A-Site Doped Brownmillerite Phases

A-site doping can often be written in terms of a reaction between a brownmillerite and a perovskite, A B Oj-A BOj (A B Og). For the BajIn Oj-LalnOj (LajIn Og) system, Ba, La In O, a brownmillerite structure, forms when x is less than 0.1. 

Above this value the structure is that of a disordered perovskite, initially with a tetragonal cell and then a cubic cell. 

An extensively studied series of brownmillerite phases can be prepared from the cubic perovskite series La, A MnOj, where A is Ca, Sr or Ba. The oxidised cubic phases contain Mn and the ratio dependent upon the value of x. The cubic form can be reduced to browmnillerite structures La, A MnO., where all the B-site cations are now Mn and Mn. The approximate phase ranges, x, over which the browmnillerite structure exists are as follows Ca, 0.225-0.5 Sr, 0.155-0.5 and Ba, 0.11-0.325. 

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