Molecular Dynamics Simulations of Chemically Disordered Ferroelectric (Ba,Sr)TiO₃ with a Semi-Empirical Effective Hamiltonian

Abstract

We present a semi-empirical effective Hamiltonian to capture effects of disorder associated with Ba and Sr cations occupying A sites in (BaxSr1−x)TiO3 on its ferroelectric phase transition. Averaging between the parameters of first-principles effective Hamiltonians of end members BaTiO3 and SrTiO3, we include a term with an empirical parameter to capture the local polarization and strains arising from the difference between ionic radii of Ba and Sr. Using mixed-space molecular dynamics of the effective Hamiltonian, we determine T -dependent ferroelectric phase transitions in (BaxSr1−x)TiO3 which are in good agreement with experiment. Our scheme of determination of semi-empirical parameters in effective Hamiltonian should be applicable to other perovskite-type ferroelectric solid solutions.

Origins of the Inverse Electrocaloric Effect

“…Ad etailed theoretical study of the direction dependence of the ECE in BaTiO 3 and its relation with the inverse effect was also reported by Marathe et al [20] using first-principlebased simulations. An inverse response has been found at the FE-FE transition between the orthorhombic and tetrago-nal phases for af ield along [001],w hereas the conventional ECE occurred for af ield along [011] and [ 111].T he correspondingr esults are reproduced in Figure 4. These theoretical predictions have also been qualitatively confirmed by direct EC temperature measurements for BaTiO 3 single crystals,s ee Figure 5.…”

“…These theoretical predictions have also been qualitatively confirmed by direct EC temperature measurements for BaTiO 3 single crystals,s ee Figure 5. [20] Furthermore,a tt he FE-FE transition between the rhombohedral and orthorhombic phases,t he EC response is inverse for applied fields along [001] and [011] but conventional if the field is along [111]. [20] Note that in all these cases the field is non-collinear to at least one of the FE phases.T he field is even non-collinear to the polarization direction of both phasesf or the orthorhombic-tetragonal transition and af ield along [111] or the rhombohedral-orthorhombict ransition and the field along [001], resultingi nt he conventional and inverse response,r espectively.…”

Chemical composition and temperature dependence of the energy storage properties of Ba1‐xSrxTiO3 ferroelectrics

“…The effective Hamiltonian equation used was the same as that used by Nishimatsu et al which was developed and based on the effective Hamiltonian model by Zhong and Waghmare …”

“…We performed molecular dynamics simulations on Ba 1‐x Sr x TiO 3 using the first‐principles effective Hamiltonian equation implanted in the mixed‐space molecular dynamics code feram . The long‐range interactions were treated in a reciprocal space for both the heating and cooling simulations in a supercell with a system size of Lx × Ly × Lz =32 × 32 × 32.…”

“…We performed molecular dynamics simulations on Ba 1-x Sr x TiO 3 using the first-principles effective Hamiltonian equation implanted in the mixed-space molecular dynamics code feram. [5][6][7] The long-range interactions were treated in a reciprocal space for both the heating and cooling simulations in a supercell with a system size of Lx 9 Ly 9 Lz=32 9 32 9 32. The temperature was held constant at each temperature step in the canonical ensemble using the Nos e-Poincar e thermostat, 12 which allowed us to use a relatively large time step of Dt = 2 fs.…”