Optical Phonons and Chemical Bonding in TlSbS2, TlSbSe2, and Tl3SbS3 Crystals

The optical phonons at k = 0 of TlSbS₂, TlSbSe₂, and Tl₃SbS₃ have been investigated by infrared reflectivity measurements from 50 to 4000 cm⁻¹ at 300 K. The factor group analysis of vibrational modes of TlSbS₂ and Tl₃SbS₃ crystal lattices has been made. The dielectric constant dispersion for E ‖ a and E ‖ b has been determined by classical dispersion relations. The Szigeti effective charges, the Born dynamic effective charge, and the Tl, Sb, S (Se) relative ion charges were calculated in dependence on the polarization of the incident light.     

Host Lattice Effect on Paramagnetic Impurity: Single Crystal EPR Study of VO(II)‐Doped Biomineral Cadmium Ammonium Phosphate Hexahydrate

Single crystal electron paramagnetic resonance studies on VO(II) doped cadmium ammonium phosphate hexahydrate were carried out at room temperature. The paramagnetic impurity VO(II) was found to enter the host lattice both substitutionally and interstitially. The spin Hamiltonian parameter values calculated from crystal rotations for both the locations are; Site1: g_∥ = 1.939, g_⟂ = 1.992, A_∥ = 16.3mT, A_⟂ = 7.7mT and site2: g_∥ = 1.933, g_⟂ = 1.998, A_∥ = 16.2mT, A_⟂ = 7.7mT. The powder spectra values agree well with the single crystal data. The two sites have been identified as at right angles to each other. The admixture coefficients and other parameter values (κ and P) were evaluated from the spin Hamiltonian parameters. The complex was found to be fairly covalent in nature.     

The superposition of the lattice radiation and reflectivity spectra of MoO3 and PbMoO4 crystals

The Raman scattering of MoO₃ at 300 and 77 K and the infrared reflectivity spectra of MoO₃ at 300 K have been investigated in different scattering geometries. The Raman spectra of PbMoO₄ crystals at 77 K have been investigated also. The reflectivity spectra of MoO₃ crystals were calculated for E ∥ c and E ∥ a. The phonon parameters and the effective ionic charges of anions and cations for MoO₃ and PbMoO₄ crystals are determined. The diagrams of the splitting of the vibrational levels by the Davydov resonance and by the factor group interactions have been determined. It is shown that the lattice radiation of crystals which have a number of vibrational oscillators (MoO₃, PbMoO₄) begins at low energy vibrational modes and at low values of the damping parameters.     

Mikrohärteuntersuchungen an Einkristallen der Verbindungen Tl3BX4, (B = V,Nb, Ta; X=S,Se)

Vickers microhardness measurements were performed on single crystals of compounds Tl₃BX₄ (B = V, Nb, Ta; X = S, Se). The anisotropy of the hardness on the (111)-plane was beyond the standard deviation. Besides the load-dependent Vickers hardness HV, the corrected, load-independent hardness HV_c was determined. Tl₃VS₄ showed the highest value of hardness (HV = 66 kp/mm² at 15 p load), the othe compounds differ only slightly in hardness.     

Temperature and excitation intensity tuned photoluminescence in Tl4GaIn3S8 layered single crystals

Photoluminescence spectra of Tl₄GaIn₃S₈ layered crystals grown by Bridgman method have been studied in the wavelength region of 500–780 nm and in the temperature range of 26–130 K with extrinsic excitation source (λ_exc = 532 nm), and at T = 26 K with intrinsic excitation source (λ_exc = 406 nm). Three emission bands A, B and C centered at 514 nm (2.41 eV), 588 nm (2.11 eV) and 686 nm (1.81 eV), respectively, were observed for extrinsic excitation process. Variations in emission spectra have been studied as a function of excitation laser intensity in the 0.9‐183.0 mW cm^–2 range for extrinsic excitation at T = 26 and 50 K. Radiative transitions from the donor levels located at 0.03 and 0.01 eV below the bottom of the conduction band to the acceptor levels located at 0.81 and 0.19 eV above the top of the valence band were proposed to be responsible for the observed A‐ and C‐bands. The anomalous temperature dependence of the B‐band peak energy was explained by configurational coordinate model. From X‐ray powder diffraction and energy dispersive spectroscopic analysis, the monoclinic unit cell parameters and compositional parameters of Tl₄GaIn₃S₈ crystals were determined, respectively. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis,crystal growth and characterization of Tl3BX4-compounds (B = V,Nb, Ta; X = S,Se)

