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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on BaO by Materials Project

BaO is Molybdenum Carbide MAX Phase-like structured and crystallizes in the monoclinic Pm space group. The structure is three-dimensional. there are nine inequivalent Ba2+ sites. In the first Ba2+ site, Ba2+ is bonded to six equivalent O2- atoms to form a mixture of distorted edge and corner-sharing BaO6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 1°. There are a spread of Ba–O bond distances ranging from 2.80–2.82 Å. In the second Ba2+ site, Ba2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ba–O bond distances ranging from 2.68–3.07 Å. In the third Ba2+ site, Ba2+ is bonded to six O2- atoms to form a mixture of edge and corner-sharing BaO6 octahedra. The corner-sharing octahedral tilt angles are 1°. There are a spread of Ba–O bond distances ranging from 2.74–2.85 Å. In the fourth Ba2+ site, Ba2+ is bonded to six O2- atoms to form a mixture of edge and corner-sharing BaO6 octahedra. The corner-sharing octahedra tilt angles range from 1–2°. There are a spread of Ba–O bond distances ranging from 2.75–2.84 Å. In the fifth Ba2+ site, Ba2+ is bonded to six O2- atoms to form edge-sharing BaO6 octahedra. There are a spread of Ba–O bond distances ranging from 2.76–2.82 Å. In the sixth Ba2+ site, Ba2+ is bonded to six O2- atoms to form a mixture of edge and corner-sharing BaO6 octahedra. The corner-sharing octahedral tilt angles are 1°. There are a spread of Ba–O bond distances ranging from 2.74–2.84 Å. In the seventh Ba2+ site, Ba2+ is bonded to six O2- atoms to form a mixture of edge and corner-sharing BaO6 octahedra. The corner-sharing octahedra tilt angles range from 1–2°. There are a spread of Ba–O bond distances ranging from 2.73–2.86 Å. In the eighth Ba2+ site, Ba2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ba–O bond distances ranging from 2.68–3.07 Å. In the ninth Ba2+ site, Ba2+ is bonded to six equivalent O2- atoms to form a mixture of distorted edge and corner-sharing BaO6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 1°. There are a spread of Ba–O bond distances ranging from 2.80–2.82 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded to six Ba2+ atoms to form a mixture of face, edge, and corner-sharing OBa6 octahedra. The corner-sharing octahedra tilt angles range from 0–51°. In the second O2- site, O2- is bonded to six Ba2+ atoms to form a mixture of face, edge, and corner-sharing OBa6 octahedra. The corner-sharing octahedra tilt angles range from 1–51°. In the third O2- site, O2- is bonded to six Ba2+ atoms to form a mixture of edge and corner-sharing OBa6 octahedra. The corner-sharing octahedral tilt angles are 1°. In the fourth O2- site, O2- is bonded to six Ba2+ atoms to form a mixture of face, edge, and corner-sharing OBa6 octahedra. The corner-sharing octahedra tilt angles range from 1–48°. In the fifth O2- site, O2- is bonded to six Ba2+ atoms to form a mixture of face, edge, and corner-sharing OBa6 octahedra. The corner-sharing octahedra tilt angles range from 1–48°. In the sixth O2- site, O2- is bonded to six Ba2+ atoms to form a mixture of face, edge, and corner-sharing OBa6 octahedra. The corner-sharing octahedra tilt angles range from 0–51°. In the seventh O2- site, O2- is bonded to six Ba2+ atoms to form a mixture of edge and corner-sharing OBa6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. In the eighth O2- site, O2- is bonded to six Ba2+ atoms to form a mixture of face, edge, and corner-sharing OBa6 octahedra. The corner-sharing octahedra tilt angles range from 0–51°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on BaO by Materials Project

BaO is Molybdenum Carbide MAX Phase-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Ba2+ is bonded to six equivalent O2- atoms to form a mixture of distorted corner and edge-sharing BaO6 pentagonal pyramids. All Ba–O bond lengths are 2.78 Å. O2- is bonded to six equivalent Ba2+ atoms to form a mixture of corner, edge, and face-sharing OBa6 octahedra. The corner-sharing octahedral tilt angles are 47°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on BaO by Materials Project

