Band-gap variation in $R$ScO${}_3$ ($R=\mathrm{Pr}$, Nd, Sm, Eu, Gd, Tb, and Dy): X-ray absorption and O $K$-edge x-ray emission spectroscopies

The electronic structure of rare-earth scandates $R$ScO${}_3$ ($R$: newly studied Pr, Nd, Eu, and Tb, compared with previously studied Sm, Gd, and Dy) was analyzed by a combined use of O $K$ absorption and emission spectroscopies and Sc $L$-edge absorption spectroscopy. This permitted the estimation of band gaps by use of a method that differed from optical measurements. The band-gap variation over the series in dependence on the rare-earth ion is analyzed, and a correlation between the Sc-O mean distance and the band gap is found and discussed.

Figure 1

O $K$ XAS (green) and XES (blue) of PrScO${}_3$, NdScO${}_3$, SmScO${}_3$, EuScO${}_3$, GdScO${}_3$, TbScO${}_3$, and DyScO${}_3$. LDA+U calculations (black) below experimental data were convoluted with 0.7 (XES) and 0.4 eV (XAS) Gaussian for experimental broadening. The calculated unoccupied states are shifted upward by 1.4 eV for SmScO${}_3$, 1.6 eV for GdScO${}_3$, and 1.5 eV for DyScO${}_3$.

Figure 2

Experimental O $K$ (blue) and Sc $L_{2,3}$ (green) XES spectra of SmScO${}_3$, GdSco${}_3$, and DyScO${}_3$ (extracted from Raekers et al.[19]).

Figure 3

Sc $L_{2,3}$ XAS spectra of $R$ScO${}_3$.

Figure 4

(a) Tolerance factor (Goldschmidt factor) for $R$ScO${}_3$, (b) Sc$-$O$-$Sc bond angles of $R$ScO${}_3$, (c) distances between Sc and the two oxygen spectra, and (d) Sc$-$O mean distance and experimental band gaps. All structural parameters have been extracted from Liferovich et al..[27]