arXiv subjects

Rajasekarakumar Vadapoo

Publications and source records attributed to Rajasekarakumar Vadapoo.

3 recordsLinked to original sources

arXiv2017

Effect of aging and Mn substitution on anisotropy of third generation piezoelectrics

We predict a new candidate high-temperature high-pressure structure of FeSiO$_3$ with space-group symmetry Cmmm by applying an evolutionary algorithm within DFT+U that we call post-perovskite II (PPv-II). An exhaustive search found no other competitive candidate structures with ABO$_3$ composition. We compared the X-ray diffraction (XRD) pattern of FeSiO$_3$ PPv-II with experimental results of the recently reported "H-phase" of (Fe,Mg)SiO$_3$. The intensities and positions of two main X-ray diffraction peaks of PPv-II FeSiO$_3$ compare well with those of the H-phase. We also calculated the static equation of state, the enthalpy and the bulk modulus of the PPv-II phase and compared it with those of perovskite (Pv) and post-perovskite (PPv) phases of FeSiO$_3$. According to the static DFT+U computations the PPv-II phase of FeSiO$_3$ is less stable than Pv and PPv phases under lower mantle pressure conditions at T=0 K and has a higher volume. PPv-II may be entropically stabilized, and may be a stable phase in Earth's lower mantle, coexisting with {\alpha-PbO$_2$ (Columbite-structure) silica and perovskite, or with magnesiowustite and/or ferropericlase, depending on bulk composition.

cond-mat.mtrl-sci↗

arXiv2016

Synthesis of Polar Ordered Oxynitride Perovskite

For decades, numerous attempts have been made to produce polar oxynitride perovskites, where some of the oxygen are replaced by nitrogen, but a polar ordered oxynitride has never been demonstrated. Caracas and Cohen studied possible ordered polar oxynitrides within density functional theory (DFT) and found a few candidates that were predicted to be insulating and at least metastable. YSiO2N stood out with huge predicted polarization and nonlinear optic coefficients. In this study, we demonstrate the synthesis of perovskite-structured YSiO2N by using a combination of a diamond anvil cell and in-situ laser heating technique. Subsequent in-situ X-ray diffraction, second harmonic generation, and Raman scattering measurements confirm that it is polar and a strong nonlinear optical material, with structure and properties similar to those predicted by DFT.

cond-mat.mtrl-sci↗

arXiv2014

First principles investigation of magnetocrystalline anisotropy at the L2$_1$ Full Heusler|MgO interfaces and tunnel junctions

Magnetocrystalline anisotropy at Heusler alloy$|$MgO interfaces have been studied using first principles calculations. It is found that Co terminated Co$_{2}$FeAl$|$MgO interfaces show perpendicular magnetic anisotropy up to 1.31 mJ/m$^2$, while those with FeAl termination exhibit in-plane magnetic anisotropy. Atomic layer resolved analysis indicates that the origin of perpendicular magnetic anisotropy in Co$_{2}$FeAl$|$MgO interfaces can be attributed to the out-of-plane orbital contributions of interfacial Co atoms. At the same time, Co$_{2}$MnGe and Co$_{2}$MnSi interfaced with MgO tend to favor in-plane magnetic anisotropy for all terminations.

cond-mat.mtrl-sci↗