BaO is Molybdenum Carbide MAX Phase-like structured and crystallizes in the orthorhombic Pbcm space group. The structure is three-dimensional. there are five inequivalent Ba2+ sites. In the first Ba2+ site, Ba2+ is bonded to six equivalent O2- atoms to form a mixture of distorted edge and corner-sharing BaO6 pentagonal pyramids. The corner-sharing octahedra tilt angles range from 1–2°. There are a spread of Ba–O bond distances ranging from 2.80–2.85 Å. In the second Ba2+ site, Ba2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ba–O bond distances ranging from 2.68–3.08 Å. In the third Ba2+ site, Ba2+ is bonded to six O2- atoms to form a mixture of edge and corner-sharing BaO6 octahedra. The corner-sharing octahedra tilt angles range from 2–3°. There are a spread of Ba–O bond distances ranging from 2.73–2.88 Å. In the fourth Ba2+ site, Ba2+ is bonded to six O2- atoms to form a mixture of edge and corner-sharing BaO6 octahedra. The corner-sharing octahedra tilt angles range from 2–3°. There are a spread of Ba–O bond distances ranging from 2.74–2.88 Å. In the fifth Ba2+ site, Ba2+ is bonded to six equivalent O2- atoms to form edge-sharing BaO6 octahedra. There are four shorter (2.77 Å) and two longer (2.83 Å) Ba–O bond lengths. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded to six Ba2+ atoms to form a mixture of edge, face, and corner-sharing OBa6 octahedra. The corner-sharing octahedra tilt angles range from 0–52°. In the second O2- site, O2- is bonded to six Ba2+ atoms to form a mixture of edge, face, and corner-sharing OBa6 octahedra. The corner-sharing octahedra tilt angles range from 1–52°. In the third O2- site, O2- is bonded to six Ba2+ atoms to form a mixture of edge and corner-sharing OBa6 octahedra. The corner-sharing octahedra tilt angles range from 1–2°. In the fourth O2- site, O2- is bonded to six Ba2+ atoms to form a mixture of edge, face, and corner-sharing OBa6 octahedra. The corner-sharing octahedra tilt angles range from 1–49°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on BaO by Materials Project

BaO is Wurtzite structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. Ba2+ is bonded to four equivalent O2- atoms to form corner-sharing BaO4 tetrahedra. All Ba–O bond lengths are 2.61 Å. O2- is bonded to four equivalent Ba2+ atoms to form corner-sharing OBa4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2024

DESI 2024: reconstructing dark energy using crossing statistics with DESI DR1 BAO data

Here, we implement Crossing Statistics to reconstruct in a model-agnostic manner the expansion history of the universe and properties of dark energy, using DESI Data Release 1 (DR1) BAO data in combination with one of three different supernova compilations (PantheonPlus, Union3, and DES-SN5YR) and Planck CMB observations. Our results hint towards an evolving and emergent dark energy behaviour, with negligible presence of dark energy at z ≳ 1, at varying significance depending on data sets combined. In all these reconstructions, the cosmological constant lies outside the 95% confidence intervals for some redshift ranges. This dark energy behaviour, reconstructed using Crossing Statistics, is in agreement with results from the conventional w 0 –w a dark energy equation of state parametrization reported in the DESI Key cosmology paper. Our results add an extensive class of model-agnostic reconstructions with acceptable fits to the data, including models where cosmic acceleration slows down at low redshifts. We also report constraints on H 0 r d from our model-agnostic analysis, independent of the pre-recombination physics.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Optimal and robust reconstruction of BAO, redshift-space distortions and the Alcock-Paczynski effect

The goal of this project is to optimally reconstruct cosmological information that has been lost from large-scale clustering of galaxies due to cosmic structure growth. The outcome of our research will be used to improve dark energy and other cosmological constraints from the ongoing extended Baryon Oscillation Spectroscopic Survey (eBOSS) and the upcoming Dark Energy Spectroscopic Instrument (DESI). The large-scale galaxy clustering data contain two important features: the Baryon Acoustic Oscillations (BAO) and the overall shape from small to large scales.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Early time solution as an alternative to the late time evolving dark energy with DESI DR2 BAO

