The dissociative adsorption of O2 demonstrates a significant correlation with the catalytic efficiency of oxygen reduction catalysts. We have performed density-functional theory calculations to investigate the dissociative adsorption of O2 on the Pd-skin Pd3Cu(1 1 1) surface. The calculated results show that the adsorption configuration denoted as “t-f(h)-b” is energetically favourable on the Pd-skin Pd3Cu(1 1 1) surface. In the context of O2 dissociation, two thermodynamically favourable dissociation pathways have been identified. The first pathway proceeds from the initial state denoted as “t-f-b” to yield two oxygen atoms occupying hcp sites. The second pathway, starting from “t-h-b,” leads to the formation of two oxygen atoms positioned at fcc sites. Furthermore, our analysis demonstrates a decrease in the stability of O2 adsorption and a slight increase in the energy barrier for the dissociation of adsorbed O2 compared to the corresponding process on the Pd(1 1 1) surface. This theoretical investigation offers valuable insights that can inform and guide the practical application of Pd-Cu alloy materials as highly effective catalysts for oxygen reduction reaction. Graphical abstract Download : Download high-res image (224KB) Download : Download full-size image
Highlights • P tends to stay at the interstitial sites while Mg will substitute the host atoms at the Ni-rich Σ5 (2 1 0) Ni3Al GBs. • Synergistic segregation of Mg can improve the detrimental effect of P in the mixed hole on the cohesion properties of the Ni-rich GBs. • The site occupation of Mg can be reversed from the Ni site to the Al site by synergistic alloying of P at the stoichiometric Σ5 (2 1 0) Ni3Al GBs. • GB strengthening of alloying elements can be attributed to the strong P/Mg-Ni interactions across the GBs. The addition of specific alloying elements can effectively control the microstructure of alloys, so as to improve the cohesive properties of the GBs. In this work, the first-principles plane-wave pseudopotential method is used to investigate the segregation behavior of P and Mg doping at the Ni3Al GBs and reveal the physical mechanism. Different 100%Ni Σ5 (2 1 0) [0 1 0] GB systems with and without doping elements are relaxed and larger volume expansions are obtained. The calculated segregation energies show that P or Mg atoms tend to segregate to the GBs relative to the bulk. P atoms tend to stay at the interstitial sites surrounded by 8 Ni atoms in the pure Ni holes of the GBs while Mg atoms tend to substitute Ni atoms. The segregation of P or Mg to the GBs leads to an increase of the Griffith work at the GBs, indicating that the segregation can improve the bonding properties of the GBs. Especially, the synergistic segregation of Mg can improve the detrimental effect of P in the mixed hole on the cohesive properties of the GBs. It is also found that the site occupation of Mg can be reversed from the Ni site to the Al site by the synergistic alloying of P at the 50%Ni Σ5 GBs. P and Mg tend to bond with the host atom Ni regardless of GB structure. The investigation of electronic structure shows that GB strengthening of alloying elements is attributed to the increasing P/Mg-Ni interactions across the GBs. Graphical abstract Download : Download high-res image (80KB) Download : Download full-size image
Highlights • Uniaxial strain is key to tuning of material properties, including magnetic phases. • Decoupling effect of type of strain from geometrical effects by forming square lattice. • Compressive strain leads to FM insulator by reduction of Jahn–Teller distortion. • Correlation plays strong role; DFT gives metal, DMFT gives insulator. • Tensile strain give AFM insulator; Flavor of strain is more important than geometry. Recent years have seen tremendous progress in experimental techniques to create uniaxial strain. Motivated by these advances we investigate the effect of uniaxial strain on LaMnO 3 employing ab-initio dynamical mean-field theory, and put it in contrast to biaxial strain that occurs in epitaxial systems. Projecting on the low-energy subspace of Mn 3 d states, and solving multi-impurity problems, our approach emphasizes on local dynamic correlations at Mn sites. At ambient pressures, LaMnO 3 crystallizes in an orthorhombic unit cell, with in-plane lattice constants a < b , and shows an A-type antiferromagnetic ground state. If we apply uniaxial compressive strain such that the in-plane lattice becomes square with lattice constant a , we find a ferromagnetic insulating state. This is in sharp contrast to DFT results using various functionals like PBE, PBE+ U , and hybrid functionals like HSE, which all predict a half-metallic ferromagnetic behavior. Interestingly, applying uniaxial tensile strain, such that the in-plane lattice becomes square with the longer lattice constant b , an antiferromagnetic insulating state is observed. We trace back these results to the reduction in Jahn–Teller distortion in the case of compressive strain, favoring a ferromagnetic state. This reduction is absent in the tensile case, and the antiferromagnetic state therefore survives. Our study shows that it is the flavor of the strain (compressive or tensile) which is decisive for the magnitude of Jahn–Teller distortions and, hence, the magnetic state. Graphical abstract Download : Download high-res image (226KB) Download : Download full-size image
