DFT modelling of oxygen adsorption on the Ag-doped LaMnO3 (001) surface

This study was partly financed by the State Education Development Agency of the Republic of Latvia via the Latvian State Scholarship (A.A.) and Latvia-Ukraine Project (Grant LV-UA/2018/2 to E.K.). The work of T.I. is performed under the state assignment of IGM SB RAS. Also, this research was partly supported by the Ministry of Education and Science of the Republic of Kazakhstan in the framework of the scientific and technology Program BR05236795 ‘‘Development of Hydrogen Energy Technologies in the Republic of Kazakhstan’’. The authors thank M. Sokolov for technical assistance and valuable suggestions.The density functional theory (DFT) method has been used to calculate oxygen adsorption on the Ag-doped MnO2- and LaO-terminated (001) LaMnO3 surfaces. The catalytic effect of Ag doping is revealed by comparison of the adsorption energies, electron charge redistribution, and interatomic distances for the doped and undoped surfaces. Adsorption of Ag on the MnO2-terminated surface increases the adsorption energy for both atomic and molecular oxygen. This increases the oxygen surface concentrations and could improve the cathode efficiency of fuel cells. The opposite effect takes place at the LaO-terminated surface. Due to the large adsorption energies, adsorbed oxygen atoms are immobile and the oxygen reduction reaction rate is controlled by the concentration and mobility of oxygen vacancies.State Education Development Agency of the Republic of Latvia via the Latvian State Scholarship (A.A.) and Latvia-Ukraine Project (Grant LV-UA/2018/2 to E.K.); Ministry of Education and Science of the Republic of Kazakhstan in the framework of the scientific and technology Program BR05236795; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Tuning Hydrated Nanoceria Surfaces: Experimental/Theoretical Investigations Of Ion Exchange And Implications In Organic And Inorganic Interactions

Long-term stability and surface properties of colloidal nanoparticles have significance in many applications. Here, surface charge modified hydrated cerium oxide nanoparticles (CNPs, also known as nanoceria) are synthesized, and their dynamic ion exchange interactions with the surrounding medium are investigated in detail. Time-dependent zeta (ζ) potential (ZP) variations of CNPs are demonstrated as a useful characteristic for optimizing their surface properties. The surface charge reversal of CNPs observed with respect to time, concentration, temperature, and doping is correlated to the surface modification of CNPs in aqueous solution and the ion exchange reaction between the surface protons (H+) and the neighboring hydroxyls ions (OH-). Using density functional theory (DFT) calculations, we have demonstrated that the adsorption of H+ ions on the CNP surface is kinetically more favorable while the adsorption of OH- ions on CNPs is thermodynamically more favorable. The importance of selecting CNPs with appropriate surface charges and the implications of dynamic surface charge variations are exemplified with applications in microelectronics and biomedical. © 2010 American Chemical Society

Aqueous Medium Induced Optical Transitions In Cerium Oxide Nanoparticles

Experimental and theoretical investigations were performed to investigate the effect of water on optical properties of nanoceria as a function of Ce3+ concentration. Theoretical studies based on density functional plane-wave calculations reveal that the indirect optical transitions in bare ceria nanoparticles are red-shifted with an increase in the concentration of Ce3+. However, ceria nanoparticles model with adsorbed water molecules show a blue shift in the indirect optical spectra under identical conditions. Direct optical transitions are almost independent of Ce3+ concentration but show a pronounced blue shift in the aqueous environment relative to the bare nanoparticles. The theoretical study is consistent with our experimental observation in difference of shift behaviour in bare and aqueous suspended ceria nanoparticles. This change from red- to blue-shift in indirect optical transitions is associated with the polarization effect of water molecules on f-electron states. This journal i

Photoinduced dynamics to photoluminescence in Ln³⁺ (Ln = Ce, Pr) doped β-NaYF₄ nanocrystals computed in basis of non-collinear spin DFT with spin-orbit coupling

<p>In this work, non-collinear spin DFT + <i>U</i> approaches with spin-orbit coupling (SOC) are applied to Ln³⁺ doped β-NaYF₄ (Ln = Ce, Pr) nanocrystals in Vienna <i>ab initio</i> Simulation Package taking into account unpaired spin configurations using the Perdew–Burke–Ernzerhof functional in a plane wave basis set. The calculated absorption spectra from non-collinear spin DFT + <i>U</i> approaches are compared with that from spin-polarised DFT + <i>U</i> approaches. The spectral difference indicates the importance of spin–flip transitions of Ln³⁺ ions. Suite of codes for nonadiabatic dynamics has been developed for 2-component spinor orbitals. On-the-fly nonadiabatic coupling calculations provide transition probabilities facilitated by nuclear motion. Relaxation rates of electrons and holes are calculated using Redfield theory in the reduced density matrix formalism cast in the basis of non-collinear spin DFT + <i>U</i> with SOC. The emission spectra are calculated using the time-integrated method along the excited state trajectories based on nonadiabatic couplings.</p

Influence of Bi Substitution with Rare-Earth Elements on the Transport Properties of BiCuSeO Oxyselenides

In this study, we demonstrate that introduction of rare-earth elements, R = La or Pr, into the Bi-O charge reservoir layer of BiCuSeO leads to an increase of both the charge carrier concentration and the effective mass. Although the charge carrier mobility slightly decreases upon Bi3+ to R3+ substitution, the electronic transport properties are significantly improved in a broad temperature range from 100 to 800 K. In particular, the electrical resistivity decreases by 2 times, while the Seebeck coefficient drops from 323 to 238 μV K-1 at 800 K. Thus, a power factor of nearly 3 μW cm-1 K-2 is achieved for Bi0.92R0.08CuSeO samples at 800 K. Meanwhile, a noticeable decrease of the lattice thermal conductivity is observed for the substituted samples, which can be attributed to the enhanced point defect scattering mostly originating from atomic mass fluctuations between R and Bi. Ultimately, a maximum zT value of nearly 0.34 at 800 K is obtained for the Bi0.92La0.08CuSeO sample, which is ∼30% higher than that of pristine BiCuSeO