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At least 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Evidence of multiscale supercurrents in K-doped BaFe 2 As 2

K-doped BaAs 2 Fe 2 (K-Ba122) superconductor is a promising material for applications. However, it has been found challenging to achieve high critical current density (J c ) in untextured bulk sample. In this paper we investigated bulk samples prepared by varying the milling energy density, which affects the grain and grain boundary microstructures, and we investigated their magnetic performance to better understand what causes their different J c . We found that in our samples, which all have small grain size, T c does not appear directly correlated to J c . Moreover, AC susceptibility reveals in at least one case obvious signs of multiscale supercurrents, not caused by granularity but that directly influence the overall J c performance. Considering the microstructural features and the magnetization response we ascribed the J c differences to lack of connectivity on a larger scale due to nano-cracks at some grain boundaries, which subdivided the samples into macroscopic regions and inevitably limited the overall performance. We discuss possible routes to overcome those extrinsic current-blocking defects.

AC susceptibility↗
DOE OSTI2024

Atomic-Scale Characterization of Dilute Dopants in Topological Insulators via STEM–EDS Using Registration and Cell Averaging Techniques

Magnetic dopants in three-dimensional topological insulators (TIs) offer a promising avenue for realizing the quantum anomalous Hall effect (QAHE) without the necessity for an external magnetic field. Understanding the relationship between site occupancy of magnetic dopant elements and their effect on macroscopic property is crucial for controlling the QAHE. By combining atomic-scale energy-dispersive X-ray spectroscopy (EDS) maps obtained by aberration-corrected scanning transmission electron microscopy (AC-STEM) and novel data processing methodologies, including semi-automatic lattice averaging and frame registration, we have determined the substitutional sites of Mn atoms within the 1.2% Mn-doped Sb 2 Te 3 crystal. More importantly, the methodology developed in this study extends beyond Mn-doped Sb 2 Te 3 to other quantum materials, traditional semiconductors, and even electron irradiation sensitive materials.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Low-temperature domain-wall freezing and nonequilibrium dynamics in the transverse-field Ising model material CoNb 2 O 6

CoNb 2 O 6 is a rare realization of the transverse-field Ising model, making it a useful tool for studying both equilibrium and nonequilibrium many-body quantum physics. Despite a large body of work dedicated to characterizing this material, details of the ordered states in the presence of relatively weak transverse fields have not been discussed in detail. Here, we present a detailed study of CoNb 2 O 6 via ac susceptibility measurements in order to further characterize its low-temperature behavior in the presence of a transverse field. Specifically, we call attention to an unconventional freezing transition in zero field below T F = 1.2 K, occurring within the well-known commensurate antiferromagnetic (CAFM) state that onsets at T N2 = 1.9 K. We performed a series of transverse-field quenches into this frozen state, which resulted in a slowly relaxing susceptibility, χ' (t), that followed a logarithmic decay within the time range measured. Additionally, we discuss the frozen state in the context of the freezing of previously discussed “free” chains arising from domain walls between the four degenerate sublattices of the CAFM state. We also attempted to observe Kibble-Zurek scaling by quenching the transverse field into the frozen state at different rates. This produced a null result; the behavior can be fully explained by coarsening of domains over the time scale of the quenches. The absence of a clear Kibble-Zurek scaling is itself surprising, given the proposed ubiquity of the phenomenon for general second-order phase transitions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Unusual coercivity and zero-field stabilization of fully saturated magnetization in single crystals of LaCrGe 3

LaCrGe 3 is an itinerant, metallic ferromagnet with a Curie temperature (T C ) of ~86 K. Whereas LaCrGe 3 has been studied extensively as a function of pressure as an example of avoided ferromagnetic quantum criticality, questions about its ambient pressure-ordered state remain: specifically, whether there is a change in the nature of the ferromagnetically ordered state below T C ~86 K. We present anisotropic M(H) isotherms, coupled with anisotropic AC susceptibility data, and demonstrate that LaCrGe 3 has a remarkable, low temperature coercivity associated with exceptionally sharp, complete magnetization reversals to and from fully polarized states. This coercivity is temperature dependent; it drops to zero in the 40–55 K region and reappears in the 70–85 K regions. Furthermore, at low temperatures LaCrGe 3 has magnetization loops and behavior that has been previously associated with micromagnetic/nanocrystalline materials, not bulk macroscopic samples.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Memory and rejuvenation in glassy systems

