Rapid Z-plate seed regeneration of large size KDP crystal from solution

Regeneration process of a 330×330×20 mm³ Z-plate seed is carried out in a 1.5 metric tonnage volume crystallizer that placed in a water bath of temperature fluctuation less than ±0.02 °C within 10 days. The surface of the whole crystal was restored by the formation of a box-like structure filled with growth solution, and then the transparent layer of perfect tetragonal KDP crystal without inclusions, crack and milky regions just like those produced by traditional slow cooling technique can be grown from solution. After the regeneration, the height of KDP crystal is merely 0.5 times the side of plate seed. We found it that the optical transmission and laser damage threshold of the KDP crystals we grown are not significantly different from those of KDP crystals grown by traditional method.     

Fluorine laser-induced silicon hydride Si–H groups in silica

Formation and destruction of silicon hydride (Si–H) groups in silica by F₂ laser irradiation and their vacuum ultraviolet (VUV) optical absorption was examined by infrared (IR) and VUV spectroscopy. Photoinduced creation of Si–H groups in H₂-impregnated oxygen deficient silica is accompanied by a growth of infrared absorption band at 2250 cm⁻¹ and by a strong increase of VUV transmission at 7.9 eV. Photolysis of Si–H groups by 7.9 eV photons in this glass was not detected when the irradiation was performed at temperature 80 K. However, a slight destruction of Si–H groups under 7.9 eV irradiation was observed at the room temperature. This finding gives a tentative estimate of VUV absorption cross section of Si–H groups at 7.9 eV as 4 × 10⁻²¹ cm², showing that Si–H groups do not strongly contribute to the absorption at the VUV fundamental absorption edge of silica glass.     

Preparation,vibrational structure and dielectric properties studies of cotton linter and its derivatives

Preparation of unhydrolyzed and hydrolyzed cotton linters as well as their derivatives (carboxylate, phosphate and phosphosulphonate), vibrational structure and dielectric properties were studied in this work. The vibrational modes were analyzed by FTIR spectroscopy and the band at 1730 cm^?1 in the carboxylation of unhydrolyzed and hydrolyzed was appeared due to introduce of carboxylic group. The new bands appeared at 1208 and 1400 cm^?1 in the phosphorylation and phosphosulphonation assigned to C–O–P and C–O–S, respectively. The data indicated that, new chemical structure for the derivatives of unhydrolyzed and hydrolyzed cotton linter was formed. The crystallinity index (CrI) was measured from absorbance ratio of the band 1428 and 900 cm^?1. The real part of dielectric constant (ε′) and AC electrical conductivity was studied in the temperature range (295–375 K) at two different frequencies, 800 and 2000 kHz. The ε′ was decreased with increasing frequency due to dispersion. The frequency–temperature dependent conductivity and mechanisms of the electronic conduction were discussed.     

The study of removing hydroxyl from silica glass

The removal of hydroxyl from silica glass produced by melting quartz powder under an atmosphere containing hydrogen was investigated. After heat-treatment at the temperature range (700–1200 °C) in nitrogen atmosphere, the effective hydrogen diffusion coefficients were evaluated based on the law of nonsteady-state diffusion. The activation energy obtained is 254 kJ mol⁻¹ for the dehydroxylation process in the heat-treatment temperature range of 700–900 °C, and a different activation energy calculated is 32 kJ mol⁻¹ in the temperature range of 900–1200 °C. The activation energies for the dehydroxylation process at the temperature (700–900 °C) and the higher temperature (900–1200 °C) correspond to the binding energy of SiO–H bond and the activation energy for the diffusion of hydrogen in silica glass respectively, which indicate there is a change of mechanism for dehydroxylation with heat-treatment temperature.     

Polarization fluctuations near the glass transition

Measurements of polarization fluctuations were performed for an epoxy glass former. The voltage noise produced by polarization fluctuations of the sample filling a capacitor was acquired via a home-made very high input impedance current–voltage converter, in series with an ultra low noise pre-amplifier, achieving high sensitivity and accuracy in the range 0.1–1000 Hz. The temperature and frequency dependence of polarization noise was investigated above and below the glass transition temperature T_g. The sample was driven to the glassy state with different cooling rate and then isothermally aged, while the noise spectral density was measured at different times and compared with the Johnson–Nyquist noise determined by the sample impedance measured by conventional dielectric spectroscopy. At thermodynamic equilibrium the polarization noise agreed with the predictions of the fluctuation–dissipation theorem linking noise spectral density to susceptibility. On the contrary, a strong violation of the theorem was observed after a fast cooling below T_g: an intense polarization noise was detected, with a power spectral density following an inverse power law frequency behavior, whose intensity was decreasing with aging time. At the same time, the amplitude of polarization fluctuations showed a non-Gaussian distribution, whose width reduced during the aging process, up to recover the Gaussian statistics on approaching the equilibrium.     

