Abstract
The origin of dielectric properties of strontium titanate ceramics is investigated using DFT calculations in periodic system. It was determined that the main factors contributing to the increase in dielectric permittivity are: tetragonal distortion of the normally cubic lattice, and charge imbalance induced displacement of titanium center from its central position. Oxygen vacancies were determined to create significantly larger effects than other types of vacancies, like Ti and SrO. The extent of tetragonal distortion was found to be determined by oxygen vacancy distribution, rather than total concentration: relatively symmetrical distribution of oxygen vacancies resulted in smaller tetragonal distortion of the lattice, and, consequently, smaller increase in dielectric permittivity. Charge imbalance naturally destabilizes the cubic lattice, forcing the Ti-atom out of its central position, resulting in tetragonal lattice with increased dielectric permittivity. The process stabilizes the strontium titanate lattice, while increasing the c/a ratio. Therefore, the dielectric permittivity of strontium titanate can be increased by changes to the system that increase tetragonal distortion of the lattice and/or introduce additional negative charge.
Highlights
Strontium titanate (SrTiO3) ceramics represents an important class of technological materials, both as pure SrTiO3 or as a part of a multi-component system [1,2,3,4,5,6,7]
Calculations with oxygen vacancies were performed at different concentrations, due to the fact that point defects tend to cluster in non-stoichiometric SrTiO3, resulting in creation of localized TiO2 and SrO islands in Sr- and Ti-poor strontium titanate systems, respectively [39,40,41,42]
These results suggest that the effects of point defects on the structure of SrTiO3 ceramics should have longer range effects than their immediate locality: introduction of sufficient concentration of oxygen vacancies should be observable in the disruption of longrange symmetry of the cubic lattice, resulting in tetragonal distortion of SrTiO3 lattice, which should be observable using methods like X-ray diffraction
Summary
Strontium titanate (SrTiO3) ceramics represents an important class of technological materials, both as pure SrTiO3 or as a part of a multi-component system [1,2,3,4,5,6,7]. Subjecting SrTiO3 single crystals to strong external electric field causes distortion of the cubic structure and establishes a polar phase due to field-induced redistribution of oxygen vacancies in SrTiO3 and a formation of an inherent dipole moment [31]. This results in a dielectric to pyroelectric phase transition and lattice distortion is field-dependent [27]. Investigation of the dependence of dielectric permittivity on oxygen vacancy concentration shows strong correlation between the extent of tetragonal distortion of the cubic lattice of SrTiO3 and the calculated values of dielectric permittivity. It is shown that excess negative charge in SrTiO3 causes the displacement of Ti-atom from the central position in the lattice, stabilizing the lattice, while reducing the calculated dielectric permittivity at the same time, indicating that both the lattice distortion and the dielectric permittivity in SrTiO3 structure with defects are caused by the existence of excess charge in the system
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
