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The study of structural, elastic, electronic and optical properties of CsYx I(1 − x)(Y = F, Cl, Br) using density functional theory

Shabeer Ahmad Mian
Shabeer Ahmad Mian
, 
Muhammad Muzammil
Muhammad Muzammil
, 
Gul Rahman
Gul Rahman
 and 
Ejaz Ahmed
Ejaz Ahmed
   | Apr 13, 2017
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Published Online: Apr 13, 2017
Page range: 197 - 210
Received: May 16, 2016
Accepted: Dec 19, 2016
DOI: https://doi.org/10.1515/msp-2017-0017
Keywords
© 2017 Shabeer Ahmad Mian, Muhammad Muzammil, Gul Rahman, Ejaz Ahmed
This article is distributed under the terms of the Creative Commons Attribution Non-Commercial License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Top panel: unit cell of binary CsBr (B2) and bottom panel: unit cell of ternary CsBr0.25I0.75.
Top panel: unit cell of binary CsBr (B2) and bottom panel: unit cell of ternary CsBr0.25I0.75.

Energy and volume of B1 CsFxI1 − x (0 ⩽ x ⩽ 1) phase, optimized using GGA method.
Energy and volume of B1 CsFxI1 − x (0 ⩽ x ⩽ 1) phase, optimized using GGA method.

Plot of bulk modulus and lattice constant of CsBrxI1−x versus composition.
Plot of bulk modulus and lattice constant of CsBrxI1−x versus composition.

Band structure of binary Cs halides (CsBr) obtained with Wu-Cohen GGA.
Band structure of binary Cs halides (CsBr) obtained with Wu-Cohen GGA.

Band structure of binary Cs halides (CsBr) obtained with EV-GGA.
Band structure of binary Cs halides (CsBr) obtained with EV-GGA.

Band structure of Br doped CsI at x = 0.25 in FCC phase obtained by Wu-Cohen GGA.
Band structure of Br doped CsI at x = 0.25 in FCC phase obtained by Wu-Cohen GGA.

Band structure of Br doped CsI at x = 0.25 in FCC phase obtained by EV-GGA.
Band structure of Br doped CsI at x = 0.25 in FCC phase obtained by EV-GGA.

DOS for CsYxI1 − x at concentrations (0 ⩽ x ⩽ 1). Substate p contributes the most in the valence band, while the mixed d-states contribute the most in the conduction band.
DOS for CsYxI1 − x at concentrations (0 ⩽ x ⩽ 1). Substate p contributes the most in the valence band, while the mixed d-states contribute the most in the conduction band.

Contour of electron density for F, Cl and Br doped cesium iodide at (0 ⩽ x ⩽ 1) in B1 phase along (1 1 0) plane.
Contour of electron density for F, Cl and Br doped cesium iodide at (0 ⩽ x ⩽ 1) in B1 phase along (1 1 0) plane.

Electron density of F, Cl and Br doped cesium iodide at (0 ⩽ x ⩽ 1) in B2 phase along (0 1 1) plane.
Electron density of F, Cl and Br doped cesium iodide at (0 ⩽ x ⩽ 1) in B2 phase along (0 1 1) plane.

Real and imaginary parts of dielectric function for CsYxI1 − x (Y = F, Cl and Br) for the concentration x (0 ⩽ x ⩽ 1) in B1 phase.
Real and imaginary parts of dielectric function for CsYxI1 − x (Y = F, Cl and Br) for the concentration x (0 ⩽ x ⩽ 1) in B1 phase.

Real and imaginary parts of dielectric function for CsYxI1 − x (Y = F, Cl and Br) for the concentration x (0 ⩽ x ⩽ 1) in B2 phase.
Real and imaginary parts of dielectric function for CsYxI1 − x (Y = F, Cl and Br) for the concentration x (0 ⩽ x ⩽ 1) in B2 phase.

Reflectivity vs. energy (eV) plot for Y (Y = F, Cl and Br) doped CsI in B1 and B2 phases. At very low and high energy values, R is less than 10 % which means that the material is transparent. Effect of doping with lighter halogens is the increase in reflectivity which is the highest at x = 1.
Reflectivity vs. energy (eV) plot for Y (Y = F, Cl and Br) doped CsI in B1 and B2 phases. At very low and high energy values, R is less than 10 % which means that the material is transparent. Effect of doping with lighter halogens is the increase in reflectivity which is the highest at x = 1.

Optical conductivity vs. energy for Y (Y= F, Cl, and Br) doped CsI at concentration (0 ⩽ x ⩽ 1).
Optical conductivity vs. energy for Y (Y= F, Cl, and Br) doped CsI at concentration (0 ⩽ x ⩽ 1).

Structural parameters of CsFxI1 − x, CsClxI1 − x and Cs BrxI1 − x in B1 phase.

