###### Abstract
An alternative way to introduce disorder in perovskite derivatives is to change the ratio of octahedra or tetrahedra (or polyhedra with a coordination number of five), which implies the obtaining of block structures (coherent intergrowth structures), e.g., Ba\({}_{5}\)Er\({}_{2}\)Al\({}_{2}\)ZrO\({}_{13}\)\(\equiv\)2 Ba\({}_{2}\)ErAlO\({}_{5}\)-BaZrO\({}_{3}\)[10]. All these paths of creating oxygen deficiency are shown in Figure 1.  
As also shown in Figure 1, such phases are capable of incorporating water from the gas phase. For acceptor-doped perovskites, the process of the appearance of proton defects (OH\({}^{-}\) groups) is described in terms of the quasi-chemical formalism as the interaction between water vapor and oxygen vacancies \(V_{\rm o}^{\bullet\bullet}\). For the perovskites or perovskite-related phases in which atoms can adopt coordination numbers lower than six, the presence of such coordinatively unsaturated polyhedrons suggests the possibility of the dissociative water insertion from the gas phase. Upon hydration, tetrahedra are transformed to octahedrons, in which OH\({}^{-}\) groups participate in the coordination of cations. These phases can uptake a significant quantity of water and show a dominant proton transport below 500-600 \({}^{\circ}\)C.  
Most research is focused on the investigations of compounds with acceptor doping; however, materials with structural oxygen vacancies have recently received considerable interest. Oxygen-deficient compounds such as Ba\({}_{4}\)Ca\({}_{2}\)Nb\({}_{2}\)O\({}_{11}\)\(\equiv\)Ba\({}_{2}\)CaNbO\({}_{5.5}\)\(\equiv\)BaCa\({}_{0.5}\)Nb\({}_{0.5}\)O\({}_{2.75}\), Sr\({}_{4}\)Sr\({}_{2}\)Nb\({}_{2}\)O\({}_{11}\), Sr\({}_{4}\)Sr\({}_{2}\)Ta\({}_{2}\)O\({}_{11}\)[9; 11; 12; 13; 14; 15; 16; 17], Ba\({}_{4}\)Ca\({}_{2}\)Ta\({}_{2}\)O\({}_{11}\)[18], Ba\({}_{4}\)Na\({}_{2}\)W\({}_{2}\)O\({}_{11}\)[19], Ba\({}_{2}\)InSnO\({}_{5.5}\)[20], Ba\({}_{2}\)YSnO\({}_{5.5}\)[21] and Ba\({}_{4}\)In\({}_{2}\)Zr\({}_{2}\)O\({}_{11}\)[22] are well known and well studied. Their structures have 8.33% vacant oxygen positions resulting from the combination of two types of cations in the B-sublattice in a 1:1 ratio. All of the aforementioned compounds are characterized  
Figure 1: Main methods for modifying of perovskite structure to create an oxygen deficiency, the examples of basic materials and basic concepts of water incorporation. by predominant oxygen ion transport at high temperatures and proton transport at low temperatures and in a humid atmosphere. The distribution of cations in the lattice can be both statistical and ordered. The tendency for the appearance of a superstructure is associated with the differences between oxidation states of B-cations (and their radii): the higher the differences, the more order. For example, the structure of Ba\({}_{4}\)Na\({}^{1+}\)\({}_{2}\)W\({}^{6+}\)\({}_{2}\)O\({}_{11}\) is ordered (with respect to B-cations) and described by the space group \(Fm3m\) with a doubled perovskite parameter and statistical arrangement of oxygen vacancies (double perovskite), but the compound Ba\({}_{4}\)In\({}^{3+}\)Zr\({}^{4+}\)\({}_{2}\)O\({}_{11}\) exhibits the space group \(Fm3m\) (ordinary perovskite). More recently, high ionic conductivity (O\({}^{2-}\), H\({}^{+}\)) has been described for phases with a more complex structure, such as coherent intergrowth structures [10]. A new trend in materials science known as the \"alkaline earth elements free strategy\" is related to the development of perovskites based on the composition A\({}^{3+}\)B\({}^{3+}\)O\({}_{3}\). That is, the investigation of compounds not containing alkaline-earth components because the presence of an alkaline earth element in the composition of perovskite can result in the formation of the corresponding carbonates [23; 24; 25; 26], and thus to the degradation of the material. The well-studied orthorhombic-doped perovskite LaScO\({}_{3}\) exhibits high oxygen-ionic and proton conductivities.