Ionic conductivity of BaF2 crystals

By fitting theoretically calculated to experimentally found lg σT ÷ 1/T dependencies (σ conductivity) there were obtained: the free formation enthalpy of anti-Frenkel defects g_AF = 1.81 eV − 7.85 kT, and the mobilities v_V and v_i of F⁻ ion vacancies and interstitials: v_VT = 240 exp (−0.59 eV/kT) cm² K/Vs, v_iT = (4080 + 610) exp (−0.79 eV/kT) cm² K/Vs. The free association enthalpies were reestimated for complexes consisting of single foreign cations (Na⁺, K⁺, Y³⁺, La³⁺, Tm³⁺, Yb³⁺) and the corresponding charge-compensating defects. At the melting point of BaF₂ at least 5.7 per cent of the F⁻ ions are disordered.     

Photo-EPR of deformation-produced defects in GaAs

Deformation-produced paramagnetic centres have been studied in GaAs crystals uniaxially compressed at 400° using EPR technique (X band). The effect of light with photon energies from 0.4 to 1.5 eV on the populations of the centres has been investigated. On the basis of the experimental results a model is proposed which locates the energy levels of two of the centres at E_c − 1.05 eV and E_v + 0.75 eV.     

Electric conductivity and lattice disorder of PbMoO4 crystals

From differential thermal analysis (DTA), thermal etching, perfectly reversable redox treatments and electric conductivity it is concluded that the Pb/Mo ratio of the PbMoO₄ crystals is always 1 and that phase transitions do not occur. Pb³⁺ ions detectable by an absorption band at 435 nm cause a p-conductivity due to the reaction Pb³⁺ ⇌ Pb⁺⁺ + e⁺. At elevated temperatures the p-conductivity increases with increasing oxygen partial pressure of the surrounding atmosphere. The influence of foreign ions on the concentration of ionic and electronic defects in PbMoO₄, CaMoO₄, PbO, and PbTiO₃ can be explained by an anti-Frenkel disorder of the oxygen ion sublattice. For PbMoO₄ crystals the mobility O⁻ ion vacancies and the free formation enthalpy of anti-Frenkel defects are found to be v_v = \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop - \limits_T^{9160} $\end{document} exp (−1.15 eV/kT) cm² K/Vs and g_AF = 3.6kT −2.2 eV, respectively.     

Absorption and electrical conductivity of CaMoO4 crystals

The electrical conductivity σ of CaMoO₄ crystals was investigated between room temperature and 850°C. The mobility v_v and the diffusion coefficient D_v of the O⁻ ion vacancies have been derived from σ: v_vT = 3300 exp (−1.52 eV/kT) cm² K/Vs, D_v = (0.1…1) × exp (−1.52 eV/kT) cm²/s. An absorption occuring in crystals which are reduced or X-irradiated at low temperatures is dichroitic and caused by Mo⁵⁺ ions. For measurement in c direction the oscillator strength of the 680 nm absorption band is found to be about 0.1.     

Strahlende Rekombination aus Nichtgleichgewichtszuständen in katodenstrahlangeregtem GaN

The radiative recombination of electron-beam excited hot carriers in GaN is investigated at liquid neon temperature. An emission peak at 3.495 eV beyond the free exciton energy level has been found which seems to arise from a band-to-band transition of free carriers. When high concentrations of carriers are created a thermal quasiequilibrium in the free carrier system is established with a temperature T_e higher than that of the lattice and growing with increasing excitation density. – Analyzing the dependence of T_e on excess-carrier generation rate, we find that the polaroptical scattering is the dominant energy loss mechanism.     

Effect of Neutron Irradiation and Annealing on the Intensity of the Copper Related 1.01 eV Emission Band in n-type GaAs

Effect of neutron irradiation (E = 2 MeV, ϕ ≤ 10¹⁵ n/cm²) and subsequent annealing (T ≤ 700 °C, t = 30 min) on the intensity of the copper-related peaked at hvm =1.01 eV emission band in n-type GaAs (n₀ = 2 × 10¹⁸ cm⁻³) is studied. A strong irradiation-induced increase of the above emission intensity was observed testifying about the irradiation-stimulated growth in the concentration of copper-related 1.01 eV radiative centres (Cu_GaV_As pairs). A model is presented to explain this effect.     