Compounda [Å]K [GPa]E0
GGAExp.Other methodGGAExp.Other method
CsI7.697.525.459 [34]8.727 .30 [34]−29815.72
CsF0:25I0:757.4313.91−105225.63
CsF0:50I0:507.1811.20−91188.56
CsF0:75I0:256.7614.73−77151.54
CsF5.996.025 [35]6.12[36]35.5−15778.67
Cs Cl0:25I0:757.4421.15−105948.774
Cs Cl0:50I0:507.2913.77−92634.72
Cs Cl0:75I0:257.0815.35−79320.675
Cs Cl6.9120.66−16501.672
Cs Br0:25I0:757.4620.25−110238.56
Cs Br0:50I0:507.3621.23−101214.29
Cs Br0:75I0:257.2711.72−92190.02
CsBr7.257.23 [32]9.8310.45 [34]−20791.45

Energy band gaps for F, Cl and Br doped CsI in rock salt (B1) phase for (0 ⩽ x ⩽ 1).

B1GGAEV-GGAExperimental
Eg [eV]Eg [eV]Eg [eV]
CsI3.70263.678
CsF0.25I0.753.60434.3164
CsF0.50I0.503.94814.4391
CsF0.75I0.254.31634.7583
CsF5.39666.37869.8 [45]
CsCl0.25I0.754.16904.9792
CsCl0.50I0.504.31635.0529
CsCl0.75I0.254.39005.151
CsCl4.83195.814
CsBr0.25I0.754.09544.9792
CsBr0.50I0.504.11995.0283
CsBr0.75I0.254.21814.9547
CsBr4.04635.1265

The Elastic constants and mechanical properties of alkali halides.

CompoundC11C12C44KGEσAK/GC12–C44
CsF(B1)49.4310.9123.7523.75221.8450.1490.151.231.09−12.8
CsCl27.347.368.96714.0219.3622.9770.230.891.50−1.60
CsBr(B1)27.051.9594.09810.3211.233.5470.440.338.40−2.14
CsI29.19−1.944.8878.4387.9518.1420.140.311.06−6.82
CsF(B2)55.5317.478.19730.15811.5730.7800.330.432.619.27
CsCl)42.33 42.6

[45]

−0.02 1.3

[45]

3.952 10.9

[45]

14.0998.3520.9200.250.191.69−3.97
CsBr28.32 30.97

[43]

 30

[44]

7.36 9.03

[43]

 7.8

[44]

12.95 7.5

[43]

 7.56

[44]

14.34811.9027.9650.181.241.21−5.59
CsI33.98 24.34

[43]

 24.6

[44]

−1.21 6.36

[43]

 6.7

[44]

6.89 6.32

[43]

 6.24

[44]

10.52310.1423.0300.140.391.04−8.10

Structural parameters of CsFxI1 − x, CsClxI1 − x and CsBrxI1 − x in B2 phase.

Compounda [Å]K [GPa]E0
GGAExp.Other methodGGAExp.Other method
CsI4.514.57 [37] 4.51 [39]4.64 [38] 4.52 [36]10.1911.9 [37]12.21 [38] 9.02 [34]−29815.72
CsF0.25I0.754.3714.19−105225.61
CsF0.50 I0.504.2112.33−45594.27
CsF0.75 I0.253.9820.48−77151.50
CsF3.593 [40]2.99 [34]35.5759.17 [34]−15778.65
Cs Cl0.25I0.754.3920.52−105948.78
Cs Cl0.50I0.504.3016.97−46317.36
Cs Cl0.75I0.254.1815.66−79320.67
Cs Cl4.084.091 [41]4.11 [36] 3.934 [34]17.9522.9 [42]12.58 [34]−16501.67
Cs Br0.25I0.754.4120.03−110238.57
Cs Br0.50I0.504.3917.59−50607.144
Cs Br0.75I0.254.2915.43−92190.02
CsBr4.264.23 [39] 4.28 [43]4.27 [36] 4.069 [34]15.4515.6 [39] 17.9 [43]16.5 [36] 13.01 [34]−20791.45

Energy band gaps for F, Cl and Br doped CsI in B2 phase for (0 ⩽ x ⩽ 1).

B2GGAEV-GGAExperimentalOther calculations
Eg [eV]Eg [eV]Eg [eV]Eg [eV]
CsI3.87445.02836.2 [46] 6.50 [32]3.91 [39] 3.97 [33]
CsF0.25I0.753.77624.611
CsF0.50I0.504.14454.8319
CsF0.75I0.254.31635.0529
CsF5.98587.361
CsCl0.25I0.754.04634.7828
CsCl0.50I0.504.29184.9546
CsCl0.75I0.254.36545.0529
CsCl5.24935.22477.90 [32]5.27 [33]
CsBr0.25I0.753.99724.8319
CsBr0.50I0.504.11995.0283
CsBr0.75I0.254.11995.0774
CsBr4.39005.83857.30 [32]4.56 [33]
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