Mechanism of the High X-ray Sensitivity of Single-Crystal CdTe<Ge> Detectors

The high x-ray sensitivity of p-type CdTe single crystals under the conditions of ambipolar conduction is interpreted in a model considering local structural changes near Ge_Cd substitutional defects. The model offers detailed insight into the mechanism responsible for the formation of the Ge_Te center at doping levels above 5.0 × 10¹⁵ cm^–3 and makes it possible to identify the optimal defect system in CdTe crystals for resistive x-ray detectors.     

Influence of different process parameters on physical properties of fluorine dopes indium oxide thin films

Fluorine-doped indium oxide films were prepared by the spray pyrolysis technique. The physical properties of these films were investigated with respect to various process parameters, namely variation of dopant concentration (in the solution), deposition temperature (T _s), carrier gas (air) flow rate and the thickness of the film. The best films had a Hall mobility of the order of 28 cm²V^–1 s^–1 and a carrier density of 2.7 × 10²⁰ cm^–3. These films were deposited at T _s=425 °C at an air flow rate of 71 min^–1 for an atomic ratio of fluorine to indium of 72%. The electrical resistivity of these films was of the order of 10^–4 cm and the average transmission in the visible range was found to be 80–90%. The films were polycrystalline, n-type semiconductors with [400] as a preferred orientation. The preferred orientation changes from [400] to [222] depending upon the process parameters.     

Carrier-Density Dependence of Faraday Rotation and Spin Splitting in Cd1?xMnxTe

We employ spin-quantum-beat spectroscopy to investigate the carrier-density dependence of the spin-precession frequency and the magnitude of the Faraday rotation of Cd_1–x Mn _x Te samples at fixed magnetic field. We find an onset of saturation of the Faraday rotation at carrier densities as low as 4× 10¹⁶ cm^–3 and attribute it to electrons (not holes which dominate in other types of experiments). The spin splitting at fixed magnetic field remains density dependent down to 3 × 10¹⁵ cm^–3 (the lowest density accessible in our measurements) which suggests a direct influence of the carrier-density on the sp–d exchange not mediated by screening effects.     

Magnetic Properties of High-Resistivity CdTe〈In〉 and CdTe〈Cl〉 Crystals

The magnetic susceptibility of high-resistivity CdTeIn and CdTeCl crystals was measured between 4.2 and 300 K. The susceptibility was found to vary anomalously with temperature. Below 50 K, all the samples were paramagnetic. The observed anomalies are interpreted in terms of donor–acceptor pairs formed by native defects and dopant or uncontrolled impurity atoms. The effect of doping on the 300-K is related to the Van Vleck paramagnetic contribution resulting from the local electric fields of X_i–V _Cdand In_i–V _Cddefect complexes. In CdTeCl, this contribution is insignificant.     

Impurities in single crystal indium phosphide

The impurity concentrations in present low carrier concentration indium phosphide single crystals (N _D-N _A=2×10¹⁵ to 5×10¹⁵cm^–3) grown by the Czochralski technique have been measured by spark-source mass spectrometry and radio-gamma activation analysis and compared with both the polycrystalline source material and the excess indium produced during compounding and growth. The predominant impurities are shown to be carbon, oxygen and silicon but the segregation of lesser impurities into the excess indium has allowed some nineteen other elements which are likely to be present in indium phosphide to be identified. No consistent correlation is evident between the measured concentration of specific impurities and the ionized donor (N _D) and acceptor (N _A) impurity levels as determined from the free-electron concentration (N _D-N _A) and Hall mobility at 77 K using the Brooks-Herring theory.     

Electrical properties of high purity tin dioxide doped with antimony

The electrical conductivity of high purity tin dioxide doped with antimony was studied at temperatures of 900 to 1200° C and partial pressures of oxygen between 10^–8 and 1 atm. For specimens having a dopant concentration over 1 × 10¹⁹Sb cm^–3, the electrical conductivity decreased slightly with temperature and independent of oxygen partial pressure. The electrical conductivity of specimens having a dopant concentration under 1 × 10^–8Sb cm^–3 increased with temperature and with decreasing partial pressure of oxygen. The significance of the dopant and the thermally created defects is discussed.     

