Simultaneous CO concentration and temperature measurements using tunable diode laser absorption spectroscopy near 2.3 μm

Simultaneous measurements of carbon monoxide (CO) mole fraction and temperature using tunable diode laser absorption spectroscopy (TDLAS) near 2.3 μm are reported. The measurement method uses ro-vibrational transitions [R(27): v″ = 1 → v′ = 3] and [R(6): v″ = 0 → v′ = 2] in the first overtone band of CO near 2.3 μm (~4,278 cm^?1). The measurements were performed in the post flame environment of fuel rich premixed ethylene–air flames with a N₂ co-flow, stabilized over a water cooled McKenna burner. Non-uniformity in the temperature and CO mole fraction, along the absorption line of sight, in the mixing layer of the co-flow, was considered during data analysis. The TDLAS based temperature measurements (±80 K) were in good agreement with those obtained using N₂ vibrational coherent anti-Stokes Raman scattering (±20 K), and the CO mole fraction measurements were in good agreement with the equilibrium values, for equivalence ratios lower than 1.8. A signal to noise ratio of 45 was achieved at an equivalence ratio of 1 for a CO concentration of 0.8 % at 1,854 K.     

Terahertz spectroscopy of central and soft phonon modes in LuFe<Subscript>2</Subscript>O<Subscript>4</Subscript>

The terahertz dielectric response of LuFe₂O₄ is investigated by terahertz time-domain spectroscopy over a temperature range of 6–290 K. It is revealed that besides the central mode associated with the charge-ordered state, a soft TO₁ mode at below ∼240 K is identified indicating the existence of displacing ferroelectricity, in addition to the charge-ordering-induced ferroelectricity at below 320 K. The anomaly of the soft mode at ∼180 K reflects the magnetoelectric correlation between the soft TO₁ mode and the spin/charge fluctuations revealed recently. Finally, the magnetic property at below ∼240 K is discussed.     

Efficient continuous-wave YVO<Subscript>4</Subscript>/Nd:YVO<Subscript>4</Subscript> Raman laser at 1176 nm

We present a simple and compact continuous-wave (CW) 1176 nm laser based on self-frequency Raman conversion in continuous-grown YVO₄/Nd:YVO₄ composite crystal. With a composite crystal 30 mm in length, a maximum output power up to 1.84 W was achieved at the incident diode pump power of 23.6 W. Corresponding to overall optical conversion, the efficiency was 7.8% and the slope efficiency was 8.5%. The conversion efficiency has been doubled compared with the conventional Nd:YVO₄ CW self-frequency Raman laser. The excellent performance of this laser shows that the long continuous-grown YVO₄/Nd:YVO₄ composite crystal is promising in the application of CW Raman lasers and ideal for miniaturization.     

Crystal Structure,Luminescence and Triboluminescence of the Complex [Eu(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>3hmpa] NO<Subscript>3</Subscript>·HQuin

The atomic structure of crystals of the complex [Eu(NO₃)₂3hmpa] NO₃·HQuin , (hmpa – hexamethylphosphortriamide, HQuin – quinaldic acid) characterized by intensive luminescence and triboluminescence has been determined by the X-ray method. The noncentro-symmetric crystals of the compound are rhombic : a = 16.8193(3), b = 12.2877(2), c = 27.6516(5) Å, пр. гр. Pca2(1), Z = 4, ρ _{calc. .} = 1.427 g/сm³. The crystals have a structure of the insular type which is presented by the isolated complex molecules, outer-sphere NO₃ ^? – groups, and neutral molecules of quinaldic acid. Some structural aspects of formation of the luminescent and triboluminescent properties of the compound were discussed: the role of break planes in the crystal destruction was revealed.     

Effect of the humidity on the uptake of NO<Subscript>3</Subscript> on coatings composed of MgCl<Subscript>2</Subscript> · 6H<Subscript>2</Subscript>O and MgBr<Subscript>2</Subscript> · 6H<Subscript>2</Subscript>O and mixtures thereof with NaCl

The reactive uptake of NO₃ radicals on the surface of wetted individual X salts and of wetted X-NaCl salts (X = MgCl₂ · 6H₂O and MgBr₂ · 6H₂O) at [H₂O] = 2 × 10¹²−2 × 10¹⁵ cm⁻³ and NO₃ (4.8 × 10¹² cm⁻³) was studied using a reactor with a movable insert covered with a salt coating in combination with a mass spectrometer for monitoring the initial reactant and products. The probabilities of NO₃ uptake γ on X-NaCl binary salts as functions of the content of doping salt were determined. A parametric approximation of the experimental data was proposed, which makes it possible to quantitatively predict the extent of surface enrichment of a wetted binary salt coating in doping salt and its dependence on the humidity and the content of this salt in the binary mixture. It was established that the relative surface density σ_X of X doping salt depends on its mole fraction μ_X in the X-NaCl binary salt as σ_X = aμ_X (a = 2.2 for MgBr₂ and 13.1 for MgCl₂) over the entire humidity range covered. The contributions of the X salts to the overall uptake of NO₃ at NO₃ concentration typical of the tropospheric conditions ([NO₃] ∼ 10⁷ cm⁻³ and relative humidities of RH ≤ 20%) were estimated.     