Influence of TiO2 on proton conductivity in fuel cell electrolytes based on sol–gel derived P2O5–SiO2 glasses

P₂O₅–TiO₂–SiO₂ based glasses have been prepared by a sol–gel process. The glasses were characterized by structural, thermal, nitrogen adsorption–desorption and conductivity measurements. The structural formation has been confirmed by the FTIR and NMR analysis. The proton conductivity of the glasses increased linearly with increase in temperature. Glasses with an average pore size less than 2 nm showed higher values of proton conductivity in humid atmosphere. The conductivity value increased from 6.47 × 10⁻⁴ S/cm to 3.04 × 10⁻² S/cm at 70% RH in the temperature range 30–90 °C. We observed in fuel cell measurements that the performance of the E1 electrode is superior to that of the other electrodes at the same operating condition. The power density shows a similar pattern to current density.     

Boron removal from metallurgical-grade silicon using lithium containing slag

The possibility of extracting boron impurity from metallurgical-grade silicon by lithium containing slag refining for solar cell application was investigated. The distribution coefficients of boron between CaO–SiO₂–Li₂O and CaO–SiO₂–LiF slags were examined. The boron content in the refined silicon was studied under different conditions of mass ratio of slag to silicon and refining time. The results showed that a small amount of Li₂O or LiF had significant effect on the distribution coefficients of boron. The removal of boron impurity using CaO–SiO₂–LiF system was more effective than using CaO–SiO₂–Li₂O system. Values of boron content in the refined silicon did not decrease significantly when the mass ratio exceeded 4, while it had been obviously falling with the increase in refining time. When the mass ratio of CaO–SiO₂–Li₂O slag to metallurgical-grade silicon was 4, the boron content in silicon was successfully reduced from 2.2 × 10^? 5 to 1.3 × 10^? 6 after slag refining for 2 h at 1823 K.     

Fabrication and ionic conductivity of amorphous Li–Al–Ti–P–O thin film

Li⁺ ion conducting Li–Al–Ti–P–O thin films were fabricated on ITO-glass substrates at various temperatures from 25 to 400 °C by RF magnetron sputtering method. When the substrate temperature is higher than 300 °C, severe destruction of ITO films were confirmed by XRD (X-ray diffraction) and the abrupt transformation of one semi-circle into two semi-circles on the impedance spectra. These as-deposited Li–Al–Ti–P–O solid state electrolyte thin films have an amorphous structure confirmed by XRD and a single semicircle on the impedance spectra. Good transmission higher than 80% in the visible light range of these electrolyte thin films can fulfill the demand of electro-chromic devices. Field emission scanning electron microscopy and atomic force microscopy showed the denser, smoother and more uniform film structure with the enhanced substrate temperature. Measurements of impedance spectra indicate that the gradual increased conductivity of these Li–Al–Ti–P–O thin films with the elevation of substrate temperature from room temperature to 300 °C is originated from the increase of the pre-exponential factor (σ₀). The largest Li-ion conductivity can come to 2.46 × 10^? 5 S cm^? 1. This inorganic solid lithium ion conductor film will have a potential application as an electrolyte layer in the field such as lithium batteries or all-solid-state EC devices.     

Effect of preparation conditions on the phase transformation of mesoporous alumina

A post-hydrolysis method is proposed for the easy-and-fast preparation of mesoporous γ-alumina (MA) at room temperature using an alkyl carboxylate as a chemical template. Water was used as an initiating solvent in the hydrolysis of aluminum alkoxide in the terminal reaction procedure. Hydrolysis and condensation reactions were simultaneously induced. The initial phase of as-made MA was bayerite and/or (pseudo)boehmite, and was transformed into active alumina at 250 °C, which remained thermally stable at temperatures up to 600 °C. The phase transformation of alumina was analyzed with DTA, XRD and ²⁷Al MAS NMR. Based on an ²⁷Al MAS NMR analysis, calcined alumina prepared via a hydrothermal method contained a high ratio of Al^VI to Al^IV (∼4.8), which is not fully transformed into active alumina, and aluminum hydroxide (AlOOH or Al(OH)₃) was detected. These results suggest that high temperature is required to obtain an active form of alumina, when the hydrothermal method is used. Another factor is the ratio of Al^VI to Al^IV in the MA, which is also dependent on the pH of the reactant. Pore size, surface area, and pore structure could be controlled by adjusting the molar ratio of water to aluminum precursor, and the preparation temperature. The pore size of MA was adjustable from 2 to 7 nm, and the MA indicated a large surface area of 300 ∼ 500 m²/g.     