Here, the memory effect in a single crystal spin glass (Cu 0.92 Mn 0.08 ) has been measured using 1 Hz ac susceptibility measurements over a reduced temperature range of 0.4 - 0.7 T g and a model of the memory effect has been developed. A double-waiting-time protocol is carried out where the spin glass is first allowed to age at a temperature below T g , T w$_{1}$ , followed by a second aging 4 K lower, T w$_{2}$ . The 4 K separation is sufficient to ensure rejuvenation has occurred. The model is based on calculating overlaps between the growth of the correlation lengths at the two temperatures. It accounts for the absolute magnitude of the memory effect as a function of both waiting times and temperatures. The data can be explained by the memory loss being a function of the relative change in the correlated volume at the first waiting temperature due to growth in the correlations at the second waiting temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Anomalous Hall effect in the polar magnet Gd 3 ⁢Ni 8 ⁢Sn 4 : A candidate for hosting skyrmions

While recent theoretical studies have positioned noncollinear polar magnets with C nv symmetry as compelling candidates for realizing topological magnetic phases and substantial intrinsic anomalous Hall conductivity, experimental realizations of the same in strongly correlated systems remain rare. Here, we present a large intrinsic anomalous Hall effect and extended topological magnetic ordering in Gd 3 ⁢Ni 8 ⁢Sn 4 with hexagonal C 6v symmetry. Observation of topological Hall response, corroborated by metamagnetic anomalies in isothermal magnetization, peak/hump features in field-evolution of ac susceptibility and longitudinal resistivity suggest the signature of topological magnetic phases. The anomalous Hall effect is quantitatively accounted for by the intrinsic Berry curvature-mediated mechanism. Finally, our results underscore polar magnets as a promising platform to investigate a plethora of emergent electrodynamic responses rooted in the interplay between magnetism and topology.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Optimized AC/DC Dual Active Bridge Converter using Monolithic SiC Bidirectional FET (BiDFET) for Solar PV Applications

Grid interface power conversion systems for commercial, industrial and residential solar power generation are becoming ubiquitous due to the competitive cost of solar energy. The AC/DC dual active bridge (DAB) converter is an upcoming topology in industrial PV energy and energy storage applications, providing bidirectional power transfer and galvanic isolation. In this paper, the properties of a DAB-type converter are leveraged to propose a design optimization process. It can optimize the high-frequency RMS current, size of magnetic elements and zero-voltage-switching (ZVS) region of the converter. The resulting design is compared against that derived from a conventional approach. In addition, an algorithm to compute the harmonic currents at the DC and line frequency AC ports of the system is proposed, and the respective filter designs are presented. The optimized design of the AC/DC DAB converter is implemented using the newly developed, 1200 V, 46 mΩ, four quadrant, SiC-based monolithic bidirectional FETs (BiDFET). Experimental results from the 2.3 kW, 400V/277VRMS hardware prototype are finally presented to verify the design process.

Bidirectional isolated AC-DC conversion, solar ene↗
DOE OSTI2021

A Cyber Threat Mitigation Approach For Wide Area Control of SVCs using Stability Monitoring

We propose a stability monitoring approach for the mitigation of cyber threats directed at the wide area control (WAC) system used for coordinated control of Flexible AC Transmission Systems (FACTS) used for power oscillation damping (POD) of active power flow on inter-area tie lines. The approach involves monitoring the modes of the active power oscillation on an inter-area tie line using the Matrix Pencil (MP) method. We use the stability characteristics of the observed modes as a proxy for the presence of destabilizing cyber threats. We monitor the system modes to determine whether any destabilizing modes appear after the WAC system engages to control the POD. If the WAC signal exacerbates the POD performance, the FACTS falls back to POD using local measurements. The proposed approach does not require an expansive system-wide view of the network. We simulate replay, control integrity, and timing attacks for a test system and present results that demonstrate the performance of the SM approach for mitigation.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2021

