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Cesium Iodide

Crystal: CsI

Structure: CsCl

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Mechanical and structural properties:

Lattice formation energy:	-6.04 eV. (theory, Mayer and al.) (Ref.1)
	-6.31 eV. (experimental) (Ref.1)
Lattice parameter:	3.95 Å
Density:	g/cm³

Stiffness constants: in 10¹¹ dynes/cm², at room temperature

c₁₁: 2.46 or 2.45 (Ref.2) or 2.725 (Ref.3)

c₁₂: 0.67 or 0.71 or 0.767

c₄₄: 0.62 or 0.62 or 0.813

Compressibility (in 10¹¹ dynes/cm²): 0.789 ??

Poisson ratio:

Debye temperature:

127.6 K (thermal) (Ref.3)

129.4 K (elastic)

Melting temperature: K

Phonon spectrum discussed by:

J.F. Vetelino, Lattice dynamics, mode Gruneisen parameters & coefficient of thermal expansion of CsCl, CsBr & CsI, Phys. Rev. B2, 2167 (1979)

W. Burher & W. Halg, Crystal dynamics of Cesium Iodide, Phys. Stat. Solidi 46, 679 (1971)

Transverse optic phonon T0 (k=0): cm^-1

Longitude optic phonon L0 (k=0): cm^-1

Gruneissen constant:

Ratio e*/e:

Photoelastic constants:

p₁₁:

p₁₂:

p₄₄:

Electronic properties:

Band gap:

direct: 6.3 eV. at K

indirect: eV. at ° K

Plasmon energy: eV.

Exciton energy: 5.30 eV. (Ref.4)

Band structure discussed by:

L. Nosenzo & E. Reguzzoni, Analysis of the electronic structure in Cesium halides by deflectance & thermoreflectance studies, Phys. Rev. B19, 2314 (1979)

Also: E. Boursey and J.-Y. Rongin, Absorption spectra of Cesium halides at 20K. from 12 to 20 eV., Sol. State Com. 9, 1049 (1971)

Static dielectric constant:

Optic dielectric constant:

Electron mobility:

Hole mobility:

Polaron coupling constant: a = 5.5 ( for m*=1 )

Effective mass:

conduction band:

valence band:

Electron affinity: ( in eV., from bottom of conduction band under vacuum)

Spin-orbit coupling: ( valence band)

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Other information:

See below for other information on CsI

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References:

1. C. Kittel, "Introduction to Solid State Physics", 2nd. Edition, New York: Wiley (1956)

2. Ted R. Musgrave, "Understanding problems for chemical principles", Philadelphia: Saunders (1978)

3. B.J. Marshall & J.R. Kunkel, Heat capacity & elastic constants of CsI at low temperatures, J. Appl. Phys. 40, 5191 (1969)

4. W.B. Fowler, "Physics of Color Centers", New York: Academic Press (1968)

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Other information on CsI:

Equation of state and metallization of CsI

J. Aidum, and M.S.T. Bukowinski. Phys. Rev. B29, 2611 (1984)

Self-consistent nonrelativistic augmented-plane-wave (APW) calculation for CsI were carried out to generate the band structure, the static-lattice equation of state (EOS), and the volume dependence of the electronic energy-band ga The theoretical room-temperature isothermal compression curve agrees well with static and ultrasonic measurements at low pressure. Our calculations do not agree with two recent sets of diamond-anvil-cell measurements above 10 GPa. The calculated band gaps are too small at low pressure, but, at high pressure, are consistent with both the experimental results and the Hezfeld-model predictions. These results suggest that the insulator-to-metal transition occurs in the range 100±10 GPa. A calculation of the shock compression curve of CsI shows that the thermally excited electrons cause a significant softening of the Hugoniot curve, The experimental zero-pressure band gaps of the isoelectronic compounds Xe, CsI, and BaTe are linearly correlated with ln(v/vH), where vH is the specific volume of metallization predicted by the Herzfeld model. Based on this correlation, and on the similarity of the APW calculated EOS’s of Xe and CsI, which agree closely with experimental compression measurements, we predict that BaTe will become metallic at approximately 30 Gpa.

Pressure-induced successive phase transitions in CsI and its equation of state in relation to metallization.

K. Asaumi Phys. Rev. B29, 1118 (1984)

A high-pressure x-ray diffraction study has been performed in CsI up to 65 GPa at room temperature by using a diamond-anvil cell. Pressure-induced successive phase transitions, apparently of second-order nature, from cubic to tetragonal and from tetragonal orthorhombic, have been observed at 40±1 and 56±1 GPa, respectively. On the basis of the present and previous work, pressure-induced metallization in CsI is expected to take place at the volume ratio V/Vo=0.50, which corresponds to the pressure 70 GPa determined by the optical-absorption data reported previously. In the present work, the volume ratio V/Vo=0.51 was achieved.

Optical absorption spectra of cesium iodide (CsI) at pressures up to 60 GPa.

I.N. Makarenkov, A.F. Goncharov, and S.M. Stishov Phys. Rev. B29, 6018 (1984)

The optical absorption spectra of CsI single crystals have been measured in a diamond anvil cell at pressures up to 60 GPa. For the first time, the fine structure of the absorption edge of CsI has been observed at high pressures. The exciton effects are shown to be responsible for the fine structure of the absorption edge. The pressure of metallization of CsI is estimated to be approximately 110 GPa.

Optical-absorption edge of CsI up to 58 GPa.

J. Ivie, A. Polian, and J.M. Besson Phys. Rev. B30, 2309 (1984)

The optical transmittancy of cesium iodide single crystals has been studied up to 58 GPa, using xenon as a pressure-transmitting medium. The shape and position of the absorption edge under pressure has been measured under controlled stress-homogeneity conditions. It is found to differ significantly from previous results obtained on highly strained powder samples. The data are analysed in terms of band-to-band transitions and show that band closing in cesium iodide is not to be expected below 90 GPa.

Equation of state and high-pressure phase transition of CsI.

T-L. Huang and A.L. Ruoff Phys .Rev, vol B29, 1112 (1984)

High-pressure diffraction patterns of CsI were obtained to 660 kbar. Diffraction peaks of a new phase appear between 370 and 385 kbar. The pressure-volume relationship of the low-pressure cubic phase was fitted to Keane’s second-order equation of state with B0=118.9 kbar, B’0=5.93, and B’’0=-0.131 kbar-1 with B0 and B’0 values forced to fit the isothermal values obtained from ultrasonic data. The d spacings of the new high-pressure phase are consistent with tetragonal indexing.

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