X-ray dosimetric properties of vapor-grown CdGa<Subscript>2</Subscript>S<Subscript>4</Subscript> single crystals

CdGa₂S₄ single crystals have been grown from a presynthesized source material by closed-tube iodine vapor transport, and their X-ray dosimetric properties have been studied. Their X-ray sensitivity coefficient K ranges from K = 1.26 × 10⁻¹¹ to 1.39 × 10⁻¹⁰ A min/(V R) at effective X-ray hardnesses V _a = 25–50 keV and dose rates E = 0.75–78.05 R/min, and increases with X-ray dose. The K(V _a) curve has a negative slope, in contrast to the K(E) curve. The photocurrent-dose curves of the CdGa₂S₄ single crystals demonstrate that the steady-state X-ray photocurrent is a power-law function of X-ray dose rate: ΔI _E,0 ∼ E ^α . With increasing V _a, the slope of the curves sharply decreases and α approaches unity.     

Electrical conductivity and dielectric properties of cadmium thiogallate CdGa<Subscript>2</Subscript>S<Subscript>4</Subscript> thin films

Cadmium thiogallate CdGa₂S₄ thin films were prepared using a conventional thermal evaporation technique. The dark electrical resistivity calculations were carried out at different elevated temperatures in the range 303–423 K and in thickness range 235–457 nm. The ac conductivity and dielectric properties of CdGa₂S₄ film with thickness 457 nm has been studied as a function of temperature in the range from 303 to 383 K and in frequency range from 174 Hz to 1.4 MHz. The experimental results indicate that σ_ac(ω) is proportional to ω ^s and s ranges from 0.674 to 0.804. It was found that s increases by increasing temperature. The results obtained are discussed in terms of the non overlapping small polaron tunneling model. The dielectric constant (ε′) and dielectric loss (ε″) were found to be decreased by increasing frequency and increased by increasing temperature. The maximum barrier height (W _m) was estimated from the analysis of the dielectric loss (ε″) according to Giuntini’s equation. Its value for the as-deposited films was found to be 0.294 eV.     

Radiative recombination in CdGa<Subscript>2</Subscript>S<Subscript>4</Subscript> single crystals

We have studied the effects of light polarization and temperature on the photoluminescence spectrum of CdGa₂S₄ single crystals at temperatures from 77 to 300 K. Based on analysis of the present experimental data in conjunction with earlier band structure, optical absorption, and photoconductivity data, we have identified the mechanism of radiative recombination in CdGa₂S₄.     

The effect of illumination on the current-voltage characteristics and conductivity of MnIn<Subscript>2</Subscript>S<Subscript>4</Subscript> single crystals

The effect of illumination on the current-voltage (J-U) characteristics and the temperature dependence of conductivity σ(T) of MnIn₂S₄ single crystals has been studied. Under illumination, the J-U curves can be divided into three parts corresponding to the linear (J ∼ U), “3/2” (J ∼ U ^1.5) and “5/2” (J ∼ U ^2.5) laws. This behavior is explained by an increase in the density of free charge carriers under the joint action of electric field and illumination. The current J ₁ in the illuminated sample is 10⁴–10⁵ times the dark J ₂ value. The positions of energy levels in the semiconductor crystal under study are determined.     

Photoconductivity and luminescence anisotropy in ZnIn<Subscript>2</Subscript>S<Subscript>4</Subscript> and ZnIn<Subscript>2</Subscript>S<Subscript>4</Subscript>:Cu<Superscript>2+</Superscript> single crystals

ZnIn₂S₄ and ZnIn₂S₄:Cu²⁺ single crystals are shown to exhibit considerable photoconductivity and luminescence anisotropy. The mechanism of carrier recombination in the crystals is polarization-dependent. Their spectra can be understood in terms of optical transitions involving donor and acceptor levels. The degree and spectral distribution of the anisotropy can be tuned via doping and alternating growth of the three- and one-layer polytypes.     

Multidimensional CdS nanowire/CdIn<Subscript>2</Subscript>S<Subscript>4</Subscript> nanosheet heterostructure for photocatalytic and photoelectrochemical applications

Nanomaterial shapes can have profound effects on material properties,and therefore offer an efficient way to improve the performances of designed materials and devices.The rational fabrication of multidimensional architectures such as one dimensional (1D)-two dimensional (2D) hybrid nanomaterials can integrate the merits of individual components and provide enhanced functionality.However,it is still very challenging to fabricate 1D/2D architectures because of the different growth mechanisms of the nanostructures.Here,we present a new solventmediated,surface reaction-driven growth route for synthesis of CdS nanowire (NW)/CdIn2S4 nanosheet (NS) 1D/2D architectures.The as-obtained CdS NW/CdIn2S4 NS structures exhibit much higher visible-light-responsive photocatalytic activities for water splitting than the individual components.The CdS NW/CdIn2S4 NS heterostructure was further fabricated into photoelectrodes,which achieved a considerable photocurrent density of 2.85 mA.cm-2 at 0 V vs.the reversible hydrogen electrode (RHE) without use of any co-catalysts.This represents one of the best results from a CdS-based photoelectrochemical (PEC) cell.Both the multidimensional nature and type Ⅱ band alignment of the 1D/2D CdS/CdIn2S4 heterostructure contribute to the enhanced photocatalytic and photoelectrochemical activity.The present work not only provides a new strategy for designing multidimensional 1D/2D heterostructures,but also documents the development of highly efficient energy conversion catalysts.     