A Localized Cyber Threat Mitigation Approach For Wide Area Control of FACTS

We propose a localized oscillation amplitude monitoring (OAM) method for the mitigation of cyber threats directed at the wide area control (WAC) system used to coordinate control of Flexible AC Transmission Systems (FACTS) for power oscillation damping (POD) of active power flow on inter-area tie lines. The method involves monitoring the inter-area tie line active power oscillation amplitude over a sliding window. We use system instability - inferred from oscillation amplitudes growing instead of damping - as evidence of an indication of a malfunction in the WAC of FACTS, possibly indicative of a cyber attack. Monitoring the presence of such a growth allows us to determine whether any destabilizing behaviors appear after the WAC system engages to control the POD. If the WAC signal increases the oscillation amplitude over time, thereby diminishing the POD performance, the FACTS falls back to POD using local measurements. The proposed method does not require an expansive system-wide view of the network. We simulate replay, control integrity, and timing attacks for a test system and present results that demonstrate the performance of the OAM method for mitigation.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2024

MgB$_{2}$ Coating by HPCVD for 1.3-GHz Superconducting RF Cavities

While MgB 2 possesses promising material parameters for SRF cavities with higher Q, higher gradient, and higher operation temperatures than Nb cavities, such cavity properties have not been demonstrated using MgB 2 . As part of a continuing effort to fabricate MgB 2 -coated SRF cavities by hybrid physical chemical vapor deposition (HPCVD), we present here an HPCVD system design for coating the inside wall of 1.3-GHz copper cavities with MgB 2 . The cavity is heated using a pair of clamshell resistive heaters that directly contact the cavity body. Here, the new heater design is more compact and requires less power to reach the deposition temperature (~500°C for MgB 2 deposition on copper.) Preliminary test of MgB 2 films grown on small copper substrates, mounted at different locations on the cavity, shows T c of 28.4 ~ 34.3 K, measured by AC susceptibility.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Machine Learning-Assisted Stability Boundary Determination of Multiport Autonomous Reconfigurable Solar Power Plants

The multiport autonomous reconfigurable solar (MARS) power plant is a promising solution to integrate renewable resources and energy storage systems into the alternating current (ac) power grid and an high-voltage direct current (HVdc) link. In the MARS system, various input power sources are connected to the individual submodules (SMs) through direct current (dc)–dc converters. However, the presence of external power sources can result in unbalanced capacitor voltages of SMs, thereby violating stability constraints under multiple/diverse operating conditions. This article aims to address the gap by accurately determining the stability boundary of the MARS system. As such, a novel machine learning (ML)-assisted energy balancing control (EBC) criterion is proposed. Further, in conjunction with a refined EBC, this approach ensures balanced capacitor voltages across various types of SMs, significantly enhancing the overall system efficiency. The proposed EBC criterion effectively controls EBC activation and deactivation, achieving remarkable accuracy. Both power systems computer aided design (PSCAD)/electromagnetic transients including direct current (EMTDC) simulations and control hardware-in-the-loop (cHIL) tests are conducted to validate the feasibility and efficiency of the proposed method. By combining the EBC and ML-assisted EBC criterion, efficient energy management is achieved for systems featuring multiple input power sources, such as MARS. This approach enables the system to fully exploit its potential across an expanded operational range while upholding high-efficiency standards.

14 SOLAR ENERGY↗
DOE OSTI2020

Materials Data on Ac2O3 by Materials Project

Ac2O3 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Ac3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ac–O bond distances ranging from 2.47–2.84 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded to four equivalent Ac3+ atoms to form OAc4 tetrahedra that share corners with six equivalent OAc6 octahedra, corners with six equivalent OAc4 tetrahedra, edges with three equivalent OAc6 octahedra, and edges with three equivalent OAc4 tetrahedra. The corner-sharing octahedra tilt angles range from 17–56°. In the second O2- site, O2- is bonded to six equivalent Ac3+ atoms to form OAc6 octahedra that share corners with twelve equivalent OAc4 tetrahedra, edges with six equivalent OAc6 octahedra, and edges with six equivalent OAc4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AcCl3 by Materials Project

AcCl3 crystallizes in the hexagonal P6_3/m space group. The structure is three-dimensional. Ac3+ is bonded in a 9-coordinate geometry to nine equivalent Cl1- atoms. All Ac–Cl bond lengths are 3.05 Å. Cl1- is bonded in a trigonal non-coplanar geometry to three equivalent Ac3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AcBr3 by Materials Project

