Transition In Sr Research Articles

Calculated high-pressure-induced electronic and structural phase transitions in Sr and Yb up to 50 kbar.

The energy band structures of Sr and Yb have been calculated by the linear-muffin-tin-orbital--atomic sphere approximation method in the pressure range of 0--50 kbar. By the inclusion of nonlocal exchange corrections to the local-density approximation, excellent agreement with regard to experiment has been found in predicting the electronic and structural phase transition pressures of these elements. \textcopyright{} 1996 The American Physical Society.

Magnetic substate transitions in collisions of Sr(5s5p 1P 1) with Ar

The collision induced magnetic substate transitions of Sr(5s5p 1P 1) from M l = 0 to M l = ± 1 with Ar as collision partner are studied in a beam-gas reaction apparatus. The depolarization rate constant k p = (2.5 ± 0.5) × 10 −9 cm 3 molecule −1 s −1 is obtained, and the magnetic substate transition rate constant k E = (1.25 ± 0.25) × 10 −9 cm 3 molecule −1 s −1 is deduced from depolarization rate constants.

Spikes in raman spectrum of miniature optically pumped NH3 fir laser

In this paper, the semiclassical density matrix equation was solved to calculate the spectral characteristics of V2:a--sR(0,0) transition in a miniature optically pumped NH3 far infrared laser (mini-NH3-OPFIRL), which was pumped by CO2-10R(6) line. The results of theoretical calculation showed that the spikes in Raman spectrum of V2:a--sR(0,0) would appear when the operating NH3 gas pressure was higher than a certain critical value or pumping power density was lower than a certain critical value, which was caused by Raman processes interaction of AC-Stark splitting. In our experiment, 298 µm FIR spetral line of a--sR(0,0) pumped by a TEA-CO2 laser with 10R(6) line was observed but the spikes could not be observed owing to the limitation of the resolution of the F-P interferometer.

Optical characteristics of a rectangular bore discharge-excited Sr+ recombination laser

We report results of studies of laser beam divergence, laser beam intensity profiles and spatial and temporal laser pulse characteristics for a rectangular bore strontium recombination laser operating on the 430.5 nm Sr transition at high pulse rates (3-10 kHz). Beam divergence is found to be very nearly diffraction limited for a flat-flat optical cavity, with a very uniform spatial distribution of laser intensity under optimum operating conditions. Laser pulse characteristics provide an indication of plasma conditions across the laser tube.

Self-focused light propagation in a fully saturable medium: Experiment.

We report observations of self-focusing and filamentation, i.e., the formation of one or more self-trapped beams, of \ensuremath{\sim}3 ns laser pulses in strontium (Sr) vapor. The experimental arrangement consists of a Sr vapor cell and a pulsed neodymium-doped yttrium aluminum garnet pumped dye laser tuned to the blue of the 461 nm transition in Sr. The spatial intensity distribution of individual self-focused beams has been measured at the exit window of a vapor cell by using a magnifying lens and video camera. Measurements of power dependence, spatial distributions, and scaling behavior for filament formation are in good agreement with theory over a wide range of vapor densities, laser detunings, and laser powers. \textcopyright{} 1996 The American Physical Society.

The phase transition and transport properties of Sr0.56C60O1.5

X-ray diffraction and dielectric measurement have been applied to investigate the phase transition and transport properties of Sr0.56C60O1.5 which is obtained by the reaction of SrCl2 with C60 anion aquatic solution. The new compound has a similar structure, but different transport properties as compared with metallic Sr-doped C60. X-ray diffraction shows that a first-order phase transition around 100 °C is related to the rearrangement of Sr2+ in the interstitial sites of the C60 lattice. The step change of ac conductivity near 100 °C is also attributed to the hopping of Sr2+ between interstitial sites. The ionic conductivity indicates the possibility of synthesizing superionic conductors based on C60 and its derivatives.

X-ray diffraction study of phase transitions in Sr0.39Ba0.61Nb2O6between 20 and 500 K

Abstract X-ray powder diffraction patterns of the ferroelectric mixed crystal Sr0.39,Ba0.61Nb2O6 (SBN-39) are recorded in Guinier geometry in a temperature range between 20 K and 500 K by means of the film-lift technique. The lattice parameters were refined for a single tetragonal structure in the whole temperature range ignoring the incommensurate (IC) modulation of the structure as well as a temperature dependent small splitting of reflections, most clearly observed for the (001)-type. These values show anomalies in the region of diffuse ferroelectric phase transition as well as below room temperature indicating the three other phase transitions. The splitting may be caused by a two-phase state of a relaxor-like ferroelectric system due to coexistence of polarized regions (clusters) and untransformed remnants of the para-phase.