Gas permeability of poly(organophosphazenes)

The gas permeability and oxygen-to-nitrogen selectivity were determined for some poly-(organophosphazenes). It was found from the data that the membrane having the highest gas permeability was [NP(NHPrⁿ)(NEt₂)] _n , which had 1.5 x 10^–6cm³ (cm cm^–2) s^–1 (cm Hg)^–1 to oxygen or 2.2 x 10^–6cm³ (cm cm^–2) s^–1 (cm Hg)^–1 to nitrogen. On the other hand, the membrane having the highest oxygen-to-nitrogen selectivity of about 3 had the formula [NP(OC₆H₄Cl-p)₂] _n Also, the selectivity did not depend on the glass transition temperature of the membranes. The membrane prepared from [NP(OC₆H₄CH₃-p)2] _n had a negative activation energy for oxygen and nitrogen permeability.     

MOCVD of p-Cd x Hg1 – x Te/GaAs Heteroepitaxial Structures

Metalorganic chemical vapor deposition from Cd and Te alkyl compounds and Hg vapor is used to grow p-type Cd _x Hg_{1 – x} Te epitaxial layers on semi-insulating GaAs(111)Bsubstrates by the interdiffused multilayer process (alternating CdTe and HgTe layers) at a substrate temperature of 350°C, followed by postgrowth annealing. Layers are obtained with x = 0.2–0.4, 77-K carrier concentrations in the range (1–5) × 10¹⁶ cm^–3, and 77-K carrier mobilities from 200 to 400 cm²/(V s). The rocking curves of the epilayers have a full width at half maximum in the range 2–4 min of arc.     

Alginate polyelectrolyte ionotropic gels

The kinetics and mechanism of exchange of Ni²⁺ by H⁺ ions in ionotropic nickel alginate polymembrane gels of capillary structure have been studied by pH-metric and conductimetric techniques. The rate of exchange conforms to; rate=k ₁ [nickel alginate] [H⁺]- k _–1 [alginic acid] [Ni²⁺] with k ₁=6.34×10^–2dm³mol^–1s^–1 and k _–1=8.83×10^–4 s^–1 at 20°C, respectively. The activation parameters have been evaluated and a mechanism consistent with the kinetic data is discussed.     

Erbium Segregation in Silicon Layers Grown by Molecular-Beam Epitaxy

In the course of molecular-beam epitaxy of Er-doped Si on Si(100) substrates at 450–650°C, the dopant tends to segregate in the surface layer at doping levels from 10¹⁷ to above 10¹⁹ cm^–3. The introduction of oxygen into the growing epilayer—either from the gas phase at an oxygen pressure of 6.7 × 10^–6 Pa or from an SiO₂ layer on the substrate surface—suppresses the surface segregation of Er.     

Size effect of trivalent oxides on low temperature phase stability of 2Y-TZP

2 mol% Y₂O₃stabilized-TZPs (2Y-TZPs) doped with oversized trivalent cations (Sc³⁺< Yb³⁺< Y³⁺< Sm³⁺< Nd³⁺< La³⁺) whose ionic radius is larger than Zr⁴⁺was sintered for 1 h at 1500°C over the range containing trivalent oxides from 0 to 2 mol% with 0.5 mol% interval to evaluate the effect of trivalent cation alloying on low temperature phase stability of 2Y-TZP by investigating the variation of Raman spectra and lattice parameters. For a given concentration of dopant, tetragonality (c/aaxial ratio) increases with raising the dopant size. However, monoclinic (m)-ZrO₂content for the specimens annealed for 500 h at 220°C in air firstly decreases with increasing dopant size and then increases as dopant size is greater than Y³⁺ion. Raman modes of Zr-O_II(260 cm^–1) and Zr-O_I(640 cm^–1) shift to higher wavenumbers only when Sm₂O₃, Nd₂O₃, and La₂O₃are added. Although full width at half maximum (FWHM) of 640 cm^–1is constant, FWHM of 260 cm^–1mode decreases with increasing dopant size, indicating that an ordered structure (pyrochlore phase) may be formed. Therefore, dopant size is dependent on phase stability of 2Y-TZP in this system.     

