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Detailed Program
Paper Number : CO-I03
Time Frame : 17:20~17:45
Presentation Date : Friday, 28, November
Session Name : Computational Ceramic Science and Engineering
Session Chair 1# : Seungwu Han
Session Chair 2# : Nakeshi Nishimatsu
Molecular dynamics simulations of caloric effects in ferroelectrics
Takeshi Nishimatsu
Tohoku University
Since 2005, we have been developing our original simulation code named feram specialized for ferroelectric materials[1]. feram is fast molecular dynamics (MD) simulation code for ABO3 perovskite-type ferroelectrics and distributed as free software from http://loto.sourceforge.net/feram/. The code is based on a first-principles effective Hamiltonian and can be applicable not only bulk ferroelectrics but also ferroelectric thin-film capacitors. Because, in the code, dipole interactions are treated in reciprocal space with fast Fourier transform (FFT), feram is fast enough for simulating ferroelectric materials with a realistic system size up to 100 nm and a realistic time span (> 1000 ns).
Recently, we have developed a direct simulation method of electrocaloric and elastocaloric effects of ferroelectric materials with our feram code[2,3]. The electrocaloric effect is an adiabatic change in the temperature, T, of a material upon applying an external electric field. In particular, if an electric field is applied to a ferroelectric material at just above its phase transition temperature, TC, and the field is then removed, a large reduction in temperature is expected. The elastocaloric effect is that of external stress field. It is widely believed that these effects are applicable to solid-state refrigeration technologies.
In Fig. 1, the temperature dependence for the electrocaloric effect T of BaTiO3, under various initial external electric fields is compared. It can be seen that even with a small initial external electric field (50 kV/cm), BaTiO3 gives a large T, but the temperature range where this large T can be obtained is narrow. By increasing the applied fields (>100 kV/cm) the range of applicable temperatures broadens.




















Figure 1 The temperature dependence of T for various initial external electric fields. The external electric field switches from Ez=5–500 to 0 kV/cm.

References:
[1] Takeshi Nishimatsu, Umesh V. Waghmare, Yoshiyuki Kawazoe and David Vanderbilt: Phys. Rev. B 78, 104104 (2008).
[2] T. Nishimatsu, J. A. Barr and S. P. Beckman, J. Phys. Soc. Jpn. 82, 114605 (2013).
Acknowledgements :