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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on La(NO3)3 by Materials Project

La(NO3)3 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. there are three inequivalent La3+ sites. In the first La3+ site, La3+ is bonded to twelve O2- atoms to form corner-sharing LaO12 cuboctahedra. There are a spread of La–O bond distances ranging from 2.66–2.72 Å. In the second La3+ site, La3+ is bonded to twelve O2- atoms to form distorted corner-sharing LaO12 cuboctahedra. There are a spread of La–O bond distances ranging from 2.65–2.82 Å. In the third La3+ site, La3+ is bonded in a 11-coordinate geometry to eleven O2- atoms. There are a spread of La–O bond distances ranging from 2.59–2.81 Å. There are six inequivalent N5+ sites. In the first N5+ site, N5+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of N–O bond distances ranging from 1.25–1.30 Å. In the second N5+ site, N5+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of N–O bond distances ranging from 1.24–1.31 Å. In the third N5+ site, N5+ is bonded in a trigonal planar geometry to three O2- atoms. There is two shorter (1.25 Å) and one longer (1.30 Å) N–O bond length. In the fourth N5+ site, N5+ is bonded in a trigonal planar geometry to three O2- atoms. There is two shorter (1.25 Å) and one longer (1.30 Å) N–O bond length. In the fifth N5+ site, N5+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of N–O bond distances ranging from 1.25–1.28 Å. In the sixth N5+ site, N5+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of N–O bond distances ranging from 1.25–1.30 Å. There are eighteen inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted single-bond geometry to one La3+ and one N5+ atom. In the second O2- site, O2- is bonded in a distorted single-bond geometry to two La3+ and one N5+ atom. In the third O2- site, O2- is bonded in a distorted single-bond geometry to two La3+ and one N5+ atom. In the fourth O2- site, O2- is bonded in a distorted single-bond geometry to one La3+ and one N5+ atom. In the fifth O2- site, O2- is bonded in a distorted single-bond geometry to one La3+ and one N5+ atom. In the sixth O2- site, O2- is bonded in a distorted single-bond geometry to two La3+ and one N5+ atom. In the seventh O2- site, O2- is bonded in a distorted single-bond geometry to one La3+ and one N5+ atom. In the eighth O2- site, O2- is bonded in a distorted single-bond geometry to one La3+ and one N5+ atom. In the ninth O2- site, O2- is bonded in a distorted single-bond geometry to one La3+ and one N5+ atom. In the tenth O2- site, O2- is bonded in a distorted single-bond geometry to two La3+ and one N5+ atom. In the eleventh O2- site, O2- is bonded in a distorted single-bond geometry to one La3+ and one N5+ atom. In the twelfth O2- site, O2- is bonded in a distorted single-bond geometry to one La3+ and one N5+ atom. In the thirteenth O2- site, O2- is bonded in a distorted single-bond geometry to one La3+ and one N5+ atom. In the fourteenth O2- site, O2- is bonded in a distorted single-bond geometry to two La3+ and one N5+ atom. In the fifteenth O2- site, O2- is bonded in a distorted single-bond geometry to one La3+ and one N5+ atom. In the sixteenth O2- site, O2- is bonded in a distorted single-bond geometry to one La3+ and one N5+ atom. In the seventeenth O2- site, O2- is bonded in a distorted single-bond geometry to one La3+ and one N5+ atom. In the eighteenth O2- site, O2- is bonded in a distorted single-bond geometry to one La3+ and one N5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on La(MgSi)2 by Materials Project

La(MgSi)2 crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. Mg is bonded in a distorted square co-planar geometry to four equivalent Si atoms. All Mg–Si bond lengths are 2.78 Å. La is bonded to eight equivalent Si atoms to form a mixture of distorted face and edge-sharing LaSi8 hexagonal bipyramids. All La–Si bond lengths are 3.26 Å. Si is bonded in a 9-coordinate geometry to four equivalent Mg, four equivalent La, and one Si atom. The Si–Si bond length is 2.31 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on La(Al10V)2 by Materials Project

