Oxygen Isotope Shift Research Articles

Doping dependence of the oxygen isotope effect in YBa 2Cu 3O x

Measurements of the total oxygen isotope shift α 0 and the condensate density of n of YBa 2Cu 3O x (6.53 < x < 6.99) are presented. The T c( n) dependence exhibits a two-plateau behavior which is associated with the ortho-I and ortho-II phase, respectively. Around optimum doping ( x ≅6.9) and at the onset of the 60 K plateau where T c only weakly depends on n the small α 0 ≅ 0.025 is associated to changes in the phonon spectrum. A further decrease of T c leads to a rapid increase of α 0 ∝ ∂T c/∂ n suggesting that α 0 is related to a change of the condensate density n upon isotope exchange.

Geochemical and petrologic evidence of the origin and diagenieis of a Late Mississippian, supratidal dolostone

We examined major element compositions, carbon and oxygen isotopic compositions, and macro/microffabrics of a 15–30 cm thick, bedded dolostone unit in the upper part of the Elwren Formation in southern Indiaan for evidence of the dolostone’s origin, early alteration, and burial diagenesis. Burial diagenetic alteration of the bedded dolostone and associated nodules is indicated by the presence of recrystallized dolomite with light oxygen isotopic compositions. However, the Elwren Formation dolostones from different outcrops exhibit similar, systematic, straitigraphic trends of key primary microfabrics, organic matter content, carbon and oxygen isotopic compositions, and major element compositions. Therefore, the oxygen isotopic shift caused by burial diagenesis is inferred to have affected the dolostones in a uniform manner so as to preserve relative, primary, oxygen isotopic differences between different parts of the dolostone system. This permits our use of the isotopic data to suggest the processes of formation of the bedded dolostone and the nature of the early alteration of the dolostone.

Reactions of Laser-Ablated Iron Atoms with Oxygen Molecules in Condensing Argon. Infrared Spectra and Density Functional Calculations of Iron Oxide Product Molecules

Reaction of laser-ablated Fe atoms with oxygen molecules in a condensing argon stream produced FeO, FeO2, FeO3, FeO4, Fe2O, Fe2O2, and Fe2O4 molecules, which are identified from oxygen isotopic shifts and multiplets in matrix infrared spectra. The Fe + O2 reaction gives symmetrical bent, symmetrical cyclic, and asymmetrical bent FeO2 isomeric products with triplet, triplet, and quartet isotopic absorptions, respectively, using statistically mixed 16,18O2 as the reagent. The major reaction product symmetrical bent OFeO iron dioxide molecule (150 ± 10°) is characterized by stretching fundamentals at 945.8 and 797.1 cm-1, and the asymmetric bent FeOO form exhibits a 1204.5 cm-1 absorption. The cyclic isomer Fe(O2) produced spontaneously during annealing in solid argon absorbs at 956.0 cm-1. Oxygen and iron isotopic absorptions show that FeOFe is a symmetrical bent (140 ± 10°) molecule. Rhombic Fe2O2 absorbs at 517.4 cm-1. Evidence is presented for isomers of FeO3, FeO4, and Fe2O4. Density functional theory was used to calculate energies, structures, and frequencies for product molecules to support their identification.

Oxygen isotope effect on the vibrational modes of Bi 2Sr 2CaCu 2O 8+δ

The 16O 18O oxygen isotope effect has been studied in the Raman spectra of single crystals of the high- T c superconductor Bi 2Sr 2CaCu 2O 8+δ. It is found that the oxygen isotope shifts of all of the vibrational peaks fall into one of three narrow ranges. The absence of a significant isotope shift for certain peaks indicates either that they correspond to normal modes that involve only the motion of cations (peaks at and below 181 cm −1), or that they involve the vibration of oxygen on sites where isotope exchange proceeds extremely slowly (peaks at 310 cm −1 and 661 cm −1). The isotope-shift data provide strong evidence that, contrary to previous assignments, the A 1g peaks at 287 cm −1 and 350 cm −1 correspond to vibrational modes of oxygen atoms in the copper layer. Large oxygen isotope shifts support the assignment of the 386 cm −1 peak to in-plane vibrations of oxygen atoms in the strontium layer, and of the 458 cm −1 peak to c-axis vibrations of these same atoms. They are inconsistent with an earlier suggestion that the 458 cm −1 peak corresponds to a vibrational mode of oxygen atoms in the copper layer.

