Cubic-free perovskites

Here, we present a screening study of well-known and characterized perovskites aimed at determining descriptors for easy assessment of the protonic flux see Ref. [77] for details. The aim of this study is not only the thermodynamic but also the kinetic properties, so limitations in the choice of materials are necessary. In cubic and dopant-free perovskites, all oxygen atoms are equivalent and all H jumps are identical as are the OH rotations, see Figure 18.9. This is... 

A simpler (in the sense of fewer free parameters) stracture derived from that of perovskite is that of caldte, CCaOa. This may be obtained from the cubic structure by concerted rotations of CaOj octahedra about axes parallel to [111], so that the coordination of C is reduced from O12 to 03 In terms of anion coordination, this corresponds... 

In the aristotype ABX3 perovskite stmcture, with Pm3m space group symmetry, there is a single free parameter, the cubic lattice parameter, a. A simple method to model the crystal stmcture is to determine the stmcture parameter(s), a in this case, that minimize(s) the Global Instability Index, G (Eq. (21) in [8]). 

Ordered perovskites with the A2BB Xg composition have two free positional parameters, the lattice parameter a and fractional coordinate x, which defines the anion position on the 24e Wyckoff position in space group Fm3m. Figure 6 shows the predicted (G optimized) and observed lattice parameters for cubic cation ordered A2BB Xg perovskites. The predicted lattice parameters are typically within a couple percent of the observed lattice parameters. Interestingly, there is a... 

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