New stable rare earth Ti-based semiconductor pyrochlore oxides for low-cost energy applications

초록

This study investigates the structural, optoelectronic, magnetic and thermophysical properties of three newly designed semiconductor pyrochlore oxides, namely RE2Ti2O7 (RE = Er, Eu, Tb), using ab-initio calculations within the density functional theory framework. The values of indirect bandgaps are 3.8, 2.2 and 3.77 eV for the spin up channel of Er2Ti2O7, Eu2Ti2O7, and Tb2Ti2O7, respectively. While the values of indirect bandgaps for the spin down channel of Er2Ti2O7, Eu2Ti2O7, and Tb2Ti2O7 are 3.56, 3.65 and 2.1 eV, respectively. The paramagnetic magnetic moments can be inferred by analyzing the distinct band shapes observed in the energy band structures of the studied compounds corresponding to the spin up and spin down states. The magnetic moments of Er2Ti2O7, Eu2Ti2O7, and Tb2Ti2O7 have significant magnitudes, specifically measuring 12.00, 24.51, and 24.00 mu(B)), respectively. Significant absorption of incident photons by the studied compounds can be noted in near UV region in both spin channels. Low reflectivity (similar to 30%) by RE2Ti2O7 (RE = Er, Eu, Tb) is evident from the R(omega) spectra in an energy range of 1.0-10.0 eV. However, these compounds exhibit similar to 50% reflectance of the incident photons in upper UV region (above 10.0 eV). The analysis of the Seebeck coefficient spectra reveals that RE2Ti2O7 (RE = Er, Eu, Tb) exhibits p-type semiconductor behavior, however, Eu2Ti2O7 also shows n-type behavior from 200 to 450 K. The presented thermodynamic characteristics reveal that the pyrochlore oxides RE2Ti2O7 (RE = Er, Eu, Tb) exhibit thermal stability.

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