The effect of γ-radiation on the optical properties of layered TlGaSe
2
and TlInS
2
crystals has been studied within a wavelength range of 400–1100 nm at 300 K. By means of analysis of optical ...absorption spectra, the energies of direct and indirect optical interbend transitions before and after γ-irradiation have been determined. It has been shown that the energies of direct and indirect nonforbidden optical transitions grow with accumulation of γ-radiation dose within 0–25 Мrad in TlGaSe
2
and TlInS
2
single crystals from
E
gd
= 2.06 eV and
E
gi
= 1.90 eV at
D
= 0 Мrad to
E
gd
= 2.11 eV and
E
gi
= 1.98 eV at
D
= 25 Мrad for TlGaSe
2
crystals and from
E
gd
= 2.32 eV and
E
gi
= 2.27 eV at
D
= 0 Мrad to
E
gd
= 2.35 eV and
E
gi
= 2.32 eV at
D
= 25 Мrad for TlInS
2
crystals. A decrease in the transmission coefficient at doses from 0 to 5 Mrad with a further increase in the transmission coefficient at a radiation dose of
D
= 25 Мrad is observed.
Charge transport in (TlGaSe
2
)
1 –
x
(TlInS
2
)
x
solid solutions in the frequency range of 20–10
6
Hz before and after γ irradiation is studied using impedance-spectroscopy methods. The relaxation ...character of the permittivity dispersion and the nature of the dielectric loss are established. The frequency dependence of the dissipation factor tanδ in the crystals of the (TlGaSe
2
)
1 –
x
(TlInS
2
)
x
solid solutions is caused not only by relaxation polarization, but also by reach-through conductivity. The relaxation times are found to be τ = 10
–3
s. It is determined that, in the frequency range of 10
5
–5 × 10
5
Hz, the electrical conductivity obeys the regularity σ ~
f
S
(0.1 ≤
S
≤ 1.0), which is indicative of the conductivity over localized states. It is shown that a further increase in the frequency leads to an increase in the ionic conductivity and transition of the system to the superionic state.
Charge transport in (TlGaSe.sub.2).sub.1 -.sub.x(TlInS.sub.2).sub.x solid solutions in the frequency range of 20-10.sup.6 Hz before and after gamma irradiation is studied using impedance-spectroscopy ...methods. The relaxation character of the permittivity dispersion and the nature of the dielectric loss are established. The frequency dependence of the dissipation factor tandelta in the crystals of the (TlGaSe.sub.2).sub.1 -.sub.x(TlInS.sub.2).sub.x solid solutions is caused not only by relaxation polarization, but also by reach-through conductivity. The relaxation times are found to be tau = 10.sup.-3 s. It is determined that, in the frequency range of 10.sup.5-5 x 10.sup.5 Hz, the electrical conductivity obeys the regularity sigma ~ f.sup.S (0.1 less than or equal to S less than or equal to 1.0), which is indicative of the conductivity over localized states. It is shown that a further increase in the frequency leads to an increase in the ionic conductivity and transition of the system to the superionic state.
The temperature dependences of electrical conductivity over localized states in the solubility region of mixed crystals of compositions (TlInSe.sub.2).sub.1- x(TlGaTe.sub.2).sub.x at x = 0, 0.1 0.2, ...0.8, 0.9, and 1 are studied. It is established that hopping conductivity with a variable hop length over localized states near the Fermi level occurs in this system. The conductivity activation energy is determined; and the density of states in the vicinity of the Fermi level, their dispersion, localization radius, and average carrier hop distance for all compositions are estimated; and the concentration dependences of the calculated parameters are plotted. DOI: 10.1134/S1063782615120192
The temperature dependences of electrical conductivity over localized states in the solubility region of mixed crystals of compositions (TlInSe
2
)
1–
x
(TlGaTe
2
)
x
at
x
= 0, 0.1 0.2, 0.8, 0.9, and ...1 are studied. It is established that hopping conductivity with a variable hop length over localized states near the Fermi level occurs in this system. The conductivity activation energy is determined; and the density of states in the vicinity of the Fermi level, their dispersion, localization radius, and average carrier hop distance for all compositions are estimated; and the concentration dependences of the calculated parameters are plotted.
The conductivity and temperature-frequency dependences of the permittivity of TlGaTe
2
crystals have been studied. Strong dielectric relaxation has been revealed. It has been shown that the mechanism ...of dielectric relaxation is associated with hopping of Tl ions over vacancies in the thallium sublattice due to the transition of the system to the superionic state.
TlInSe
2
crystals are investigated in dc and ac electric fields in the temperature range of 100–400 K. A decrease in the electrical conductivity σ with time in a dc field is revealed. The ...complex-impedance spectra
Z
*(
f
) are measured in the frequency range of 10–10
6
Hz. Diagrams in the (
Z
″-
Z
′) complex plane are analyzed using the method of equivalent circuits. It is shown that the electrical properties of TlInSe
2
crystals in the investigated ranges of temperatures and frequencies are determined by hopping conductivity and the accumulation of charge carriers near blocking platinum electrodes.
The temperature dependences of the conductivity σ(
T
) and the switching and memory effects in one-dimensional TlInSe
2
and TlInTe
2
single crystals have been studied. A specific feature is found in ...the dependence σ(
T
) above 333 K, which is related to the transition of crystals to the state with superionic conductivity. It is suggested that the ion conductivity is caused by the diffusion of Tl
+
ions over vacancies in the thallium sublattice between (In
3+
Te
2
2−
)
−
and (In
3+
Se
2
2−
)
−
nanochains (nanorods).
S
-type switching and memory effects are revealed in TlInSe
2
and TlInTe
2
crystals, as well as voltage oscillations in the range of negative differential resistance. It is suggested that the switching effect and voltage oscillations are related to the transition of crystals to the superionic state, which is accompanied by “melting” of the Tl sublattice. The effect of electric-field-induced transition of TlInSe
2
and TlInTe
2
crystals to the superionic state is found.
The switching effect, field and temperature dependences of the permittivity and conductivity of TlGaTe
2
crystals subjected to various γ-irradiation doses are studied. Under rather low electric ...fields, the phenomenon of threshold switching with an
S
-shaped current-voltage characteristic containing a portion with negative differential resistance is observed in the crystals. In the region of critical voltages, current and voltage oscillations and imposed modulation are observed. Possible mechanisms of switching, ionic conductivity, disorder, and electrical instability in TlGaTe
2
crystals are discussed.
Superionic conductivity in TlGaTe2 crystals Sardarli, R. M.; Samedov, O. A.; Abdullayev, A. P. ...
Semiconductors (Woodbury, N.Y.),
08/2011, Volume:
45, Issue:
8
Journal Article
Peer reviewed
Temperature dependences of electrical conductivity σ(
T
) and permittivity ɛ(
T
) of one-dimensional (1D) TlGaTe
2
single crystals are investigated. At temperatures higher than 305 K, superionic ...conductivity of the TlGaTe
2
is observed and is related to diffusion of Tl
+
ions via vacancies in the thallium sublattice between (Ga
3+
Te
2
2−
−
nanochains. A relaxation character of dielectric anomalies is established, which suggests the existence of electric charges weakly bound to the crystal lattice. Upon the transition to the superionic state, relaxors in the TlGaTe
2
crystals are Tl
+
dipoles ((Ga
3+
Te
2
2−
)
−
chains) that arise due to melting of the thallium sublattice and hops of Tl
+
ions from one localized state to another. The effect of a field-induced transition of the TlGaTe
2
crystal to the superionic state is detected.
