Measurement of temperature and temperature gradient in?millimeter samples by chlorine NQR

A mini-thermometer based on the ³⁵Cl nuclear quadrupole resonance (NQR) frequency temperature dependence in the chlorates KClO₃ and NaClO₃ was built and successfully tested by measuring temperature and temperature gradient at 77 K and higher in about 100 mm³ active volume of a mini Joule–Thomson refrigerator. In the design of the tank-circuit coil, an array of small coils connected in series enabled us (a) to achieve a suitable ratio of inductance to capacity in the NQR spectrometer input tank circuit, (b) to use a single crystal of KClO₃ or NaClO₃ (of 1–2 mm³ size) in one coil as a mini-thermometer with a resolution of 0.03 K and (c) to construct a system for measuring temperature gradients when the spatial coordinates of each chlorate single crystal within an individual coil are known.     

Inelastic intermolecular exchange of vibrational quanta and relaxation of vibrationally excited states in binary solid systems

The processes of molecular relaxation in the binary nitrate–perchlorate solid systems LiNO₃–LiClO₄, NaNO₃–NaClO₄, and KNO₃–KClO₄ have been investigated using Raman spectroscopy. It has been found that the relaxation time of the ν₁(A) vibration of the NO₃ ^- anion in the binary solid system is shorter than that in the pure metal nitrates. It has been shown that an increase in the relaxation rate is caused by the existence of an additional mechanism of relaxation of vibrationally excited states of the nitrate ion in the system. This mechanism is associated with the excitation of a vibration of another anion (ClO₄ ^-), as well as with the “creation” of a lattice phonon. It has been established that the condition for the realization of the relaxation mechanism is that the difference between the frequencies of the aforementioned vibrations should correspond to the range of sufficiently high densities of states of the phonon spectrum.     

Far infrared optical properties of polycrystalline NaClO3, KClO3, NaBrO3 and KBrO3

The resonant frequencies, damping constants and oscillator strengths of far infrared lattice vibrations of polycrystalline NaClO₃, KClO₃, NaBrO₃ and KBrO₃ have been obtained through classical dispersion (CD) analysis of transmission data. Space group analysis has been applied for attribution assignments and to ascertain the translational and rotational character of the respective lattice bands. The damping constants were found to be unusually large indicating short lifetimes of the excited states in spite of an apparent absence of phonon-phonon coupling. The CD analysis of the spectra also provide reliable values of oscillator strength and resonant frequency.     

Performance of frequency-modulated pulses in NQR

This paper presents an analysis of the performance of frequency-modulated pulses and of pulses modulated simultaneously in amplitude and frequency in the pure nuclear quadrupolar resonance (NQR) spectroscopy of spin 3/2 nuclei. Computer simulations are given of the offset compensation efficiency of such pulses as applied to single crystals. Spin evolution equations were solved numerically. Experimental measurements, using FM pulses, of the³⁵Cl NQR of sodium chlorate (NaClO₃) single crystal and of mercuric chloride (HgCl₂) powder are reported. The results suggest that frequency modulated pulses are alternative pulses to composite pulses in NQR.     

Ab initio investigations of the elastic properties of chlorates and perchlorates

Elastic properties of NaClO₃, KClO₃, LiClO₄, NaClO₄, and KClO₄ have been investigated from first principles by the method of linear combination of atomic orbitals in the gradient approximation of the density functional theory using CRYSTAL software. The elastic constants and moduli, hardness, Poisson’s ratio, and the anisotropy parameters have been calculated. The velocities of sound, the Debye temperature, the thermal conductivity, and the Grüneisen parameter have been estimated. It has been found that these compounds are mechanically stable, anisotropic, and ductile materials. The dependences of their elastic parameters on the atomic number of the cation have been calculated. The obtained results are in good agreement with the available experimental data.     

Effects of nonresonant rf photon dressing on NQR in NaClO3

Splittings and shifts of Na NQR frequencies and lengthening of T₂ of Cl NQR due to nonresonant photons in a mixed mode are observed in NaClO₃ and interpreted by using the theory of dressed atoms.     