Mixed transition-ion effect in the glass system: Fe2O3-MnO-TeO2

In earlier studies on phosphate and tellurite glasses containing vanadium and iron oxides, non-linear variation of physical properties as functions of the ratios of the transition ions (V/V + Fe) were observed. The most striking effect was observed with electrical conductivity, where a 3 orders of magnitude reduction in conductivity was observed at a V/V + Fe ratio of ~ 0.4. The effect was termed Mixed Transition-ion Effect or MTE. In phosphate glasses, however, MTE was not observed when one of the transition ions was manganese. It was concluded that Mn does not contribute to conduction in these glasses. In the present study, we demonstrate a mixed transition ion effect in tellurite glasses containing MnO and Fe₂O₃ (xFe₂O₃(0.2 ? x) MnO0.8TeO₂ with x varying from 0 to 0.2). A maximum in the property at an intermediate composition (x = 8.5 mol%), was observed in DC resistivity, activation energy, molar volume etc. Mossbauer and optical absorption (UV–VIS–NIR) measurements were performed on these glasses and the transport mechanism has been identified to be hopping of small polarons between Fe^3 + (Mn^3 +) and Fe^2 + (Mn^2 +) sites.     

Magnetic interactions in CrSbVO6 studied by EPR

Powder samples of CrSbVO₆ were synthesized from a mixture of appropriate oxides by the solid state reaction technique and investigated by the electron paramagnetic resonance (EPR) in the 4–300 K temperature range. At room temperature the EPR spectrum consisted of two widely differing components: a narrow (～10 mT) line centered at g_na = 1.967 and an intense, almost Lorentzian broad (～100 mT) line at g_br = 1.975. The EPR spectral parameters (linewidth, g-factor, amplitude, integrated intensity) of both components displayed a marked thermal dependence. The temperature dependence of the broad component showed a very interesting behavior – its amplitude increased on cooling from room temperature, reaching a maximum at 50 K and decreased sharply on further cooling. The narrow line in the EPR spectrum of CrSbVO₆ was attributed to strongly interacting V⁴⁺ and Cr³⁺ monomers and Cr³⁺–Cr³⁺ pairs, while the broad line was due to the V⁴⁺–V⁴⁺ dimers and spin clusters involving Cr³⁺ and V⁴⁺ ions.     

Vacuum ultraviolet excitation of the 2.7 eV emission band in neutron irradiated silica

The temperature dependence of the photoluminescence induced at 2.7 eV by ultraviolet (UV) and vacuum ultraviolet (VUV) excitation of neutron irradiated (10²¹ n/m² and 10²² n/m²) KU1 and KS-4V high purity silica, with different OH content, have been studied. Commercial silica Infrasil 301 has also been studied for comparison. At the highest neutron fluence and at the same temperature, the three irradiated silica grades show similar excitation spectra. Two close UV excitation bands, which show opposite temperature dependence, are observed at 4.8 and 5.1 eV. The 4.8 eV band, related to the triplet–singlet transition in SiODCs(II), decreases on decreasing temperature from 300 to 10 K and the band at 5.1 eV, probably related to SiODCs(I), is observed only at very low temperatures (～10 K). An important VUV excitation structure, observed at low temperature, could also be related to SiODCs(I). A shift of the irradiated bands is detected at low temperature.     

Characteristics of heteroepitaxial Cu2−xMnxO/Nb–SrTiO3 p–n junction

Mn-doped cuprous oxide Cu_2?xMn_xO (CMO), where x = 0.03, is a p-type diluted magnetic semiconductor (DMS) with Curie temperature above room temperature [M. Wei, N. Braddon, et al., Appl. Phys. Lett. 86 (2005) 0725141; Y.L. Liu, S. Harrington, et al., Appl. Phys. Lett. 87 (2005) 222108]. We have grown CMO (x = 0.03) thin films of about 200 nm thick on n-type semiconducting (0 0 1)Nb–SrTiO₃(NSTO) single crystal substrates by pulsed laser deposition. Cubic crystalline phases of CMO layers were obtained in a narrow deposition pressure window of about 20 mTorr at growth temperature of 650 °C. X-ray diffraction and TEM studies of these heterostructures reveal a cube-on-cube epitaxial relationship of [CMO]₀₀₁/[NSTO]₀₀₁. All the oxide p–n junctions with the size of 500 × 500 μm were fabricated by the shadow masking technique. These junctions show highly asymmetric I–V characteristics. The rectification ratio at room temperature is about 10³ at ±2 V. Leakage current density of 10^?4 A cm^?2 at ?1 V is observed. No apparent junction breakdown is recorded at reverse bias voltages down to ?5 V. From the 1/C²–V plots, the forward bias turn on voltage is ～1.4 V. Clear junction current rectifying property is maintained at up to 200 °C. Our results have demonstrated that epitaxial CMO films can be fabricated on lattice matched cubic substrates. They are suitable DMS for above room temperature spintronic junction applications.     