AcBr3 crystallizes in the hexagonal P6_3/m space group. The structure is three-dimensional. Ac3+ is bonded in a 9-coordinate geometry to nine equivalent Br1- atoms. There are six shorter (3.21 Å) and three longer (3.26 Å) Ac–Br bond lengths. Br1- is bonded in a trigonal non-coplanar geometry to three equivalent Ac3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AcF3 by Materials Project

AcF3 is alpha bismuth trifluoride structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ac3+ is bonded to twelve F1- atoms to form AcF12 cuboctahedra that share corners with four equivalent AcF12 cuboctahedra, corners with eight equivalent FAc4F8 cuboctahedra, corners with sixteen equivalent FAc4F4 tetrahedra, edges with eight equivalent AcF12 cuboctahedra, edges with eight equivalent FAc4F4 tetrahedra, faces with four equivalent AcF12 cuboctahedra, and faces with six equivalent FAc4F8 cuboctahedra. There are eight shorter (2.64 Å) and four longer (2.83 Å) Ac–F bond lengths. There are two inequivalent F1- sites. In the first F1- site, F1- is bonded to four equivalent Ac3+ and four equivalent F1- atoms to form distorted FAc4F4 tetrahedra that share corners with eight equivalent AcF12 cuboctahedra, corners with eight equivalent FAc4F8 cuboctahedra, corners with eight equivalent FAc4F4 tetrahedra, edges with four equivalent AcF12 cuboctahedra, edges with four equivalent FAc4F8 cuboctahedra, edges with twelve equivalent FAc4F4 tetrahedra, and faces with six equivalent FAc4F4 tetrahedra. All F–F bond lengths are 2.64 Å. In the second F1- site, F1- is bonded to four equivalent Ac3+ and eight equivalent F1- atoms to form distorted FAc4F8 cuboctahedra that share corners with four equivalent FAc4F8 cuboctahedra, corners with eight equivalent AcF12 cuboctahedra, corners with sixteen equivalent FAc4F4 tetrahedra, edges with eight equivalent FAc4F8 cuboctahedra, edges with eight equivalent FAc4F4 tetrahedra, faces with four equivalent FAc4F8 cuboctahedra, and faces with six equivalent AcF12 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AcH3 by Materials Project

AcH3 is alpha bismuth trifluoride structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Ac3+ is bonded in a distorted body-centered cubic geometry to fourteen H1- atoms. There are eight shorter (2.51 Å) and six longer (2.90 Å) Ac–H bond lengths. There are two inequivalent H1- sites. In the first H1- site, H1- is bonded to four equivalent Ac3+ atoms to form HAc4 tetrahedra that share corners with twelve equivalent HAc6 octahedra, corners with sixteen equivalent HAc4 tetrahedra, edges with six equivalent HAc4 tetrahedra, and faces with four equivalent HAc6 octahedra. The corner-sharing octahedral tilt angles are 55°. In the second H1- site, H1- is bonded to six equivalent Ac3+ atoms to form HAc6 octahedra that share corners with six equivalent HAc6 octahedra, corners with twenty-four equivalent HAc4 tetrahedra, edges with twelve equivalent HAc6 octahedra, and faces with eight equivalent HAc4 tetrahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on RbAcTe2 by Materials Project

RbAcTe2 is Heusler structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Rb1+ is bonded in a body-centered cubic geometry to eight equivalent Te2- atoms. All Rb–Te bond lengths are 3.61 Å. Ac3+ is bonded in a body-centered cubic geometry to eight equivalent Te2- atoms. All Ac–Te bond lengths are 3.61 Å. Te2- is bonded in a body-centered cubic geometry to four equivalent Rb1+ and four equivalent Ac3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KAcTe2 by Materials Project

KAcTe2 is Heusler structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. K1+ is bonded in a body-centered cubic geometry to eight equivalent Te2- atoms. All K–Te bond lengths are 3.56 Å. Ac3+ is bonded in a body-centered cubic geometry to eight equivalent Te2- atoms. All Ac–Te bond lengths are 3.56 Å. Te2- is bonded in a body-centered cubic geometry to four equivalent K1+ and four equivalent Ac3+ atoms.

36 MATERIALS SCIENCE↗