Motion of the water molecules and phase transitions in Sr[Fe(CN)5NO]*4H2O studied by proton NMR

The mobility of the water molecules and the phase transitions in strontium nitroprusside (SrNP) have been studied by proton spin-lattice relaxation time and proton NMR spectra over a wide temperature range. The activation energies for 180° flip motions of three distinct water molecules existing in the unit cell of the SrNP have been determined to be 23·4, 6·69, and 8·37 kJ mol-1. Four phase transitions at T c1 = 197 K, T c2 = 192 K, T c3 = 182 K and T c4 = 174 K have been discovered, and some of the nature of these transitions were brought to light.

Tractor-trailer crashes in Indiana: A case-control study of the role of truck configuration : E. R. Braver, P. L Zador, D. Thum, E. L. Mitter, H. M. Baum and F. J. Vilardo. Insurance Institute for Highway Safety, January 1994

Compositionally induced phase transitions in the system Sr(ZrxTi1−x)O3 were analyzed using a combination of X-ray diffraction, FT-Raman and FTIR spectroscopy. Sr(ZrxTi1−x)O3 system showed at least two tilting of phase transitions, pm3m–I4mcm and I4/mcm–pnma. The structural transition occurred due to tilting of BO6 octahedra. Dielectric constant measured with Hakki–Coleman technique decreased from 253 to 25 with increase of Zr content. The value of τf found 1771 ppm/°C for SrTiO3 which decreased to −82 ppm/°C for the SrZrO3. The dielectric resonator antenna (DRA) was investigated experimentally and numerically using a monopole antenna through an infinite ground plane and Ansoft's high frequency structure simulator software, respectively. The required resonance frequency and bandwidth of DRA were investigated in the composition between 0 ≤ x ≤ 1.0.

A microwave-excited strontium-ion (?430.5 nm) recombination laser

Laser oscillation on the 430.5 nm transition of Sr+, which replies on three-body electron-ion recombination for its excitation, has been achieved in a pulsed, selfheated, microwave-pumped discharge.

Interrelation between atomic and electronic structures of alkaline-earth adlayers on Mo(112) and Re(10 [formula omitted]0)

A pronounced correlation between electronic structure and two-dimensional phase transitions in Mg, Sr and Ba monolayers on (112)Mo and (10 1 0)Re surfaces is found by LEED, UPS and LEELS techniques. At low coverages, the adsorbed atoms are arranged in linear chains oriented across the rows of substrate atoms, while UPS and LEELS indicate the appearance of adsorption induced resonances. At 0>0.5 the commensurate-incommensurate transition is accompanied by sharp changes in photoemission spectra and emergence of energy losses due to plasmon excitations revealing the metallization of the adlayers.

Development of All-Semiconductor Laser Sources for Studies of 88Sr+ Ions Confined in RF Trap

Semiconductor-laser-based light sources have been developed for cooling and depopulating Sr+ ions confined in an rf trap. Single-mode laser oscillation at 422 nm and 21 µ W power was obtained, which corresponds to transition 5s 2S1/2-5p 2P1/2 of Sr+. An external-cavity-stabilized semiconductor laser with 1.8 mW power has been developed for pumping ions back from the 4d 2D3/2 metastable state to the cooling cycle. In this paper we present the reference spectrum for both lasers, which confirms the laser oscillation at appropriate transition of Sr+.

Sr 2+-doping effect on the phase transition in Pb 5Ge 3O 11 single crystals

The dielectric and the pyroelectric measurements of Sr 2+-doped Pb 5Ge 3O 11 single crystals were carried out in the frequency range 100 Hz to 15 MHz from room temperature up to 600°C. With increasing Sr 2+-concentration, ferroelectric phase transition temperatures shifted to lower temperature and the phase transitions were diffused. The deviation from Curie-Weiss behavior of the dielectric constant was analyzed on the basis of Benguigui's theory [L. Benguigui, Solid State Commun. 14, 669 (1974)]. Estimation of the local order parameter suggests that the diffuse phase transition of Sr 2+-doped Pb 5Ge 3O 11 single crystal is caused by the local polarization due to a positional disorder.

Observation of the 5s^2S_1/2−4d^2D_5/2 transition in a single laser-cooled trapped Sr^+ ion by using an all-solid-state system of lasers

The first application, to our knowledge, of an all-solid-state system of lasers to the study of a single cooled trapped Sr(+) ion is described. Quantum jumps have been observed by driving the 674-nm 5s(2)S(1/2)-4d(2)D(5/2) transition, and preliminary observations of the line shape are reported. An upper limit for the temperature of a single ion, derived from the 674-nm linewidth, was 200 mK. If non-Doppler sources of broadening such as unresolved Zeeman structure dominate, then the temperature limit would be even lower.