Photoelectric and X-ray dosimetric properties of TlGa<Subscript>0.97</Subscript>Mn<Subscript>0.03</Subscript>S<Subscript>2</Subscript> single crystals

It is established that the partial substitution of gallium for manganese (3 mol %) in TlGaS₂ single crystals leads to a decrease in width of the band gap (from 2.62 to 2.5 eV), broadening of the peak of intrinsic photocurrent, and appearance of a broad band of extrinsic photocurrent over the photon energy range hν = 1.7–2.4 eV. Upon the partial substitution Ga → Mn in TlGaS₂, the X-ray sensitivity coefficient increases significantly (by a factor of 24–57) within an irradiation dose of 0.75–78 R/min, and the current-dose characteristics of TlGa_0.97Mn_0.03S₂ have good reproducibility.     

Growth and thermal expansion of In<Subscript>2</Subscript>S<Subscript>3</Subscript> single crystals

In₂S₃ single crystals have been grown by the Bridgman-Stockbarger method. Their composition has been determined by electron probe x-ray microanalysis, and their phase-transition temperatures have been evaluated by differential thermal analysis. The thermal expansion coefficient of In₂S₃ has been determined in the range 80–1000 K by dilatometry.     

Anomalous dielectric and piezoelectric properties and electrical conductivity of heavily doped LiNbO<Subscript>3</Subscript>:Zn crystals

In LiNbO₃:Zn crystals with near-threshold doping levels ( 4.5–4.7 mol % Zn), high-temperature measurements and high-temperature annealing under short-circuit conditions lead to considerable changes in spontaneous unipolarity. The considerable changes in spontaneous unipolarity are accompanied by well-defined low-frequency dielectric dispersion and sharp anomalies in temperature dependences of electrical conductivity and dielectric permittivity. As a result, the piezoelectric modulus d₃₃₃ increases to a level approaching the highest values reported in the literature for single-domain nominally pure LiNbO₃ crystals.     

Elastic properties of Li<Subscript>2</Subscript>Zn<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> single crystals

The complete elastic modulus matrix of Li₂Zn₂(MoO₄)₃ single crystals has been measured for the first time. The sound velocity has been measured in different directions of the crystals by a pulse-phase method. The measurement results have been used to calculate elastic moduli. The sound velocity has been calculated in the three main crystallographic planes of the crystals.     

Dielectric properties and electrical conductivity of ZrO<Subscript>2</Subscript>-CeO<Subscript>2</Subscript> ceramics

ZrO₂-CeO₂ (10, 18, and 23 mol % CeO₂) solid solutions have been synthesized via coprecipitation. The powders have been sintered at 1875 K, and the electrical conductivity and dielectric properties of the resultant ceramics have been studied. The dielectric relaxation observed in the ceramics can be understood in terms of ionic transport accompanied by the formation of dipoles relaxing in an ac electric field.     

Anisotropy of dielectric losses in Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and SiO<Subscript>2</Subscript> single crystals

The procedure and results of measurements of the dielectric loss tangent using the dielectric resonator technique on azimuthal modes of the HE (quasi-E) and EH (quasi-H) types are considered. The measurements were performed for uniaxial anisotropic single crystals of Al₂O₃ (at a frequency of 11 GHz) and SiO₂ (at 39 GHz) in a temperature range of 80–373 K and for an isotropic single crystal of Y₃Al₅O₂ (YAG) at room temperature in a frequency range of 9–15 GHz. The proposed method revealed the anisotropy of dielectric losses in Al₂O₃ and SiO₂ single crystals in the temperature range studied. According to this, losses along the optical axis of these crystals are lower than in the transverse plane. In the YAG crystal, the Q values for modes of the two types with the same frequency are close, which corresponds to isotropic losses. The dielectric losses in YAG increase in proportion to the frequency.     

Phase relations in the TlInS<Subscript>2</Subscript>-TlYbS<Subscript>2</Subscript> system and electrical properties of Tl<Subscript>2</Subscript>InYbS<Subscript>4</Subscript> crystals

We have studied phase relations in the TlInS₂-TlYbS₂ system and showed that it contains a congruently melting compound of composition Tl₂InYbS₄ (1: 1 ratio of the constituent sulfides). According to X-ray diffraction results, the compound Tl₂InYbS₄ crystallizes in tetragonal symmetry. Temperature-dependent electrical conductivity and Hall data for Tl₂InYbS₄ single crystals demonstrate that this compound is a p-type semiconductor with a band gap of 1.60 eV. The temperature variation of the carrier Hall mobility in Tl₂InYbS₄ corresponds to carrier scattering by acoustic phonons.     