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).     

Effect of Al addition on the crystallization of a-AlxSi1−x (0.025 x 0.100) by electron-beam irradiation

Si crystals and nano-rods were formed in Al-added amorphous Si films (a-Al_xSi_1−x; 0.025 x 0.100) by the irradiation of a focused electron-beam; the films were in situ heated to be kept at 400 °C and the current density of the electron-beam was 15.7 pA/cm². The size, shape, and concentration of the Si crystallites were varied sensitively with the Al content as well as the irradiation time. Under the electron-beam irradiation, crystallization occurred to produce polycrystalline phases in the a-Al_0.025Si_0.975 film, while rod-shaped Si nanostructures were formed in the a-Al_0.050Si_0.950 and a-Al_0.100Si_0.900 film. It is evident that the removal of Al and as a result the atomic rearrangements and/or local restructuring in the Al/a-Si film are critically affected by the electron-beam irradiation, which lead to the local crystallization and growth of Si nanocrystallites.     

Comparison of lead solubility in NaCl crystals from data obtained by different methods

The solvus of the NaCl: Pb²⁺ system was found in the concentration range from 1.5 × 10⁻³ to 1.9 × 10⁻² mol% at temperatures ranging from 375 to 430 °C from the data of flotation measurements of the crystal density. The heat of impurity dissolution equal to 2.0 ± ± 0.6 eV and the change in the vibrational entropy in the formation of the solid solution S_v/K= 20 ± 10 were determined. Reasons for a difference in the estimates of lead solubility in NaCl, obtained from temperature dependences of light scattering and by other methods: measurement of the density, electric conductivity, and the electron-microscopic decoration of the same crystals are discussed.     

Density and mobility of anti-frenkel defects in SrF2 crystals

By fitting the theoretically calculated temperature-dependent conductivity σ to the measured dependencies log σT ÷ 1/T the following parameters have been determined: free formation enthalpy of anti-Frenkel defects g_AF = 2.05 eV – 6.35 kT; mobilities of F⁻ion vacancies F and interstitials F: v_νT = 600 exp (-0.70 eV/kT) cm² K/Vs, v_iT = 1.1 · 10⁴ exp (-0.93 eV/kT) cm² K/Vs. — The free association enthalpies of complexes consisting of single foreign ions (Sc³⁺, Y³⁺, La³⁺, Sm³⁺, Li⁺, K⁺, Na⁺, O⁻) and the charge-compensating defect were obtained. The vibration frequency of F⁻ ions in the neighbourhood of F and F is changed by a factor of 2.6 and 0.6, respectively.     

Crystal Data,Electrical Resisitivity and Mobility in Cu3In5Se9 and Cu3In5Te9 Single Crystals

X-ray powder diffraction data were obtained for Cu₃In₅Se₉ and Cu₃Te₉, which were found to crystallize in orthorhombic and tetragonal systems, respectively. The electrical resistivities and Hall mobilities of these compounds were investigated in the temperature range 35–475 K. Cu₃In₅Se₉, was identified to be n-type with a room temperature resistivity of 3 × 10³ Ω·cm which decreases with increasing temperature. For T < 65 K impurity activation energy of 0.03 eV and for T > 350 K onset of intrinsic conduction yielding a band gap energy of 0.99eV were detected. The neutral impurity scattering was found to dominate at low temperatures, while in the high temperature region thermally activated mobility was observed. Cu₃In₅Te₉ exhibits p-type conduction with a room temperature resistivity of 8.5 × 10⁻³ Ω·cm decreasing sharply above 400 K and yielding an impurity ionization energy of 0.13 eV. The temperature dependence of mobility indicates the presence of lattice and ionized impuritiy scattering mechanisms above and below 160 K, respectively.     

Deformation behaviour of single crystals of GaP in uniaxial compression

LEC n-GaP:S single crystals were deformed in uniaxial compression parallel [321] and [110] direction. Plastic deformation by (111) slip has been observed between 511 °C and 717 °C. Indications for (111) twinning were obtained. Yield stress exhibits activation enthalpies U = Q(m + 2) and stress exponents m of U₃₂₁ = (0.54 ± 0.05) eV, U₁₁₀ = = (0.46 ± 0.05) eV, m = 1.1 ± 0.2 and m = 3 ± 1, respectively.     