Role of structural instability in high-temperature superconductivity and its effect on isotope effect

Abstract The tetragonal-orthorhombic structural phase transition of La2-x Sr x CuO4 is analyzed within an anharmonic electron-phonon interaction model. x-dependence as well as temperature T-dependence of the soft mode are calculated and in quantitative agreement with experimental data. To evaluate the importance of the soft mode for the superconducting properties Eliashberg equations are solved for this specific mode. The resulting electron-phonon coupling Λ is found to be strongly x and T dependent with characteristic anomalies around the structural transition temperature T s . The calculated x-dependent superconducting transition temperature T c follows closely the experimental values but underestimates T c . This discrepancy is attributed to the neglect of higher order electron-phonon interactions. Inclusion of these terms leads to a strong decrease of the isotope effect α from the BCS value of 0·5 to a varied value of 0·1.

Lithosphere-scale thrusting in the western U.S. Cordillera as constrained by Sr and Nd isotopic transitions in Neogene volcanic rocks

The western Idaho suture zone juxtaposes continental and oceanic terranes with distinctive Sr and Nd isotopic signatures across a sharp isotopic transition coincident with the Mesozoic {sup 87}Sr/{sup 86}Sr = 0.706 line (MSL). Late Cretaceous to Eocene granitic plutons that define the MSL are allochthonous and were transported eastward by {approximately}150 km during late Mesozoic to Tertiary (ca. 100-55 Ma) thrusting. Sr and Nd isotopic compositions of Neogene rhyolites and basalts from southwestern Idaho, southeastern Oregon, and northern Nevada define isotopic transitions coincident with the MSL; there are continental affinities east of long 116{degree}30minutesW and oceanic affinities west of 119W. Between these longitudes, intermediate isotopic compositions imply derivation of magmas from both continental and oceanic mantle (basalts) and crustal (rhyolites) sources. It is inferred that the basal decollement of the Mesozoic and Tertiary contractional orogen dips westward below depths of segregation of basaltic magmas, and that oceanic lithospheric mantle was thrust eastward over a shelf of old, isotopically evolved continental lithospheric mantle that now protrudes {approximately}150 km west of the MSL.

Collisional redistribution of polarized radiation for Sr-Ar(He) systems: a numerical comparison of the semiclassical decoupling/locking model to exact results

Semiclassical formulations of collisional redistribution of polarized radiation are presented at several levels of approximation, from full classical path coupled equations to the locking/decoupling model. These are numerically tested against the results of a quantum mechanical coupled-channels formalism, by the comparison of polarization curves in both spectral wings of the Sr(1S0-1P1) transition, with Ar and He as collisional perturbers. It is found that the locking/decoupling model can often produce good agreement with exact results if the effects due to trajectories and multiple Condon points are treated properly. Significant discrepancies due to the Condon approximation used by the model are seen in the near blue wing of the spectra and attributed to antistatic effects.

Fluorescence from excited states of Ca+ and Sr+ following photoionization

The simultaneous photoionization and excitation of Ca and Sr atoms from the ground state into the first excited ionic P state has been investigated by measuring the intensity and the polarization of the emitted fluorescence radiation at 3933 AA and 4078 AA respectively. Cross sections for the direct excitation of the Ca+(42P) and Sr+(52P) states were found to be extremely small ((10-19 cm2 at threshold). However, these states can also be populated by resonant photoexcitation of atomic inner-shell states in the region of the Ca(3p64s2-3p53d4s2) transition at 394.8 AA and the Sr(4p65s2-4p54d5s2) transition at 490.9 AA, followed by autoionization processes. The ionic fluorescence in the respective resonance regions of Ca and Sr has been measured and compared with the corresponding photoelectron and photoion spectra.

Complexity and simplicity of the metal-superconductor-insulator transition in the (Tl 1−xPb x)Sr 2(Ca 1−yY y)Cu 2O 7−δ system

The (Tl 1−xPb x)Sr 2(Ca 1−yY y)Cu 2O 7−δ system exhibits the highest superconducting transition temperature, T c=110K, at x=0.5 and y=0.2, yet observed in the TlBa 2CaCu 2O 7−δ (1212) structure type. This complex, six-blended combination of metallic elements which make up the material is, however, compensated by a relatively simple crystal structure, which bears many similarities to that of 90K superconductor YBa 2Cu 3O 7−δ. Here, we report some of the important features of the cation-substitution chemistry of the title compound, drawing attention to fundamental changes in the electronic properties and the Metal-Superconductor-Insulator transition of the (Tl 1−xPb x)Sr 2(Ca 1−yY y)Cu 2O 7−δ system as Tl 3+ a Ca 2+ is replaced by Pb 4+ and Y 3+, respectively. In addition, we also report preliminary results concerning the effects of the chemical substitution in the (Tl,Pb)O layers.

Observation of electromagnetically induced transparency.

We report the first demonstration of a technique by which an optically thick medium may be rendered transparent. The transparency results from a destructive interference of two dressed states which are created by applying a temporally smooth coupling laser between a bound state of an atom and the upper state of the transition which is to be made transparent. The transmittance of an autoionizing (ultraviolet) transition in Sr is changed from exp(-20) without a coupling laser present to exp(-1) in the presence of a coupling laser.