Photoelectric properties of ordered-vacancy Ga<Subscript>2</Subscript>Se<Subscript>3</Subscript> single crystals

We have studied the photoconductivity spectrum, thermally stimulated current, current-light characteristics, and temperature-dependent photocurrent in Bridgman-grown ordered-vacancy Ga₂Se₃ crystals. The observed temperature quenching of photoconductivity and two regions of its thermal activation in Ga₂Se₃ crystals are interpreted in terms of a multicenter recombination model which incorporates an s-channel of active recombination, r-centers of photosensitivity, and traps for nonequilibrium majority carriers.     

Acousto-optic properties of LiBi(MoO<Subscript>4</Subscript>)<Subscript>2</Subscript> single crystals grown at low temperature gradients

This paper reports the starting charge composition and process parameters for low thermal gradient (<1°C/cm) Czochralski growth of uniform bulk LiBi(MoO₄)₂ crystals. The acousto-optic figure of merit (M ₂) of a LiBi(MoO₄)₂ crystal has been measured in different directions.     

Ho<Subscript>2</Subscript>S<Subscript>3</Subscript>-Ga<Subscript>2</Subscript>S<Subscript>3</Subscript> phase diagram

The Ho₂S₃-Ga₂S₃ system has been studied using differential thermal analysis, X-ray diffraction, microstructural analysis, microhardness tests, and density measurements, and its phase diagram has been constructed. The system contains three ternary compounds: Ho₃GaS₆, HoGaS₃, and Ho₆Ga_10/3S₁₄. Their melting behavior has been studied for the first time. The compound Ho₆Ga_10/3S₁₄ melts congruently at 1435 K; Ho₃GaS₆ and HoGaS₃ melt incongruently at 1370 and 1250 K, respectively. The Ho₂S₃-Ga₂S₃ system is a pseudobinary join of the ternary system Ho-Ga-S. At room temperature, the β-Ga₂S₃-based solid solution extends to 1.5 mol % Ho₂S₃; the Ho₂S₃ solubility in γ-Ga₂S₃ is 10 mol %. The compounds HoGaS₃ and Ho₃GaS₆ crystallize in orthorhombic symmetry (Ho₃GaS₆: a = 10.40 Å, b = 13.20 Å, c = 6.44 Å, Z = 4; HoGaS₃: a = 6.8 Å, b = 9.92 Å, a = 3.08 Å, Z = 4). Ho₆Ga_10/3S₁₄ has a hexagonal structure (a = 9.62 Å, c = 6.04 Å).     

Peculiarities of the electric conductivity of As<Subscript>2</Subscript>S<Subscript>3</Subscript>〈Au〉 and As<Subscript>2</Subscript>S<Subscript>5</Subscript>〈Au〉 glasses

The temperature dependences of the dc conductivity in glasses of the (As₂S₃)_1−x Au_x and (As₂S₅)_1−x Au_x systems (0.04 at. % ≥x≥0) are reported for the first time. The curves show an anomalous behavior in the temperature interval of 360 K<T<300 K and exhibit a break for glass compositions with a low gold content. A model explaining the existence of impurity conductivity is proposed.     

Thermal conductivity of LaF<Subscript>3</Subscript>-based single crystals and ceramics

The thermal conductivity of lanthanum fluoride based single crystals and ceramics (LaF₃, La_0.975Nd_0.025F₃, and La_0.95Sr_0.05F_2.95) has been measured at temperatures from 50 to 693 K by an absolute steady-state axial flow technique. We have not detected any anomalies indicative of “two-level systems.” The heat capacity of LaF₃ single crystals has been measured in the temperature range 56–300 K. The results are used to evaluate the c-axis phonon mean free path as a function of temperature for single-crystal LaF₃.     

Photoluminescence of Ga<Subscript>2</Subscript>S<Subscript>3</Subscript>:Sm<Superscript>2+</Superscript> crystals

The photoluminescence spectra of Ga₂S₃:Sm²⁺ crystals have been measured in a wide temperature range (77–450 K). The results have been used to identify the mechanisms of the luminescence and energy transfer from the host to the rare-earth ion.     

Dielectric properties of Be(IO<Subscript>3</Subscript>)<Subscript>2</Subscript>⋅4H<Subscript>2</Subscript>O crystals

The article studies the dielectric properties, dc conductivity and ac conductivity of Be(IO₃)₂⋅4H₂O single crystals. The dielectric constant ε has been defined for the three directions of the vectors a, b and c in the crystals in the temperature interval 280–340 K and frequency range 100 Hz–10⁶ Hz. The crystals show strongly expressed anisotropy, at 20 ^∘C and frequency 100 Hz ε_a = 235, ε_b = 30 and ε_c = 85. The frequency dependence of ε is evidence of the presence of low-frequency relaxation polarization in the crystals. The activation energies of the three directions in the crystals have been derived from the temperature dependence of dc conductivity, and they are 1.03 eV, 0.836 eV and 1.2 eV respectively.