We have investigated the evolution of the electronic properties of $\mathrm{L}{\mathrm{a}}_{1-x}\mathrm{S}{\mathrm{r}}_x\mathrm{Cr}{\mathrm{O}}_3(0\le x\le 1)$ epitaxial films deposited by molecular beam epitaxy (MBE) using x-ray diffraction, x-ray photoemission spectroscopy, Rutherford backscattering spectrometry, x-ray absorption spectroscopy, electrical transport, and ab initio modeling. $\mathrm{LaCr}{\mathrm{O}}_3$ is an antiferromagnetic insulator, whereas $\mathrm{SrCr}{\mathrm{O}}_3$ is a metal. Substituting $\mathrm{S}{\mathrm{r}}^{2+}$ for $\mathrm{L}{\mathrm{a}}^{3+}$ in $\mathrm{LaCr}{\mathrm{O}}_3$ effectively dopes holes into the top of valence band, leading to $\mathrm{C}{\mathrm{r}}^{4+}$ (${3d}^2$) local electron configurations. Core-level and valence-band features monotonically shift to lower binding energy with increasing $x$, indicating downward movement of the Fermi level toward the valence band maximum. The material becomes a $p$-type semiconductor at lower doping levels and an insulator-to-metal transition is observed at $x\ge 0.65$, but only when the films are deposited with in-plane compression via lattice-mismatched heteroepitaxy. Valence-band x-ray photoemission spectroscopy reveals diminution of electronic state density at the $\mathrm{Cr}d{t}_{2g}$-derived top of the valence band, while O K-edge x-ray absorption spectroscopy shows the development of a new unoccupied state above the Fermi level as holes are doped into $\mathrm{LaCr}{\mathrm{O}}_3$. The evolution of these bands with Sr concentration is accurately captured using density functional theory (DFT) with a Hubbard U correction of 3.0 eV $(\mathrm{DFT}+U)$. Resistivity data in the semiconducting regime $(x\le 0.50)$ do not fit perfectly well to either a polaron hopping or band conduction model but are best interpreted in terms of a hybrid model. The activation energies extracted from these fits are well reproduced by $\mathrm{DFT}+U$.

• Received 17 October 2014
• Revised 20 January 2015

DOI:https://doi.org/10.1103/PhysRevB.91.155129