Pyroelectric Energy Conversion Research Articles

Improper ferroelectrics as high‐efficiency energy conversion materials

An improper ferroelectric is a certain type of ferroelectrics whose primary order parameter is not polarization but another physical quantity such as magnetization. In contrast to a conventional proper ferroelectrics as represented by Pb(Zr,Ti)O3 and BaTiO3, the improper ferroelectrics has been inconceivable for practical applications thus far. Herein, we illustrate the great potential of improper ferroelectrics for efficient conversion of temperature fluctuation to electric energy, as demonstrated with (Ca0.84Sr0.16)8[AlO2]12(MoO4)2 (CSAM‐16). The present study has experimentally proven that CSAM‐16 achieves an excellent electrothermal coupling factor and high electric field sensitivity for pyroelectric energy conversion that approach a practical level for application to self‐powered autonomous electronic devices for rapidly spreading wireless sensor networks. The present results provide a novel approach to developing innovative pyroelectric energy harvesting devices using improper ferroelectrics.

High Power Density Pyroelectric Energy Conversion in Nanometer-Thick BaTiO3 Films

ABSTRACTSolid-state pyroelectric nanomaterials can be used for thermal-to-electrical energy conversion in the presence of temperature fluctuations. This article reports investigation of energy conversion in a 200 nm thick BaTiO3 film using the pyroelectric Ericsson cycle at cycle frequencies up to 3 kHz. The high cycle frequencies were achieved due to the low thermal mass of the nanometer-scale film, unlike previous studies in which the electrical power output was limited by the rate of heat transfer through the pyroelectric material. A microfabricated platform that allowed precise thermal and electrical cycling enabled us to study the effect of electric field range, temperature oscillation amplitude, and cycle frequency on the electrical power output from pyroelectric Ericsson cycles. We measured a maximum power density of 30 W/cm3 for a temperature range 20–120°C and electric field range 100–125 kV/cm, which represents a significant improvement over past work on pyroelectric cycles. The approach presented in this article could lead to high-power waste heat harvesting in systems with high-frequency temperature oscillations.

Phase transformation based pyroelectric waste heat energy harvesting with improved practicality

In 2014, almost 60% of thermal energy produced in the United States was lost to the environment as waste heat. Ferroelectric based pyroelectric devices can be used to convert some of this waste heat into usable electrical energy using the Olsen cycle, an ideal thermodynamic cycle, but there are a number of barriers to its realization in a practical device. This study uses the Olsen cycle to benchmark a less efficient thermodynamic cycle that is more easily implemented in devices. The ferroelectric pyroelectric material used was (Pb0.97La0.02)(Zr0.55Sn0.32Ti0.13)O3 ceramic, a ferroelectric material that undergoes a temperature driven phase transformation. A net energy density of 0.27 J cm−3 per cycle was obtained from the ferroelectric material using the modified cycle with a temperature change between 25°C and 180°C. This is 15.5% of the Olsen cycle result with the same temperature range and 1–8 MV m−1 applied electric field range. The power density was estimated to 13.5 mW cm−3 with given experimental conditions. A model is presented that quantitatively describes the effect of several parameters on output energy density and can be used to design ferroelectric based pyroelectric energy converters. The model indicates that optimization of material geometry and heating conditions can increase the output power by an order or magnitude.

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.

Ferroelectric phase transitions in nanoscale HfO2 films enable giant pyroelectric energy conversion and highly efficient supercapacitors

