Crystal structure and properties of SrTi_1-xMn_xO₃ perovskites – from calculations to experiments

M. Lebeda¹, J. Drahokoupil²

¹Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Prague, Czech Republic

²Institute of Physics of the Czech Academy of Sciences, Prague, Czech Republic

leb.miroa@seznam.cz

The SrTi_1-xMn_xO₃ ceramics were experimentally studied by X-ray diffraction and resonant ultrasound spectroscopy and the results were compared with the theoretical calculation from DFT. Firstly, it was confirmed that our samples were crystallized as cubic and the dependence of lattice parameter a on Mn concentration was determined. The linear decrease of a with increasing Mn can be seen in Fig. 1 - left. Therefore, it can be expected that it follows Vegard’s law. Subsequently the comparison between those lattice parameters obtained by X-ray diffraction measurements and the values calculated by DFT method in CASTEP module of Materials Studio was performed.

Secondly, the calculation of the free energy of SrTi_1-xMn_xO₃ as a function of the volume of the unit cell was calculated from the first-principles and the obtained dependence was fitted by Birch-Murnaghan equation of state [1], which allowed the estimation of the bulk modulus and equilibrium volume of the unit cell. Furthermore, the change of the calculated bulk modulus caused by the different fitted volume range was tested and the resulting dependence is emphasized for the pure SrTiO₃ in Fig.1 – right, with the experimental value [2]. The calculated data are in very good agreement with the corresponding experiment: in all studied perovskites the relative deviations from the experimental values are in the case of the lattice parameter only up to two percent and in the case of the bulk modulus up to four percent.

Figure 1. Left: experimentally observed linear decrease of the lattice parameter a with increasing Mn concentration at SrTi_1-xMn_xO₃ cubical perovskites (squares) and the lattice parameters data from ab-initio simulations with GGA, resp. GGA+U functional (triangles, resp. rhombuses). Right: dependence of the SrTiO₃ bulk modulus on the different fitted percentage range of the volume (lattice parameter) of the unit cell at Birch-Murnaghan equation of state. The straight line indicates the experimental value [2].

1. F. Birch. Finite elastic strain of cubic crystals. Phys. Rev. 71(11): 809, 1947.

2. R. O. Belt, G. Rupprecht. Elastic constants of strontium titanite. Phys. Rev. 129(1): 90, 1963.

This work was supported by the Grant Agency of the Czech Technical University in Prague, grant No. SGS19/190/OHK4/3T/14.