Single crystals of Tl₃BX₄-compounds (B = V, Nb, Ta; X = S, Se) were grown by the Bridgman-Stockbarger technique. The compounds were synthesized from the high-purity elements. The melting points were determined by differential thermal analysis. Tl₃VS₄, Tl₃TaS₄ and Tl₃TaSe₄ yielded single crystals up to 10 cm³. The other compounds show single crystalline pieces up to 1 cm³. Infrared photographs and electron microprobe analyses revealed inclusions of TlS in the sulfur compounds, in Tl₃VSe₄ and Tl₃NbSe₄ inclusions of TlSe and in Tl₃TaSe₄ small amounts of Ta.     

NMR and infrared study of cation motion in vitreous and polycrystalline TlPO3

The activation energy for Tl⁺ conduction in TlPO₃ glass is obtained from analysis of temperature-dependent motional narrowing for Tl²⁰⁵ NMR spectra and determinations of the localized far infrared (FIR) vibrational frequency for Tl⁺. Use is made of the phenomenological equation of Hendrickson and Bray to analyze the NMR data, yielding E_a = 1.19 eV; the measured FIR Tl⁺ vibrational frequency of 80 cm^?1 yields E_a = 1.09 eV. No significant ionic conduction is observed in polycrystalline TlPO₃. Differential scanning calorimeter measurements yield a glass transition temperature T_g of 96°C and the onset of crystallization temperature of 132°C. Measurements of the Tl²⁰⁵ chemical shift interaction as a function of frequency indicate that (1) the Tl⁺ sites in both polycrystalline and glassy TlPO₃ are ionic, the sites in the polycrystal being slightly more ionic than in the glass; (2) the chemical shift interaction is anisotropic in the glass and isotropic in the polycrystal; and (3) distributions in the values of the principal components of the chemical shift tensor exist in the glass, corresponding to a variety of TlO bond lengths and bond strengths.     

Absorption and Circular Dichroism Spectra of La<Subscript>3</Subscript>Ga<Subscript>5</Subscript>SiO<Subscript>14</Subscript> Crystals Doped with Pr<Superscript>3+</Superscript>, Ho<Superscript>3+</Superscript>, and Er<Superscript>3+</Superscript> Ions

The absorption and circular dichroism (CD) spectra of La₃Ga₅SiO₁₄ langasite crystals doped with Pr³⁺, Ho³⁺, and Er³⁺ ions have been studied in the wavelength range of 350–700 nm. The electronic transitions of these ions, which replace La3+ ions in the 3e position with the symmetry 2, are observed in the spectra. All transitions are active in both the absorption and CD spectra. The dipole strengths D _om, rotational strengths R _om, and anisotropy factors g have been calculated for well-resolved bands. Some features are noted for the spectra that were obtained, and their relationship with the structure disorder is considered     

Electrical Characterization of Irradiation plus Annealing – induced VAsZnGa Pairs in p-type GaAs (Zn) Crystals

Effect of fast electron irradiation (E =2.2 Mev, ϕ_c = 1 × 10¹⁶ el/cm²) and subsequent annealings (T = 150 to 350 °C, t = 10 to 600 min) of zinc-doped p-type GaAs crystals on the formation and dissociation of V_AsZn_Ga, pairs is studied. An analysis of the formation and dissociation kinetics of V_AsZn_Ga pairs permitted to find the diffusion coefficient of radiation-induced arsenic vacancies D(D = 1.5 × 10⁻¹⁸, 1 × 10⁻¹⁷ and 5 × 10⁻¹⁷ cm²/s at 150, 175 and 200 °C accordingly), their migration energy ϵ_m(ϵ_m = 1.1 eV), the binding energy of V_AsZn_Ga, pairs ϵ_b(ϵ_b = 0.5 eV), and also their dissociation energy ϵ_d(ϵ_d = 1.6 eV).     

