Ybaco <sub> 4 </ Sub> O <sub> 7 </ Sub> First Principle Of The Oxygen Absorption Properties

In this paper,we carried out the first-principles calculations to study the nature of oxygen absorption in YBaCo₄O₇ as well as in AI or Fe partial substitution Co systems.In the first part of the paper,the oxygen absorption property of perovskite-like composite material YBaCo₄O₇ was studied.The lattice constants were optimized,and the stable insert positions of the YBaCo₄O₇ system were found.The results showed that due to the large interstitial space in the system,YBaCo₄O₇ can absorb 0.5 oxygen atoms easily.The lattice structure of YBaCo₄O_7.5 is not obviously changed and it remains the lattice structure of YBaCo₄O₇.The biggest change in lattice parameter is 0.14(?) in[100]direction,while that is less than 0.1(?) in other directions.The inserted oxygen has a large binding energy(5.84eV),implying that the system can absorb 0.5 O atoms very easily.The binding energy of the inserted oxygen for the YBaCo₄O₇ absorbing one oxygen is 5.35eV.In the case the largest change in the[010] direction is of reducing 0.17(?),and the changes of other directions are less than 0.1 (?),too.In the second part of this paper,we researched the systems in which some of Co in the YBaCo₄O₇ system replaced by Al as well as the oxygen absorbing property of the A1 substitutional systems.The stable structure of 0.5 Co substituted by Al is almost unchanged.The lattice constant in[010]direction decreases by 0.15(?),and by 0.18(?) in[001]direction,and in the[100]direction it increases only by 0.06(?).From the research of oxygen uptake in YBaCo_3.5Al_0.5O₇ and YBaCo₃AlO₇,we found that the YBaCo₃AlO₇ absorbs O more easily than YBaCo_3.5Al_0.5O₇ because the binding energy of the former is bigger.In the third part of this paper,the Fe substitutional systems and the oxygen absorption uptake nature were studied and the most stable structure of 0.5 and 1 Fe substitution sysyems were found,respectively.By calculating their substituting energy, we found that the system for one Co replaced by Fe is not stable,for its subsituting, energy is smaller than zero.The nature of oxygen absorption was studied and found that the ability of oxygen absorption for the system in which 0.5 Co replaced by Fe is not effcted and the binding energy is higher than Al substituted system.To explain these phenomena,we have analyzed the density of states of YBaCo₄O₇,as well as the partial substitution systems YBaCo_3.5Al_0.5O₇,YBaCo₃AlO₇ and YBaCo_3.5Fe_0.5O₇.