Magnetic and magnetoresistive properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–Sr<Subscript>2</Subscript>FeMoO<Subscript>6–δ</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoheterostructures

A method has been developed for fabricating nanoporous matrices based on anodic aluminum oxide for the deposition of ferromagnetic nanoparticles in them. The modes of deposition of strontium ferromolybdate thin films prepared by the ion-plasma method have been worked out, and the magnetic and magnetoresistive properties, structure, and composition of the films have been investigated. It has been revealed that the microstructure and properties of the strontium ferromolybdate films deposited by ionplasma sputtering depend on the deposition rate and the temperature of the substrate. Based on the measurement of the electrical resistivity of nanoheterostructures in a magnetic field, it has been found that the magnetoresistance reaches 14% at T = 15 K and B = 8 T, which is due to the manifestation of tunneling magnetoresistance.     

Quantitative analysis of dilute mixtures of SO<Subscript>2</Subscript> in N<Subscript>2</Subscript> at 7.4 μm by difference frequency spectroscopy

We describe a 7.4-μm source based on difference frequency generation with 6.5 mW of 1278-nm radiation from an extended cavity laser and 66 mW of 1544-nm radiation from another extended cavity laser, amplified in an erbium-doped fibre amplifier. Optimum focusing of the input beams in the 5×5×10-mm³ AgGaSe₂ crystal, and the spatial and temporal characteristics of the output beam, are determined. The source is used for accurate determination of line parameters for selected lines of the ν₃ band of SO₂, centred at 1361 cm^-1. Subsequently, these lines are used for performing quantitative analysis of gas mixtures containing SO₂ at concentration levels down to 4 ppm without relying on any calibration with certified gas mixtures. This demonstrates the potential of infrared spectroscopy as a primary method for low-concentration gas analysis. Received: 16 January 2003 / Revised version: 19 February 2003 / Published online: 9 April 2003 RID="*" ID="*"Corresponding author. Fax: +45-4593/1137, E-mail: jh@dfm.dtu.dk     

Diode-pumped Nd:YVO<Subscript>4</Subscript> and Nd:KGd(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> 1.3 μm lasers passively Q-switched with PbS-doped glass

Diode-pumped Nd:YVO₄ and Nd:KGW lasers passively Q-switched with PbS-quantum dot-doped phosphate glass were demonstrated. For the Nd:YVO₄ laser, pulses 110 ns in duration with a 13% Q-switching efficiency were obtained. The absorption recovery time of the PbS-doped glass was measured to be 27±4 ps. Some recommendations for more efficient use of PbS-doped glasses for Q-switching of diode-pumped lasers are suggested on the basis of our analysis. Received: 29 July 2002 / Revised version: 18 September 2002 / Published online: 12 February 2003 RID="*" ID="*"Corresponding author. Fax: +375-17/232-6286, E-mail: savitski@eudoramail.com     

Effect of annealing temperature on microstructures and optical properties of Ba<Subscript>0.9</Subscript>Sr<Subscript>0.1</Subscript>TiO<Subscript>3</Subscript> films

Evolution of microstructure and optical property with annealing temperature has been examined for Ba_0.9Sr_0.1TiO₃ films derived from one single precursor solution containing polyethylene glycol polymer. The films sintered below 750°C exhibit a uniform phase structure across the cross-sections and an ordinary optical thin film feature, while the Ba_0.9Sr_0.1TiO₃ films crystallized at 750°C or higher temperature render a lamellar texture consisting of dense and porous Ba_0.9Sr_0.1TiO₃ layers and a good performance as a one-dimensional photonic crystal. The discrepancy in cross-sectional morphology and reflectance property observed in these Ba_0.9Sr_0.1TiO₃ films has been preliminarily explained.     

XRD,impedance, and Mössbauer spectroscopy study of the Li<Subscript>3</Subscript>Fe<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> + Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> composite for Li ion batteries

The synthesis procedure of the Li₃Fe₂(PO₄)₃?+?Fe₂O₃ composite is presented. The monoclinic (A type) and hematite phases were detected by X-ray diffraction after the synthesis of the composite. The structural α–β (at a temperature of 460 K) and β–γ (at a temperature of 523 K) phase transitions in the composite were indicated by the anomalies of the electrical conductivity, dielectric permittivity, and changes of activation energies of conductivity. Two phase transitions have been detected in the Li₃Fe₂(PO₄)₃?+?Fe₂O₃ composite by ⁵⁷Fe Mössbauer spectroscopy: the phase transition in Li₃Fe₂(PO₄)₃ from the paramagnetic to antiferromagnetic phase at temperature T _N?=?29.5 K and the Morin phase transition in Fe₂O₃ at temperature T _M?=?235 K.     