LaV2Al20 crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. La is bonded in a 4-coordinate geometry to sixteen Al atoms. There are four shorter (3.16 Å) and twelve longer (3.25 Å) La–Al bond lengths. V is bonded to twelve Al atoms to form VAl12 cuboctahedra that share corners with six equivalent VAl12 cuboctahedra, edges with eighteen equivalent AlLaAl10V cuboctahedra, and faces with six equivalent AlLaAl10V cuboctahedra. There are six shorter (2.59 Å) and six longer (2.81 Å) V–Al bond lengths. There are three inequivalent Al sites. In the first Al site, Al is bonded in a 12-coordinate geometry to two equivalent V and ten Al atoms. There are a spread of Al–Al bond distances ranging from 2.73–2.86 Å. In the second Al site, Al is bonded in a linear geometry to two equivalent La and twelve equivalent Al atoms. All Al–Al bond lengths are 3.13 Å. In the third Al site, Al is bonded to one La, one V, and ten Al atoms to form distorted AlLaAl10V cuboctahedra that share corners with fifteen equivalent AlLaAl10V cuboctahedra, edges with two equivalent AlLaAl10V cuboctahedra, edges with three equivalent VAl12 cuboctahedra, a faceface with one VAl12 cuboctahedra, and faces with fifteen equivalent AlLaAl10V cuboctahedra. There are a spread of Al–Al bond distances ranging from 2.73–2.92 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on La(Cd10Ni)2 by Materials Project

LaNi2Cd20 crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. La is bonded in a 4-coordinate geometry to sixteen Cd atoms. There are four shorter (3.43 Å) and twelve longer (3.48 Å) La–Cd bond lengths. Ni is bonded to twelve Cd atoms to form NiCd12 cuboctahedra that share corners with six equivalent NiCd12 cuboctahedra, edges with eighteen equivalent CdLaCd10Ni cuboctahedra, and faces with six equivalent CdLaCd10Ni cuboctahedra. There are six shorter (2.81 Å) and six longer (3.08 Å) Ni–Cd bond lengths. There are three inequivalent Cd sites. In the first Cd site, Cd is bonded in a 2-coordinate geometry to two equivalent Ni and ten Cd atoms. There are a spread of Cd–Cd bond distances ranging from 2.98–3.12 Å. In the second Cd site, Cd is bonded to one La, one Ni, and ten Cd atoms to form distorted CdLaCd10Ni cuboctahedra that share corners with fifteen equivalent CdLaCd10Ni cuboctahedra, edges with two equivalent CdLaCd10Ni cuboctahedra, edges with three equivalent NiCd12 cuboctahedra, a faceface with one NiCd12 cuboctahedra, and faces with fifteen equivalent CdLaCd10Ni cuboctahedra. There are a spread of Cd–Cd bond distances ranging from 2.93–3.37 Å. In the third Cd site, Cd is bonded in a distorted linear geometry to two equivalent La and twelve equivalent Cd atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on La(TiAl10)2 by Materials Project

Ti2Al20La crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. La is bonded in a 4-coordinate geometry to sixteen Al atoms. There are four shorter (3.20 Å) and twelve longer (3.27 Å) La–Al bond lengths. Ti is bonded to twelve Al atoms to form corner-sharing TiAl12 cuboctahedra. There are six shorter (2.62 Å) and six longer (2.85 Å) Ti–Al bond lengths. There are three inequivalent Al sites. In the first Al site, Al is bonded in a 12-coordinate geometry to one La, one Ti, and eight Al atoms. There are a spread of Al–Al bond distances ranging from 2.76–2.97 Å. In the second Al site, Al is bonded in a 12-coordinate geometry to two equivalent Ti and ten Al atoms. All Al–Al bond lengths are 2.87 Å. In the third Al site, Al is bonded in a linear geometry to two equivalent La atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on La(SeO3)2 by Materials Project

