period of X-ray radiation became approximately two times longer and the X-ray intensity became approximately 20 times higher at a maximum. Moreover, the stability of X-ray radiation for the repetition of temperature could be improved.

Abstract: The gas pressure and the types of ambient gas dependence of X-ray intensity were investigated for LiNbO3 single crystals polarized in the c-axis direction at pressures of approximately 1 to 30 Pa. The integrated X-ray intensity showed a local maximum value at the pressure Pmax. Pmax moved to the high-pressure side in the ambient with a large first ionization energy. Pmax was proportional to the Boltzmann factor using the first ionization energy of each ambient gas molecule. The X-ray intensity was approximated using the quadratic function, which was convex upward for the pressure. It was found that one of the causes of the decrease in X-ray intensity on the pressure side higher than Pmax was the adsorption of positive ions on the crystal electric surface.