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A theory to describe the dielectric anomalies and the ferroelectric phase transition induced by oxygen isotope replacement in SrTiO$_3$ is developed. The proposed model gives consistent explanation between apparently contradictory…
Using first-principles calculations, the phonon frequencies at the $\Gamma$ point and the dielectric tensor are determined and analysed for the cubic and rhombohedral phases of BaTiO$_{3}$. The dipole-dipole interaction is then separated…
We performed first principles calculations for epitaxially strained orthorhombic CaTiO$_3$. The computational results reveal the existence of a metastable ferroelectric phase at compressive strain with unexpected in-plane polarization.…
A monoclinic phase was recently discovered near the morphotropic phase boundary in several high-performance piezoelectric perovskite solid solutions, but its properties have not been reported. In this paper the dielectric, piezo- and…
Recently the ferroelectric anomaly (Nad, Monceau, et al) followed by the charge disproportionation (Brown, et al) have been discovered in (TMTTF)2X compounds. The corresponding theory of the combined Mott-Hubbard state describes both…
The c(2$\times$2) reconstruction of (001) PbTiO$_3$ surfaces is studied by means of first principles calculations for paraelectric (non-polar) and ferroelectric ([001] polarized) films. Analysis of the atomic displacements in the…
The ferroelectricity in $\mathrm{HfO}_2$ thin films is widely attributed to the formation of a polar orthorhombic phase named OIII phase. However, the complexity of OIII phase originated from its low symmetry becomes an obstacle for…
Molecular-dynamics simulations of KNbO$_3$ reveal preformed dynamic chain-like structures, present even in the paraelectric phase, that are related to the softening of phonon branches over large regions of the Brillouin zone. The phase…
Structural, magnetic, and dielectric properties of Sm$_2$CoMnO$_6$ have been studied. X-ray diffraction and Rietveld analysis show that the sample crystallizes in the monoclinic structure with \textit{P2$_1$/n} space group. Magnetic study…
3$d$ based double perovskite materials have received much attention in recent years due to their exotic magnetic structure and magneto-electric coupling. In this work we have prepared and studied the nano-crystalline sample of…
We report a systematic study of the structure, electric and magnetic properties of Ca$_3$Co$_{2-x}$Mn$_x$O$_6$ single crystals with $x =$ 0.72 and 0.26. The DC and AC magnetic susceptibilities display anomalies with characteristic of the…
First-principles calculations based on density-functional theory in the pseudo-potential approach have been performed for the total energy, crystal structure and cell polarization for SrTaO$_2$N/SrTiO$_3$ heterostructures. Different…
We measured the temperature dependent infrared reflectivity spectra of TbMnO3 with the electric field of light polarized along each of the three crystallographic axes. We analyzed the effect, on the phonon spectra, of the different phase…
Cathode materials undergo various phase transitions during the charge/discharge process, and the structural transitions significantly affect the battery performance. Although phonon properties can provide a direct clue for structural…
We present an inexpensive first-principles approach for describing quantum paraelectricity that combines density functional theory (DFT) treatment of the electronic subsystem with quantum mechanical treatment of the ions through solution of…
Hafnia (HfO2) is a silicon-compatible dielectric material, yet stabilizing its desired but metastable ferroelectric phase remains challenging. Phase stability predictions by density functional theory (DFT) have provided crucial guidance,…
The electronic and structural properties of Li$B$O$_3$ ($B$=V, Nb, Ta, Os) are investigated via first-principles methods. We show that Li$B$O$_3$ belong to the recently proposed hyperferroelectrics, i.e., they all have unstable longitudinal…
We present neutron total scattering and density functional theory studies on quasi-one-dimensional superconducting K$_2$Cr$_3$As$_3$ revealing a frustrated structural instability. Our first principles calculations find a significant phonon…
The structure and the dielectric properties of Pb(Zn1/3Nb2/3)O3 (PZN) crystal have been investigated by means of high-resolution synchrotron x-ray diffraction (with an x-ray energy of 32 keV) and dielectric spectroscopy (in the frequency…
First-principles density-functional calculations within the local-density approximation and the pseudopotential approach are used to study and characterize the ferroelastic phase transition in calcium chloride (CaCl_2). In accord with…