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Results for “BiIrS”

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4 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Direct Observation of Pressure-Driven Valence Electron Transfer in Ba 3 BiRu 2 O 9 , Ba 3 BiIr 2 O 9 , and Ba 4 BiIr 3 O 12

The hexagonal perovskites Ba3BiIr2O9, Ba3BiRu2O9 and Ba4BiIr3O12 all undergo pressure-induced 1% volume collapses above 5 GPa. These first-order transitions have been ascribed to internal transfer of valence electrons between bismuth and iridium/ruthenium, which is driven by external applied pressure because the reduction in volume achieved by emptying the 6s shell of bismuth upon oxidation to Bi5+ is greater in magnitude than the increase in volume by reducing iridium or ruthenium. Here, we report direct observation of these valence transfers for the first time, using high-pressure X-ray absorption near-edge spectroscopy (XANES) measurements. Our data also support the highly unusual “4+” nominal oxidation state of bismuth in these compounds, although the possibility of local disproportionation into Bi3+/Bi5+ cannot be definitively ruled out. Ab initio calculations reproduce the transition, support its interpretation as a valence electron transfer from Bi to Ir/Ru, and suggest that the high-pressure phase may show metallic behavior (in contrast to the insulating ambient-pressure phase).

Blanchard, Peter E. R.↗
DOE OSTI2018

Materials Data on BiIrS by Materials Project

IrBiS is Spinel-like structured and crystallizes in the cubic P2_13 space group. The structure is three-dimensional. Ir is bonded to three equivalent Bi and three equivalent S atoms to form IrBi3S3 octahedra that share corners with twelve equivalent IrBi3S3 octahedra, corners with three equivalent BiIr3S tetrahedra, and corners with three equivalent SBiIr3 trigonal pyramids. The corner-sharing octahedral tilt angles are 63°. All Ir–Bi bond lengths are 2.71 Å. All Ir–S bond lengths are 2.47 Å. Bi is bonded to three equivalent Ir and one S atom to form distorted BiIr3S tetrahedra that share corners with three equivalent IrBi3S3 octahedra, corners with six equivalent BiIr3S tetrahedra, and corners with nine equivalent SBiIr3 trigonal pyramids. The corner-sharing octahedral tilt angles are 80°. The Bi–S bond length is 2.66 Å. S is bonded to three equivalent Ir and one Bi atom to form SBiIr3 trigonal pyramids that share corners with three equivalent IrBi3S3 octahedra, corners with nine equivalent BiIr3S tetrahedra, and corners with six equivalent SBiIr3 trigonal pyramids. The corner-sharing octahedral tilt angles are 80°.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Epitaxial thin films of pyrochlore iridate Bi 2+x Ir 2-y O 7-δ : structure, defects and transport properties

While pyrochlore iridate thin films are theoretically predicted to possess a variety of emergent topological properties, experimental verification of these predictions can be obstructed by the challenge in thin film growth. We report on the pulsed laser deposition and characterization of thin films of a representative pyrochlore compound Bi 2 Ir 2 O 7 . Moreover, the films were epitaxially grown on yttria-stabilized zirconia substrates and have lattice constants that are a few percent larger than that of the bulk single crystals. The film composition shows a strong dependence on the oxygen partial pressure. Density-functional-theory calculations indicate the existence of BiIr antisite defects, qualitatively consistent with the high Bi: Ir ratio found in the films. Both Ir and Bi have oxidation states that are lower than their nominal values, suggesting the existence of oxygen deficiency. The iridate thin films show a variety of intriguing transport characteristics, including multiple charge carriers, logarithmic dependence of resistance on temperature, antilocalization corrections to conductance due to spin-orbit interactions, and linear positive magnetoresistance.

36 MATERIALS SCIENCE↗