35Cl NQR spectra of group 1 and silver dichloromethanesulfonates

The dichloromethanesulfonates of silver and other +1-charged cations, M ^?+?(Cl₂CHSO $_{3}^{-})$ (M = Ag, Tl, Li, Na, K, Rb, Cs) were synthesized and studied by ³⁵Cl NQR. Dichloromethanesulfonic acid was prepared by the methanolysis of dichloromethanesulfonyl chloride, and was then neutralized with the carbonates of the +1-charged cations to produce the corresponding dichloromethanesulfonate salt. This NQR study completed the investigation of the chloroacetates and chloromethanesulfonates of silver, Ag^?+?(Cl _x CH_3???x SO $_{3}^{-})$ and Ag^?+?(Cl _x CH_3???x CO $_{2}^{-})$ , and suggests (1) that the ability of organochlorine atoms to coordinate to silver decreases as the number of electron-withdrawing groups (Cl, SO $_{3}^{-}$ , CO $_{2}^{-})$ attached to the carbon atom increases; (2) that the unusually large NQR spectral width found among M ^?+?(Cl₂CHCO $_{2}^{-})$ salts is not present among M ^?+?(Cl₂CHSO $_{3}^{-})$ salts, and therefore is not generally characteristic of the dichloromethyl group in salts.     

New submillimetre laser lines from CH3OD and CD3OD

Thirteen new submillimetre emission lines have been observed when pumping CH₃OD using isotopic CO₂ lasers, and fourteen when pumping CD₃OD. Three isotopic CO₂ lasers were used¹²C¹⁶O₂,¹²C¹⁸O₂, and¹³C¹⁶O₂. The new lines were observed in a Fabry-Perot resonator. The wavelength ranges observed were from 55 to 320 m for CH₃OD and from 66 to 531 m for CD₃OD. The polarisation of the submillimetre laser lines relative to the CO₂ pump line has also been determined.     

Ion bombardment induced amorphous layers on single crystal stainless steel-a combined rutherford backscattering and transmission electron microscopy study

Abstract

Decomposition reactions of NaClO₃, KClO₃, and KIO₄ induced by 3 keV Ar⁺ ions and 1254 eV X-rays are investigated by X-ray photoelectron spectroscopy (XPS). The reactions lead to the formation of binary halides with preferential losses of oxygen. The decomposition pattern, monitored at the various stages of reaction, indicates almost direct changeover to the final products with only a few intermediate species formed. Product abundancies are compared for the ion, X-ray, and electron induced reactions and discussed in relation to the various radiation induced reaction mechanisms.     

Electronic structure and lattice dynamics of domeykite Cu<Subscript>3</Subscript>As according to nuclear quadrupolar resonance of<Superscript>75</Superscript>As and<Superscript>63,65</Superscript>Cu

The temperature dependences of nuclear quadrupole resonance (NQR) frequencies, the line width and nuclear relaxation of⁷⁵As and^63,65Cu, as well as the electrical resistivity in domeykite Cu₃As are studied in the temperature range of 4.2-300 K. The comparison of the calculated with the measured lattice contribution to the NQR frequencies points at a substantial role played by the conduction electrons in creating the electric field gradient at the nuclei sites. The temperature dependence of the copper and arsenic nuclear spin-lattice relaxation linear at 4.2<T<200 K and that of the electric resistivity (30<T<200 K) prove the metallic character of the conductivity of domeykite. The enhancement of nuclear relaxation, the narrowing of copper and arsenic NQR line widths are considered as arising due to the ionic movement starting beyond 200 K. This movement influences the electric resistivity, most likely due to the inreasing density of states at the Fermi surface.     

Electron paramagnetic resonance of Gd<Superscript>3+</Superscript> aqua complexes in vitrified aqueous solutions and Gd<Superscript>3+</Superscript> aqua ions adsorbed on the capillary surface

Electron paramagnetic resonance (EPR) spectra of Gd³⁺ aqua complexes are measured in dilute aqueous solutions of Gd(NO₃)₃ (C<0.2 M) at room temperature. A partial resolution of the fine structure observed in the spectra is characteristic of solid disordered systems and results in an increase in the effective width of the EPR line with a decrease in the Gd³⁺ concentration. This phenomenon is explained in terms of adsorption of Gd³⁺ aqua ions on the surface of the measuring capillaries. The fine structure is revealed in the EPR spectra of Gd(NO₃)₃ aqueous solutions, namely, the Gd(NO₃)₃ solutions vitrified at a temperature of 77 K (with an addition of 10–15 vol % glycerol) and Gd(NO₃)₃ solutions quasi-vitrified at 298 K (with an addition of 70–90 vol % glycerol). Analysis of the EPR spectra demonstrates that these solutions contain two types of aqua complexes with fine structure parameters D₁=180 G and D₂=580 G. Reasoning from a comparison with x-ray diffraction data, the fine structure parameters D₁ and D₂ are assigned to higher symmetric eight-coordinate and lower symmetric nine-coordinate Gd³⁺ aqua complexes, respectively.     

