Abstract
The self-consistent band structure calculation for potassium iodide (KI) performed both in NaCl and CsCl structures using the full potential linear muffin-tin orbital (FP-LMTO) method is reported. The equilibrium lattice constant, bulk modulus and the phase transition pressure at which the compound undergoes structural phase transition from NaCl to CsCl are predicted from the total energy calculations. The band structure, density of states (DOS), electronic charge distributions, metallization and superconducting transition temperature (Tc) of KI are obtained as a function of pressure for both in NaCl and CsCl structures. The density of states at the Fermi level (N(EF)) gets enhanced under pressure, which leads to metallization in KI. It is found that, the charge transfer from s and p states to d state causes structural phase transition and superconductivity in KI. The pressure corresponding to structural phase transition from NaCl structure (B1) to the CsCl structure (B2) is 0.02 Mbar in KI. This value is agreement with the experimental value of 0.019 Mbar. In KI, the metallization occurs through indirect closing of the band gap between Γ and H points at the reduced volume V/Vo=0.43 (CsCl structure), the corresponding metallization pressure is 1.228Mbar. Our results completely agree with the experimental observation of 1.31 Mbar. The highest Tc estimated is 2.151 K and the corresponding pressure is 4.945 Mbar in the NaCl structure and 0.107 K in the CsCl structure.
Highlights
There is lot of interest in the study of structural changes and phase stability of materials under pressure[1,2]
Eremets [3] could experimentally find the evidences for the metallization and superconductivity of CsI at high pressure
Here we have presented the density of states and band structures along the symmetry directions L-Γ-X-W- K-Γ corresponding to volume compressions V/Vo=1.0 and V/Vo=0.43 for KI only (Figures 1and 2)
Summary
There is lot of interest in the study of structural changes and phase stability of materials under pressure[1,2]. With the development of high pressure experimental techniques, research on pressure-induced structural phase transition, insulator – metal transition and superconducting transition are getting the attention of all [4,5,6,7,8,9,10]. The band structure results are used in analyzing metallization and superconductivity of ionic insulators [14]. It was felt that many disagreements exist between theory and experiment [13] in the prediction of lattice constant, band gap, phase transition, metallization and superconductivity of KI and this necessitated further theoretical studies in this system.
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