Efficiency of thermoelectric conversion in ferroelectric film capacitive structures

Abstract

792Nowadays, semiconductor photovoltaic elements, more specifically, solar cells of different types, offer the most effective conversion of optical radiation energy to electrical energy. However, all photovoltaic devices have a common disadvantage: frequency selectivity, which keeps them from converting heat fluxes in a wide frequency range. Therefore, there arises the need for new approaches to energy conver sion and new efficient materials for converters.The capacitive way of converting the thermal energy of the environment to electrical energy seems today to be very promising [1,2]. The basic idea underlying direct thermal to electrical energy con version using electric capacitors is the following: elec trical energy W stored in a capacitor with capacitance C (W = Q 2 /2C, where Q is the electrical charge in the capacitor) rises due to thermal energy when the capac itance decreases provided that the charge of the capac itor remains constant. Capacitive thermo to electrical energy conversion is implemented using variable capacitors with a mechanically varied or temperature dependent capacitance and mechanical or optical heat flux modulators [3,4].In this work, we concentrate on developing a new class of ferroelectric conversion devices converting the energy of IR radiation from different sources (Sun, blast furnaces, nuclear reactors, electronics, etc.) in a wide frequency range to disposable electrical energy. Unlike ferroelectric converters exploiting the pyro electric properties of ferroelectrics in the ferroelectric phase (polarization reversal in response to a tempera ture change), devices based on our approach exploit the temperature dependent nonlinearity of the mate rial (a change in the permittivity induced by a temper ature change) both in the ferroelectric and in the paraelectric phases.The unique properties of ferroelectrics, an anoma lously high permittivity and its sharp temperature dependence near the phase transition [5, 6], render them promising materials for heat flux energy convert ers. The possibility of varying the permittivity of capacitive metal-insulator-metal (MIM) ferroelec tric structures (Fig. 1) under the periodic action of heat makes it possible to bring about a closed cyclic process of thermal to electrical energy conversion with accumulation of electrical energy after each cycle.The higher the thermocycling frequency, the higher the electrical power resulting from thermocycling. In Abstract-Thermal heating/cooling conditions for metal-insulator-metal structures based on barium strontium titanate ferroelectric films are studied by numerical methods with the aim of their application in capacitive thermoelectric converters. A correlation between the thermal and capacitive properties of thin film ferroelectric capacitors is considered. The time of the temperature response and the rate of variation of the capacitive properties of the metal-insulator-metal structures are determined by analyzing the dynamics of thermal processes. Thermophysical calculations are carried out that take int...

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