Structural and magnetic phase transformations in the BiFeO<Subscript>3</Subscript>-CaFe<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>O<Subscript>3</Subscript> system

The crystal structure and magnetic properties of the Bi_{1 ? x} Ca _x Fe_{1 ? x/2}Nb _x/2O₃ system were studied. It is shown that, at x ≤ 0.15, the unit-cell symmetry of solid solutions is rhombohedral (space group R3c). Solid solutions with x ≥ 0.3 have an orthorhombic unit cell (space group Pbnm). The rhombohedral compositions are antiferromagnetic, while the orthorhombic compositions exhibit a small spontaneous magnetization due to Dzyaloshinski?-Moriya interaction. In CaFe_0.5Nb_0.5O₃, the Fe³⁺ and Nb⁵⁺ ions are partially ordered and the unit cell is monoclinic (space group P2₁/n). In the concentration range 0.15 < x < 0.30, a two-phase state (R3c + Pbnm) is revealed.     

Luminescence of Sc3+ and La3+ isoelectronic impurities in Lu3Al5O12 single-crystal films

The time-resolved luminescence and luminescence excitation spectra, and luminescence decay kinetics at 8 and 300 K of Lu₃A₁₅O₁₂ (LuAG) single-crystal films doped with Sc³⁺ and La³⁺ isoelectronic impurities and excited by synchrotron radiation are investigated. It is established that the La³⁺ isoelectronic impurity in the ?ub;c?ub; positions of the garnet lattice forms La _Lu ³⁺ luminescence centers emitting in the band with λ_max = 280 nm and the decay time of the main component τ = 300 ns at 300 K. The Sc³⁺ isoelectronic impurity located in the ?ub;c?ub; and (a) positions of the LuAG lattice forms two luminescence centers, Sc _Lu ³⁺ and Sc _Al ³⁺ , emitting in the bands with λ_max = 290 nm and τ = 240 ns and λ_max = 335 nm and τ = 375 ns, respectively, at 300 K. It is shown that the luminescence excitation of the La³⁺ and Sc³⁺ isoelectronic impurities in LuAG single-crystal films occurs through radiative decay of excitons localized near La _Lu ³⁺ , Sc _Lu ³⁺ , and Sc _Al ³⁺ centers. The energies of formation of these excitons are determined to be 6.8, 6.88, and 7.3 eV, respectively. It was found that the excited state of the excitons genetically related to the La _Lu ³⁺ , Sc _Lu ³⁺ , and Sc _Al ³⁺ enters has two radiative levels with different transition probabilities. This configuration leads to the presence of fast (2.3–8.4 ns) and slow (150–375 ns) main components in the luminescence of the centers formed by isoelectronic impurities in garnets.     

Fluorescence and attenuation properties of Er3+ -doped phosphate-glass fibers and efficient infrared-to-visible up-conversion

Fluorescence spectra of phosphate glasses with different erbium doping have been measured. The flourescence intensity reaches its maximum at an Er³⁺-doping concentration of 0.75 mol%. When the Er³⁺ doping exceeds 0.75 mol%, the fluorescence intensity decreases due to concentration quenching. The attenuation at 1.53 µm of the fiber is 12.8 db/m. The fluorescence up-conversion of 1.064 µm Nd:YAG laser pulses into intense green 547 and 667 nm light in the fiber has been measured. The fluorescence output power of green (547 nm) and red (667 nm) light is 178 and 42 W, respectively with an excitation power of 1 W. The two signals are referred to as⁴ S _3/2 ⁴ I _{1 5/2} and⁴ F _9/2 ⁴ I _{1 5/2} transitions through two-photon absorption fluorescence.     