La(SeO3)2 crystallizes in the orthorhombic Pca2_1 space group. The structure is two-dimensional and consists of two La(SeO3)2 sheets oriented in the (0, 0, 1) direction. there are two inequivalent La2+ sites. In the first La2+ site, La2+ is bonded in a 10-coordinate geometry to ten O2- atoms. There are a spread of La–O bond distances ranging from 2.51–2.80 Å. In the second La2+ site, La2+ is bonded in a 10-coordinate geometry to ten O2- atoms. There are a spread of La–O bond distances ranging from 2.48–2.85 Å. There are four inequivalent Se5+ sites. In the first Se5+ site, Se5+ is bonded in a trigonal non-coplanar geometry to three O2- atoms. There are a spread of Se–O bond distances ranging from 1.71–1.78 Å. In the second Se5+ site, Se5+ is bonded in a trigonal non-coplanar geometry to three O2- atoms. There are a spread of Se–O bond distances ranging from 1.71–1.77 Å. In the third Se5+ site, Se5+ is bonded in a trigonal non-coplanar geometry to three O2- atoms. There are a spread of Se–O bond distances ranging from 1.67–1.73 Å. In the fourth Se5+ site, Se5+ is bonded in a trigonal non-coplanar geometry to three O2- atoms. There are a spread of Se–O bond distances ranging from 1.68–1.74 Å. There are twelve inequivalent O2- sites. In the first O2- site, O2- is bonded in a 1-coordinate geometry to three La2+ and one Se5+ atom. In the second O2- site, O2- is bonded in a distorted water-like geometry to one La2+ and one Se5+ atom. In the third O2- site, O2- is bonded in a 1-coordinate geometry to two La2+ and one Se5+ atom. In the fourth O2- site, O2- is bonded in a single-bond geometry to one Se5+ atom. In the fifth O2- site, O2- is bonded in a 1-coordinate geometry to three La2+ and one Se5+ atom. In the sixth O2- site, O2- is bonded in a 3-coordinate geometry to two La2+ and one Se5+ atom. In the seventh O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent La2+ and one Se5+ atom. In the eighth O2- site, O2- is bonded in a distorted water-like geometry to one La2+ and one Se5+ atom. In the ninth O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent La2+ and one Se5+ atom. In the tenth O2- site, O2- is bonded in a 3-coordinate geometry to two La2+ and one Se5+ atom. In the eleventh O2- site, O2- is bonded in a single-bond geometry to one Se5+ atom. In the twelfth O2- site, O2- is bonded in a 1-coordinate geometry to two La2+ and one Se5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Perovskite evolution on La modified Mn 1.5 Co 1.5 O 4 spinel through thermal ageing with enhanced oxidation activity: Is sintering always an issue?

Non-precious metal oxides have great potential in catalytic deep oxidation of emitted hydrocarbons to help address various environmental pollution concerns. However, sintering issue is a stumbling block in practical application upon long-term high-temperature operation or thermal shock experience. Herein, La was applied to modify Mn 1.5 Co 1.5 O 4 spinel to get a highly active oxidation catalyst with exceptional stability against high-temperature thermal ageing treatment. With thermal ageing at 750 °C for 100 h, the La modified Mn–Co composite reached 90 % conversion in toluene oxidation at 265 °C under the high WHSV of 120,000 mL g -1 h -1 , while this value increased to 312 °C over blank Mn–Co spinel. The addition of La not only inhibited the growth of spinel nanocrystals, but also brought about perovskite formation through sintering, generating perovskite-spinel interfaces, thus enhancing both activity and stability. Meanwhile, the La modified Mn–Co spinel exhibited superior performance in presence of water or sulfur dioxide after thermal ageing treatment. In conclusion, this work offers a versatile strategy to design anti-sintering and active oxidation nanocatalysts based on non-precious metal oxides for industrial applications.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Broad-range tuning of ferroelectric switching of La x Bi 1−x FeO 3 epitaxial films via digital doping using off-axis co-sputtering

