arXiv subjects

Anna Gruenebohm

Publications and source records attributed to Anna Gruenebohm.

3 recordsLinked to original sources

arXiv2023

Ab initio based study on atomic ordering in {(Ba, Sr)}TiO$_3$

\ We combine density functional theory and molecular dynamics simulations to investigate the impact of Sr concentration and atomic ordering on the structural and ferroelectric properties of (Ba, Sr)TiO$_3$. On one hand, the macroscopic structural properties are rather insensitive to atomic ordering. On the other hand, the Curie temperature and polarization differ by $9$\% and $17$\% for different symmetries of the Sr distribution, respectively. Local ordering of Sr induces preferential polarization directions and influences the relative stability of the three ferroelectric phases.

cond-mat.mtrl-sci↗

arXiv2016

Molecular Dynamics Simulations of Chemically Disordered Ferroelectric (Ba,Sr)TiO$_3$ with a Semi-Empirical Effective Hamiltonian

We present a semi-empirical effective Hamiltonian to capture effects of disorder associated with Ba and Sr cations occupying $A$ sites in (Ba$_{x}$Sr$_{1-x}$)TiO$_3$ on its ferroelectric phase transition. Averaging between the parameters of first-principles effective Hamiltonians of end members BaTiO$_3$ and SrTiO$_3$, 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 (Ba$_{x}$Sr$_{1-x}$)TiO$_3$ 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.

cond-mat.mtrl-sci↗

arXiv2013

Ab initio study of the TiO$_2$ Rutile(110)/Fe interface

Adsorption of Fe on the rutile (110)-surface is investigated by means of {\it ab initio} density functional theory calculations. We discuss the deposition of single Fe atoms, an increasing Fe coverage, as well as the adsorption of small Fe clusters. It is shown that the different interface structures found in experiment can be understood in terms of the adsorption of the Fe atoms landing first on the rutile surface. On the one hand, strong interface bonds form if single Fe atoms are deposited. On the other hand, the Fe-Fe bonds in deposited Fe clusters lead to a three-dimensional growth mode. Mainly ionic Fe-oxide bonds are formed in both cases and the electronic band gap of the surface is reduced due to interface states. Besides the structural and electronic properties, we discuss the influence of the interface on the magnetic properties finding stable Fe moments and induced moments within the interface which leads to a large spin polarization of the Fe atoms at the rutile (110)/Fe interface.

cond-mat.mtrl-sci↗