arXiv subjects

Alexander I. Lebedev

Publications and source records attributed to Alexander I. Lebedev.

20 records · Page 2Linked to original sources

arXiv2012

First-principles study of ferroelectricity and pressure-induced phase transitions in HgTiO$_3$

Ground-state structure is found and pressure-induced phase transitions up to 210 kbar are studied in mercury titanate from first principles within the density functional theory. It is established that the $R3c$ structure experimentally observed in HgTiO$_3$ is metastable at ambient pressure. With increasing the hydrostatic pressure, the ground-state structure changes following the $R{\bar 3} \to R3c \to Pbnm$ sequence. It is shown that the appearance of ferroelectricity in HgTiO$_3$ at $P = 0$ is associated with an unstable phonon mode. Optical and elastic properties of different phases of mercury titanate are calculated. The quasiparticle band gap calculated in the \emph{GW} approximation ($E_g = 2.43$ eV) agrees with experimental data better than the value obtained in the LDA approximation (1.49 eV). Analysis of the thermodynamic stability explains why the synthesis of mercury titanate is possible only at high pressures.

cond-mat.mtrl-sci↗

arXiv2012

Ground-state structure of KNbO$_3$/KTaO$_3$ superlattices: Array of nearly independent ferroelectrically ordered planes

Phonon spectra of the paraelectric phase, structure and distribution of polarization in the polar ground state, and energies of ferroelectrically and antiferroelectrically ordered phases were calculated for stress-free (KNbO$_3$)$_1$(KTaO$_3$)$_n$ superlattices ($n = {}$1--7) from first principles within the density-functional theory. Quasi-two-dimensional ferroelectric state with the polarization localized in the KNbO$_3$ layer was revealed to be the ground state for the superlattices with $n \ge 2$. The interaction between these polarized layers decreases exponentially with increasing the interlayer distance, and the ground-state structure transforms to an array of nearly independent ferroelectrically ordered planes at large $n$.

cond-mat.mtrl-sci↗