SVM Applied to New Compound Synthesis Problems

The most exciting achievement of materials research is to find some new compound (or new phases) with specified structure and outstanding properties. In this chapter, the materials design problems of compounds 

1 Materials design problems for materials with perovskite structure 

The crystal structure of compounds with ideal perovskite structure is illustrated in Fig. 8.1. It is the structure of a unit cell of SrTiOs crystal. In this structure, tetravalent Ti cation is surrounded by six oxygen anions to form octahedral structure, and bivalent Sr cation is surrounded by twelve oxygen anions to form cubo-octahedral structure. Based on the understanding of such type of crystal structure, Goldschmidt proposed a famous crystal-chemical criterion of the formability or the stability of perovskite structure for ABXs-type compounds  

Owing to the accumulation of the crystallographic data of compounds with perovskite structure, it is now widely recognized that the range of tolerance factor for the stability of perovskite structure should be 0.75 t 1.00. 

Although Goldschmidt s tolerance factor t is indeed very useful for the exploration of new compounds with perovskite structure, it is only a necessary condition but not the sufficient condition for the formation or the stability of perovskite structure [145]. Many systems having t in the range of 0.75—1.0 do not form perovskite-type compound. 

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