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.
Plot of bulk modulus and lattice constant of CsBrxI1−x versus composition.
Table 1
Structural parameters of CsFxI1 − x, CsClxI1 − x and Cs BrxI1 − x in B1 phase.
| Compound | a [Å] | K [GPa] | E0 | ||||
|---|---|---|---|---|---|---|---|
| GGA | Exp. | Other method | GGA | Exp. | Other method | ||
| CsI | 7.69 | 7.52 | 5.459 [34] | 8.72 | 7 .30 [34] | −29815.72 | |
| CsF0:25I0:75 | 7.43 | 13.91 | −105225.63 | ||||
| CsF0:50I0:50 | 7.18 | 11.20 | −91188.56 | ||||
| CsF0:75I0:25 | 6.76 | 14.73 | −77151.54 | ||||
| CsF | 5.99 | 6.025 [35] | 6.12[36] | 35.5 | −15778.67 | ||
| Cs Cl0:25I0:75 | 7.44 | 21.15 | −105948.774 | ||||
| Cs Cl0:50I0:50 | 7.29 | 13.77 | −92634.72 | ||||
| Cs Cl0:75I0:25 | 7.08 | 15.35 | −79320.675 | ||||
| Cs Cl | 6.91 | 20.66 | −16501.672 | ||||
| Cs Br0:25I0:75 | 7.46 | 20.25 | −110238.56 | ||||
| Cs Br0:50I0:50 | 7.36 | 21.23 | −101214.29 | ||||
| Cs Br0:75I0:25 | 7.27 | 11.72 | −92190.02 | ||||
| CsBr | 7.25 | 7.23 [32] | 9.83 | 10.45 [34] | −20791.45 | ||
Table 2
Structural parameters of CsFxI1 − x, CsClxI1 − x and CsBrxI1 − x in B2 phase.
| Compound | a [Å] | K [GPa] | E0 | ||||
|---|---|---|---|---|---|---|---|
| GGA | Exp. | Other method | GGA | Exp. | Other method | ||
| CsI | 4.51 | 4.57 [37] 4.51 [39] | 4.64 [38] 4.52 [36] | 10.19 | 11.9 [37] | 12.21 [38] 9.02 [34] | −29815.72 |
| CsF0.25I0.75 | 4.37 | 14.19 | −105225.61 | ||||
| CsF0.50 I0.50 | 4.21 | 12.33 | −45594.27 | ||||
| CsF0.75 I0.25 | 3.98 | 20.48 | −77151.50 | ||||
| CsF | 3.59 | 3 [40] | 2.99 [34] | 35.57 | 59.17 [34] | −15778.65 | |
| Cs Cl0.25I0.75 | 4.39 | 20.52 | −105948.78 | ||||
| Cs Cl0.50I0.50 | 4.30 | 16.97 | −46317.36 | ||||
| Cs Cl0.75I0.25 | 4.18 | 15.66 | −79320.67 | ||||
| Cs Cl | 4.08 | 4.091 [41] | 4.11 [36] 3.934 [34] | 17.95 | 22.9 [42] | 12.58 [34] | −16501.67 |
| Cs Br0.25I0.75 | 4.41 | 20.03 | −110238.57 | ||||
| Cs Br0.50I0.50 | 4.39 | 17.59 | −50607.144 | ||||
| Cs Br0.75I0.25 | 4.29 | 15.43 | −92190.02 | ||||
| CsBr | 4.26 | 4.23 [39] 4.28 [43] | 4.27 [36] 4.069 [34] | 15.45 | 15.6 [39] 17.9 [43] | 16.5 [36] 13.01 [34] | −20791.45 |
Table 3
The Elastic constants and mechanical properties of alkali halides.