Space-charge-limited current analysis in amorphous InSe thin films

The study of space-charge-limited currents (SCLC) in amorphous InSe thin films is presented. The temperature-dependent current–voltage (J–V) measurements were carried out for TO/a-InSe/Au sandwich structures in the range of 200–320 K. For all samples, ohmic behavior was observed up to an electric field strength of about 2×10⁵ V cm^–1. From the temperature dependence of conductivity data, the position of the thermal equilibrium Fermi level E _fo is determined as 250 meV above the valence band E _v. At higher electric field strength values in the SCLC regions, the proportionality constant of voltage changes is between 2 and 2.9 with temperature. The analysis of J–V characteristics using the SCLC method and analytical approach for the determination of density of states (DOS) in the energy range of 190–250 meV shows that DOS changes between 3.8×10¹⁷–1.7×10¹⁸ eV^–1cm^–3 with energy. The energy distribution of DOS is temperature independent indicating that the SCLC in these amorphous films is related to the bulk, not to the surface layer between the contact and the film.     

Grain growth in copper and alpha-brasses

The wires of 99.999% copper and alpha-brasses containing 12, 20, 30 and 35 at % Zn have been annealed in vacuum for 30 to 240 min at 873, 923, 973 and 1023 K. The grain-growth data obtained are well encompassed by the relationD ², —D ₀ ² , =Kt exp(-H/kT), whereD is the instantaneous mean grain diameter at the time,t, of isothermal anneal andD ₀ refers to the initial mean grain diameter. In alpha-brasses the activation energy for grain-boundary self-diffusion,H, and the pre-exponential factor,K, depends on the zinc concentration,c, asH = (H ₀ — 1.1c) eV andK =K ₀ exp(-10.7c) cm² sec^–1. The values ofH ₀ andK ₀, referred to the base metal are respectively 0.87 eV and 3.0 × 10^–4 cm² sec^–1, which are in good agreement with those (0.85 eV and 3.6 × 10^–4 cm² sec^–1) found for copper.     

The crystallization and electrical properties of lead-based ferroelectric thin films for uncooled pyroelectric infrared detector

Epitaxially grown and polycrystalline PT, PLT and PZT thin films with thickness from 1 to 2 m have been prepared on Pt/Ti/SiO₂/Si substrates by means of the modified sol–gel spin-coating technique. The ferroelectric thin films have good crystallization behavior, excellent dielectric and pyroelectric properties. The pyroelectric coefficients of PT and PLT thin films are 2.9×10^–8 C/cm² k and (3.37–5.25)×10^–8 C/cm² k, respectively. The figures of merit for voltage responsivity of PT and PLT thin films (F _I ) are 0.60×10^–10 Ccm/J and (0.79–1.13)×10^–8 Ccm/J, respectively. The figures of merit for current responsivity of these films are 9.0×10^–9 Ccm/J and (10.5–16.0)×10^–9 Ccm/J, and the figures of merit for detectivity of these films are 0.74×10^–8 Ccm/J and (0.79–1.13)×10^–8 Ccm/J, respectively.     