Thermoelectric properties of Tl‐doped Bi2Se3 single crystals

The single crystals of the ternary system based on Bi_2‐xTl_xSe₃ (nominaly x = 0.0‐0.1) were prepared using the Bridgman technique. Samples with varying content of Tl were characterized by the measurement of lattice parameters, electrical conductivity σ_⊥c , Hall coefficient R_H (B∥c), and Seebeck coefficient S (ΔT ⊥c). The measurements indicate that by incorporating Tl in Bi₂Se₃ one lowers the concentration of free electrons and enhances their mobility. This effect is explained in terms of the point defects in the crystal lattice – formation of substitutional defects thallium on the site of bismuth Tl_Bi and the decrease of concentration of selenium vacancies V_Se⁺². We also discuss the temperature dependence of the power factor σS² of the samples. Upon the thallium doping we observe a significant increase of the power factor compare to the parental Bi₂Se₃. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Infrared Lattice Vibrations of TI3AsS4

Infrared reflectivity spectra of TI₃AsS₄ single crystals are measured at room temperature in the wavenumber range from 30 to 4000 cm⁻¹ for the polarization directions E ‖ c and E ‖ a. An analysis of the spectra with the Kramers-Kronig method reveals 10 infrared active modes for each of the polarization directions. On the basis of theoretical estimates the modes due to TI-S and As–S bond vibrations are identified.     

Temperature‐tuned band gap energy and oscillator parameters of Tl2InGaSe4 semiconducting layered single crystals

The optical properties of Tl₂InGaSe₄ layered single crystals have been studied through the transmission and reflection measurements in the wavelength range of 500‐1100 nm. The analysis of room temperature absorption data revealed the presence of both optical indirect and direct transitions with band gap energies of 1.86 and 2.05 eV, respectively. Transmission measurements carried out in the temperature range of 10‐300 K revealed that the rate of change of the indirect band gap with temperature is γ = – 4.4 × 10^‐4 eV/K. The absolute zero value of the band gap energy was obtained as E_gi(0) = 1.95 eV. The dispersion of the refractive index is discussed in terms of the single oscillator model. The refractive index dispersion parameters: oscillator wavelength and strength were found to be 2.53 × 10^–7 m and 9.64 × 10¹³ m^–2, respectively. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Excitation intensity and temperature‐dependent photoluminescence and optical absorption in Tl4Ga3InSe8 layered crystals

Photoluminescence (PL) spectra of Tl₄Ga₃InSe₈ layered crystals grown by Bridgman method have been studied in the wavelength region of 600‐750 nm and in the temperature range of 17‐68 K. A broad PL band centered at 652 nm (1.90 eV) was observed at T = 17 K. Variations of emission band has been studied as a function of excitation laser intensity in the 0.13 to 55.73 mW cm^‐2 range. Radiative transitions from donor level located at 0.19 eV below the bottom of conduction band to shallow acceptor level located at 0.03 eV above the top of the valence band were suggested to be responsible for the observed PL band. From X‐ray powder diffraction and optical absorption study, the parameters of monoclinic unit cell and the energy of indirect band gap were determined, respectively. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal data and some physical properties of Tl2InGaTe4 crystals

The room temperature crystal data, Debye temperature, dark and photoelectrical properties of the Bridgman method grown Tl₂InGaTe₄ crystals are reported for the first time. The X‐ray diffraction technique has revealed that Tl₂InGaTe₄ is a single phase crystal of tetragonal body‐centered structure belonging to the space group. A Debye temperature of 124 K is calculated from the results of the X‐ray data. The current‐voltage measurements have shown the existence of the switching property of the crystals at a critical voltage of 80 V. The dark electrical resistivity and Hall effect measurements indicated the n ‐type conduction with an electrical resistivity, electron density and Hall mobility of 2.49×10³ Ω cm, 4.76×10¹² cm^–3 and 527 cm²V^–1s^–1, respectively. The photosensitivity measurements on the crystal revealed that, the variation of photocurrent with illumination intensity is linear, indicating the domination of monomolecular recombination at room temperature. Moreover, the spectral distribution of the photocurrent allowed the determination of the energy band gap of the crystal studied as 0.88 eV. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Anisotropy of the ionic conductivity of CsCu2Cl3 single crystals

The conductivity of CsCu₂Cl₃ single crystals (orthorhombic system, sp. gr. Cmcm) has been investigated for different electric-field directions, perpendicular to the crystallographic c axis and along it, in the temperature range 390–530 K. The increase in conductivity with temperature is due to the ion-carrier transport with activation energies E _a = 0.65 and 0.80 eV for the directions perpendicular to and along the crystallographic axis, respectively. The anisotropy of the crystal ionic conductivity is found to be σ_⊥c /σ_∥c ≈ 40 at 435 K. The thermally activated contribution to the conductivity in the CsCu₂Cl₃ structure is determined by the transport of Cu⁺ ions.     