Interstitial O isotope effects in silicon

The oxygen isotope shifts of the vibrational modes of interstitial oxygen in silicon, obtained from isotopically enriched silicon samples, are compared with the predictions of a calculation based on a bond-centred location of the O atom, as is obtained from first principles. This comparison confirms the existence of a Raman-active mode in which the O atom is weakly involved and of a resonance producing a broadening and a small shift of the 17O asymmetric mode.

The relation between widespread 18 O depletion patterns and precious metal mineralization in the Tayoltita Mine, Durango, Mexico

The delta 18 O values of the wall rocks in the vicinity of the Tayoltita mine were shifted to significantly lower values as a result of interaction with geothermal fluids of predominantly meteoric origin. The areas of strongest 18 O depletion (delta 18 O rock < 4%) form a north-northwest-south-southeast trend coinciding with the areas of Au-Ag mineralization in the vein system. At a detailed level, however, there is only minor isotopic evidence for interaction between the vein fluids and the wall rocks. This finding is confirmed by the oxygen isotope compositions of mineral separates from the rocks and quartz and calcite from the veins. Chlorite, epidote, and feldspar in the wall rock have delta 18 O values too high to have formed in equilibrium with the same fluids that formed the vein minerals. Further, except for chlorite close to major vein structures (< or =2 m), the delta 18 O values of neither chlorite nor epidote were significantly shifted by interaction with the later fluids. The delta 18 O values of feldspar do appear to have partially equilibrated with the later fluids. By estimating the delta 18 O values of the evolving fluids from analyses of the other minerals, we have calculated that the degree of oxygen isotope shift of the feldspars is consistent with a period of fluid circulation lasting 10,000 to 100,000 years at a Darcy flow velocity of 10 (super -9) to 10 (super -11) m/s. This indicates that although pervasive fluid flow through the rocks may have occurred during the formation of the veins, it was extremely limited and had little effect on the regional delta 18 O rock patterns. The coincidence of the veins with the areas of strong 18 O depletion of the rocks must, therefore, be an indication that there was a single, long-lived episode of hydrothermal activity that remained focused in the same vicinity throughout the life of the system.

A stable isotopic record of the Maastrichtian ocean-climate system: South Atlantic DSDP site 528

The upper Maastrichtian interval of mid-latitude South Atlantic Deep Sea Drilling Project site 528 spans approximately the last 4 million years of the Cretaceous. The isotopic record of this sequence indicates that relatively large (0.5–1.0%) late Maastrichtian oxygen and carbon isotopic shifts occurred on geologically short time scales (less than 100–500 kyr). Comparison with previous oxygen isotopic data suggests that in high- and mid-latitude southern oceans the multimillion-year Maastrichtian cooling trend largely resulted from geologically rapid climatic ‘steps’. Coincidence of the largest carbon and oxygen isotopic excursions suggests that relatively large and geologically rapid changes in marine and atmospheric carbon content may have directly contributed to the long-term cooling of the Late Cretaceous ‘greenhouse’.

Low frequency vibrational modes of oxygenated myoglobin, hemoglobins, and modified derivatives.

The low frequency resonance Raman spectra of the dioxygen adducts of myoglobin, hemoglobin, its isolated subunits, mesoheme-substituted hemoglobin, and several deuteriated heme derivatives are reported. The observed oxygen isotopic shifts are used to assign the iron-oxygen stretching (approximately 570 cm-1) and the heretofore unobserved delta (Fe-O-O) bending (approximately 420 cm-1) modes. Although the delta (Fe-O-O) is not enhanced in the case of oxymyoglobin, it is observed for all the hemoglobin derivatives, its exact frequency being relatively invariable among the derivatives. The lack of sensitivity to H2O/D2O buffer exchange is consistent with our previous interpretation of H2O/D2O-induced shifts of v(O-O) in the resonance Raman spectra of dioxygen adducts of cobalt-substituted heme proteins; namely, that those shifts are associated with alterations in vibrational coupling of v(O-O) with internal modes of proximal histidyl imidazole rather than to steric or electronic effects of H/D exchange at the active site. No evidence is obtained for enhancement of the v(Fe-N) stretching frequency of the linkage between the heme iron and the imidazole group of the proximal histidine.

