We report on the first NMR study of powder and single crystal samples of thallium indium sulfide, TlInS(2). The crystal under study is a pure single-layer TlInS(2) polytype. Our findings show that ...transformation from the high temperature paraelectric phase to the low temperature ferroelectric phase occurs via an incommensurate phase that exists in the temperature range from T(c) = 192 K to T(i) = 205 K. On approaching the phase transition at T(i) from above, the crystal exhibits a soft mode behavior. A discrepancy in the literature data on the phase transitions in TlInS(2) is discussed and ascribed to polytypism of the TlInS(2) crystals.
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.
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.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
Vibrational spectra of TlInS
2
crystals in the terahertz frequency range (0.1–3 THz) have been obtained and analyzed. The observed low-frequency band is attributed to the libration oscillations of ...nanolayers (so-called boson peak). A correlation between the coherent low-frequency oscillation and a disordered character of the crystal structure is shown. A conclusion is made on the presence of a topological disorder that manifests itself on the layered subsystem level.
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.
Insertion of proper amounts of nickel oxide into alumina-supported V-Sb oxide catalyst for the oxidative dehydrogenation of isobutane substantially increases isobutane conversion (from 36 to 42–44%) ...at selectivity to isobutene ∼70%. Fresh and used catalysts (including reference bulk V-Sb-O and V-Sb-Ni-O systems) were characterised by BET, XRD, XPS and H
2-TPR. Formation of new phase of nickel vanadate NiV
2O
6 at the expense of free VO
x
-phase leads to more reducible catalyst with increased amounts of mobile lattice oxygen. The facile redox cycle of vanadium species is considered to improve the catalyst activity.
