Alexander S. Starkov

Simulation of a solid-state cooler with electrocaloric elements

The dynamics of change in temperature at the edges of a layered structure consisting of one or more electrocaloric and heat-conducting elements in response to pulses of a periodic electric field has been studied with the use of the finite-element method. The possibility of using ceramic materials and (Ba,Sr)TiO3 films as electrocaloric and heat-conducting elements of linear and radial cooling structures is considered. The difference between the temperatures at the center and periphery of the radial film microstructure with two interdigital circular electrode lines is 2.5 K. An increase in the number of lines and the electric field frequency leads to an increase of the thermal effect.

Electrocaloric response of a ferroelectric capacitor to a periodic electric field

The electrocaloric response of a ferroelectric capacitor to a periodic electric field has been analyzed in terms of the nonstationary heat conduction equation. A linear physical model is considered for an electrocaloric element in which one end (x = 0) is thermally insulated and a constant temperature T0 is maintained at the boundary x = l. The effect of a periodic electric field on the capacitor gives rise to temperature oscillations about a decreasing average value that reaches saturation. A relatively simple analytic expression is derived for the temperature distribution along the electrocaloric element and the heat flux density under stationary conditions. The calculations are carried out using the results obtained from measurements performed for a PMN-PT relaxor ferroelectric in the temperature range of the phase transition. A temperature gradient and a heat flux of ∼150 W/cm2 are observed in an electric field of 2.4 V/μm at a frequency of 10 Hz.

Solid-State Cooler: New Opportunities

The main physical ideas behind the development of the novel solid-state cooling system have been summarized. The basic strategy relies on strengthening of the electrocaloric effect. We show that for this purpose additional piezoelectric layers or new multiferroic materials can be used as a practical realization. Moreover, a combination of the electrocaloric effect and an external force is very promising. This force can be either the magnetic field or the mechanical stress. The proposed concept is supported by experimental data and theoretical calculations.

Thermodynamic estimation of cooling efficiency using an electrocaloric solid-state line

A thermodynamic cycle in a solid-state cooling line including two ferroelectric capacitors which exhibit the electrocaloric (EC) effect is considered. Expressions are derived for determining the cooling factor and the efficiency of the EC cooling line in terms of the Carnot cycle. Numerical estimates obtained for barium-strontium titanate ferroelectric capacitors make it possible to determine the cooling efficiency upon a change in temperature by ΔT = 2 K. At the initial temperature of 272 K, the efficiency is 0.6 Carnot, which considerably exceeds the efficiency of vapor-compression refrigerators.

Effect of thermal phenomena on a second-order phase transition in the Landau-Ginzburg model

The influence of electrocaloric and pyroelectric effects on a phase transition in a ferroelectric material has been studied. The difference in the parameters of the Landau model for isothermal and adiabatic processes has been indicated. The temperature dependence of the spontaneous polarization is described by a special function (the probability integral) that results in the disappearance of the second-order phase transition.

Modeling of efficient solid-state cooler on layered multiferroics

We have developed theoretical foundations for the design and optimization of a solid-state cooler working through caloric and multicaloric effects. This approach is based on the careful consideration of the thermodynamics of a layered multiferroic system. The main section of the paper is devoted to the derivation and solution of the heat conduction equation for multiferroic materials. On the basis of the obtained results, we have performed the evaluation of the temperature distribution in the refrigerator under periodic external fields. A few practical examples are considered to illustrate the model. It is demonstrated that a 40-mm structure made of 20 ferroic layers is able to create a temperature difference of 25K. The presented work tries to address the whole hierarchy of physical phenomena to capture all of the essential aspects of solid-state cooling.

Account for Mutual Influence of Electrical, Elastic, and Thermal Phenomena for Ferroelectric Domain Wall Modeling

The theoretical model of the ferroelectric domain wall motion has been developed. It is demonstrated that for a proper phenomenon description it is necessary to consider the thermoelectroelasticity gradient terms. It is shown that in the linear approximation the general solution of three-dimensional problem in transversely isotropic thermoelectroelastic media can be obtained by means of five newly introduced harmonic potential functions. As an example of the proposed model applicability, the electroelastic field induced by a sphere (SPM tip) located near a plane boundary of two half-spaces is considered and described.

Parametric enhancement of electrocaloric effect by periodically varying external field

The mutual influence of an external electric field and mechanical stresses on the electrocaloric effect has been studied. Under certain conditions, the varying external field produces parametric enhancement of the electrocaloric effect. Using this phenomenon, it is possible to realize the Carnot cycle in ferroelectric energy converters and solid-state coolers.

New Approaches to Electrocaloric-Based Multilayer Cooling

The research and development works directed to a creation of solid state coolers and refrigerators based on the electrocaloric effect have been initiated in various countries, mainly in USA and USSR, in the 70s of the last century The goal of these works was formed as a creation of microcryogenic cooling systems for infrared radiation receivers for space optoelectronic systems.

Effective parameters of nanomatryoshkas

Abstract. The problem of finding effective characteristics of the nanostructure consisting of spherical shells (nanomatryoshka) is solved using the matrix homogenization method. According to the problem formulation, each of the system layers possesses piezoelectric and/or piezomagnetic properties. Thus, the mutual influence of the elastic, electrical, and magnetic characteristics of the shells on their homogenized values is investigated. In particular, the dependence of the dielectric and magnetic permittivity on the geometrical parameters of the layers is studied and analyzed. The performance of the model is illustrated for a two-layer structure.