Far Infrared and Raman Optical Study of CdInGaS4, CdIn2S4, HgInGaS4 and CdIn2S2Se2 Crystals

Raman and infrared reflectivity spectra of CdInGaS₄, CdIn₂G₄, HgInGaS₄, and CdIn₂S₂Se₂ crystals have been investigated. The fiindamental phonon parameters, the limiting dielectric constants ϵ₀ and ϵ∞ and the reflectivity spectrum contours have been calculated using classical dispersion relations.     

The structures of three trimethylarsine-boron trihalide adducts: (CH3)3AsBCl3, (CH3)3AsBBr3, and (CH3)3AsBI3

An X-ray structure analysis of three trimethylarsine-boron trihalide adducts has been undertaken. Crystals of (CH₃)₃AsBCl₃ and (CH₃)₃AsBBr₃ are monoclinic with space groupP2₁/m (No. 11) withZ=2 while those of (CH₃)₃AsBI₃ are orthorhombic with space groupPnma (No. 62) withZ=4. For (CH₃)₃AsBCl₃,a=6.497(3) Å,b=10.735(3) Å,c=7.070(2) Å,=111.8(3)°,V=458.4(3) ų,R=0.0343. For (CH₃)₃AsBBr₃,a=6.672(4) Å,b=11.135(7) Å,c=7.199(4) Å,=111.5(1)°,V=497.7(5) ų,R=0.0434. For (CH₃)₃ÅsBI₃,a=13.113(7) Å,b=11.733(5) Å,c=7.387(3) Å,V=1136.5(5) ų,R=0.0329. The As-B bond lengths are 2.065(6), 2.04(1), and 2.03(1) Å, respectively, for the chloride, bromide, and iodide. These and other structural parameters are discussed with reference to previous predictions based on vibrational spectra and previous structural studies on the trimethyl-phosphine and trimethylamine adducts.     

Spectroscopic properties of Tm,Ho:CaYAlO4 single crystal

A Tm,Ho:CaYAlO₄ single crystal was grown using the Czochralski (CZ) method. The absorption spectra, the fluorescence spectrum around 2 μm, the upconversion spectrum and energy‐transfer (ET) schemes between Tm³⁺ ions and Ho³⁺ ions have been studied. The crystal boule was free from cracks, inclusions and scattering centers. The broad FWHM of the 797‐nm absorption band (with E//c polarization is 19 nm and with E//a polarization is 18 nm), the large emission bandwidth (about 600 nm) and the intense ET from Tm³⁺ ions to Ho³⁺ ions make Tm,Ho:CaYAlO₄ a promising media for tunable and ultrashort pulses.     

Crystal structure of (E)-5-hydroxypyrrolizidin-3-one and (Z)-5-thioketalpyrrolizidin-3-one

The crystal structures of (E)-5-hydroxypyrrolizidin-3-one (2) and (Z)-5-thioketalpyrrolizidin-3-one (3) have been determined by single-crystal x-ray diffraction techniques and refined by full-matrix least squares. Molecule2 crystallizes in the monoclinic space groupP2₁/a(No. 14) witha=7.887(3) Å,b=9.788(5) Å,c=9.316(4) Å,=100.6(1), andZ=4. Molecule 3 crystallizes in the monoclinic space groupP2₁/c witha=12.947(14) Å,b=10.553(14) Å,c=9.629(14) Å,=101.4(1), andZ=4. The calculated density for both molecules is 1.33 g cm^–1. FinalR-factors were 5.1% for2 and 8.59% for3. The x-ray results showed that a change in configuration occurred in the reaction going from2 to3.     

Synthesis,properties, and structure of 1,3-dimethyl-2(3H)-imidazolethione hydrogen bromide

The compound dmit·HBr (dmit=1,3-dimethyl-2(3H)-imidazolethione) has been synthesized and characterized. The crystal and molecular structure of dmit·HBr has also been determined. The compound, C₅H₉BrN₂S, crystallizes in space groupP2₁/c with four formula units in a cell of dimensionsa= 7.331(1),b=7.744(2),c=14.626(4) Å, and=99.56(2)°. The calculated and observed densities are 1.678 and 1.68(2) g cm^–3, respectively. X-ray results along with physical characterization show this compound to be a molecular adduct of dmit and hydrogen bromide which is sensitive to air, light, and moisture. Specific conductivity (10^–3 M in PhNO₂), infrared, and¹H-NMR data have also been obtained. X-ray results reveal intermolecular contracts between S and Br to be primarily van der Waals in nature. Molecular units are linked through long zigzag Br-S-Br-S chains.