On the electrical properties of the Bi2−ySryIr2O7 pyrochlore solid solution: Quantum ab initio and classic calculations

• Electrical properties of Bi2−ySryIr2O7 system are studied by Quantum Mechanical Calculations.
• The effect of Bi substitution by Sr on the electrical resistivity is studied.
• The main effect of the Bi substitution by Sr is on the lattice dynamic behavior.
• The electronic structure of the A2O2 sublattice does not contribute to DOS.
• The increase of the electrical resistivity is due to the shortening of the relaxation time.

In this work, a theoretical study of the electrical properties of the Bi2−ySryIr2O7 (Bi2−ySryIr2O16O2) α-pyrochlore-type solid solution is presented. Quantum ab initio DFT(WIEN2k) calculations were performed in order to understand the electrical resistivity changes associated to the Bi substitution by Sr in this system. The main crystallographic modification associated to this substitution is the x position of the 48f oxygen (x  , 18, 18) (O1); this substitution substantially modifies the Bi/Sr–O1 and Ir–O1 atomic distances, increasing the former and diminishing the latter. Experimentally, the Bi2−ySryIr2O7 samples are metallic and the electrical resistivity increases with the Sr content. Electronic structure calculations for Bi2Ir2O7 and BiSrIr2O7 show that, regardless of structural changes, there is only a small change of electrical conductivity with the Sr substitution, and the experimentally observed increase of the resistivity can be explained in terms of a larger impact on the electronic structure of both; the Sr ‘impurities’ as well as of the thermal Sr oscillations.

The experimental electrical resistivity of Bi2-ySryIr2O7 increases with temperature and Sr content. This behavior can be explained with ab initio electronic calculations and classical considerations on the atom oscillations. The Sr is substituted in the A2O2 sublattice (green and red atoms), however, the results indicates that the changes on electrical conductivity are produced by an indirect effect of the Sr substitution on the Ir2O6 sublattice (blue octahedra).Figure optionsDownload as PowerPoint slide