To investigate the scope of ferroelectric behavior in La-substituted BiFeO 3 films, La x Bi 1−x FeO 3 epitaxial films were synthesized using off-axis co-sputtering on SrTiO 3 (001) and DyScO 3 (110) substrates with a SrRuO 3 bottom electrode layer. A digital-doping deposition method was used to enable precise control and continuous tuning of La concentration in high-quality LaxBi 1−x FeO 3 films across a wide range of x = 0.05–0.60, which was systematically investigated using piezoresponse force microscopy. Robust and reversible out-of-plane ferroelectric switching has been observed up to x = 0.35, while films with x ≥ 0.37 exhibit no measurable ferroelectric behavior, indicating a sharp ferroelectric-to-paraelectric phase transition between x = 0.35 and 0.37. This represents the highest reported La concentration in LaxBi 1−x FeO 3 films that retains ferroelectric ordering, highlighting opportunities to engineer ferroelectric and multiferroic properties in complex oxide heterostructures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Stabilization of Catalytically Active Surface Defects on Ga-doped La–Sr–Mn Perovskites for Improved Solar Thermochemical Generation of Hydrogen

Solar thermochemical hydrogen (STCH) production from water splitting typically requires performing redox cycles at temperatures above 1200 °C to reduce and re-oxidize the bulk of a reversible material. Bulk processes such as oxygen vacancy formation and oxygen diffusion energies dictate the viability of a material for STCH. The surface plays an important role in the formation and destruction of vacancies and interacts with gas phase water and surface adsorbed species. These surface processes can lead to surface reconfigurations and even the formation of surface phases with stoichiometry and oxygen content very different from the bulk composition. Understanding in-situ the surface chemical state and its evolution under water splitting is important to design nonstoichiometric oxides capable of longer-lasting STCH generation at lower temperatures. In this work, we describe the water splitting active defect sites in LSM ((La 0.65 Sr 0.35 ) 0.95 MnO 3–δ ) and Ga-doped LSM ((La 0.6 Sr 0.4 ) 0.95 (Mn 0.8 Ga 0.2 )O 3–δ ) perovskites during Operando thermochemical water splitting conditions using ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) experiments at 800 °C under steam. We show that sub-stoichiometric La +3 in the oxygen-vacancy rich surface at operating conditions can be used to correlate surface water splitting activity and the creation of surface hydroxide intermediates. The addition of Ga in LSM is shown to drastically stabilize the surface chemical composition by preventing Sr segregation and stabilizing catalytically active surface defects that promote the binding of adsorbed hydroxides. Here, we use Operando AP-XPS quantification of metastable surface hydroxide intermediates (La(OH) 3 ) to determine the amount of catalytically active surface sites in LSM (2.9%) and in LSMG (7.8–8.1%, depending on the bulk oxidation state).

08 HYDROGEN↗
DOE OSTI2023

Evidence of redox cycling as a sub-mechanism in hydrogen production during ethanol steam reforming over La 0.7 Sr 0.3 MnO 3-x perovskite oxide catalysts

Ethanol steam reforming (ESR) is of societal interest. Here, in this work, experiments were conducted to ascertain if some of the H 2 is produced by a redox cycle involving H 2 O filling oxygen vacancies over reducible oxide catalysts. Redox cycling experiments were performed over La 0.7 Sr 0.3 MnO 3-x (100) in ultra-high vacuum. It was found that H 2 was produced from redox cycling with alternating ethanol and water exposures over La 0.7 Sr 0.3 MnO 3-x (100), with both half-cycles occurring at temperatures ≤800 K. In the first half-cycle, ethanol ‘directly’ reduced the surface to create oxygen vacancies (not by a CO intermediate), and in the second half-cycle water filled oxygen vacancies to make H 2 . The H 2 production during the water exposure has a half-cycle turnover frequency of >3.2 × 10 -2 molecules site -1 s -1 in the temperature range of 700–800 K, which is fast enough to be part of the ESR full catalytic cycle. Flowing both reactant gases together, ethanol and water, over La 0.7 Sr 0.3 MnO 3-x (100) and La 0.7 Sr 0.3 MnO 3-x powders significantly increases hydrogen production compared to pure ethanol. The results suggest that steady state ESR includes a sub-mechanism of ethanol ‘directly’ reducing the surface to create oxygen vacancy, and water filling oxygen vacancy to make some of the H 2 by a Mars van Krevelen type mechanism.

