**7. References**


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I would like to thank Rom Harré for his second reading of this paper, his advice and his generosity. I also would like to thank Miss Zgela, the Publishing Process Manager in charge

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of the concept of affinity to scrutiny in modern chemistry.

**6. Acknowledgments** 

**7. References** 


**19** 

*1Germany 2,3Latvia* 

**Thermodynamics of ABO3-Type** 

*1Max Planck Institute for Solid State Research, Stuttgart, 2Institute of Solid State Physics, University of Latvia, Riga, 3Department of Computer Science, University of Latvia, Riga,* 

Eugene Heifets1, Eugene A. Kotomin1,2, Yuri A. Mastrikov2,

The ABO3-type perovskite manganites, cobaltates, and ferrates (A= La, Sr, Ca; B=Mn, Co, Fe) are important functional materials which have numerous high-tech applications due to their outstanding magnetic and electrical properties, such as colossal magnetoresistance, half-metallic behavior, and composition-dependent metal-insulator transition (Coey et al., 1999; Haghiri-Gosnet & Renard, 2003). Owing to high electronic and ionic conductivities. these materials show also excellent electrochemical performance, thermal and chemical stability, as well as compatibility with widely used electrolyte based on yttrium-stabilized zirconia (YSZ). Therefore they are among the most promising materials as cathodes in solid oxide fuel Cells (SOFCs) (Fleig et al., 2003) and gas-permeation membranes (Zhou, 2009). Many of the above-mentioned applications require understanding and control of surface properties. An important example is LaMnO3 (LMO). Pure LMO has a cubic structure above 750 K, whereas below this temperature the crystalline structure is orthorhombic, with four formula units in a primitive cell. Doping of LMO with Sr allows one to increase both the ionic and electronic conductivity as well as to stabilize the cubic structure down to room temperatures - necessary conditions for improving catalytic performance of LMO in electrochemical devices, e.g. cathodes for SOFCs. In optimal compositions of

b b <sup>3</sup> 1-x x La Sr MnO (LSM) solid solution the bulk concentration of Sr reaches xb0.2 .

Understanding of LMO and LSM basic properties (first of all, energetic stability and reactivity) for pure and adsorbate-covered surfaces is important for both the lowtemperature applications (e.g., spintronics) and for high-temperature electrochemical processes where understanding the mechanism of oxygen reduction on the surfaces is a key issue in improving the performance of SOFC cathodes and gas-permeation membranes at relatively high (~800 C) temperatures. First of all, it is necessary to determine which LMO/LSM surfaces are the most stable under operational conditions and which terminations are the energetically preferential? For example, the results of our simulations described below show that the [001] surfaces are the most stable ones in the case of LMO (as

**1. Introduction** 

**Perovskite Surfaces** 

Sergej Piskunov3 and Joachim Maier1

