1,379 research outputs found
Polarization Enhancement in Short Period Superlattices via Interfacial Intermixing
The effect of intermixing at the interface of short period
PbTiO/SrTiO superlattices is studied using first-principles density
functional theory. The results indicate that interfacial intermixing
significantly enhances the polarization within the superlattice. This
enhancement is directly related to the off-centering of Pb and Sr cations and
can be explained through a discussion of interacting dipoles. This picture
should be general for a wide range of multicomponent superlattices and may have
important consequences for the design of ferroelectric devices.Comment: 4 pages, 6 figure
First principles predictions of van der Waals bonded inorganic crystal structures: Test case, HgCl2
We study the crystals structure and stability of four possible polymorphs of HgCl2 using first principles density functional theory. Mercury (II) halides are a unique class of materials which, depending on the halide species, form in a wide range of crystal structures, ranging from densely packed solids to layered materials and molecular solids. Predicting the groundstate structure of any member of this group from first principles, therefore, requires a general purpose functional that treats van der Waals bonding and covalent/ionic bonding adequately. Here, we demonstrate that the non-local van der Waals density functional paired with the C09 exchange functional meets this bar for HgCl2. In particular, this functional is able to predict the correct groundstate among the structures tested as well as having extremely good agreement with the experimentally known crystal structure. These results highlight the maturity of this functional and open the door to using this method for truly first principles crystal structure predictions
Enhancing piezoelectricity through polarization-strain coupling in ferroelectric superlattices
Short period ferroelectric/ferroelectric BaTiO3 (BTO)/PbTiO3 (PTO)
superlattices are studied using density functional theory. Contrary to the
trends in paraelectric/ferroelectric superlattices the polarization remains
nearly constant for PTO concentrations below 50%. In addition, a significant
decrease in the c/a ratio below the PTO values were observed. Using a
superlattice effective Hamiltonian we predict an enhancement in the d33
piezoelectric coefficient peaking at ~75% PTO concentration due to the
different polarization-strain coupling in PTO and BTO layers. Further analysis
reveals that these trends are bulk properties which are a consequence of the
reduced brought about by the polarization saturation in the BTO layers
- …