Density Functional Theory Prediction of the Second Harmonic Generation and Linear Pockels Effect in Trigonal BaZnO₂

Abstract

Polycrystalline powder of trigonal BaZnO2 has been synthesized and characterized by X-ray diffraction, dielectric measurements, and vibrational spectroscopy (infrared and Raman). These properties have been also calculated using the density functional theory and compared with the experimental ones. The experimental phonon modes have been assigned, and we have revisited the previous theoretical assignment reported in the literature combining the calculated and the experimental data. The dielectric constant has been analyzed by decoupling it into three contributions (electronic, phonon, and strain). The second-order nonlinear susceptibility and the electro-optic response have been predicted as no theoretical or experimental investigations of these optical properties have been previously reported in the literature. The second-order nonlinear optical susceptibility and the electro-optic coefficients of BaZnO2 are predicted to be significantly higher than those reported in α-quartz or α-GeO2. Thus, considering the stability of BaZnO2 within a large range of temperature, this compound could be a possible candidate for nonlinear optical applications when compared with α-quartz.

BaCoO2 with Tetrahedral Cobalt Coordination: The Missing Element to Understand Energy Storage and Conversion Applications in BaCoO3−δ-Based Materials

“…It is therefore important to note that the mechanism of oxygen release occurs at the interface of the pellet with the secondary vacuum atmosphere as the tetragonal phase is absent at the surface of the pellet, i.e., Cu Kα X-rays are strongly absorbed by the barium cobalt oxide pellet and probe only its first-micron surface. BaCoO 2 presents an arrangement of intermediate compactness between the quartz and BaZnO 2 structures, 38 as determined from the c/a unit cell parameter ratio, the tetrahedral tilt angle δ, and the intertetrahedral bridging angle θ, Figure S4 and Table S1, whereas the CoO 4 tetrahedra are found to be slightly distorted (1.906(13) and 2.023( 14) Å Co−O bonds). 41 Bond Valence Sum (BVS) information is shown in Table S2 and shows an appropriate value for the cobalt cation charge (1.94(3)).…”

“…The latter phase is proposed to have a quartz-derived trigonal structure with a helicoidally corner-sharing, CoO 4 -tetrahedral-framework, Figure S2. However, only the BaCoO 2 unit cell parameters have been determined, and from the similarities between the X-ray diffraction powder patterns, the BaZnO 2 -type structure with the P 3 1 21 space group was proposed. , Recently, a tetragonal, highly oxygen-deficient metastable phase BaCoO 2+δ with the P 4/ mmm space group and another P 2 1 / m monoclinic BaCoO 2.67 form derived from the cubic perovskite structure were also reported, Figure S3. The latter structure has three different Co coordination environments, an octahedral, a square pyramidal, and a tetrahedral one.…”

A Framework for Biosensors Assisted by Multiphoton Effects and Machine Learning

“…Since the discovery of quartz’s piezoelectricity more than a century ago, the need for effective materials for novel piezoelectric and NLO applications has steadily increased. Although piezoelectric materials are supposed to have the highest electromechanical coefficients, excellent SHG characteristics are crucial for NLO applications [ 191 ]. ANNs speed up optimization of genetic algorithms and store sample information that can be easily generalized to other samples with minimal additional training [ 192 ].…”

Machine Learning based prediction of noncentrosymmetric crystal materials

“…On the other hand, direct numerical calculation of the optical properties of a single crystalline material from its atomic structure by accurate first-principles without any other inputs has just been made available for a few years. Studies have focused on properties such as second harmonic generation (SHG) coefficients [7] and other important optical properties such as energy band gap, refractive indices [8], and birefringence. While first-principles calculations make it possible to predict some optical properties without any experimental data, such computation is usually tedious and very computationally demanding even for not too complicated primitive cells.…”