08 HYDROGEN↗
DOE OSTI2022

Energetics of hydroxylbastnäsite solid solutions, La 1-$\chi$ Nd $\chi$ CO 3 OH

Bastnäsites (LnCO 3 (F,OH)) are a group of common rare earth elements (REE)-bearing minerals and are one of the primary global sources of REE. Due to the chemical similarities among REE, bastnӓsites tend to occur as solid solutions instead of end members in REE containing ores. To better understand the processes and the mechanisms of formation of such deposits, it is essential to determine the thermodynamic properties of bastnӓsites, including hydroxylbastnӓsite (LnCO 3 OH) solid solutions. In this work, we performed detailed structural and calorimetric investigations on synthetic hexagonal La–Nd hydroxylbastnӓsite (La 1-$\chi$ NdCO 3 OH, $\chi$ = 0, 0.25, 0.5, 0.75, 1) solid solutions. X-ray diffraction confirms the crystal structure of the solid solution series in the $\ P$6 space group, and pair distribution function (PDF) analysis reveals local bonding environments characterized by three different types of 9-coordinated metal-oxygen polyhedra. Unit cell parameters of La1–xNdxCO3OH exhibit a nearly linear relation with the Nd content x, suggesting a random distribution of La and Nd in the structure. Their standard enthalpies of formation (Δ$\ H$° f ) were determined by high temperature oxide melt drop solution calorimetry, from which the enthalpies of mixing (Δ$\ H$ mix ) were derived. The Δ$\ H$ mix can be fitted by a regular solution model with an interaction parameter of 12.58 ± 0.16 kJ/mol, suggesting enthalpic metastability of La1–xNdxCO3OH relative to the two endmembers. Combining entropy and enthalpy, we further estimated the Gibbs free energies of mixing (Δ$\ G$ mix ) at relevant temperatures, revealing favorable temperatures under which the intermediate La 1-$\chi$ NdCO 3 OH phases can be stabilized. Such entropy-driven stabilization, as is consistent with our geochemical modeling results, may explain the enhancement of thermal stability of the solid solutions in nature. Additionally, the temperature range constrained from this study may be used to estimate the thermal history of REE bastnӓsite deposit.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

An experimental study of synthetic Hydroxybastnäsite-(La) solubility and speciation in carbonate bearing aqueous solutions at 175–250 °C

The transport and enrichment of rare earth element (REE) ore bodies are dependent on the stability of aqueous metal ligand complexes and the solubility of REE bearing minerals. REE ores are commonly associated with igneous systems having aqueous fluids with high carbonate concentrations and REE solubilities have been shown to be dependent on temperature and associate anion aqueous ligands present in solution. Furthermore, this work presents solubility experiments of hydroxybastnäsite-(La) at elevated temperatures in aqueous solutions of varying carbonate concentrations. At lower temperatures, hydroxybastnäsite-(La) solubility is controlled by neutral mono-carbonate LaCO 3 OH° but at higher temperatures and activities of carbonate species, charged di-carbonate La(CO 3 ) 2 - increases and predominates. This divergence, and the difference in solubility products of other hydroxybastnäsite-(REE) phases, provides a potential mechanism for REE fractionation in carbonate dominated aqueous solutions. To illustrate one such mechanism the solubility data of hydroxybastnäsite-(La) is compared with previously reported data of hydroxybastnäsite-(Nd) at elevated temperatures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Structure, Magnetism, and First-Principles Modeling of the Na 0.5 La 0.5 RuO 3 Perovskite