Comprehensive characterization of hydride VPE grown GaN layers and templates

GaN community has recently recognized that it is imperative that the extended, and point defects in GaN and related materials, and the mechanisms for their formation are understood. This is a first and an important step, which must be followed by defect reduction before full implementation of this material and its allied binaries/ternaries in devices. This review is based on a recent concerted effort to establish benchmarks as far as defects are concerned, and identify the basic issues involved. Samples were analyzed for extended defects by TEM and chemical etches, for polarity by electric force microscopy and convergent beam electron diffraction (CBED), for point defects by DLTS, for optical quality and deep defects by photoluminescence (PL), for vacancies by positron annihilation, for donor and acceptor like states within the gap by ODMR and EPR, and for carrier transport targeted for defects and impurities by variable temperature and magnetic field-dependent Hall measurements.Hydride VPE samples grown at Lincoln Laboratories with 1.5, 5.5 and 55 μm thicknesses were investigated for defects by TEM, and their polarity was found to be Ga-polarity, as expected, by CBDE combined with simulations. The density of misfit dislocations at the substrate/EPI interface was determined to be on the order of 10¹³ cm⁻² based on high-resolution electron microscopy images. The threading dislocation density decreased gradually with distance from the interface, reaching a value of about 10⁸ cm⁻² at the surface of a 55 μm film. A 200 μm thick laser separated and free-standing HVPE grown GaN template grown at Samsung was also characterized similarly. The free surface and substrate sides were confirmed to be Ga- and N-polarity, respectively. The density of dislocations near the N-face was determined to be, in order, (3±1)×10⁷ and (4±1)×10⁷ by cross-sectional TEM and plan-view TEM, respectively. Identical observations on the Ga-face revealed the defect concentration to be less than 1×10⁷ cm⁻² by plan-view TEM and 5×10⁵ cm⁻² by cross-sectional TEM.Defects in a 10 μm thick GaN layer grown by HVPE at Lincoln Laboratory have been investigated by photo electrochemical (PEC) etching, and by wet etching in hot H₃PO₄ acid and molten KOH. Threading vertical wires (i.e. whiskers) and hexagonal-shaped etch pits are formed on the etched sample surfaces by PEC and wet etching, respectively. Using atomic force microscopy, one finds the density of “whisker-like” features to be 2×10⁹ cm⁻², the same value found for the etch-pit density on samples etched with both H₃PO₄ and molten KOH. Values agree well with TEM results.A free standing GaN template has been characterized for its structural and optical properties using X-ray diffraction, defect delineation etch followed by imaging with atomic force microscopy (AFM). The Ga-face and the N-face of the c-plane GaN exhibited a wide variation in terms of the defect density. The defect concentrations on Ga- and N-faces were about 5×10⁵ cm⁻² for the former and about 1×10⁷ cm⁻² for the latter, again in good agreement with TEM results mentioned above.High resolution X-ray rocking curves (omega scans) were measured. The [0 0 2] symmetric and [1 0 4] asymmetric peaks in 10 μm thick HVPE films had FWHM values between 5.8 and 7.9 arcmin, and 3.9 and 5.2 arcmin, respectively. The Samsung template investigated had wide diffraction peaks (20.6 and 24 arcmin for [0 0 2] and [1 0 4] diffractions, respectively) on the Ga-face, similar for the N-face, when a 2 mm slit size was used. When the slit size was reduced to 0.02 mm, the Ga- and N-face [0 0 2] peaks reduced to 69 and 160 arcsec. A bowing radius of 1.2 m was calculated to account for increased broadening with wider slits.In the HVPE layer studied, SIMS investigations indicate that both O and Si concentrations drop rapidly away from the surface into the sample — mainly due in part to the artifact of the technique and in part due to condensates on the surface of the sample, down to about 10¹⁷ cm⁻³ for Si and high 10¹⁶ cm⁻³ for O. The Ga-face profile in the Samsung template indicated levels below mid-10¹⁶ cm⁻³ for all three of the impurities. The picture is different for the N-side, however, as it was juxtaposed to the substrate during growth and was mechanically polished after laser separation. The impurity concentration on this face, depending on the species, is some 1–3 orders of magnitude higher than the case for the Ga-face.Transport properties as a function of the layer thickness, ranging from about 1 to 68 μm, while all the other parameters being the same, as they evolve from the sapphire/GaN interface and up were determined in epitaxial layers. A strong dependence on distance from the interface was observed