Out of the blue: semiconductor laser pumped visible rare‐earth doped lasers

The rise of semiconductor‐based pump sources such as In_xGa_1‐xN‐laser diodes or frequency‐doubled optically pumped semiconductor lasers with emission wavelengths in the blue encourages a revisitation of the rare‐earth ions Pr³⁺, Sm³⁺, Tb³⁺, Dy³⁺, Ho³⁺ and Er³⁺ with respect to their properties as active ions in crystalline solid‐state laser materials with direct emission in the visible spectral range. Nowadays, some of these blue‐pumped visible lasers compete with Nd³⁺‐lasers in terms of efficiency and direct lasing at various colors from the cyan‐blue to the deep red can be addressed in very simple and compact laser setups. This paper highlights the spectroscopic properties of suitable rare‐earth ions for visible lasing and reviews the latest progress in the field of blue‐pumped visible rare‐earth doped solid‐state lasers.

     

Phenomenological rules for the computation of magneto-electric susceptibilities

Applying the model of the anharmonic oscillator, phenomenological expressions were derived, allowing calculation of the components of tensors describing non-linear magneto-electric susceptibilities. Detailed calculations were carried out for the pseudo-tensor of fourth order ^eeem in terms of which magneto-optical birefringence and rotation are expressed for the monocrystals KDP, DKDP, ADP, KDA, LiNbO₃, LiTaO₃ and NaClO₃. From the results obtained it follows that non-linear magneto-electric susceptibilities, which are described by the pseudo-tensor ^eeem are of the order of 10^–16 m V^–1T^–1.Part of this work was carried out under Research Project MR 15.     

Differential thermal analysis and nuclear quadrupole resonance study on polymorphic 1,4-dichlorobutane

Differential thermal analysis (DTA), and the ³⁵Cl nuclear quadrupole resonance (NQR) frequency (v _Q ) and line width (Δv _Q ) were measured as a function of the temperature in solid 1,4-Dichlorobutane (DCB). Two crystalline modifications forms I and II, stables above and below T _c = 210 K respectively were found according to the thermal history of the sample. A comparative analysis of the NQR frequency in both phases suggests that the crystal structure in form II is closer-packed than in form I. The NQR line width shows the existence of a thermal activated process with an activation energy E _a ? 20 kJ mol^?1, probably related with reorientations of the CH₂Cl end groups. Some orientational disorder is expected in the low temperature modification since the line width is twice as much as that in the high temperature phase.     

Peculiarities of the magnetic state in the system La<Subscript>0.70</Subscript>Sr<Subscript>0.30</Subscript>MnO<Subscript>3−γ</Subscript> (0 ≤ γ ≤ 0.25)

The results of experimental investigation of the chemical phase composition, crystal structure, and magnetic properties of the manganite La_0.70Sr_0.30MnO_3?γ (0 ≤ γ ≤ 0.25) with perovskite structure depending on the concentration of oxygen vacancies are presented. It is found that the mean grain size of the stoichiometric solid solution of La_0.70Sr_0.30MnO₃ amounts approximately to 10 μm, while the grain size for anion-deficient solid solutions of La_0.70Sr_0.30MnO_3?γ is approximately 5 μm. It is found that samples with 0 ≤ γ ≤ 0.13 have a rhombohedral unit cell (with space group \(R\bar 3c\), Z = 2), while samples with γ ≥ 0.20 have a tetragonal unit cell (space group I4/mcm, Z = 2). It is proved experimentally that the magnetic phase state of the manganite La_0.70Sr_0.30MnO_3?γ changes upon a decrease in the oxygen content. It is shown that anion-deficient solid solutions of La_0.70Sr_0.30MnO_3?γ experience a number of successive magnetic phase transformations in the ground state from a ferromagnet (0 ≤ γ ≤ 0.05) to a charge-disordered antiferromagnet (γ = 0.25) via an inhomogeneous magnetic state similar to a cluster spin glass (0.13 ≤ γ ≤ 0.20). The mean size of ferromagnetic clusters (r ≈ 50 nm) in the spin glass state is estimated. It is shown that oxygen vacancies make a substantial contribution to the formation of magnetic properties of manganites. The generalized magnetic characteristics are presented in the form of concentration dependences of the spontaneous magnetic moment, coercive force, and the critical temperature of the magnetic transition. The most probable mechanism of formation of the magnetic phase state in Sr-substituted anion-deficient manganites is considered. It is assumed that in the absence of orbital ordering, a decrease in the magnetic ion coordination number leads to sign reversal in indirect superexchange interactions Mn³⁺-O-Mn³⁺.     