Long-range magnetic order in copper nitrate monohydrate Cu(NO<Subscript>3</Subscript>)<Subscript>2</Subscript> · H<Subscript>2</Subscript>O

The magnetic phase diagram of copper nitrate monohydrate Cu(NO₃)₂ · H₂O and the basic parameters of its magnetic subsystem have been determined by measuring the thermodynamic properties of this compound. This compound becomes antiferromagnetically ordered at T _N = 3.6 K, undergoes the spin-flop and spin-flip transitions at H _C1 ～ 0.06 T and H _C2 ～ 1.1 T, respectively, at low temperatures. The magnetization of Cu(NO₃)₂ · H₂O at T _SR = 2.7 K exhibits an additional anomaly, which is likely attributed to the spin-reorientation transition.     

Sensitive measurements of stable carbon isotopes of CO<Subscript>2</Subscript> with wavelength modulation spectroscopy near 2 μm

We performed highly sensitive measurements of stable carbon isotopes of CO₂ using wavelength modulation spectroscopy with a distributed feedback laser diode in the 2-μm wavelength range. Ro-vibrational transitions, which belong to the different combination bands, were selected to measure the ¹³CO₂/¹²CO₂ carbon isotope ratio. The δ ¹³C value was determined through the signals obtained in a Herriott-type multipass cell with an optical path length of 29.9 m. The limit of detection for CO₂ using our measurement system was 16±1 parts per billion by volume at the strongest absorption peak that is assigned to the 2ν ₁+ν ₃ R(16) line within the laser emitting frequency region. The 10-h long term precision was a δ ¹³C standard deviation of 0.24‰ (1σ) with the best suited line pairs of ¹²CO₂ and ¹³CO₂ and with careful temperature and pressure control in the cell. The 3-min response and high precision of this measurement allows for precise continuous measurements of stable carbon isotopes in ambient CO₂.     

Effect of γ irradiation on the thermochromic phase transition in [(C<Subscript>2</Subscript>H<Subscript>5</Subscript>)<Subscript>2</Subscript>NH<Subscript>2</Subscript>]<Subscript>2</Subscript>CuCl<Subscript>4</Subscript> crystals (as derived from heat capacity measurements)

The heat capacity of [(C₂H₅)₂NH₂]₂CuCl₄ crystals, both nonirradiated and γ-irradiated to a dose of 10⁷R, was studied in the temperature interval 90–330 K by adiabatic calorimetry. The temperature dependence of C_p(T) was found to have a peak-shaped anomaly in the region of the thermochromic phase transition (PT) at T = 322.7 K. Smoothened experimental heat capacity data were used to calculate the changes in the thermodynamic functions. The changes in the entropy and enthalpy of the thermochromic PT were determined to be ΔS = 42 J K^?1 mol^?1 and ΔH = 13653 J mol^?1 for the nonirradiated crystals and ΔS = 39 J K^?1 mol^?1 and ΔH = 12120 J mol^?1 for the irradiated crystals, respectively. Irradiation of a [(C₂H₅)₂NH₂]₂CuCl₄ crystal by γ rays to a dose of 10⁷ R was shown to shift the PT point toward lower temperatures by ΔT ≈ 1.7 K.     

O<Subscript>2</Subscript> photodesorption from AuO<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> and Au<Subscript>2</Subscript>O<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack>

Using time-resolved photoelectron spectroscopy, the decay channels of AuO₂⁻ and Au₂O₂⁻ following photoexcitation with 3.1-eV photons have been studied. For AuO₂⁻, a state with a rather long lifetime of 30 ps has been identified. Its decay path could not be determined but photodesorption can be excluded. For Au₂O₂⁻, the spectra indicate O₂ desorption after 3.1-eV photoexcitation on a time scale of 1 ps. While comparing these results on Au _n O₂⁻ with analogous data on Ag _n O₂⁻ clusters, a discernible pattern emerges: for dissociatively bound O₂(AuO₂⁻, Ag₃O₂⁻), there are long-living excited states which do not decay by oxygen desorption, while for molecular chemisorption (Au₂O₂⁻, Ag₂O₂⁻, Ag₄O₂⁻, Ag₈O₂⁻), the 3.1-eV photoexcitation triggers fast O₂ desorption with a high quantum yield.     