with the averaged mobility figures increasing from 190 cm²/V s in the 5 μm film to 740 cm²/V s in the 68 μm film. The preliminary differential Hall measurements indicate that the mobility at the surface of the thick layer is about 1200 cm²/V s. Electron mobilities in free-standing template were 1425 cm²/V s at T=273 K and 7385 cm²/V s at T=48.2 K. By using the most recent unscreened acoustic deformation potential and allowing only the acceptor concentration to vary (2.4×10¹⁵ cm⁻³ for the best fit), one obtains an excellent fit to the measured mobility in the temperature range of 30–273 K by using an iterative BTE method. In addition, an excellent fit for the temperature-dependent electron concentration was also obtained utilizing the acceptor concentration determined from the fit to the Hall data, and the charge balance equation. This led to a donor concentration of 1.6×10¹⁶ cm⁻³, and activation energy of 26 meV, the latter being the highest reported in the literature for GaN.In the free-standing template, the Γ₅ and Γ₆ free excitons were identified from emission measurements by utilizing polarization geometries where the E field is perpendicular to the c-axis, favoring the Γ₅ exciton, and E field parallel to the c-axis (incident beam from the edge of the wafer) favoring the Γ₆ exciton. Focusing on the defect region of the PL spectrum, the N-face of the sample exhibited the usual yellow line. However, the Ga-face exhibited a broad band encompassing both yellow and green bands. The yellow luminescence in the free-standing template is weak and can be easily saturated. In contrast, the green luminescence is dominant and is attributed to the isolated defect involving gallium vacancy, whereas the yellow luminescence is related to the same defect bound to dislocation or surface-bound structural defect.Deep centers have been characterized by DLTS in HVPE-grown GaN epilayers of different thickness and dislocation densities, and templates. The main deep centers, such as A₁, B, and D, show higher concentrations in thinner samples, which suggests a correlation to the high dislocation densities. Based on the anti-correlation between A₁ and B, which is observed in thin HVPE-GaN layers, the defect B was tentatively attributed to N_Ga. Centers A₁ and E₁ found in thin HVPE-GaN are very similar to centers A₂ and E induced by electron-irradiation, indicating their point-defect nature. Centers A, C, and D are not affected by 1 MeV electron-irradiation, thus ruling out the possibility of these centers being identical to any EI-induced centers; however, their nature remains unknown. As the layer thickness decreases, an increase of deep centers, both in species and concentrations, was clearly observed, which is believed to be closely associated with the significant increase of threading dislocations as revealed by TEM. Based on a comparison with EI-induced centers and an observation of anti-correlation, A₁ is tentatively assigned to N_I, and B to N_Ga. The template exhibited a new trap B′, with parameters E_T=0.53 eV and σ_T=1.5×10⁻¹⁵ cm² on the Ga-face, in addition to the four traps commonly observed in various epitaxial GaN layers. For the N-face, an N vacancy-related trap E₁, with E_T=0.18 eV and σ_T=4×10⁻¹⁷ cm², was observed. On the other hand, the Ga-face sample contained trap C, with E_T=0.35 eV and σ_T=1.6×10⁻¹⁵ cm². This trap may be related to surface damage caused by the RIE process employed.Electron beam and optical depth-profiling of thick (5.5–68 μm) n-type HVPE-GaN samples have been carried out using electron beam-induced current (EBIC) and micro-PL to determine the minority carrier diffusion length, L, and minority carrier lifetime. The minority carrier diffusion length increased linearly from 0.25 μm, at a distance of about 5 μm from the GaN/sapphire interface, to 0.63 μm at the GaN surface for a 36 μm thick sample. The increase in L was accompanied by a corresponding increase in PL band-to-band radiative transition intensity as a function of distance from the GaN/sapphire interface. These observations in PL intensity and minority carrier diffusion length have been attributed to a reduced carrier mobility and lifetime at the interface and to scattering at threading dislocations.Positron annihilation experiments have been conducted in HVPE films with varying thicknesses from 1 to 68 μm. Mg-doped samples and bulk GaN platelets have also been investigated and the behavior of positron annihilation in Mg-doped samples established. Unlike the Mg-doped samples, the positron lifetime in the HVPE samples increased with decreasing lattice temperature. This was interpreted as acceptors in these n-type samples being due to Ga vacancies as opposed to relatively shallow acceptor impurities. The similarities in the behavior of these samples and those