| Compound | C11 | C12 | C44 | K | G | E | σ | A | K/G | C12–C44 |
|---|---|---|---|---|---|---|---|---|---|---|
| CsF(B1) | 49.43 | 10.91 | 23.75 | 23.752 | 21.84 | 50.149 | 0.15 | 1.23 | 1.09 | −12.8 |
| CsCl | 27.34 | 7.36 | 8.967 | 14.021 | 9.36 | 22.977 | 0.23 | 0.89 | 1.50 | −1.60 |
| CsBr(B1) | 27.05 | 1.959 | 4.098 | 10.321 | 1.23 | 3.547 | 0.44 | 0.33 | 8.40 | −2.14 |
| CsI | 29.19 | −1.94 | 4.887 | 8.438 | 7.95 | 18.142 | 0.14 | 0.31 | 1.06 | −6.82 |
| CsF(B2) | 55.53 | 17.47 | 8.197 | 30.158 | 11.57 | 30.780 | 0.33 | 0.43 | 2.61 | 9.27 |
| CsCl) | 42.33 42.6c | −0.02 1.3c | 3.952 10.9c | 14.099 | 8.35 | 20.920 | 0.25 | 0.19 | 1.69 | −3.97 |
| CsBr | 28.32 30.97a 30b | 7.36 9.03a 7.8b | 12.95 7.5a 7.56b | 14.348 | 11.90 | 27.965 | 0.18 | 1.24 | 1.21 | −5.59 |
| CsI | 33.98 24.34a 24.6b | −1.21 6.36a 6.7b | 6.89 6.32a 6.24b | 10.523 | 10.14 | 23.030 | 0.14 | 0.39 | 1.04 | −8.10 |
(a, b, c) experimental values.
c [45]
c [45]
c [45]
a [43]
b [44]
a [43]
b [44]
a [43]
b [44]
a [43]
b [44]
a [43]
b [44]
a [43]
b [44]
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 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.
Table 4
Energy band gaps for F, Cl and Br doped CsI in rock salt (B1) phase for (0 ⩽ x ⩽ 1).
| B1 | GGA | EV-GGA | Experimental |
|---|---|---|---|
| Eg [eV] | Eg [eV] | Eg [eV] | |
| CsI | 3.7026 | 3.678 | |
| CsF0.25I0.75 | 3.6043 | 4.3164 | |
| CsF0.50I0.50 | 3.9481 | 4.4391 | |
| CsF0.75I0.25 | 4.3163 | 4.7583 | |
| CsF | 5.3966 | 6.3786 | 9.8 [45] |
| CsCl0.25I0.75 | 4.1690 | 4.9792 | |
| CsCl0.50I0.50 | 4.3163 | 5.0529 | |
| CsCl0.75I0.25 | 4.3900 | 5.151 | |
| CsCl | 4.8319 | 5.814 | |
| CsBr0.25I0.75 | 4.0954 | 4.9792 | |
| CsBr0.50I0.50 | 4.1199 | 5.0283 | |
| CsBr0.75I0.25 | 4.2181 | 4.9547 | |
| CsBr | 4.0463 | 5.1265 |
Table 5
Energy band gaps for F, Cl and Br doped CsI in B2 phase for (0 ⩽ x ⩽ 1).
| B2 | GGA | EV-GGA | Experimental | Other calculations |
|---|---|---|---|---|
| Eg [eV] | Eg [eV] | Eg [eV] | Eg [eV] | |
| CsI | 3.8744 | 5.0283 | 6.2 [46] 6.50 [32] | 3.91 [39] 3.97 [33] |
| CsF0.25I0.75 | 3.7762 | 4.611 | ||
| CsF0.50I0.50 | 4.1445 | 4.8319 | ||
| CsF0.75I0.25 | 4.3163 | 5.0529 | ||
| CsF | 5.9858 | 7.361 | ||
| CsCl0.25I0.75 | 4.0463 | 4.7828 | ||
| CsCl0.50I0.50 | 4.2918 | 4.9546 | ||
| CsCl0.75I0.25 | 4.3654 | 5.0529 | ||
| CsCl | 5.2493 | 5.2247 | 7.90 [32] | 5.27 [33] |
| CsBr0.25I0.75 | 3.9972 | 4.8319 | ||
| CsBr0.50I0.50 | 4.1199 | 5.0283 | ||
| CsBr0.75I0.25 | 4.1199 | 5.0774 | ||
| CsBr | 4.3900 | 5.8385 | 7.30 [32] | 4.56 [33] |
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.
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 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.
Optical conductivity vs. energy for Y (Y= F, Cl, and Br) doped CsI at concentration (0 ⩽ x ⩽ 1).