Site-selective oxygen isotope effect in optimally doped YBa2Cu3O6 + x

IN CONVENTIONAL superconductors, the large dependence of the superconducting transition temperature (Tc) on the isotope mass (Tc∝m−α, with α≈0.5) gives strong evidence for electron pairing by a phonon-mediated mechanism. The copper oxide superconductors, on the other hand, exhibit a small oxygen isotope effect (α≈0.02; see, for example, refs 1–14), suggesting a mechanism more complex than simple phonon-mediated pairing15. To obtain further insight into this mechanism, it is important to determine the contribution from different oxygen sites in the crystal lattice to the total oxygen isotope effect. Recently, a negative isotope effect associated with oxygen atoms in the copper oxide planes of the crystal structure was reported13 for highly doped YBa2Cu3O6 + x, implying that the apical/chain oxygens make a substantial contribution to the total oxygen isotope shift. Here we investigate this effect in optimally doped YBa2Cu3O6 + x, by measuring separately the contributions to the total isotope shift of the planar and apical/chain oxygen sites. The sum of the site-selective isotope shifts equals that of the total measured shift, illustrating the self-consistency of our results. In contrast to the previous work13, we find that more than 80% of the total (positive) isotope effect is associated with the copper oxide planes.

Stable isotopic and fluid inclusion evidence for meteoric fluid penetration into an active mountain belt; Alpine Schist, New Zealand

ABSTRACTCalcite and quartz veins have formed, and are forming, in steeply dipping fissures in the actively rising Alpine Schist metamorphic belt of New Zealand. The fluids that deposited these minerals were mostly under hydrostatic pressure almost down to the brittle‐ductile transition, which has been raised to 5‐6 km depth by rapid uplift. Some fluids were trapped under lithostatic pressures. Fluids in the fissure veins were immiscible H2O + NaCl‐CO2 mixtures at 200‐350d̀ C. Bulk fluid composition is 15‐20 mol% CO2 and &lt;4.3 total mol CH4+ N2+ Ar/100mol H2O. Water hydrogen isotopic ratio δDH2O in the fissure veins spans ‐29 to ‐68‰, δ18OH2O ‐0.7 to 8.5‰, and bulk carbon isotopic ratio δ13C ranges from ‐3.7 to ‐11.7‰. The oxygen and hydrogen isotopic data suggest that the water has a predominantly meteoric source, and has undergone an oxygen isotope shift as a result of interaction with the host metamorphic rock. Similar fluids were present during cooling and uplift. Dissolved carbon is not wholly derived from residual metamorphic fluids; part may be generated by oxidation of graphite.

Reactions of laser ablated Be atoms with O2: Infrared spectra of beryllium oxides in solid argon

Pulsed-laser ablated beryllium atoms codeposited with O2 in excess argon at 10 K yielded new beryllium–oxygen molecules. The initial reaction to make BeO is endothermic, but activation energy is provided by hyperthermal Be atoms. A strong band at 1572.9 cm−1 and a weak band at 398.9 cm−1 gave oxygen isotopic shifts consistent with a BeO diatomic molecule and are assigned to the O2–BeO complex analogous to the Ar–BeO complex. A sharp band at 1413.2 cm−1 exhibited an oxygen isotopic triplet with 16,18O2 and shifts appropriate for linear OBeO. A nearly coincident band at 1412.4 cm−1 gave an isotopic doublet and shifted in agreement with linear BeOBe. Quantum chemical calculations at the second-order many-body perturbation theory [MBPT(2)] level predict 3Σ ground states and ν3 fundamentals at 1422.5 and 1418.2 cm−1 for OBeO and BeOBe, respectively, in excellent agreement with the observed values. Three bands at 1131.2, 866.3, and 522.4 cm−1 increased together on photolysis, yielded isotopic triplets, and agreed with MBPT(2) calculations for rhombic Be2O2. A sharp photosensitive band at 988.6 cm−1 gave oxygen isotopic shifts consistent with another linear OBeO species and is tentatively assigned to the molecular anion. An intense band at 1465.1 cm−1 that appeared on annealing gave oxygen isotopic shifts in agreement with calculations for linear BeOBeO. Two bands at 1288.9 and 1264.1 cm−1 appeared on photolysis and gave isotopic triplets and shifts that are in excellent agreement with calculations for branched BeBeO2. Annealing produced bands at 871.8 and 436.1 cm−1 that decreased on photolysis and are assigned to BeO3.

