Density-functional theory calculations of the ${\text{LiNbO}}_{3}$ $(2\overline{1}\overline{1}0)$, $(1\overline{1}00)$, and (0001) surfaces, commonly referred to as $X$, $Y$, $Z$ cuts, are presented. In case cut, we find a pronounced dependence surface structure stoichiometry on direction ferroelectric polarization. contrast, influence chemical potentials constituents is limited. Rather electrostatics governs stability. Different from $X$ cut $Y$ clearly dependent preparation conditions. The...

${\mathrm{LiTaO}}_{3}$ and ${\mathrm{LiNbO}}_{3}$ crystals are investigated here in a combined experimental theoretical study that uses Raman spectroscopy complete set of scattering geometries corresponding density-functional theory calculations to provide microscopic information on their vibrational properties. The efficiency is computed from first principles order univocally assign the measured peaks calculated eigenvectors. Measured spectra shown be qualitative agreement confirm mode...

A large number of oxides has been investigated in the last twenty years as possible new materials for various applications ranging from opto-electronics to heterogeneous catalysis. In this context, ferroelectric are particularly promising. The electric polarization plays a crucial role at many oxide surfaces, and it largely determines their physical chemical properties. Ferroelectrics offer addition possibility control/switch hence surface chemistry, allowing realization domain-engineered...

The temperature and oxygen partial pressure (pO2) dependent electrical conductivity of LiNbO3, LiTaO3, LiNb1-xTaxO3 (LNT) solid solutions up to 900 °C is presented. found be isotropic about 700 °C. Different Nb/Ta ratios do not affect activation energies at temperatures below 600 °C, which suggests an identical conduction mechanism, namely the migration Li ions by means vacancies. Above this temperature, noticeable deviations in Nb rich samples emerge due strongly increasing electronic...

Abstract Given the vast range of lithium niobate (LiNbO 3 ) applications, knowledge about its electronic and optical properties is surprisingly limited. The direct band gap 3.7 eV for ferroelectric phase – frequently cited in literature concluded from experiments [1]. Recent theoretical investigations [2] show that band‐structure are very sensitive to quasiparticle electron‐hole attraction effects, which were included using GW approximation electron self‐energy Bethe‐Salpeter equation...

We present a comprehensive theoretical investigation of paraelectric (cubic) and ferroelectric (tetragonal) BaTiO${}_{3}$. The atomic electronic structure, piezoelectric tensor, Debye temperature, zone center phonon frequencies, optical absorption are calculated for both phases from first principles. structural vibrational properties predicted density functional theory in good agreement with experiment earlier work. structure response found to be very sensitive quasiparticle electron-hole...

We used ultrafast electron diffraction and density-functional theory calculations to gain insight into the charge density wave (CDW) formation on In/Si(111). Weak excitation by a femtosecond-laser pulse results in melting of CDW. The immediate freezing is hindered barrier for motion atoms during phase transition: melted CDW constitutes long-lived, supercooled strong evidence first-order transition. triggered preexisting adsorbates. Starting at these condensation nuclei, expands one...

We report the discovery of a temperature-induced phase transition between α and β structures antimonene. When antimony is deposited at room temperature on bismuth selenide, it forms domains α-antimonene having different orientations with respect to substrate. During mild annealing, grows prevails over phase, eventually forming single domain that perfectly matches surface lattice structure selenide. First-principles thermodynamics calculations this van der Waals heterostructure explain...

Specific heat capacity measurements by differential scanning calorimetry (DSC) of single crystals solid solutions LiNbO3 and LiTaO3 are reported compared with corresponding ab initio calculations, the aim to investigate variation ferroelectric Curie temperature as a function composition. For this purpose, these were grown Czochralski pulling along c-axis. Elemental composition Nb Ta was investigated using XRF analysis, small samples homogeneous well known used for DSC measurements. We...

Adamantane-type clusters exhibit a huge diversity of chemical compositions, structural details, and resulting properties.

Stress plays a crucial role in thin films and layered systems, thus significantly influences the material's electrical, mechanical (nonlinear) optical responses. Despite lithium niobate's wide applicability as nonlinear material, impact of stress on its properties is not well characterized. In this work, we systematically study both experimentally theoretically, responses film niobate (TFLN) single crystals. Compressive tensile applied our experiment using piezodriven strain cell. We then...

We investigate the influence of molecular vibrations on tunneling electrons through an octane−thiolate sandwiched between two gold contacts. The coherent and incoherent currents are computed using non-equilibrium Green's functions formalism. Both system Hamiltonian electron−phonon interaction obtained from first-principles DFT calculations, including a microscopic treatment This method allows to study explicitly each individual vibrational mode show detailed analysis power dissipated in wire.

