Perovskites acceptor doping

Acceptor doping in perovskite oxides gives materials with a vacancy population that can act as proton conductors in moist atmospheres (Section 6.9). In addition, the doped materials are generally p-type semiconductors. This means that in moist atmospheres there is the possibility of mixed conductivity involving three charge carriers (H+, O2-, and h ) or four if electrons, e, are included. 

The situation can be illustrated with respect to the acceptor-doped perovskite structure SrZrC>3, with Y3+ substituted for Zr4+ to give compositions SrZrj YVC>3-0.5.V The doping reaction can be written ... 

Important contributions to the area of defect chemistry of the acceptor-doped Lnj.xAxBOs, perovskites, where B is selected from Cr, Mn, Fe or Co, have been made by a number of investigators. Particular reference is made to reviews provided by Anderson [159,160] and Mizusaki [161]. The substitution of divalent alkaline-earth ions on the A-site increases the concentration of oxygen vacancies. Temperature and oxygen partial pressure determine whether charge compensation occurs by an increased valency of the transition metal ion at the B-site or by the formation of ionized oxygen vacancies. Thermogravimetric studies have indicated that in, for example, LaCrOs, YCrOs and LaMnOs the... 

This will, for instance, be valid in certain ranges of oxygen activity and temperature for many acceptor-doped LaM03 (M = transition metal) perovskites with small band gaps. 

De Souza, R.A., Kilner, J.A., and Steele, B.C.H. (1995) A SIMS study of hydrogen in acceptor-doped perovskite oxides. Solid State Ionics, 77, 180-184. 

The acceptor-doped perovskites (general formula of ABOs-a) have shown much promise as MIECs. Much attention has been focused on these versatile metal oxides as they exhibit catalytic activity [24] and therefore their use in some applications can avoid the need for catalytic modification of the membrane surface. This activity has meant that MIECs can be used as electrode materials in solid-oxide fuel cell systems for the reduction of oxygen simultaneously, this inherent catalytic activity means that problems with chemical stability can arise. 

V. Acceptor-Doped Perovskite and Perovskite-Related Oxides A. Introduction... 

V. ACCEPTOR-DOPED PEROVSKITE AND PEROVSKITE-RELATED OXIDES... 

Important contributions to the area of defect chemistry of the acceptor-doped Ln, x A BOj, perovskites, where B is selected from Cr, Mn, Fe, or Co, have been made by a number of investigators. Particular reference is made to reviews provided by Anderson - and... 

Membranes based on acceptor-doped ceria may represent a promising alternative to Ln,Tm-based perovskites. Ceria has a much wider pOg stability range and a higher ionic conductivity than most of the Tm-based perovskites at 700 °C the ionic conductivity of Ceo.gGdo.iOi 95 is 0.04 while the ionic conductivity of... 

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