Temperature- and field-induced phase transitions in ferroelectric nanoscale TiN/Si:HfO2/TiN capacitors with 3.8 to 5.6mol% Si content are investigated for energy conversion and storage applications. Films with 5.6mol% Si concentration exhibit an energy storage density of ~40J/cm3 with a very high efficiency of ~80% over a wide temperature range useful for supercapacitors. Furthermore, giant pyroelectric coefficients of up to −1300µC/(m2K) are observed due to temperature dependent ferroelectric to paraelectric phase transitions. The broad transition region is related to the grain size distribution and adjustable by the Si content. This strong pyroelectricity yields electrothermal coupling factors k2 of up to 0.591 which are more than one order of magnitude higher than the best values ever reported. This enables pyroelectric energy harvesting with the highest harvestable energy density ever reported of 20.27J/cm3 per Olsen cycle. Possible applications in infrared sensing are discussed. Inversely, through the electrocaloric effect an adiabatic temperature change of up to 9.5K and the highest refrigerant capacity ever reported of 19.6J/cm3 per cycle is achievable. This might enable energy efficient on-chip electrocaloric cooling devices. Additionally, low cost fabrication of these films is feasible by existing semiconductor process technology.

Study on Pyroelectric Harvesters Integrating Solar Radiation with Wind Power

Pyroelectric harvesters use temperature fluctuations to generate electrical outputs. Solar radiation and waste heat are rich energy sources that can be harvested. Pyroelectric energy converters offer a novel and direct energy-conversion technology by transforming time-dependent temperatures directly into electricity. Moreover, the great challenge for pyroelectric energy harvesting lies in finding promising temperature variations or an alternating thermal loading in real situations. Hence, in this article, a novel pyroelectric harvester integrating solar radiation with wind power by the pyroelectric effect is proposed. Solar radiation is a thermal source, and wind is a dynamic potential. A disk generator is used for harvesting wind power. A mechanism is considered to convert the rotary energy of the disk generator to drive a shutter for generating temperature variations in pyroelectric cells using a planetary gear system. The optimal period of the pyroelectric cells is 35 s to harvest the stored energy, about 70 μJ, while the rotary velocity of the disk generator is about 31 RPM and the wind speed is about 1 m/s. In this state, the stored energy acquired from the pyroelectric harvester is about 75% more than that from the disk generator. Although the generated energy of the proposed pyroelectric harvester is less than that of the disk generator, the pyroelectric harvester plays a complementary role when the disk generator is inactive in situations of low wind speed.

Pyroelectric Harvesters for Generating Cyclic Energy

Pyroelectric energy conversion is a novel energy process which directly transforms waste heat energy from cyclic heating into electricity via the pyroelectric effect. Application of a periodic temperature profile to pyroelectric cells is necessary to achieve temperature variation rates for generating an electrical output. The critical consideration in the periodic temperature profile is the frequency or work cycle which is related to the properties and dimensions of the air layer; radiation power and material properties, as well as the dimensions and structure of the pyroelectric cells. This article aims to optimize pyroelectric harvesters by matching all these requirements. The optimal induced charge per period increases about 157% and the efficient period band decreases about 77%, when the thickness of the PZT cell decreases from 200 μm to 50 μm, about a 75% reduction. Moreover, when using the thinner PZT cell for harvesting the pyroelectric energy it is not easy to focus on a narrow band with the efficient period. However, the optimal output voltage and stored energy per period decrease about 50% and 74%, respectively, because the electrical capacitance of the 50 μm thick pyroelectric cell is about four times greater than that of the 200 μm thick pyroelectric cell. In addition, an experiment is used to verify that the work cycle to be able to critically affect the efficiency of PZT pyroelectric harvesters. Periods in the range between 3.6 s and 12.2 s are useful for harvesting thermal cyclic energy by pyroelectricity. The optimal frequency or work cycle can be applied in the design of a rotating shutter in order to control the heated and unheated periods of the pyroelectric cells to further enhance the amount of stored energy.

