Improvement of Pyroelectric Cells for Thermal Energy Harvesting

This study proposes trenching piezoelectric (PZT) material in a thicker PZT pyroelectric cell to improve the temperature variation rate to enhance the efficiency of thermal energy-harvesting conversion by pyroelectricity. A thicker pyroelectric cell is beneficial in generating electricity pyroelectrically, but it hinders 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 a 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

DEVELOPMENT OF INFRARED AND TERAHERTZ BOLOMETERS BASED ON PALLADIUM AND CARBON NANOTUBES USING ROLL TO ROLL PROCESS

Terahertz region in the electromagnetic spectrum is the region between Infrared and Microwave. As the Terahertz region has both wave and particle nature, it is difficult to make a room temperature, fast, and sensitive detector in this region. In this work, we fabricated a Palladium based IR detector and a CNT based THz bolometer. In Chapter 1, I give a brief introduction of the Terahertz region, the detectors already available in the market and different techniques I can use to test my detector. In Chapter 2, I explain about the Palladium IR bolometer, the fabrication technique I have used, and then we discuss the performance of the detector. In Chapter 3, I explained about the Roll to Roll based THz bolometer, its working and fabrication techniques, and at the end we discussed its performance

Pyroelectric and electrocaloric effects in hafnium oxide thin films

The material class of hafnium oxide-based ferroelectrics adds an unexpected and huge momentum to the long-known phenomenon of pyroelectricity. In this thesis, a comprehensive study of pyroelectric and electrocaloric properties of this novel ferroelectric material class is conducted. hafnium oxide is a lead-free, non-toxic transition metal oxide, and abundant in the manufacturing of semiconductor devices. The compatibility to existing fabrication processes spawns the possibility of on-chip infrared sensing, energy harvesting, and refrigeration solutions, for which this dissertation aims to lay a foundation. A screening of the material system with respect to several dopants reveals an enhanced pyroelectric response at the morphotropic phase boundary between the polar orthorhombic and the non-polar tetragonal phase. Further, a strong pyroelectric effect is observed when applying an electric field to antiferroelectric-like films, which is attributed to a field-induced transition between the tetragonal and orthorhombic phases. Primary and secondary pyroelectric effects are separated using high-frequency temperature cycles, where the effect of frequency-dependent substrate clamping is exploited. The piezoelectric response is determined by comparing primary and secondary pyroelectric coefficients, which reproduces the expected wake-up behavior in hafnium oxide films. Further, the potential of hafnium oxide for thermal-electric energy conversion is explored. The electrocaloric temperature change of only 20 nm thick films is observed directly by using a specialized test structure. By comparing the magnitude of the effect to the pyroelectric response, it is concluded that defect charges have an important impact on the electrocaloric effect in hafnium oxide-based ferroelectrics. Energy harvesting with a conformal hafnium oxide film on a porous, nano-patterned substrate is performed, which enhances the power output. Further, the integration of a pyroelectric energy harvesting device in a microchip for waste heat recovery and more energy-efficient electronic devices is demonstrated. High dielectric breakdown fields of up to 4 MV/cm in combination with a sizable pyroelectric response and a comparably low dielectric permittivity illustrate the prospect of hafnium oxide-based devices for future energy conversion applications

NASA patent abstracts bibliography: A continuing bibliography. Section 1: Abstracts (supplement 19)

Abstracts are cited for 130 patents and patent applications introduced into the NASA scientific and technical information system during the period of January 1981 through July 1981. Each entry consists of a citation, an abstract, and in most cases, a key illustration selected from the patent or application for patent

Structural studies of lead-free piezoelectrics with the fresnoite structure type

The lead free piezoelectric fresnoite A2M3O8 (A = Ba, Sr, K, Cs; M = Ti, V, Si, Ge) modulated structure type has been investigated owing to its potential to exhibit excellent piezoelectric response coefficients. Ba2TiSi2O8, Sr2TiSi2O8, and Ba2TiGe2O8 end members in addition to members of the Ba2xSr2-2xTiSi2O8, Ba2xSr2 2xTiGe2O8, Ba2TiGe2ySi2 2yO8, and BaSrTiGe2ySi2 2yO8 series were synthesised and characterised using a combination of variable temperature diffraction techniques. The Ba2TiSi2O8 and Sr2TiSi2O8 modulated structures at ambient temperature were characterised using neutron powder diffraction for the first time. Variable temperature synchrotron X ray diffraction data showed a new means of identifying the incommensurate to prototypic structural phase transition at 433 K. Resonant ultrasound spectroscopy has shown coupling between the elastic moduli and structural changes in fresnoite samples. Polycrystalline Sr2TiSi2O8 samples were shown to undergo a first order phase transition from a two phase mixture of incommensurately modulated tetragonal and orthorhombic phases to a single incommensurately modulated orthorhombic phase that is complete by 567 K. The proportion of the orthorhombic phase Sr2TiSi2O8 samples was shown to slowly decrease on cooling to 125 K. The Sr2TiSi2O8 structure was also shown to undergo an additional phase transition from the incommensurately modulated orthorhombic phase to a tetragonal phase at 1323 K for the first time. The inclusion of barium or germanium into the Sr2TiSi2O8 structure was shown to suppress the formation of the orthorhombic phase at ambient temperature and elevated temperatures. New phase diagrams for the Ba2xSr2-2xTiSi2O8 and Sr2TiGe2ySi2 2yO8 systems summarise the phase transitions investigated. The intrinsic piezoelectric coefficients were calculated to be approximately 5 pm V 1 and 27 pm V 1 for polycrystalline samples of Ba2TiSi2O8 and Sr2TiSi2O8 respectively and compared to common piezoelectric materials