Characterization of Sr2FeIrO6 and Ba2FeIrO6 double perovskites under extreme conditions

The versatility of the well-known ABX3 perovskites to host almost all the elements of the periodic table leads to the formation of the so-called double perovskites or elpasolites, with A2B’B’’O6 stoichiometry. The literature contains very few studies on this kind of compounds under high pressure (HP). Nevertheless, from them several trendlines depending on the oxidation state of A cation can be discerned. A high stability on these compounds are exhibited when the A cation is trivalent. When it comes to a divalent A cation, the AO12 polyhedral unit is more compressible than those octahedron of B’ and B’’ cations, triggering the increase of the distortion of the latter units with compression. This feature would lead to the observation of a high-spin to low-spin (HS-LS) transition in the Fe cation in Sr2FeIrO6 and Ba2FeIrO6 in the Mbar regime, similar to what happens in many other Fe compounds like in Fe2O3 polymorphs or the B1 phase of (Mg1-xFex)O.