Toward a multifunctional monolithic device based on pyroelectricity and the electrocaloric effect of thin antiferroelectric HfxZr1−xO2 films

Antiferroelectric HfxZr1−xO2 (HZO, x=0.1–0.3) films are reported herein as new Si-compatible materials for monolithic devices for pyroelectric energy harvesting, electrocaloric cooling, electrostatic energy storage, and infrared sensing. Hf0.2Zr0.8O2 and Hf0.3Zr0.7O2 films could work as pyroelectric energy harvesters using the Olsen cycle with the harvested energy densities of 11.5 and 5.7Jcm−3cycle−1, which are ~7.6 and ~3.7 times larger than the largest value ever reported. The electrocaloric effect (ECE) of HZO films was also firstly examined, and the maximum ΔT values of the Hf0.2Zr0.8O2 and Hf0.3Zr0.7O2 films were 13.4 (at 307K) and 9.8K (at 448K), respectively. The wide temperature range for the large ECE of the HZO films was highly promising for the actual cooling cycle with large reversible work values. Moreover, the large capacitance of the HZO films due to the field-induced phase transition between the poled and anti-poled states can be used for electrostatic energy storage and high-charge capacitors. The k2 and Fv values, which are the figures of merit for conventional pyroelectric energy conversion and infrared detection for thermal imaging, of the Hf0.2Zr0.8O2 film were 24.4×10−3 and 32.0×10−2m2C−1, respectively, which prove that Hf0.2Zr0.8O2 is also a promising material for these applications.

High-frequency thermal-electrical cycles for pyroelectric energy conversion

We report thermal to electrical energy conversion from a 150 nm thick BaTiO3 film using pyroelectric cycles at 1 kHz. A microfabricated platform enables temperature and electric field control with temporal resolution near 1 μs. The rapid electric field changes as high as 11 × 105 kV/cm-s, and temperature change rates as high as 6 × 105 K/s allow exploration of pyroelectric cycles in a previously unexplored operating regime. We investigated the effect of phase difference between electric field and temperature cycles, and electric field and temperature change rates on the electrical energy generated from thermal-electrical cycles based on the pyroelectric Ericsson cycle. Complete thermodynamic cycles are possible up to the highest cycle rates tested here, and the energy density varies significantly with phase shifts between temperature and electric field waveforms. This work could facilitate the design and operation of pyroelectric cycles at high cycle rates, and aid in the design of new pyroelectric systems.

Modulating Frequency and Responsivity of Pyroelectric Energy Converters by Finite Element Analysis

Pyroelectric energy conversion techniques can be used to convert radiated heat, especially in pulsed periodic waveforms, to electric output. Most existing modeling of the response is done through a lumped capacitance heat model which assumes a sufficiently thin sample with adiabatic substrate. A finite element model of a pulsed heat source and the resultant heat distribution is developed to study the optimization of the pyroelectric energy conversion process. The model uses simultaneous analysis of a temperature domain and the attached circuitry for the determination of the voltage responsivity. It is found that the low frequency cutoff of the responses is limited by the thermal time constant of the pyroelectric elements including the sample and the substrate; while the high frequency limit is due to combined effects of the electrical time constant of the material and the trans-impedance of the amplifier. For thin samples the results are consistent with the lumped capacitance model that is effective in predicting the response. For thicker samples however the behavior of the pyroelectric conversion deviates appreciably from that of the lumped model.

Polar elastic dielectric of large electrocaloric effect and deformation

The alternation of temperature and entropy induced by an electric field in a polar dielectric material is known as the electrocaloric effect (ECE). This paper develops a thermodynamic theory of the polar elastic dielectric with large ECE and large deformation compatibility. The theory characterizes the equilibrium condition of the polar elastic dielectric which is subjected to mechanical forces, electric field and thermal field. The mechanical behavior and large deformation of the polar elastic dielectric thermo-electro-mechanical system are analyzed under the coupling influence of hyperelastic, polarization, electrostriction and thermal contribution on the system. The typical thermodynamics cycles of the polar elastic dielectric are described as cooling devices and generators and the electrocaloric and pyroelectric energy conversion are calculated. Ferroelectric polymer, as an important category of electroactive polymers, is a typical polar dielectric with a large ECE and a large deformation. As an example, when subjected to different voltage, the ferroelectric polymers are regarded as cooling devices. We calculated their temperature change, entropy change, heat absorptions and work generation. We also calculated the voltage change, electric quantity change and work of the ferroelectric polymer which is regarded as generators when subjected to different temperatures. Finally, we investigated the thermo-electro-mechanical coupling behavior of the ferroelectric polymers undergoing ferroelectric–paraelectric phase transition.