Recently the Dark Energy Spectroscopic Instrument (DESI) provided constraints on the expansion history from their Data Release 2 (DR2). The DESI baryon acoustic oscillation (BAO) measurements are well described by a flat $\Lambda$CDM model, but the preferred parameters are in mild ($2.3\sigma$) tension with those determined from the cosmic microwave background (CMB). The DESI collaboration has already explored a variety of solutions to this tension relying on variations in the late-time evolution of dark energy. Here we test an alternative -- the introduction of an ``early dark energy'' (EDE) component. We find that EDE models can alleviate the tension, though they lead to differences in other cosmological parameters that have observational implications. Particularly the EDE models that fit the acoustic datasets prefer lower $\Omega_m$, higher $H_0$, $n_s$ and $\sigma_8$ in contrast to the late-time solutions. We discuss the current status and near-future prospects for distinguishing amongst these solutions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Evaluation of polymorphism and charge transport in a BaO–CaO–Ta 2 O 5 perovskite phase diagram using TOF-neutron and synchrotron X-ray diffraction, the bond-valence method and impedance spectroscopy

In the present work, we develop a comprehensive functional phase diagram for the Ba–Ca–Ta–O quaternary system Ba 3 Ca 1+ x Ta 2− x O 9−3 x /2 (0 ≤ x ≤ 0.36) between 1000 and 1550 °C, coupled with theoretical calculations of the cationic ordering in supercells.

Singh, Kalpana↗
DOE OSTI2025

Extended dark energy analysis using DESI DR2 BAO measurements

We conduct an extended analysis of dark energy constraints, in support of the findings of the Dark Energy Spectroscopic Instrument (DESI) second data release cosmology key paper, including DESI data, Planck cosmic microwave background observations, and three different supernova compilations. Using a broad range of parametric and nonparametric methods, we explore the dark energy phenomenology and find consistent trends across all approaches, in good agreement with the 𝑤 0⁢ 𝑤 𝑎⁢ CDM (cold dark matter) key paper results. Even with the additional flexibility introduced by nonparametric approaches, such as binning and Gaussian processes, we find that extending Λ⁢ CDM to include a two-parameter 𝑤⁡(𝑧) is sufficient to capture the trends present in the data. Finally, we examine three dark energy classes with distinct dynamics, including quintessence scenarios satisfying 𝑤 ≥ −1, to explore what underlying physics can explain such deviations. The current data indicate a clear preference for models that feature a phantom crossing; although alternatives lacking this feature are disfavored, they cannot yet be ruled out. Our analysis confirms that the evidence for dynamical dark energy, particularly at low redshift (𝑧 ≲ 0.3), is robust and stable under different modeling choices.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Constraints on neutrino physics from DESI DR2 BAO and DR1 full shape

The Dark Energy Spectroscopic Instrument (DESI) Collaboration has obtained robust measurements of baryon acoustic oscillations in the redshift range 0.1 < 𝑧 < 4.2, based on the Lyman-𝛼 forest and galaxies from data release 2. We combine these measurements with cosmic microwave background (CMB) data from Planck and the Atacama Cosmology Telescope to place our tightest constraints yet on the sum of neutrino masses. Assuming the cosmological Λ⁢ CDM model and three degenerate neutrino states, we find ∑𝑚 𝜈 < 0.0642 eV (95%) with a marginalized error of 𝜎⁡(∑𝑚 𝜈 ) = 0.020 eV. We also constrain the effective number of neutrino species, finding 𝑁 eff = 3.2⁢3$^{+0.35}_{−0.34}$ (95%), in line with the Standard Model prediction. When accounting for neutrino oscillation constraints, we find a preference for the normal mass ordering and an upper limit on the lightest neutrino mass of 𝑚 𝑙 < 0.023 eV (95%). However, we determine using frequentist and Bayesian methods that our constraints are in tension with the lower limits derived from neutrino oscillations. Correcting for the physical boundary at zero mass, we report a 95% Feldman-Cousins upper limit of ∑𝑚 𝜈 < 0.053 eV, breaching the lower limit from neutrino oscillations. Considering a more general Bayesian analysis with an effective cosmological neutrino mass parameter, ∑𝑚 𝜈,eff , that allows for negative energy densities and removes unsatisfactory prior weight effects, we derive constraints that are in 3⁢𝜎 tension with the same oscillation limit, while the error rises to 𝜎⁡(∑𝑚 𝜈,eff ) = 0.053 eV. In the absence of unknown systematics, this finding could be interpreted as a hint of new physics not necessarily related to neutrinos. The preference of DESI and CMB data for an evolving dark energy model offers one possible solution. In the 𝑤 0 ⁢𝑤 𝑎 ⁢CDM model, we find ∑𝑚 𝜈 < 0.163 eV (95%), relaxing the neutrino tension. These constraints all rely on the effects of neutrinos on the cosmic expansion history. Using full-shape power spectrum measurements of data release 1 galaxies, we place complementary constraints that rely on neutrino free streaming. Our strongest such limit in Λ ⁢CDM, using selected CMB priors, is ∑𝑚 𝜈 < 0.193 eV (95%).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Construction of the damped Ly⁢𝛼 absorber catalog for DESI DR2 Ly⁢𝛼 BAO

