Pressure-induced phase transition, metallization, and superconductivity in boron triiodide

Abstract

Pressure evolution of structural and electrical properties of boron triiodide, a highly anisotropic molecular crystal consisting of stacked layers of planar BI 3 molecules, has been studied by x-ray diffraction and resistivity measurements. A new phase transition was observed to occur at 6.2 GPa from the molecular phase with hexagonal structure to a monatomic phase with the face-centered-cubic lattice of iodine atoms. This first-order phase transition is characterized by the discontinuous crush of stacking of molecular layers. The monatomic phase becomes metallic at ϳ23 GPa and exhibits superconductivity above ϳ27 GPa. The process of molecular dissociation and electrical properties of BI 3 are discussed in comparison with those of iodine and other simple molecular iodides.

Equations of state of anhydrous AlF3 and AlI3: Modeling of extreme condition halide chemistry

“…This cell cannot represent the actual unit cell due to the number of iodine atoms, 4 atoms per cell in the fcc lattice. For this reason, the volume of the fcc cell was normalized to the volume per formula unit (V PFU ), i.e., V PFU = 3V fcc /4 following the same analysis used by Hamaya et al 24 for the high pressure phase of BI 3 . The pressure dependent V PFU is shown in the plot of Figure 8.…”

“…There are additional materials aspects worth pursuing too. A recent high-pressure study of boron triiodide (BI 3 ) 24 concluded that a high-pressure phase exists above 6.2 GPa that becomes metallic and superconducting with T c = 1 K above 23 and 27 GPa, respectively. Yao and Klug 25 attributed the appearance of superconductivity to the coordination change from planar BI 3 monomers to B 2 I 6 dimers, i.e., isostructural to ambient phase of AlI 3 .…”

Pressure-Induced Formation of Molecular B2X4(μ-X)2 (X = Cl, Br, I) Species

“…The transition pressure of about 5.4 GPa for the BI 3 P6 3 /m phase to the P1 structure is in good agreement with the recently reported experimental value of 6.2 GPa. 12 Predicted transition pressures for BBr 3 and BCl 3 solids are at 9 and 15 GPa, respectively. It is interesting to note that, for phase transitions in the alkali halides and hydrides, the transition pressures for NaCl-to CsCl-type structures also decreases with increasing alkali-metal atomic number.…”

“…12 A recent density functional theory (DFT) study 13 has predicted a B 2 I 4 (μ-I) 2 molecular solid structure to form at high pressure. This structure is consistent with all of the basic features of the experimental study, 12 suggesting that the first new pure-phase binary trihalide of boron has been prepared in more than a century. (The last of the binary boron(III) halides, BI 3 , has been known since 1891.…”

“…21 The gas-phase structures and relative energies of the mono-and binuclear boron(III) halides predicted by this functional are in good agreement with correlated ab initio results, lending additional confidence in the results of solid-state simulations. The predicted high-pressure P1 crystal structures for the BX 3 boron trihalides were obtained from a detailed structural search of candidate structures for BI 3 based on the initial structural data of Hamaya et al 12,13 The B, I, Br, and Cl potentials used 2s 5 as valence states, respectively, and an energy cutoff of 500 eV.…”