High-purity polycrystalline Na 0.5 La 0.5 RuO 3 was synthesized by a solid-state method, and its properties were studied by magnetic susceptibility, heat capacity, and resistivity measurements. In this study, we find it to be an orthorhombic perovskite, in contrast to an earlier report, with random La/Na mixing. With a Curie–Weiss temperature of –231 K and an effective moment of 2.74 μB/mol Ru, there is no magnetic ordering down to 1.8 K. A broad hump at 1.4 K in the heat capacity, however, indicates the presence of a glassy magnetic transition, which we attribute to the influence of the random distribution of Na and La on the perovskite A-sites. Comparison to CaRuO 3 , a structurally ordered ruthenate perovskite with a similar A-site ionic radius and magnetic properties, is presented. First-principles calculations indicate that the Na–La distribution determines the local magnetic exchange interactions between Ru ions, favoring either antiferromagnetic or ferromagnetic coupling when the local environment is Na- or La-rich. Thus, our data and analysis suggest that mixing cations with different charges and sizes on the A-site in this perovskite results in magnetic frustration through a balance of local magnetic exchange interactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Effects of Site and Magnetic Disorder on the Oxygen Vacancy Formation and Electronic and Optical Properties of La x Sr 1– x CoO 3–δ and SrFe y Co 1– y O 3–δ [plus supplemental information]

Disorder is an inevitable issue in practical applications of perovskites with the A-site occupied by La/Sr and the B-site occupied by Co/Fe. We performed density functional theory calculations to reveal the site and magnetic disorder effect on the oxygen vacancy formation and the electronic and optical properties of La x Sr 1–x CoO 3–δ and SrFe y Co 1–y O 3–δ systems. Generally, site disorder has little influence on the physical properties we studied, while magnetic disorder has a property-dependent effect for La A-site and Fe B-site doping of SrCoO 3 . Compared to ordered ferromagnetic (FM) calculations, disordered paramagnetic (PM) results can better describe the high-temperature behavior of lattice expansion and the multiple spin states of Co ions in La x Sr 1–x CoO 3 . The oxygen vacancy formation energy results show that the magnetic disorder has a more remarkable effect on SrFe y Co 1–y O 3–δ systems with a robust magnetic order than that on the La x Sr 1–x CoO 3–δ systems with a fragile magnetic order. The electronic structures in the PM phase have less spin polarization and broadened bands, by which the optical absorptions from the single spin channel transition in the FM phase have an obvious change in the magnitude and/or the trend. Furthermore, our work provides guidance for where and why to consider the disorder.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

La-Based Perovskite Oxide Catalysts for Alkaline Oxygen Reduction: The Importance of Electrochemical Stability

Alkaline fuel cells represent a promising energy conversion technology since they enable the use of precious metal-free electrocatalysts for the oxygen reduction reaction. Among these, La-based perovskite oxides, with great compositional and structural tunability, are especially attractive. However, we believe that the current literature lacks a thorough understanding of their inherent (in)stability issues. Here, in this study, we report on nine La-based perovskite oxide electrocatalysts for the oxygen reduction reaction, including LaMO 3 (M = Mn, Co, Ni) and LaCo x M 1–x O 3 (M = Mn, Ni; x = 0.9, 0.5, 0.1). While some exhibited initial promising activity, they all degraded significantly, even after brief electrochemical testing. Through comprehensive structural characterization of LaCo 0.9 Mn 0.1 O 3 , particularly scanning transmission electron microscopy, we found evidence to support a degradation mechanism in which the B-site cation species irreversibly leach from the perovskite under testing conditions. A sample cycled 10 000 times from +0.4 to +1.2 V vs reversible hydrogen electrode (RHE) showed an amorphous La oxide shell 1–2 nm thick. Bulk analyses showed that B-site leaching also occurs for samples soaked in 1 M KOH or pure EtOH. The mechanistic insights provided here should help inform the future design of La-based perovskite oxide electrocatalysts for alkaline fuel cells and stress the importance of stability metrics validating claims of promising electrocatalytic activity.