We present the Damped Ly⁢𝛼 Toolkit for automated detection and characterization of damped Ly⁢𝛼 absorbers (DLAs) in quasar spectra. Our method uses quasar spectral templates with and without absorption from intervening DLAs to reconstruct observed quasar forest regions. The best-fitting model determines whether a DLA is present while estimating the redshift and HI column density. With an optimized quality cut on detection significance (Δ⁢𝜒$^{2}_{𝑟}$ >0.03), the technique achieves an estimated 80% purity and 79% completeness when evaluated on simulated spectra with S/N>2 that are free of broad absorption lines (BALs). We provide a catalog containing candidate DLAs from the DLA Toolkit detected in DESI DR1 quasar spectra, of which 21 719 were found in S/N>2 spectra with predicted log 10 ⁡(𝑁 𝙷𝙸 )>20.3 and detection significance Δ⁢𝜒$^{2}_{𝑟}$ >0.03. We compare the Damped Ly⁢𝛼 Toolkit to two alternative DLA finders based on a convolutional neural network and Gaussian process models. We present a strategy for combining these three techniques to produce a high-fidelity DLA catalog from DESI DR2 for the Ly⁢𝛼 forest baryon acoustic oscillation measurement. The combined catalog contains 41 152 candidate DLAs with log 10 ⁡(𝑁 𝙷𝙸 )>20.3 from quasar spectra with S/N>2. We estimate this sample to be approximately 85% pure and 79% complete when BAL quasars are excluded.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Early time solution as an alternative to the late time evolving dark energy with DESI DR2 BAO

Recently the Dark Energy Spectroscopic Instrument (DESI) provided constraints on the expansion history from their Data Release 2. The DESI baryon acoustic oscillation measurements are well described by a flat Λ CDM model, but the preferred parameters are in mild ( 2.3 σ ) tension with those determined from the cosmic microwave background. The DESI Collaboration has already explored a variety of solutions to this tension relying on variations in the late-time evolution of dark energy. Here we test an alternative—the introduction of an “early dark energy” (EDE) component. We find that EDE models can alleviate the tension, though they lead to differences in other cosmological parameters that have observational implications. Particularly the EDE models that fit the acoustic datasets prefer lower Ω m , higher H 0 , n s and σ 8 in contrast to the late-time solutions. Finally, we discuss the current status and near-future prospects for distinguishing amongst these solutions.

Baryon acoustic oscillations↗
DOE OSTI2025

Exploiting Synergies Between Lensing and BAO Surveys for Improved Cosmological Constraints

Pinning down the nature of dark energy is one of the most pressing questions in modern physics and is one of the five key science drivers identified in the P5 report [P514]. Dark energy is thought to be either a cosmological constant with an equation of state w = P/ρ = −1 which remains constant at all times, a new type of fluid with an equation of state that varies with time (w ̸= constant), or dark energy might indicate a breakdown of Einstein’s Theory of General Relativity (GR). It is of critical importance to distinguish between these three scenarios. This can only be accomplished by ambitious and demanding measurements of both the expansion rate of the universe (to track the time evolution of dark energy) together with measurements of the rate at which cosmic structures, such as galaxies and clusters of galaxies, grow with time (the “growth rate”). Because of the challenging nature of such observations, and because no single probe simultaneously measures both expansion and growth, the Dark Energy Task Force [A+06] emphasized the importance of using multiple distinct methods to characterize dark energy.

79 ASTRONOMY AND ASTROPHYSICS↗