Pyroelectric energy conversion using PLZT ceramics and the ferroelectric–ergodic relaxor phase transition

This paper is concerned with direct conversion of waste heat into electricity by executing the Olsen cycle on lead lanthanum zirconate titanate (PLZT) ceramics undergoing a relaxor–ferroelectric phase transition. The Olsen cycle consists of two isothermal and two isoelectric field processes. First, the temperature-dependent dielectric properties were measured for x/65/35 PLZT. The polarization transition temperature of x/65/35 PLZT was found to decrease from 240 to 10 °C as x increased from 5 to 10 mol%. This suggests that the different compositions should be operated over different temperature ranges for maximum thermal to electrical energy conversion. The energy and power densities generated by the Olsen cycle using x/65/35 PLZT samples were measured by successively dipping the samples in isothermal dielectric oil baths. Large energy and power densities were obtained when the samples underwent the ergodic relaxor–ferroelectric phase transition. A maximum energy density of 1014 J l−1 per cycle was obtained with a 190 μm thick 7/65/35 PLZT sample cycled at 0.026 Hz between 30 and 200 °C and between 0.2 and 7.0 MV m−1. To the best of our knowledge, this is the largest pyroelectric energy density ever demonstrated experimentally with ceramics, single crystals, or polymers. A maximum power density of 48 W l−1 was achieved using a 200 μm thick 6/65/35 PLZT sample for temperatures between 40 and 210 °C and electric fields between 0 and 8.5 MV m−1 at a frequency of 0.060 Hz. The maximum applied electric field and temperature swings of these materials were physically limited by dielectric breakdown and thermomechanical stress.

Phase transitions and thermal expansion in pyroelectric energy conversion

This paper elucidates dynamic effects of phase transitions and thermal expansion on pyroelectric energy conversion. The Olsen cycle was performed on [001]-oriented 0.72PbMg1/3Nb2/3O3−0.28PbTiO3 (PMN-28PT) single crystals at different frequencies with electric field cycled between 0.2 and 0.75 MV/m and temperature between 22 and 140 ∘C. The measured energy density more than doubled as frequency increased from 0.0173 to 0.0211 Hz. This was attributed to secondary pyroelectric effect caused by thermal expansion. At 0.0211 Hz, the samples transitioned from pseudocubic to highly polarized tetragonal phase during cooling. At lower frequency, it underwent additional phase transition from tetragonal to less polarized monoclinic phase.

Pyroelectric energy converter for harvesting waste heat: Simulations versus experiments

This paper is concerned with numerical simulations of a pyroelectric converter for direct energy conversion of waste heat into electricity. The simulated prototypical device consisted of a hot and cold source separated by a series of vertical microchannels supporting pyroelectric thin films made of co-polymer P(VDF-TrFE) and undergoing the Olsen cycle. A piston was used to vertically oscillate a working fluid back and forth between the thermal sources. The experimental device was instrumented with thermocouples and a pressure sensor. The two-dimensional transient mass, momentum, and energy equations were solved numerically using finite element methods to determine the local and time-dependent temperature at various locations inside the device microchannels. The operating frequency varied from 0.025 to 0.123Hz and the working fluid was 1.5 or 50cSt silicone oil. Good agreement was found between the simulated and experimentally measured local mean temperatures for both working fluids at all operating frequencies considered. The local temperature swings were underestimated slightly for 50cSt silicone oil and significantly more for 1.5cSt silicone oil. Overall, this study confirms our previous numerical results. Moreover, this numerical model could be used to design and operate the next generation of pyroelectric energy converters based on oscillatory convective heat transfer.

