The electronic structure of Pr1−xCaxMnO3 has been investigated using a combination of firstprinciples calculations, X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), electron-energy loss spectroscopy (EELS), and optical absorption. The full range of compositions, x = 0, 1/2, 1, and a variety of magnetic orders have been covered. Jahn-Teller as well as Zener polaron orders are considered. The free parameters of the local hybrid density functionals used in this study has been determined by comparison with measured XPS spectra. A model Hamiltonian, valid for the entire doping range, has been extracted. A simple local-orbital picture of the electronic structure for the interpretation of experimental spectra is provided. The comparison of theoretical calculations and different experimental spectra provide a detailed and consistent picture of the electronic structure. The large variations of measured optical absorption spectra are traced back to the coexistence of magnetic orders respectively to the occupation of local orbitals. A consistent treatment of the Coulomb interaction indicate a partial cancellation of Coulomb parameters and support the dominance of the electron-phonon coupling.

Periodic density functional theory calculations have been performed to study the migration of various charge carriers in spinel-type MgSc 2 Se 4. This compound exhibits low barriers for Mg ion diffusion, making it a potential candidate for solid electrolytes in Mg-ion batteries. In order to elucidate the decisive factors for the ion mobility in spinel-type phases, the diffusion barriers of other mono-and multivalent ions (Li + , Na + , K + , Cs + , Zn 2+ , Ca 2+ , and Al 3+) in the MgSc 2 Se 4 framework have been determined as well. This allows for disentangling structural and chemical factors, showing that the ion mobility is not solely governed by size and charge of the diffusing ions. Finally, our results suggest that charge redistribution and rehybridization caused by the migration of the multivalent ions increase the resulting migration barriers.

Understanding and controlling the relaxation process of optically excited charge carriers in solids with strong correlations is of great interest in the quest for new strategies to exploit solar energy. Usually, optically excited electrons in a solid thermalize rapidly on a femtosecond to picosecond timescale due to interactions with other electrons and phonons. New mechanisms to slow down thermalization will thus be of great significance for efficient light energy conversion, e.g., in photovoltaic devices. Ultrafast optical pump–probe experiments in the manganite Pr0.65Ca0.35MnO3, a photovoltaic, thermoelectric, and electrocatalytic material with strong polaronic correlations, reveal an ultraslow recombination dynamics on a nanosecond‐time scale. The nature of long living excitations is further elucidated by photovoltaic measurements, showing the presence of photodiffusion of excited electron–hole polaron pairs. Theoretical considerations suggest that the excited charge carriers are trapped in a hot polaron state. Escape from this state is possible via a slow dipole‐forbidden recombination process or via rare thermal fluctuations toward a conical intersection followed by a radiation‐less decay. The strong correlation between the excited polaron and the octahedral dynamics of its environment appears to be substantial for stabilizing the hot polaron.

Ion mobility is a critical performance parameter not only in electrochemical energy storage and conversion but also in other electrochemical devices. On the basis of first-principles electronic structure calculations, we have derived a descriptor for the ion mobility in battery electrodes and solid electrolytes. This descriptor is entirely composed of observables that are easily accessible: ionic radii, oxidation states, and the Pauling electronegativities of the involved species. Within a particular class of materials, the migration barriers are connected to this descriptor through linear scaling relations upon the variation of either the cation chemistry of the charge carriers or the anion chemistry of the host lattice. The validity of these scaling relations indicates that a purely ionic view falls short of capturing all factors influencing ion mobility in solids. The identification of these scaling relations has the potential to significantly accelerate the discovery of materials with desired mobility properties.

 10 À4 % of Li. The ionic radii of Mg 2þ , 0.86 Å, and Li þ , 0.90 Å, are rather similar, [1] but Mg has the advantage of being a bivalent ion, which leads to a higher volumetric capacity of Mg metal anodes compared to Li, 3833 mAh cm À3 versus 2062 mAh cm À3 , and also to a low reduction potential of À2.37 V versus the standard hydrogen electrode (SHE) compared to À3.05 V of Li. [9,10] Furthermore, Mg-ion batteries (MIBs) exhibit a low tendency for dendrite formation [11][12][13][14][15] and a high melting point.A high multivalent ionic conductivity of 1-10 mS cm À1 has been achieved in MIBs at high temperatures. [16,17] However, a major problem for MIBs lies in the sluggish kinetics during intercalation at room temperature. [2,18] It should be noted that the design of chemically stable electrodes with high ionic conductivity is highly desirable, [2,[19][20][21][22][23] as a low ionic mobility can severely limit the performance of batteries.To address the slow migration of Mg ions in cathode materials at low temperatures, Chevrel phases and layered and spinel TiS 2 structures have been studied in detail. [24] A Mg-ion migration barrier of about 550 meV was found in cubic Ti 2 S 4 using galvanostatic intermittent titration technique measurements. Note that typically maximum migration barriers of %525 meV for micron-sized particles and %650 meV for nanosized particles are assumed to be compatible with an adequate battery operation. [25] Studies on the sulfide and selenide spinel frameworks indicate low-energy barriers for Mgion diffusion comparable to those of LIBs. [26] In contrast, oxide spinel cathode materials exhibit high migration barriers for Mg ions, which are caused by the relatively strong Coulombic attraction between the guest Mg 2þ and host oxygen lattice, [23] which leads to a lower ion mobility. The smaller electronegativity of sulfur and selenium lattices enlarges the lattice constant of these materials and thus also their ion mobility as typically diffusion barriers become smaller for larger lattice constants. Nevertheless, the increase of the ion mobility through the lowering of diffusion barriers is also accompanied by lower Mg insertion energies into the spinel structures, which lowers the voltage [27,28] and thus causes a reduction of the energy densities of chalcogenide materials.Recently, MgSc 2 Se 4 has been found to be a super ionic conductor exhibiting a high Mg-ion conductivity of 0.1 mS cm À1 at room temperature. [26] This high ion mobility not only makes MgSc 2 Se 4 a promising cathode material for MIBs, but also suggests that it could be used as a solid electrolyte. However, solid