investigated previously where the III/V ratio was changed also lend support to the Ga vacancy argument. Previous investigations established that as the III/V is lowered by increasing the ammonia flow during the growth, the Ga vacancy concentration increased. Using Mg-doped samples as a standard, the vacancy concentration was determined to be about 10¹⁷ cm⁻³ near the surface for the layer with a thickness greater than 30 μm. Assuming that the growth parameters in the set of layers with varying thicknesses that were investigated are the same, the Ga vacancy concentration increases to mid-10¹⁹ cm⁻³ near the interface. Since the interfacial region is n-type and highly conductive, this region must also contain even larger concentrations of O and/or N vacancies which lead to n-type material. SIMS results already indicate mid-10¹⁹ cm⁻³ levels of O being present in this region. This has been attributed to O out-diffusion from sapphire as previously reported.FTIR, ODMR and EPR measurements have been performed in GaN layers and templates. In FTIR measurements, two absorption bands corresponding to binding energies of 30.9 (Si) and 33.9 meV were found. Splitting of the binding energies with magnetic field is consistent with an effective mass of 0.22m₀. Angular rotation studies were performed with the magnetic field oriented perpendicular and parallel to the c-axis to provide symmetry information. The ODMR on the 2.2 eV peak in a 5–10 μm thick GaN layer, the notorious yellow emission, showed signatures of shallow donor (effective mass like) and deep defect centers with g-values of 1.95 and 1.99, respectively. The 3.27 eV peak with resolved LO phonon replicas, which is the blue peak observed in many GaN films grown by a variety of methods, is attributed to transitions involving shallow acceptors with g2.1 and g2.0. ODMR on the 2.4 eV “green” PL band in the free-standing template also revealed evidence for shallow donors with a g-value of 1.95 and other deeper centers. The larger line width of the shallow donor signal from the template, relative to that found for the epitaxial layers, is indicative of a lower concentration of this center, which leads to an increased hyperfine interaction. EPR studies confirmed the notable difference between the epilayers and the template, particularly the larger line widths in the template due to the lower concentration of shallow donors. Specifically, the free-standing sample has about 6×10¹⁵ cm⁻³ uncompensated donors while the epilayers have a concentration about a factor of four higher.Calculations indicate that incorporation of Si has a negligible effect on the lattice constant, but O and Mg can lead to an observable expansion of the lattice. Since values of the GaN lattice constant have often been based on bulk crystals that are now known to contain large concentrations of oxygen, the “true” GaN lattice constant is actually smaller than what has been measured for such crystals. Boron is an unintentional impurity that can be introduced during MBE growth. There has been speculation about whether B might act as an acceptor in GaN; this would require it to be incorporated on the nitrogen site. Computations indicate that incorporating B on the N site is energetically unfavorable. Even if it did incorporate there, it would act as a deep, rather than a shallow acceptor. Formation energies of H in AlN and GaN have also been calculated. The behavior of H in AlN is very similar to GaN: H⁺ dominates in p-type, H⁻ in n-type. Surprisingly, H in InN behaves exclusively as a donor, i.e. it is not amphoteric as in GaN and AlN, but actually contributes to the n-type conductivity of the material.Scanning thermal microscopy (SThM) has been applied to measure the local thermal conductivity of epitaxial GaN as it is affected to a large extent by phonon scattering, and a closer to the true value of this parameter can be obtained by a local measurement in areas of lower defect concentration such as those found in the wing regions of lateral epitaxially grown GaN. The method relies on a thermo-resistive tip forming one quadrant of a Winston bridge. The bridge is balanced with the tip heated followed by bringing the tip in contact with the sample under test which cools down due to thermal dissipation. However, the feedback circuit attempts to keep the thermo-resistance and thus the tip temperature the same. The square of the feedback voltage necessary for this is proportional to the thermal conductivity. Accurate values can be obtained with calibration using known substrates such as GaSb, GaAs, InP, Si and Al metal. Using SThM, thermal conductivity, κ, values of 2.0–2.1 W/cm K in the wing regions of lateral epitaxially grown GaN, 1.70–1.75 W/cm K in HVPE grown GaN, and 3.0–3.3 W/cm K for free-standing AlN have been measured.     