Redox reactions during temperature change in soda-lime–silicate melts doped with copper and iron or copper and manganese

Glasses with the base composition 16Na₂O · 10CaO · 74SiO₂ doped with copper and iron or copper and manganese were studied by high temperature UV–vis–NIR spectroscopy. The spectra exhibited distinct absorption bands attributed to the respective transition metal ions present (Cu²⁺, Fe²⁺, Fe³⁺, Mn³⁺). In glasses doped with only one polyvalent element, the absorption decreases linearly with increasing temperature, the absorption bands are shifted to smaller wave numbers and get broader. In glasses doped with two types of transition metals, the situation is the same up to a temperature of around 550 °C. At larger temperature, the Cu²⁺-absorption in glasses also co-doped with iron increases again, while in glasses doped with both copper and manganese the absorption is approximately the same as in glasses solely doped with copper. It is shown that this is due to redox reactions between polyvalent species. These reactions are frozen in at temperatures <550 °C.     

Photo-crystallization in a-Se imaging targets: Raman studies of competing effects

Photo-induced crystallization of a-Se is investigated by Raman spectroscopy as a function of temperature (250–340 K) and exposure time in thin-film structures used as targets in high-gain avalanche rushing photoconductor (HARP) video cameras. The Stokes-to-Antistokes ratio is monitored to obtain the local temperature T_loc at the laser spot; fluxes (632 nm) of 17 and 10 W/cm² are used. We find a rich temperature behavior that reflects the competition of changes in viscosity and strain, and defines four distinct regimes. No photo-crystallization is seen for T_loc below 260 K, nor in a 15 K range around T_g ～ 310 K. For T_loc in the regime 260–302 K the initial rate of crystal growth after onset of photo-crystallization is temperature independent, whereas for T_loc > 318 K the growth rate is thermally enhanced. Our results are in qualitative accord with a theory by Stephens treating the effects of local strain on the secondary growth of crystalline nuclei in a-Se. We conclude that the observed growth rate between 260 and 302 K is driven by local strain, and that relaxation of this strain near T_g suppresses crystal growth until thermally assisted processes accelerate the photo-crystallization at higher temperatures.     

Molecular dynamics in glass-forming poly(phenyl methyl siloxane) as investigated by broadband thermal,dielectric and neutron spectroscopy

The molecular dynamics of glass-forming poly(methyl phenyl siloxane) (PMPS) is studied by thermal (10⁻³–5 × 10² Hz), dielectric (10⁻³–10⁹ Hz) and neutron (5 × 10⁸–10¹² Hz) spectroscopy. Because of the broad frequency range of 15 orders of magnitude the study provides a precise determination of glassy dynamics in a wide temperature range using different probes. The relaxation rates extracted from the different methods agree quantitatively in both their absolute values and in their temperature dependencies. A detailed analysis of the temperature dependence of the relaxation rate f_p by a derivative technique shows that the α-relaxation of PMPS has to be characterized by a high and a low temperature branch separated by a crossover temperature T_B = 250 K. In both temperature ranges the temperature dependence of f_p has to be described by Vogel/Fulcher/Tammann laws with different Vogel temperatures. Also the analysis of the dielectric strength in its temperature dependence gives a crossover behavior from a low to a high temperature region with a similar value of T_B. T_B can be interpreted as onset of cooperative fluctuations and the formation of dynamical heterogeneities. The dependence of the relaxation rate on the scattering vector Q extracted from neutron scattering obeys a power law τ ∼ Q^−Slope, where the power Slope varies between Slope = 2 and Slope = 3.5 with increasing temperature. This anomalous dependence of the relaxation time on the momentum transfer is discussed in terms of dynamic heterogeneities in the underlying motional processes even at temperatures above T_B. Besides the segmental dynamics the fast Methyl group rotation is considered as well. The relaxation rates of this process have an activated temperature dependence with an activation energy of 8.3 kJ/mol. The data were discussed in the framework of the threefold jump model were the incoherent elastic scattering from ‘fixed’ atoms which are frozen on the time scale of the Methyl group rotation was taken into account.     

