Pyroelectric energy conversion: Optimization principles

Abstract

In the framework of microgenerators, we present in this paper the key points for energy harvesting from temperature using ferroelectric materials. Thermoelectric devices profit from temperature spatial gradients, whereas ferroelectric materials require temporal fluctuation of temperature, thus leading to different applications targets. Ferroelectric materials may harvest perfectly the available thermal energy whatever the materials properties (limited by Carnot conversion efficiency) whereas thermoelectric material's efficiency is limited by materials properties (ZT figure of merit). However, it is shown that the necessary electric fields for Carnot cycles are far beyond the breakdown limit of bulk ferroelectric materials. Thin films may be an excellent solution for rising up to ultra-high electric fields and outstanding efficiency. Different thermodynamic cycles are presented in the paper: principles, advantages, and drawbacks. Using the Carnot cycle, the harvested energy would be independent of materials properties. However, using more realistic cycles, the energy conversion effectiveness remains dependent on the materials properties as discussed in the paper. A particular coupling factor is defined to quantify and check the effectiveness of pyroelectric energy harvesting. It is defined similarly to an electromechanical coupling factor as k2=p2theta0/(epsilontheta33cE), where p, theta0, epsilontheta33, cE are pyroelectric coefficient, maximum working temperature, dielectric permittivity, and specific heat, respectively. The importance of the electrothermal coupling factor is shown and discussed as an energy harvesting figure of merit. It gives the effectiveness of all techniques of energy harvesting (except the Carnot cycle). It is finally shown that we could reach very high efficiency using 1110.75Pb(Mg1/3Nb2/3)-0.25PbTiO3 single crystals and synchronized switch harvesting on inductor (almost 50% of Carnot efficiency). Finally, practical implementation key points of pyroelectric energy harvesting are presented showing that the different thermodynamic cycles are feasible and potentially effective, even compared to thermoelectric devices.

Tuning of dielectric, pyroelectric and ferroelectric properties of 0.715Bi0.5Na0.5TiO3-0.065BaTiO3-0.22SrTiO3 ceramic by internal clamping

“…This phenomenon has been widely employed for a host of applications including infra-red detectors, thermal imaging, and energy harvesting. [51][52][53][54] Such applications in particular require pyroelectric materials with low dielectric constant and loss, low specific heat capacity, low thermal conductivity and high pyroelectric coefficient. [51][52][53][54] Since most of this can be achieved through internal clamping, hence, one of the focus of this work is to analyze the effect of glass addition on pyroelectricity.…”

“…A number of FOMs have been derived for pyroelectric materials based on application specific requirements such as thermal/infrared imaging. [51][52][53][54] The most common FOMs are based on consideration of thermal and electrical circuits employed or maximum current/voltage for a given input. In this direction, for maximizing the pyroelectric voltage for a given heat input, high voltage responsivity (F v ) FOM can be expressed as F v = p/C v εε 0 where C e or C v is volume specific heat (constant electric field) and ε 0 is permittivity of free space.…”

“…For energy harvesting FOM (F e ) is proposed as F e = p 2 /ε. 51,52,54 This F e FOM has been widely used by a number of researchers for pyroelectric energy harvesting material selection and design problems. 51,52,54 However, for energy harvesting a new FOM (F * e ) has been recently proposed as F * e = p 2 /εC 2 v .…”

“…It can be further expressed in terms of F * e = F i × F v . 51,52,54 Table I shows various FOMs (F v F i , F d , F e and F * e ) for pure and glass added BNT-BT-ST ceramics. It is observed that the FOMs increase with increasing glass content.…”

“…This could be credited to the start of diffuse phase transition as marked by square symbol. Additionally, according to the classical theory of nucleation by random fluctuations, it is observed that rate of nucleation (ϑ) increases with increase in T. The temperature dependence of dynamic relaxation response (τ) for domain nucleation and growth can be determined by: 54,55 FIG …”