Impurity diffusion of 114In in Cu

Using the tracer-standard sectioning technique the impurity diffusion of indium in copper has been investigated in the temperature range from 798.1 to 1081.0°C. For the frequency factor and the activation energy, respectively, the following values were determined: D₀₂ = 1.87 cm² · s⁻¹; Q₂ = 2.034 eV. The results are compared with predictions of theoretical models of the impurity diffusion in metals.     

Luminescence and defects of Yb3+-doped sol–gel silica glasses

The optical properties of Yb-doped sol–gel silica glasses were studied by optical absorption and radio-luminescence (RL) measurements, that revealed the typical absorption and emission pattern of Yb³⁺ ions. Moreover, RL bands in the 1.5–3.5 eV interval were also observed, and related to defects of the silica matrix. The RL intensity temperature dependence, investigated in the 10–320 K interval, evidenced the presence of the SiO₂ self-trapped exciton emission at 2.2 eV, whose intensity was rapidly quenched by temperature increasing. At variance, the Yb³⁺ emission intensity increased markedly by temperature increasing. This phenomenon is interpreted by considering a competitive role of point defects in free carrier trapping, evidenced by parallel wavelength resolved thermally stimulated luminescence measurements.     

Electrical Conductivity of Phenoxazine-Iodine (2:3) and Phenothiazine-Iodine (2:3) Crystals

Abstract

Single crystals of phenoxazine-iodine (2 : 3) and phenothiazine-iodine (2 : 3) salts are found to be highly conducting ([sgrave] _R.T. = 5–20 ohm^?1 cm^?1). The observed deviation from the exponential temperature dependence of the conductivities is ascribed to the degenerate semiconducting phases or alternatively to the metallic phases with impurities. However, phenoxazine-iodine and phenothiazine-iodine are perfect semiconductors below 220° K with activation energies of 0.12 eV and 0.14 eV, respectively. The absorption features related with (phenoxazine)⁺ ₂ and (phenothiazine); cations are observed in the infrared spectra of the salts.     

Effect of high-energy electron irradiation in an electron microscope column on fluorides of alkaline earth elements (CaF2, SrF2, and BaF2)

The effect of high-energy (150 eV) electron irradiation in an electron microscope column on crystals of fluorides of alkaline earth elements CaF₂, SrF₂, and BaF₂ is studied. During structural investigations by electron diffraction and electron microscopy, the electron irradiation causes chemical changes in MF₂ crystals such as the desorption of fluorine and the accumulation of oxygen in the irradiated area with the formation of oxide MO. The fluorine desorption rate increases significantly when the electron-beam density exceeds the threshold value of ∼2 × 10³ pA/cm²). In BaF₂ samples, the transformation of BaO into Ba(OH)₂ was observed when irradiation stopped. The renewal of irradiation is accompanied by the inverse transformation of Ba(OH)₂ into BaO. In the initial stage of irradiation of all MF₂ compounds, the oxide phase is in the single-crystal state with a lattice highly matched with the MF₂ matrix. When the irradiation dose is increased, the oxide phase passes to the polycrystalline phase. Gaseous products of MF₂ destruction (in the form of bubbles several nanometers in diameter) form a rectangular array with a period of ∼20 nm in the sample.     

Single crystals of the fluorite nonstoichiometric phase Eu 0.9162+ Eu 0.0843+ F2.084 (conductivity, transmission, and hardness)

The nonstoichiometric phase EuF_2+x has been obtained via the partial reduction of EuF₃ by elementary Si at 900–1100°C. Eu_0.916²⁺Eu_0.084³⁺F_2.084 (EuF_2.084) single crystals have been grown from melt by the Bridgman method in a fluorinating atmosphere. These crystals belong to the CaF₂ structure type (sp. gr. Fm $ \bar 3 $ \bar 3 m) with the cubic lattice parameter a = 5.8287(2) ?, are transparent in the spectral range of 0.5–11.3 μm, and have microhardness H _μ = 3.12 ± 0.13 GPa and ionic conductivity σ = 1.4 × 10⁻⁵ S/cm at 400°C with the ion transport activation energy E _a = 1.10 ± 0.05 eV. The physicochemical characteristics of the fluorite phases in the EuF₂ − EuF₃ systems are similar to those of the phases in the SrF₂ − EuF₃ and SrF₂ − GdF₃ systems due to the similar lattice parameters of the EuF₂ and SrF₂ components. Europium difluoride supplements the list of fluorite components MF₂ (M = Ca, Sr, Ba, Cd, Pb), which are crystal matrices for nonstoichiometric (nanostructured) fluoride materials M _{1 − x} R _x F_{2 + x} (R are rare earth elements).     