Seok, Jeesoo↗
DOE OSTI2024

Reverse Polarizability of Rare Earth Ions (La 3+ , Gd 3+ , Lu 3+ , Y 3+ ) in Tellurite Glasses and Glass Ceramics for Optical Limiting

All-optical modulation using inherent third-order optical nonlinearity of a medium has garnered considerable interest in photonics and optoelectronics. Herein, nonlinear optical (NLO) properties of tellurite glasses and glass ceramics (GCs) containing four different rare earths (RE = La, Gd, Lu, and Y) have been deliberated in near-infrared regions under an ultrafast regime. The La-based glass exhibits ~10 times higher nonlinear refraction (n 2 ) and absorption (α 2 ) than reported NLO materials. The NLO susceptibility [χ (3) ] trend in the studied glasses is La > Gd > Lu > Y, matching with RE 3+ polarizability. Furthermore, Ln 2 Te 6 O 15 nanocrystallite-embedded transparent GCs exhibit a larger NLO coefficient due to the enhanced local field from oxygen vacancies in crystallites. Interestingly, the trend of χ (3) in GCs follows the sequence of Y > Lu > Gd > La, precisely opposite to the glasses. This observation challenges the general polarizability approach of RE 3+ ions, emphasizing that quadratic hyperpolarizability of RE 3+ is pivotal for NLO properties of GCs. Among the studied matrices, Y-containing GCs showed the lowest optical limiting (OL) threshold (5.4 mJ/cm 2 at 800 nm), much lower than those of the reported NLO materials, suggesting its potential as a femtosecond NIR-laser safety material. A combination of large α 2 and n 2 from the studied matrices indicates their advantage for harmonic generation, potentially aiding in the design of ultrafast signal processing devices.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Unlikelihood of a phonon mechanism for the high-temperature superconductivity in La 3 Ni 2 O 7

The discovery of ~80 K superconductivity in nickelate La 3 Ni 2 O 7 under pressure has ignited intense interest. Here, we present a comprehensive first-principles study of the electron-phonon (e-ph) coupling in La 3 Ni 2 O 7 and its implications on the observed superconductivity. Our results conclude that the e-ph coupling is too weak (with a coupling constant λ ≲ 0.5) to account for the high T c , albeit interesting many-electron correlation effects exist. While Coulomb interactions (via GW self-energy and Hubbard U) enhance the e-ph coupling strength, electron doping (oxygen vacancies) introduces no major changes. Additionally, different structural phases display varying characteristics near the Fermi level, but do not alter the conclusion. The e-ph coupling landscape of La 3 Ni 2 O 7 is intrinsically different from that of infinite-layer nickelates. These findings suggest that a phonon-mediated mechanism is unlikely to be responsible for the observed superconductivity in La 3 Ni 2 O 7 , pointing instead to an unconventional nature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Bulk high-temperature superconductivity in pressurized tetragonal La 2 PrNi 2 O 7

The Ruddlesden–Popper (R–P) bilayer nickelate, La 3 Ni 2 O 7 , was recently found to show signatures of high-temperature superconductivity (HTSC) at pressures above 14 GPa . Subsequent investigations achieved zero resistance in single-crystalline and polycrystalline samples under hydrostatic pressure conditions. Yet, obviousdiamagnetic signals, the other hallmark of superconductors, are still lacking owing to the flamentary nature with low superconducting volume fraction. The presence of a new 1313 polymorph and competing R–P phases obscured proper identification of the phase for HTSC. Thus, achieving bulk HTSC and identifying the phase at play are the most prominent tasks. Here we address these issues in the praseodymium (Pr)-doped La 2 PrNi 2 O 7 polycrystalline samples. We find that substitutions of Pr for La efectively inhibit the intergrowth of diferent R–P phases, resulting in a nearly pure bilayer structure. For La 2 PrNi 2 O 7 , pressure-induced orthorhombic to tetragonalstructural transition takes place at P c ≈ 11 GPa, above which HTSC emerges gradually on further compression. The superconducting transition temperatures at 18–20 GPa reach $T$ $^{onset}_{c}$ = $82.5$ $K$ and $T$ $^{zero}_{c}$ = $60$ $K$, which are the highest values, to our knowledge, among known nickelate superconductors. Importantly, bulk HTSC was testified by detecting clear diamagnetic signals below about 75 K with appreciable superconducting shielding volume fractions at a pressure of above 15 GPa. Further, our results not only resolve the existing controversies but also provide directions for exploring bulk HTSC in the bilayer nickelates.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