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In situ growth of pyrochlore iridate thin films has been a long-standing challenge due to the low reactivity of Ir at low temperatures and the vaporization of volatile gas species such as IrO₃(g) and IrO₂(g) at high temperatures and highP_O2. To address this challenge, we combine thermodynamic analysis of the Pr-Ir-O₂system with experimental results from the conventional physical vapor deposition (PVD) technique of co-sputtering. Our results indicate that only high growth temperatures yield films with crystallinity sufficient for utilizing and tailoring the desired topological electronic properties and the in situ synthesis of Pr₂Ir₂O₇thin films is fettered by the inability to grow withP_O2on the order of 10 Torr at high temperatures, a limitation inherent to the PVD process. Thus, we suggest techniques capable of supplying high partial pressure of key species during deposition, in particular chemical vapor deposition (CVD), as a route to synthesis of Pr₂Ir₂O₇.

 

The interactions between solute atoms and crystalline defects such as vacancies, dislocations, and grain boundaries are essential in determining alloy properties. Here we present a general linear correlation between two descriptors of local electronic structures and the solute-defect interaction energies in binary alloys of body-centered-cubic (bcc) refractory metals (such as W and Ta) with transition-metal substitutional solutes. One electronic descriptor is the bimodality of thed-orbital local density of states for a matrix atom at the substitutional site, and the other is related to the hybridization strength between the valancesp-andd-bands for the same matrix atom. For a particular pair of solute-matrix elements, this linear correlation is valid independent of types of defects and the locations of substitutional sites. These results provide the possibility to apply local electronic descriptors for quantitative and efficient predictions on the solute-defect interactions and defect properties in alloys.

 

Abstract An unprecedented NiSn 2 intermetallic with CoGe 2 -type crystal structure has been recovered (at ambient conditions) after high-pressure high-temperature treatment of a Ni 33 Sn 67 precursor alloy at 10 GPa and 400 °C. The orthorhombic structure with Aeam space group symmetry is pseudotetragonal. Based on the evaluation of powder X-ray diffraction data, lattice parameters of a  =  b  = 6.2818 Å and c  = 11.8960 Å have been determined. Complicated line broadening and results of a further microstructure analysis, however, imply a defective character of the crystal structure. First-principles calculations with different model structures and a comparison with structural trends in the literature suggest that at the high-pressure high-temperature conditions a CuAl 2 -type crystal structure might be stable, which transforms to the recovered CoGe 2 -type crystal structure upon cooling or the release of pressure.