Long multifilament Bi-2223 Ag-sheathed superconducting tapes and solenoids

Multifilament Ag-sheathed BiPbSrCaCuO (2223) superconducting tapes containing 49 filaments were fabricated by the powder-in-tube route and the roll-anneal process. The transport critical current densityJ _c was 1.3×10⁴ A cm^–2 at 77 K and 7×10⁴ A cm^–2 at 4.2 K in self-field. A 12-m-long tape was used to construct superconducting solenoids (50, 28, and 14 mm internal diameters) generating dc fields 380–1070 G at 4.2 K. Measurements of the variation ofJ _c with field (0–1.6 T) and bend strain (0–5%) are used to explain the performance of the solenoids. The critical bend strain of tapes was about 1.5%.     

Measurement of the Surface Tension of Undercooled Liquid Ti90Al6V4 by the Oscillating Drop Technique

The surface tension of liquid Ti₉₀Al₆V₄ was measured. The samples have been processed containerlessly by electromagnetic levitation, which allows the handling of highly reactive materials and measurements in the undercooled temperature region. The use of digital image processing allows the identification of oscillation modes and calculation of the surface tension from the l = 2 and m = 0, m = 2 oscillation modes. A linear least squares fit to the data showed the following temperature dependence: = 1.389 ± 0.09 – 9.017 × 10^–4 ± 5.64 × 10^–5(T – 1660°C) [Nm^–1]     

Zr-Hf interdiffusion in polycrystalline Y2O3-(Zr+Hf)O2

Lattice and grain-boundary interdiffusion coefficients were calculated from the concentration distributions determined for Zr-Hf interdiffusion in polycrystalline 16Y₂O₃·84(Zr_1–x Hf _x )O₂ withx=0.020 and 0.100. The lattice interdiffusion coefficients were described byD=0.031 exp [–391 (kJ mol^–1)/RT] cm² sec^–1 and the grain-boundary diffusion parameters byD=1.5×10^–6exp [–309(kJ mol^–1)/RT] cm³ sec^–1 in the temperature range 1584–2116° C. Comparison of the results with those for the systems CaO-(Zr+Hf)O₂ and MgO-(Zr+Hf)O₂ indicated that the Zr self-diffusion coefficient was insensitive to the dopants in the fluorite-cubic ZrO₂ solid solutions.     

Oxygen gas permeability in water and the properties of poly(organophosphazene) films

[NP(NR₂)(NHR)] _n and [NP(NR₂) (NHR)_1–x (OCH₂CH₂COOCH = CH₂) _x ] _n type polymers were prepared by the reaction of (NPCl₂) _n with various secondary or primary amines and 2-hydroxyethylacrylate. Membranes were prepared by casting, the mixing mill technique and ultraviolet radiation. The oxygen gas permeability of the membranes and the mechanical properties of the membranes were determined using a film oxygen gas permeater and an Instron tester. It was found that [NP(Di-n-hexylamine) (n-butylamine)] _n had the highest oxygen gas permeability value; Dk = 116×10^–11 cm³ ml cm^–2s^–1 mm Hg^–1. Also, it was found that the oxygen gas permeability of poly (aminophosphazenes) was not directly related to the dielectric constant and mechanical properties of the membranes in wet conditions (water).     

Modeling of Point Defects in Cl-Doped CdTe Crystals Annealed in Cd Vapor

Equations are proposed for quasi-chemical reactions leading to the formation of intrinsic and impurity defects and defect complexes in Cl-doped cadmium telluride crystals during annealing in cadmium vapor at different temperatures. The equilibrium constants for the formation of (Cl _Te ⁺ V _Cd ²⁻ )⁻ defect complexes and Te _Cd ²⁺ antisite defects are calculated. An analytical expression is derived for the cadmium partial pressure corresponding to a type conversion. The conditions are established for producing n- and p-type CdTe〈 Cl〉 crystals with controlled carrier concentration.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 6, 2005, pp. 656–661.Original Russian Text Copyright © 2005 by Freik, Pysklynets, Mezhylovska.