Reaction of pulsed laser evaporated magnesium atoms with oxygen. Infrared spectra of linear OMgO and MgOMgO in solid argon

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTReaction of pulsed laser evaporated magnesium atoms with oxygen. Infrared spectra of linear OMgO and MgOMgO in solid argonLester Andrews and Jason T. YusteinCite this: J. Phys. Chem. 1993, 97, 49, 12700–12704Publication Date (Print):December 1, 1993Publication History Published online1 May 2002Published inissue 1 December 1993https://doi.org/10.1021/j100151a012RIGHTS & PERMISSIONSArticle Views100Altmetric-Citations28LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (667 KB) Get e-Alerts

Locus of pairing interaction in YBa2Cu3O7 by site-selective oxygen isotope shift: 18O in CuO2 plane layers.

The oxygen isotope shift of [ital T][sub [ital c]] in YBa[sub 2]Cu[sub 3]O[sub 7] has been measured for samples containing [similar to]95% [sup 18]O in the CuO[sub 2] plane [O2,O3] sites and primarily [sup 16]O in the apical [O4] and chian [O1] sites. The [ital T][sub [ital c]] of the site-selectively substituted samples is [ital higher] than that of the [sup 16]O control samples by 0.10--0.14 K, in contrast to the [ital decrease] in [ital T][sub [ital c]] of 0.20--0.23 K for complete [sup 18]O substitution at all sites. Our results inicate that the phonon-mediated contribution to the pairing mechanism in YBa[sub 2]Cu[sub 3]O[sub 7] involves the apical [O4] sites, and not just the CuO[sub 2] plane [O2,O3] sites.

Paleoceanographic significance of Neogene benthic foraminiferal changes in a southwest Pacific bathyal depth transect

Temporal changes in benthic foraminiferal assemblages were quantitatively examined (> 63 μm fraction) in four southwest Pacific deep-sea Neogene sequences in a depth transect between approximately 1300 and 3200 m to assist in evaluating paleoceanographic history. The most conspicuous changes in benthic foraminiferal assemblages occurred in association with paleoclimatic changes defined at least in part by oxygen isotopic changes. The largest, centered at ∼ 15 Ma (early Middle Miocene), is represented by an increase in the relative frequencies of Epistominella exigua, which underwent a major upward depth migration at that time. This was contemporaneous with the well-known positive oxygen isotopic shift in the early Middle Miocene. In Sites 588 and 590, most of the increase in relative abundances of E. exigua occurred during the middle to later part of the δ 18O shift, following major growth of the east Antarctic ice sheet. Later assemblage changes occurred at 8.5 and 6.5 Ma. These associations indicate that the benthic foraminiferal assemblages in this depth transect largely adjusted to changes in deep waters related to Antarctic cryospheric evolution. In general, the Neogene benthic foraminiferal assemblages in this region underwent little change during the last 23 million years. This faunal conservatism suggests that deep-sea environments underwent relatively little change in the southwest Pacific during much of the Neogene. Although paleoceanographic changes did occur, partly in response to high-latitude cryospheric evolution, these were not of sufficient magnitude to create major deep-sea faunal changes in this part of the ocean. The benthic foraminiferal assemblages are dominated by individuals smaller than 150 μm. Most taxonomic turnover occurred in the larger (> 150 μm) size fractions.

HIGH-TEMPERATURE SUPERCONDUCTIVITY FROM ELECTRON-LATTICE COUPLING

Within the polaron theory of superconductivity for La 2−x Sr x CuO 4 and La 2−x Ba x CuO 4 the coupling is considered between the charge carriers and both the stretching mode of the apical oxygens and the sheet-bending mode of the basal-plane oxygens, the latter via the tilting angle of the Cu-oxygen octahedra. The same tilting angle enters the coupling strengths of these lattice vibrations, leading to renormalized frequencies and their oxygen-isotope shifts. It is suggested that the anomalies occurring in the superconducting critical temperature, its isotope shift and the isotope shifts of the lattice frequencies around x=0.12 are related to the orthorhombic-tetragonal transition of these compounds.

On the oxygen isotope shift in La2?xSrxCuO4

The anomalous oxygen isotope shift observed in the high-temperature superconductors La2−xSrxCuO4 and La2−xBaxCuO4 is discussed within the model of superconductivity in which the apex oxygen vibrations play the major role in the pairing mechanism. We show that the dependence of both the critical temperature and its isotope shifts on the doping level is consistently described within this model. The anomaly occurring in the isotope shift between x = 0.11 andx=0.15 is traced back to the oxygen mass exponent associated with the apex oxygen frequency.

