Shedding light on the structural, optoelectronic, and thermoelectric properties of pyrochlore oxides (La2Q2O7 (Q = Ge, Sn)) for energy applications: A first-principles investigation

Abstract

This paper presents an analysis of the electronic, optical, and thermoelectric properties of two newly designed pyrochlore oxides, La2Q2O7 (Q ​= ​Ge, Sn), based on first-principles calculations in the framework of DFT. The energy band gap shifts from direct to indirect band gap as Sn cation is replaced with Ge cation. The energy band gaps are 1.12 and 2.60 ​eV for La2Ge2O7 and La2Sn2O7, respectively. The TDOS spectra clearly indicate that there is no magnetic moment in the studied compounds. The ε2(ω) spectra reveal that these materials absorb maximum photons in the visible and lower UV regions. La2Q2O7 (Q ​= ​Ge, Sn) are efficient optical materials as their n(ω) value is between 1.0 and 2.0. The R(ω) spectra show up to 50% photon reflection in the UV region; however, the reflectance is negligible in the IR and visible regions. The Seebeck coefficient spectra reveal that these pyrochlore oxides are p-type semiconductors over the entire temperature range. La2Q2O7 (Q ​= ​Ge, Sn) are efficient thermoelectric materials as their figure of merit (ZT) is approximately 1.