Emission spectra and stimulated emission characteristics of [N<Subscript>2</Subscript>]<Subscript>2</Subscript>−N<Subscript>2</Subscript> molecular dimer

It has been proved byab initio calculation and theoretical analysis that there exist [N₂]₂−N₂ molecular dimers with D_2h symmetry group, and there also exists an electric dipole excimer-like transition a¹B_2g→a¹B_3u. The theoretical spectra accord with the experimental results for transition a¹B_2g→a¹B_3u. The stimulated emission characteristic of N₂ molecular dimer was researched through the microwave excited highly pure nitrogen and the method of amplified spontaneous emission. The experimental results show that N₂ molecular dimer has stimulated emission characteristics when the microwave power is more than 100 W and the N₂ pressure is in the range from 260 Pa to 2200 Pa.     

Preparation and characterization of organic–inorganic hybrid compound [N(C<Subscript>4</Subscript>H<Subscript>9</Subscript>)<Subscript>4</Subscript>]<Subscript>2</Subscript>Cu<Subscript>2</Subscript>Cl<Subscript>6</Subscript>

Organic–inorganic hybrid sample [N(C₄H₉)₄]₂Cu₂Cl₆ was prepared via the reaction between copper chloride and tetrabutylammonium chloride. The compound was characterized by X-ray powder diffraction, IR, Raman, differential scanning calorimetry (DSC), DTA-TGA analysis and electrical impedance spectroscopy. DSC studies indicate a presence of one-phase transition at 343 K. The complex impedance of compound [N(C₄H₉)₄]₂Cu₂Cl₆ have been investigated in temperature and frequency ranges 300–380 K and 200 Hz–5 MHz, respectively. The Z′ and Z″ versus frequency plots are well fitted to an equivalent circuit model. The circuits consist of the parallel combination of bulk resistance R _p and constant phase elements CPE. The frequency dependence of the conductivity is interpreted in term of Jonscher's law: s(w) = s_dc + Awⁿ \sigma (\omega ){ } = {\sigma_{\rm{dc}}} + { }A{\omega^n} . The conductivity follows the Arrhenius relation. The variation of the value of these elements with temperatures confirmed the availability of the phase transition at 343 K detected by DSC and electrical measurements.     

μSR study of Eu<Subscript>0.8</Subscript>Ce<Subscript>0.2</Subscript>Mn<Subscript>2</Subscript>O<Subscript>5</Subscript> and EuMn<Subscript>2</Subscript>O<Subscript>5</Subscript> multiferroics

A comparative μSR study of ceramic samples of the EuMn₂O₅ and Eu_0.8Ce_0.2Mn₂O₅ multiferroics is performed in the temperature range from 15 to 300 K. It is found that the Ce doping of the EuMn₂O₅ sample slightly reduces the temperature of the magnetic phase transition from T _N = 45 K for the EuMn₂O₅ sample to T _N = 42.5 K for the Eu_0.8Ce_0.2Mn₂O₅ sample. Below the temperature T _N for both samples, there are two types of localization of a thermalized muon with different temperature dependences of the precession frequency of the magnetic moment of the muon in an internal magnetic field. The higher frequency in both samples refers to the initial antiferromagnetic matrix. The behavior of this frequency in Eu_0.8Ce_0.2Mn₂O₅ follows the Curie–Weiss law with the exponent β = 0.29 ± 0.02, which differs from the value β = 0.39 standard for 3D Heisenberg magnetics and is observed in EuMn₂O₅, because of the strong frustration of the doped sample. The temperature-independent low frequency is due to the presence of Mn³⁺–Mn⁴⁺ ferromagnetic pairs located along the b axis of the antiferromagnetic matrix and in the regions of phase separation, which contain such ion pairs and e _g electrons recharging them. In both samples, polarization losses are the same (about 20%) and are associated with the formation of Mn⁴⁺–Mn⁴⁺ + Mu complexes near Mn³⁺–Mn⁴⁺ ferromagnetic pairs. In the temperature interval from 25 to 45 K, the separation of the Eu_0.8Ce_0.2Mn₂O₅ structure into two fractions where the relaxation rates of polarization of muons differ by an order of magnitude is revealed. This effect is due to a change in the state of regions of phase separation (1D superlattices) at the indicated temperatures. Such effect in EuMn₂O₅ is significantly weaker.     

High-Temperature Heat Capacity of Zn<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript>–Cu<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript> Solid Solutions

Differential scanning calorimetry has been used to study the influence of temperature on the heat capacity of synthesized vanadates Zn₂V₂O₇, (Cu_0.56Zn_1.44)V₂O₇, and (Cu_1.0Zn_1.0)V₂O₇. It is found that dependences C_p = f(T) have extremes. The thermodynamic properties of Zn₂V₂O₇ have been determined.