Thermal decomposition and new luminescence bands in wet,dry, and additional oxygen implanted silica layers

Wet and dry silica oxide layers have been treated thermally up to T_a = 1300 °C and were investigated by cathodoluminescence (CL) spectroscopy. Whereas the dry oxides after high temperature treatment show an increase of the yellow–red spectra region, contrary, in wet oxides the UV–blue region is enhanced. Even a new strong band in the near-UV region (NV) at 330 nm (3.76 eV) is found for wet oxides at liquid nitrogen temperature (LNT), but much broader and with lower intensity for room temperature (RT) in a triple band structure UV: 290 nm, NV: 330 nm, and V: 400 nm. These violet bands should be associated with a thermally decomposed and rapidly cooled-down silica network in presence of OH groups or even dissociated oxygen. Additional oxygen implantation into dry silica with high doses up to 10¹⁷ ions/cm² and high thermal treatment T > 1100 °C leads as well to enhanced UV–NV–V luminescence emission bands supporting the fact that oxygen and structural decomposition play a decisive role in formation of near-UV luminescent defects in silica.     

Thermal and optical properties of CuO–BaO–B2O3–P2O5 glasses

CuO-doped barium borophosphate glasses in a series of xCuO–(45 − x)BaO–10B₂O₃–45P₂O₅ in molar ratio with x = 0–15 mol% were prepared by a melt-quenching technique. All the glasses had excellent thermal stability against crystallization. Glass transition temperature, thermal expansion coefficient and molar volume decrease with increasing CuO concentration. The linear relationship between the absorption coefficient and CuO concentration exists for a peak wavelength in the transitions of ²A_1g → ²B_1g, ²B_2g → ²B_1g, ²E_g → ²B_1g. The relationship between the properties and glass structure evaluated by Raman spectroscopy is discussed.     

Influence of Ar/C2H2 ratio on the structure of hydrogenated carbon films

The amorphous hydrogenated carbon films (a-C:H) were obtained on Si (1 1 1) wafers by plasma jet chemical vapor deposition (PJCVD). a-C:H coatings have been prepared at 1000 Pa in argon/acetylene mixture. The Ar/C₂H₂ gas volume ratio varied from 1:1 to 8:1. It was demonstrated that by varying the Ar/C₂H₂ ratio the composition, growth rate of the coatings, and consequently the structure of the film, can be controlled. The growth rate and surface porosity of coatings deposited at Ar/C₂H₂ = 8:1 ratio decrease slightly with an increase in the distance between the plasma torch nozzle and substrate from 0.04 to 0.095 m. The transmittance of the coatings in the IR region of 2.5–25 μm slightly increases, while the absorption peaks at 2850–2960 cm^?1 related with sp³ CH_2–3 modes remain unchanged with an increase in the distance. The Raman spectroscopy indicated that the a-C:H coating formed at the Ar/C₂H₂ = 8:1 and 0.06 m has the highest sp³ C–C fraction. The proposed PJCVD technique allows to achieve the growth rates up to 300 nm/s.     

Effect of OH-content on thermal and chemical properties of SnOP2O5 glasses

Glasses with 55–60 mol% SnO and 40–45 mol% P₂O₅ have shown extremely large differences in the chemical and thermal properties depending on the temperature at which they were melted. Glasses prepared at low melting temperature, 450–550 °C, had low T_g, 150–200 °C, and low chemical stability. Glasses prepared at high melting temperature, 800–1200 °C, had much higher T_g, 250–300 °C, and much higher chemical stability. No significant differences were found by ¹¹⁹Sn Mössbauer and ³¹P Nuclear Magnetic Resonance spectroscopy. Large differences in the OH-content could be detected as the reason by infrared absorption spectroscopy, thermal analyses, and ¹H Nuclear Magnetic Resonance spectroscopy. In samples with low T_g, a broad OH – vibration band around 3000 nm with an absorption intensity >20 cm^?1, bands at 2140 nm with intensity ～5 cm^?1, at 2038 nm with intensity ～2.7 cm^?1, and at 1564 nm with intensity ～0.4 cm^?1 were measured. These samples have shown a mass loss of 3–4 wt% by thermal gravimetric analyses under argon in the temperature range 400–1000 °C. No mass loss and only one broad OH-band with a maximum at 3150 nm and low absorption intensity <4 cm^?1 could be detected in samples melted at high temperature, 1000–1200 °C, which have much higher T_g, ～300 °C, and much higher chemical stability.