Pressure dependence of structural phase transition and superconducting transition in CsI

Abstract

The self-consistent band structure calculation for CsI performed both in CsCl and HCP structures using the TB-LMTO method is reported. The equilibrium lattice constant, bulk modulus and the phasetransition pressure at which the compound undergoes structural phase transition from CsCl to HCP are predicted from the total-energy calculations. The band structure, density of states (DOS), electronic charge distributions, metallization and superconducting transition temperature (T c ) of CsI are obtained as a function of pressure for both the CsCl and HCP structures. It is found that the charge transfer from s and p states to d state causes metallization and superconductivity in CsI. The highest T c estimated is 2.11 K and the corresponding pressure is 1.8 Mbar. This value is in agreement with the recent experimental observation. The experimental trend -"metallization and superconductivity is rather insensitive to the crystal structure of CsI" -is also confirmed in our work.

Pressure induced weakness of electrostatic interaction and solid decomposition in Cs−I compounds

“…Our simulations successfully reproduced the previously reported Pm 3̄ m and Pnma phases of CsI 9,10,29–31 and the Pnma and Pm 3̄ n phases of CsI 3 10,12,13 from both experimental and theoretical studies. To determine the stable structures of the Cs−I system, we systematically performed extensive exploration on Cs x I y ( x , y = 1–4) with 1–4 formula units at pressures of 0, 50, 100, 200, and 400 GPa and a temperature of 0 K. Additionally, we discovered four new stable phases: the Fmmm and I 4/ mmm phases of Cs 2 I, the I 4/ m phase of Cs 4 I and the P 4 3 phase of CsI 3 .…”

Pressure dependence of metallization and superconducting transition in AgCl and AgBr

“…All ionic solids would become superconductors due to high compression [3,49]. The continuous promotion of s, p electrons to d shells in solids under pressure is one of the factors which will induce superconductivity [49]. Under very high pressure, silver halides are not only metals but also superconductors.…”

“…where M is the atomic mass, ω 2 is an average of the phonon frequency square and I 2 is an average (over the Fermi energy) of the electron-phonon matrix element square. I 2 (in Rydbergs) can be written as [42,49]…”

“…S is the radius of the muffin-tin sphere. The above quantities are taken from the band structure results [42,49]. We have calculated λ separately for silver and halide atoms and for the T c -calculation (equation ( 8)) the mean value of λ is used [49].…”

“…where N(E F ) is the density of levels per atom per electronvolt at E F . With these results we have analysed the variation of θ D , λ, µ * and T c with pressure using equations ( 4)-( 9) [42,49]. The calculated values for θ D , λ, µ * and T c under various pressures are given in table 7 (for AgCl) and table 8 (for AgBr).…”