Characterization of deep levels in a-plane GaN epi-layers grown using various growth techniques

To study the correlation between defects and deep levels in a-plane GaN films grown on r-plane sapphire substrates, transmission electron microscopy (TEM) and deep level transient spectroscopy (DLTS) have been performed on three types of a-plane GaN samples grown using modified two-step growth (sample I), SiN_x interlayer (sample II), and patterned insulator on sapphire substrate (sample III). From the microstructure evolution in cross-sectional TEM images, it was shown that combination of growth techniques is highly efficient in the reduction of dislocation densities. Average dislocation densities of samples I, II, and III were about 2.2×10⁹ cm^?2, 1.1×10⁹ cm^?2, and 3.4×10⁸ cm^?2, respectively. The trap a_t E_c–E_t～0.13 eV (E1) was observed in only sample I, and three electron traps at 0.28–0.33 eV (E2), 0.52–0.58 eV (E3), and 0.89–0.95 eV (E4) from the conduction band edge were measured common to all the samples. The analysis of trap properties indicated that E2 and E3 trap levels are strongly associated with the partial dislocations in a-plane GaN films.     

Effect of Fast Electron Irradiation and Annealing on the Luminescence in GaAs(Zn) crystals. Irradiation-induced 1.26 and 1.39 eV Emission Bands

The effect of 2.2 MeV electron irradiation and subsequent annealings on the photoluminescence in zinc-doped p-type GaAs crystals is studied and analyzed. Rather strong emission bands peaked at hv_m (77 K) near 1.26 eV (induced by electron irradiation) and 1.39 eV (induced by annealing of irradiated crystals) are observed. Evidence is presented that the 1.26 and 1.39 eV emission bands occur due to radiative electronic transitions in As_iZn_Ga and V_AsZn_Ga pairs induced by irradiation and annealing of irradiated crystals, accordingly. The observed variations in the intensities of the 1.26 and 1.39 eV emission bands upon irradiation and subsequent annealings of GaAs(Zn) crystals are explained in terms of irradiation and annealing-induced variations in the amount of 1.26 and 1.39 eV radiative centres resulting from: a) the effective interaction of mobile radiation-induced defects in the arsenic sublattice with zinc atoms leading to the formation of As_iZn_Ga and V_AsZn_Ga pairs; b) the thermal dissociation of As_iZn_Ga and V_AsZn_Ga pairs on individual components.     

Electron irradiation‐induced effects on optical spectra of (NH4)2ZnCl4: x Sr2+ single crystals

The effect of electron‐beam irradiation with different doses on optical constants of (NH₄)₂ZnCl₄: x Sr²⁺ crystals with x=0.000, 0.020, 0.039, 0.087 or 0.144 wt% has been studied. The optical transmission in the energy range 3.4‐6.4 eV was measured hence the absorption coefficient was computed as a frequency function. The absorption coefficient was also calculated as a function of electron‐beam dose. Irradiation with e‐beam did not affect the allowed indirect type of transition responsible for interband transitions of (NH₄)₂ZnCl₄: x Sr²⁺ crystals. Values of the optical energy gap E_g and optical moment E_p for electronic interband transition of unexposed and (NH₄)₂ZnCl₄: x Sr²⁺ crystals after e‐beam exposure were deduced. The area under the absorption band at 5.30 eV was used to evaluate the effect of e‐irradiation on optical parameters of samples with x=0.00, 0.020 or 0.039. A shift in the position and a nonmonotonic change in the intensity of this band with increasing e‐beam dose was observed. Changes in the E_g value were used to evaluate the effect of e‐beam exposure dose on (NH₄)₂ZnCl₄: x Sr²⁺ samples with x=0.087 or 0.144. The obtained results were compared with those obtained for the same crystals after irradiation with different γ‐doses.