Magnetic properties of high-T c superconductors from NQR and NMR measurements

NMR and NQR spectra and spin-lattice relaxation measurements carried out in LASCO and YBCO-type crystals are presented and analyzed in order to derive insights on the correlations and spin-dynamics of the Cu²⁺ ions and on the microscopic mechanisms of high-T _c superconductivity. As an illustrative example on how the magnetic correlation length and spin dynamics properties can be extracted from the relaxation rateW, the³⁵Cl NMR data in the two-dimensional Heisenberg system Sr₂CuCl₂O₂, around the paramagnetic-antiferromagnetic (PA-AF) transition are first considered. Then the¹³⁹La NQR relaxation measurements in La_2?xSr_xCuO₄ are briefly reviewed and it is shown how a simple picture of localized Cu²⁺ magnetic moments, whose spin fluctuation times are controlled by the charge defects induced by the doping, leads in a direct way to quantitative estimates for the progressive shift, on cooling, of the spectral density of the low-frequency spin excitations towards the high frequency range. This phenomenon can be described in terms of effective spin at the Cu²⁺ ions, and its similarities with the analogous effect of progressive delocalization in Heavy Fermions systems are pointed out. Thus, the superconducting transition appears to occur in an unconventional Fermi liquid with AF correlations among itinerant pseudoparticles, possibly involving a mechanism not directly related to the magnetic correlated dynamics. In fact, a universal behavior of the relaxation rates as a function of temperature is observed, regardless of the transition temperatureT _c. The independence ofT _c from the low frequency static and dynamical spin properties is also indicated by⁸⁹Y Knight shifts and from⁶³Cu relaxation rates in systems like YBa₂Cu₄O₈ (Y124), whereT _c can be changed by atomic substitutions and by controlling the oxygen stoichiometry. The effect of an external magnetic field on the correlated spin dynamics of the AF Fermi liquid is investigated and from a comparison of Cu NQR relaxation and NMR relaxation in oriented powder of YBCO and LASCO it is shown that the external field has the small but unambiguous effect of depressing the relaxation rates aboveT _c, besides strongly enhancing them in the superconducting phase. A maximum in the ratio \({{W\left( {NQR} \right)} \mathord{\left/ {\vphantom {{W\left( {NQR} \right)} {W\left( {\vec H\left\| {\vec c} \right.} \right)}}} \right. \kern-0em} {W\left( {\vec H\left\| {\vec c} \right.} \right)}}\) is thus observed around 80 K, either in LASCO or in YBCO, again indicating that the transition could be driven by a mechanism not directly involving the spin dynamic properties. To study the role of the fluxions belowT _c ⁸⁹Y NMR shifts and spectra in oriented powders of YBCO are analyzed. Information on the spin susceptibility and on the structure of the vortex lattice is obtained. In addition, from the temperature behavior of the linewidth a motional narrowing related to flux melting is evidenced. The effective correlation time for the vortex motion is derived and it is discussed why μ⁺SR cannot detect it in view of the different rigid-lattice line broadening.     

High-power diode-cladding-pumped Tm<Superscript>3+</Superscript>, Ho<Superscript>3+</Superscript>-doped silica fibre laser

The fundamental characteristics of a continuous-wave high-power diode-pumped Tm³⁺, Ho³⁺-doped double-clad silica fibre laser are presented. A maximum output power of 5.2 W was measured and was generated at a slope efficiency of 42 (44)% with respect to the launched (absorbed) pump power. At the optimum length of 7 m (_effL=2.9, where _eff is the effective absorption coefficient of the fibre and L is the fibre length), the fibre laser output was measured to have a centre wavelength of 2105 nm and a line width of 20 nm. The centre wavelength of the emission was tunable over a 32-nm extent when 0.68<_effL<3.28 or for a 6.2-m change in L. PACS 42.55.Wd; 42.55.Xi; 42.60.Lh; 42.60.Pk