The structural and electronic properties of rare-earth (RE) (Eu, Er, Tm) related defect pairs in GaN have been investigated theoretically. Based on $\text{LDA}+U$ total-energy calculations, their possible role the luminescence process is discussed. In all charge states, lanthanides show a strong preference for Ga-lattice site, either as isolated substitutional or complexed with intrinsic defects. With respect to valence, proper description correlation effects strongly localized $4f$...

The structure and stability of defect clusters in ${\mathrm{LiNbO}}_{3}$, as well their influence on the linear nonlinear optical susceptibilities, are calculated within density functional theory (DFT) using semilocal hybrid exchange-correlation functionals. In particular, complexes modeling Li shortage during crystal growth, Li-vacancy model Nb-vacancy model, examined detail. It is found that clustering significantly decreases formation energies all considered defects with respect to dilute...

The influence of electronic many-body interactions, spin-orbit coupling, and thermal lattice vibrations on the structure lithium niobate is calculated from first principles. Self-energy calculations in $GW$ approximation show that inclusion self-consistency Green function $G$ screened Coulomb potential $W$ opens band gap far stronger than found previous ${G}_{0}{W}_{0}$ but slightly overestimates its actual value due to neglect excitonic effects $W$. A realistic frozen-lattice about 5.9 eV...

Lithium niobate and lithium tantalate crystals are technologically important metal oxides with exceptional combinations of ferroelectric, piezoelectric, acoustic, optical, electrical properties. The self-diffusion both, the ionic constituents underlying point defects, is especially for overall conductivity. To get insight into their dynamics, we investigate in this work Li congruent ${\mathrm{LiNbO}}_{3}$ ${\mathrm{LiTaO}}_{3}$ single from different suppliers up to a temperature...

In this paper, we report the ability of self-consistent-charge density-functional based tight-binding method to describe small gold clusters. We concentrate our investigations mainly on anions, and find that describes their geometric electronic structures fairly well, in comparison with calculations. particular, correctly reproduces planarity ground-state up cluster sizes agreement experiment theory.

The frequency-dependent dielectric function and the second-order polarizability tensor of ferroelectric ${\mathrm{LiNbO}}_{3}$ are calculated from first principles. calculations based on electronic structure obtained density-functional theory. subsequent application $GW$ approximation to account for quasiparticle effects solution Bethe-Salpeter equation stoichiometric material yield a that slightly overestimates absorption onset oscillator strength in comparison with experimental...

The vibrational properties of stoichiometric LiNbO3 are analyzed within density-functional perturbation theory in order to obtain the complete phonon dispersion material. density states ferroelectric (paraelectric) phase shows two (one) distinct band gaps separating high-frequency (∼800 cm(-1)) optical branches from continuum acoustic and lower states. This result leads specific heat capacites close agreement with experimental measurements range 0-350 K a Debye temperature 574 K. calculated...

Abstract Different aspects of ferroelectric LiTaO 3 (LT) such as polaronic defects, optical response and electrical conductivity are investigated by the most recent theoretical experimental approaches. Comparing results with state-of-the-art knowledge widely studied LiNbO (LN), we evaluate general assumption that there is little difference between aforementioned properties LT LN. First-principles calculations reveal existence point defects in qualitatively compatible picture established...

The ferroelectric to paraelectric phase transition in ${\mathrm{LiTaO}}_{3}$ and pure as well Mg-doped ${\mathrm{LiNbO}}_{3}$ is investigated theoretically by atomistic calculations the framework of density functional theory, experimentally calorimetry electrical conductivity measurements. First-principles models within stochastic self-consistent harmonic approximation (SSCHA) allow consider anharmonic effects thus obtain a realistic estimate Curie temperature ${T}_{C}$ both ferroelectrics....

The density functional based tight-binding (DFTB) method can benefit substantially from a number of developments in theory (DFT) while also providing simple analytical proving ground for new extensions. This contribution begins by demonstrating the variational nature charge-self-consistent DFTB (SCC-DFTB), presence defined ground-state this class methods. Because state SCC-DFTB itself be qualitatively incorrect some systems, suitable forms recent LDA+U functionals are presented. leads to...

The formation energies and charge transition levels of the most relevant $\mathrm{Li}\mathrm{Nb}{\mathrm{O}}_{3}$ intrinsic point defects, i.e., Nb antisites Li as well vacancies, are studied from first principles. Thereby isolated defects modeled in framework density functional theory with local hybrid exchange-correlation functionals. inclusion nonlocal exchange opens fundamental band gap by nearly 2 eV modifies considerably relative stability investigated respect to values calculated On...