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Experiments reveal that PbK2LiNb5O15 which belongs to the tetragonal tungsten bronze family presents paraelectric and ferroelectric phases and a complex structural change between them. High and low temperature phases are of symmetry P4/mbm…

Group theoretical aspects of the three temperature-dependent and temperature-reversible experimentally observed phase transitions in the KNbO3 crystal (cubic-tetragonal, tetragonal-orthorhombic, orthorhombic-rhombohedral) in the framework…

Using first-principles methods, we predict the energy landscape and ferroelectric states of double perovskites of the form AA$'$BB$'$O$_6$ in which the atoms on both the A and B sites are arranged in rock-salt order. While we are not aware…

Structural phase transformations of [110] electric field cooled Pb(Mg1/3Nb2/3)O3-30%PbTiO3 (PMN-30%PT) crystals have been performed by x-ray diffraction in a field-cooled (FC) condition. A phase sequence of…

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…

The octahedral tilting and ferroelectric-like structural transition of LiOsO3 metallic perovskite [Nature Materials 12, 1024 (2013)] was examined using first-principles density-functional theory. In LiOsO3, a-a-a- octahedral titling mode is…

A complete mapping in the Brillouin zone of the structural instability associated with the ferroelectric phase transitions of KNbO$_3$ has been obtained by first-principles calculations using an LAPW linear response approach. The wavevector…

We report a systematic first-principles study based on density functional theory (DFT) of the structural and ferroelectric properties of the $R_2$Ti$_2$O$_{7}$ perovskite-related oxides with $R=$ La, Ce, Pr, and Nd. We show that, in all…

In recent yerars, Bismuth sodium titanate (BNT) and BNT-based piezoelectric materials have proved potential for lead-free piezoelectric technologies. Such materials' complicated phase structure is crucial to their thermo-electromechanical…

We extend our previous first-principles theory for perovskite ferroelectric phase transitions to treat also antiferrodistortive phase transitions. Our approach involves construction of a model Hamiltonian from a Taylor expansion,…

The structural energetics of PdTi and PtTi have been studied using first-principles density-functional theory with pseudopotentials and a plane-wave basis. We predict that in both materials, the experimentally reported orthorhombic $B19$…

We introduce an open-source, fully atomistic second-principles interatomic potential for lead titanate (PbTiO3), a benchmark ferroelectric material known for its strong polarization and hightemperature phase transitions. While density…

We have studied the structural phase transition of multiferroic YMnO$_3$ from first principles. Using group-theoretical analysis and first-principles density functional calculations of the total energy and phonons, we perform a systematic…

Raman Spectroscopic measurements are carried out to investigate the structural phase transitions as a function of composition in modified sodium niobate [(1-x) NaNbO3-xBaTiO3:NNBTx] for x=0.0 to 0.15 at room temperature. The characteristic…

The structural phase transition in hexagonal BaMnO$_3$ occurring at $T_c$=130 K was studied in ceramic samples using electron and X-ray diffraction, second harmonic generation as well as by dielectric and lattice dynamic spectroscopies. The…

Recently, the two dimensional (2D) materials have become a potential candidates for various technological applications in spintronics and optoelectronics. In the present study, the structural, electronic, and phase stability of 2D layered…

First principles density functional calculations for Fe$_{2}$O$_{3}$ has been performed over a wide range of pressures. The ground state is corundum-type hematite and is an antiferromagnetic insulator. This is in good agreement with…

Low temperature studies of the behavior of the sound velocity and attenuation of acoustic modes have been performed on a single crystal NdFe_3(BO_3)_4. Transitions of the magnetic subsystem to the antiferromagnetically ordered state at T_N…

First-principles calculations were performed to investigate the ferroelectric properties of barium titanate and bismuth ferrite, as well as phonon dispersion of BaTiO3, using density functional theory and density functional perturbation…

We demonstrate that small but finite ferroelectric polarization ($\sim$0.01 $\mu$C/cm$^2$) emerges in orthorhombic LuFeO$_3$ ($Pnma$) at $T_N$ ($\sim$600 K) because of commensurate (k = 0) and collinear magnetic structure. The synchrotron…