Early Oligocene ice-sheet expansion on Antarctica: Stable isotope and sedimentological evidence from Kerguelen Plateau, southern Indian Ocean

Sedimentological and stable isotope data from a pelagic sequence recovered from the southern Indian Ocean provide the most convincing evidence to date for short-term expansion of a large ice sheet on Antarctica during the earliest Oligocene (∼36 Ma). Terrigenous debris identified as ice-rafted in origin on the basis of textural, compositional, and size criteria is present at the same stratigraphic level as the ubiquitous early Oligocene oxygen isotope shift. The highest benthic foraminiferal δ18O values (>3.0‰) of the Paleogene occur in samples from within the ice-rafted debris interval. These values are similar to those recorded by Holocene benthic foraminifera, implying that the ice sheet may have attained a volume similar to that of the present-day ice sheet on Antarctica. The stratigraphic distribution of ice-rafted debris and high oxygen isotope values indicate that these conditions persisted for roughly 100 ka.

Reactions of boron atoms with molecular oxygen. Infrared spectra of BO, BO2, B2O2, B2O3, and BO−2 in solid argon

Boron atoms from Nd:YAG laser ablation of the solid have been codeposited with Ar/O2 samples on a 11±1 K salt window. The product infrared spectrum was dominated by three strong 11B isotopic bands at 1299.3, 1282.8, and 1274.6 cm−1 with 10B counterparts at 1347.6, 1330.7, and 1322.2 cm−1. Oxygen isotopic substitution (16O18O and 18O2 ) confirms the assignment of these strong bands to ν3 of linear BO2. Renner–Teller coupling is evident in the ν2 bending motion. A sharp medium intensity band at 1854.7 has appropriate isotopic ratios for BO, which exhibits a 1862.1 cm−1 gas phase fundamental. A sharp 1931.0 cm−1 band shows isotopic ratios appropriate for another linear BO2 species; correlation with spectra of BO−2 in alkali halide lattices confirms this assignment. A weak 1898.9 cm−1 band grows on annealing and shows isotopic ratios for a BO stretching mode and isotopic splittings for two equivalent B and O atoms, which confirms assignment to B2O2. A weak 2062 cm−1 band grows markedly on annealing and shows isotope shifts appropriate for a terminal–BO group interacting with another oxygen atom; the 2062 cm−1 band is assigned to B2O3 in agreement with earlier work. A strong 1512.3 cm−1 band appeared on annealing; its proximity to the O2 fundamental at 1552 cm−1 and pure oxygen isotopic shift suggest that this absorption is due to a B atom–O2 complex.

Correlation between oxygen isotope shift and T c in 2- and 3-layer high temperature superconductors

Oxygen isotope shift experiments were performed on several series of high temperature superconductors doped with various ions (isovalent and non-isovalent) at different sites. Substantial oxygen isotope shifts are found even above 70 K, but α 0 does not rise with decreasing T c in all cases. Changes in T c and α 0 can be correlated with the total hole concentration in several systems. Comparing different cuprate superconductors there appears to be an overall monotonic trend to lower values of α 0 with increasing T c and number of copper layers. This trend continues even above 100 K where α 0 becomes negative in Bi-2223. Our results strongly suggest that all oxide high-temperature superconductors are phonon-coupled with near cancellation of α 0 by opposing effects when T c is high.

Negative oxygen isotope shift in Bi-2223 (Bi 1.6Pb 0.4Sr 2Ca 2Cu 3O 10) with T c ≈ 108 K

Oxygen isotope shift experiments were performed on several series of high temperature superconductors doped with various ions (isovalent and non-isovalent) at different sites. Among these was Bi-2223 which contains three CuO 2 sheets and has T c ≈ 108 K. Bi-2223 samples were substituted with 18O to the extent of ≈90%. The oxygen isotope T cs were measured with high precision (resolution 2.5 mK, reproducibility 10 mK). We find Δ T c= -0.14±0.02K. Extrapolating to 100% exchange this yields α o=-0.013. In other high temperature superconducting compounds which we have also studied, substantial oxygen isotope shifts even above 70 K are found, but α o does not rise with decreasing T c in all cases. Changes in T c and α o can be correlated with the total hole concentration in several systems. Comparing different cuprate superconductors there appears to be an overall monotonic trend to lower values of α o with increasing T c and number of copper layers. This trend continues even above 100 K in Bi-2223 where α o becomes negative. Our results strongly suggest that phonon mediated electron pairing plays a vital role in high temperature superconductivity with near cancellation of α o by opposing effects when T c is high.