钙钛矿化合物 LaGaO3的电子、传输和光学性质

The perovskite-type oxides ABO3 have a multifunctional application in different area such as promising new anode for rechargeable batteries(Ni/MH), photovoltaic and photochromic, because of their properties variety. In this work, we interested on the calculation of the electronic, optical and transport properties of the lanthanum gallate perovskite oxides compound, using the fifirst-principles calculations based on the density functional theory. We determined the exchange and correlation effects by a Generalized Gradient Approximation of Perdew−Burke−Ernzerhof (GGA-PBE). As results the energy gaps of LaGaO₃ compound with GGA-PBE have been found as 3.61 eV, from the transport properties we notice that LaGaO₃ is P-type materials with electrical conductivity varied from 0 (Ω.m.s) ⁻¹ at 0 K to 10 × 1020 (Ω.m.s) ⁻¹ at 800 K.

In this work all calculations are based on the density functional theory (DFT), the solution of Kohn–Sham equations are obtained by usingWien2k ab initio simulation program .We determined the exchange and correlation effects by GGA-PBE. The electronic, transport and optical properties have been calculated in stable orthorhombic phase which conforms to Pnma space group. In these calculations we had a 7 × 5 × 7Monkhorst −Pack set of k-point mesh of Brillouin zone integration generated automatically, the Rmt* Kmax value was fifixed to 7 (RMT present the small atomic radius in the unit cell, while Kmax present the size of the largest vector in the plane wave expansion). The optimization of LaGaO₃ lattice parameters is calculated using Tomas Kana package. The transport proprieties are calculated using BoltzTraP code . The hybrid exchange correlation functionals like B3LYP and B3PW allows to achieve much better agreement with the experiment for the band gaps of perovskite materials, than the GGA-PBE exchange-correlationfunctional.

LaGaO₃ perovskite oxide with Pnma space group have a structure with four atoms of Lanthanum, four atoms of Gallium and twelve of Oxygen. The calculated and experimental lattice parameters are given in table 1. We used the experimental lattice parameters to do the optimization using a package developed by Tomas Kana. As a result of our calculation from the standard DFT calculation we obtained a = 5.580 Å, b = 5.554 Å and c = 7.874 Å, which gives results close to the experiment with in an error of 1%.

The total(DOS) and partial(PDOS) density of state of LaGaO₃ perovskite compound are shown in figure 2, where we observe that in the entire range La and Ga states hybridize with O, inclusive of the conduction and valence bands, which indicate that La-O and Ga-O bonding are principally covalent. The electron charge was transferred from La and Ga to O due to the large difference between states, revealing the ionic bonding characteristic.

Fig1

In this paper we determined the electronic, optical and transport proprieties of LaGaO₃ perovskite compound using GGA-PBE approximation. The transport proprieties are investigated using BoltzTraP code. According to the electronic band structure calculated with GGA-PBE approximation, we conclude that we have an indirect gap, the value of the band gap determined from GGA-PBE 3.61 eV. From the density of states we notice that we have a covalent and ionic hybridization between La and O and also between Ga and O in the entire range of energy. All optical properties are calculated and illustrated in details, showing that our materiel is a good absorber at ultraviolet, and the reflflectivity don’t exceed 20% in the entire range of wavelength. From the transport properties we notice that LaGaO₃ is P-type materials with electrical conductivity varied from 0 (Ω.m.s) ⁻¹ at 0 K to 10 × 1020 (Ω.m.s) ⁻¹ at 800 K.