As the following reaction shows, in exothermic solution combustion synthesis (SCS) process, a high amount of gaseous by-products liberated in an extremely short period of time which could expel the oxygen from the reaction media. Oxygen driving out from the reaction vessel decrease its concentration and as a result, instant vacuum could happen during combustion process. A NO s X B NO s Y Fuel s AB O s nH O g mCO g oN g Hea( ) ( ) ( ) ( ) ( ) ( ) ( )3 d d X1 + + = + + + +3 2 d Xd1+ 2 ( ) ( ) ( ) ( ) t22 2 2 In which d1 and d2 are the capacityof cations. X, Y, n, m, and o are molar coefficients, as well. (A) represents the basic structure, and B is the doped material oxide. At absolute vacuum in which oxygen pressure equals to zero, the reaction + += +−AB O AB OX d Xd X d Xd Oξξ1 221 22 2 2, spontaneously proceeds as ΔG = -∞. AB OX d Xd1+2 2 is a commonly expected product, +− AB OX d Xd 1 2 ξ 2 is its corresponding defective structure, and ξ is the concentration of oxygen vacancies in structure of AB OX d Xd1+ 2 2 oxide. However, H2O and CO2 can partially decompose. Thus, due to the released O2 from decomposition of H2O/CO2 the relative vacuum must be taken into considered. Based on this relative vacuum, a simple model proposed in order to estimate and compare the concentration of oxygen vacancies in SCS method. In this proposed model the comparable values of oxygen vacancy concentrations in the reaction + += + − AB O AB OX d Xd X d Xd O ξ ξ 1 2 2 1 2 2 2 2 as a function of Tce, (the temperature of the cooling environment) can be expressed as. = − ∗ ⎛⎜⎝ ⎞⎟⎠ ξ RT ce LnP max formation O T RTce 2 O2, – G , 2, ce 0 .

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