Melioration of Pyroelectric Cells for Power Conversion

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.

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.

A Bimetallic Micro Heat Engine for Pyroelectric Energy Conversion

Abstract We present a novel concept of electric power generation from a spatial temperature gradient, achieved by integrating pyroelectric generators (PEGs) into a self-oscillating micro heat engine. The micro heat engine moves the PEGs between a hot and cold reservoir, thus bringing them in an alternating contact with a higher and lower temperature. By their pyroelectric nature, the PEGs convert this periodic temperature variation into electrical energy. The micro heat engine is fabricated from a 280 μm thick bimetallic strip and the PEGs from a 250 μm thick PZT sheet. At an oscillation frequency of 0.19 Hz the device generates 4.4 μW of electrical power from a 96 K temperature difference.

2008 Outstanding Paper Award of the IEEE Ultrasonics, Ferroelectrics, and Frequency Control Society

The Administrative Committee of the IEEE Ultrasonics, Ferroelectrics, and Frequency Control Society takes great pleasure in announcing the selection of the Outstanding Paper published in its 2008 Transactions, Vol. 55. The award was presented during ceremonies at the 2009 IEEE International Ultrasonics Symposium in Rome, Italy, September 21st, 2009. The award winners are Gael Sebald, Elie Lefeuvre, and Daniel Guyomar for their paper entitled Pyroelectric Energy Conversion: Optimization Principles.

Harvesting Nanoscale Thermal Radiation Using Pyroelectric Materials

Pyroelectric energy conversion offers a way to convert waste heat directly into electricity. It makes use of the pyroelectric effect to create a flow of charge to or from the surface of a material as a result of heating or cooling. However, an existing pyroelectric energy converter can only operate at low frequencies due to a relatively small convective heat transfer rate between the pyroelectric materials and the working fluid. On the other hand, energy transfer by thermal radiation between two semi-infinite solids is nearly instantaneous and can be enhanced by several orders of magnitude from the conventional Stefan–Boltzmann law as the gap separating them becomes smaller than Wien’s displacement wavelength. This paper explores a novel way to harvest waste heat by combining pyroelectric energy conversion and nanoscale thermal radiation. A new device was investigated numerically by accurately modeling nanoscale radiative heat transfer between a pyroelectric element and hot and cold plates. Silica absorbing layers on top of every surface were used to further increase the net radiative heat fluxes. Temperature oscillations with time and performances of the pyroelectric converter were predicted at various frequencies. The device using 60/40 porous poly(vinylidene fluoride–trifluoroethylene) achieved a 0.2% efficiency and a 0.84 mW/cm2 electrical power output for the cold and hot sources at 273 K and 388 K, respectively. Better performances could be achieved with 0.9Pb(Mg1/3Nb2/3)–0.1PbTiO3 (0.9PMN-PT), namely, an efficiency of 1.3% and a power output of 6.5 mW/cm2 between the cold and hot sources at 283 K and 383 K, respectively. These results are compared with alternative technologies, and suggestions are made to further improve the device.

Towards optimization of a pyroelectric energy converter for harvesting waste heat

This paper reports numerical simulations of a prototypical pyroelectric energy converter as a novel approach for directly converting waste heat into electricity. The two-dimensional mass, momentum, and energy equations were solved to predict the local time-dependent pressure, velocity, and temperature. Then, heat input, pumping power, and electrical power generated were estimated, along with the thermodynamic energy efficiency and power density of the device. It was established that reducing the length of the device and/or the viscosity of the working fluid improved the energy efficiency and power density of the device by increasing the optimum operating frequency. Results show that a maximum efficiency of 5.2% at 0.5 Hz corresponding to 55.4% of the Carnot efficiency between 145 and 185 °C can be achieved with commercial 1.5 cst silicone oil as the working fluid and PZST as the pyroelectric material. The associated power density was found to be 38.4 W/L of material.