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DOE OSTI2020

Materials Data on Ho2Cu(GeO3)4 by Materials Project

Ho2Cu(GeO3)4 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. Ho3+ is bonded to seven O2- atoms to form distorted HoO7 pentagonal bipyramids that share corners with six GeO4 tetrahedra, edges with two equivalent HoO7 pentagonal bipyramids, and an edgeedge with one GeO4 tetrahedra. There are a spread of Ho–O bond distances ranging from 2.24–2.57 Å. Cu2+ is bonded in a square co-planar geometry to four O2- atoms. All Cu–O bond lengths are 1.98 Å. There are two inequivalent Ge4+ sites. In the first Ge4+ site, Ge4+ is bonded to four O2- atoms to form GeO4 tetrahedra that share corners with four equivalent HoO7 pentagonal bipyramids and corners with two equivalent GeO4 tetrahedra. There are a spread of Ge–O bond distances ranging from 1.76–1.80 Å. In the second Ge4+ site, Ge4+ is bonded to four O2- atoms to form GeO4 tetrahedra that share corners with two equivalent HoO7 pentagonal bipyramids, corners with two equivalent GeO4 tetrahedra, and an edgeedge with one HoO7 pentagonal bipyramid. There are a spread of Ge–O bond distances ranging from 1.75–1.82 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Ho3+ and one Ge4+ atom. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Ho3+ and one Ge4+ atom. In the third O2- site, O2- is bonded in a 3-coordinate geometry to one Ho3+ and two Ge4+ atoms. In the fourth O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the fifth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ho3+, one Cu2+, and one Ge4+ atom. In the sixth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ho3+, one Cu2+, and one Ge4+ atom.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Ho4GaSbS9 by Materials Project

Ho4GaSbS9 crystallizes in the orthorhombic Aea2 space group. The structure is three-dimensional. there are four inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded in a 6-coordinate geometry to six S2- atoms. There are a spread of Ho–S bond distances ranging from 2.72–2.84 Å. In the second Ho3+ site, Ho3+ is bonded in a 6-coordinate geometry to six S2- atoms. There are a spread of Ho–S bond distances ranging from 2.71–2.82 Å. In the third Ho3+ site, Ho3+ is bonded in a 7-coordinate geometry to seven S2- atoms. There are a spread of Ho–S bond distances ranging from 2.70–3.00 Å. In the fourth Ho3+ site, Ho3+ is bonded in a 6-coordinate geometry to six S2- atoms. There are a spread of Ho–S bond distances ranging from 2.69–2.80 Å. Ga3+ is bonded to four S2- atoms to form corner-sharing GaS4 tetrahedra. There are a spread of Ga–S bond distances ranging from 2.29–2.32 Å. Sb3+ is bonded in a rectangular see-saw-like geometry to four S2- atoms. There are a spread of Sb–S bond distances ranging from 2.48–2.85 Å. There are ten inequivalent S2- sites. In the first S2- site, S2- is bonded in a distorted water-like geometry to two equivalent Ga3+ atoms. In the second S2- site, S2- is bonded in a distorted T-shaped geometry to two Ho3+ and one Ga3+ atom. In the third S2- site, S2- is bonded to four Ho3+ atoms to form distorted SHo4 trigonal pyramids that share a cornercorner with one SHo3Ga tetrahedra, corners with four SHo4 trigonal pyramids, an edgeedge with one SHo3Ga tetrahedra, and edges with two SHo4 trigonal pyramids. In the fourth S2- site, S2- is bonded to four Ho3+ atoms to form distorted SHo4 trigonal pyramids that share a cornercorner with one SHo3Ga tetrahedra, corners with four SHo4 trigonal pyramids, an edgeedge with one SHo3Ga tetrahedra, and edges with two SHo4 trigonal pyramids. In the fifth S2- site, S2- is bonded in a rectangular see-saw-like geometry to four Ho3+ atoms. In the sixth S2- site, S2- is bonded in a distorted rectangular see-saw-like geometry to three Ho3+ and one Sb3+ atom. In the seventh S2- site, S2- is bonded to four Ho3+ atoms to form distorted SHo4 trigonal pyramids that share a cornercorner with one SHo3Ga tetrahedra, corners with four SHo4 trigonal pyramids, an edgeedge with one SHo3Ga tetrahedra, and edges with two SHo4 trigonal pyramids. In the eighth S2- site, S2- is bonded in a 3-coordinate geometry to one Ho3+ and two equivalent Sb3+ atoms. In the ninth S2- site, S2- is bonded in a 4-coordinate geometry to two Ho3+, one Ga3+, and one Sb3+ atom. In the tenth S2- site, S2- is bonded to three Ho3+ and one Ga3+ atom to form a mixture of distorted edge and corner-sharing SHo3Ga tetrahedra.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on MgP(HO)7 by Materials Project

MgP(HO)7 crystallizes in the orthorhombic Pbca space group. The structure is three-dimensional. Mg2+ is bonded to six O2- atoms to form MgO6 octahedra that share corners with three equivalent PO4 tetrahedra. There are a spread of Mg–O bond distances ranging from 2.01–2.17 Å. P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with three equivalent MgO6 octahedra. The corner-sharing octahedra tilt angles range from 13–44°. There are a spread of P–O bond distances ranging from 1.50–1.61 Å. There are seven inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. In the third H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. In the fourth H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.02 Å) and one longer (1.56 Å) H–O bond length. In the fifth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. In the sixth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the seventh H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. There are seven inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to one P5+ and one H1+ atom. In the second O2- site, O2- is bonded in a distorted water-like geometry to one Mg2+ and two H1+ atoms. In the third O2- site, O2- is bonded in a 2-coordinate geometry to one Mg2+ and one P5+ atom. In the fourth O2- site, O2- is bonded in a distorted water-like geometry to one Mg2+ and two H1+ atoms. In the fifth O2- site, O2- is bonded in a 3-coordinate geometry to one Mg2+, one P5+, and one H1+ atom. In the sixth O2- site, O2- is bonded in a distorted water-like geometry to one Mg2+ and two H1+ atoms. In the seventh O2- site, O2- is bonded in a linear geometry to one Mg2+ and one P5+ atom.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Epitaxial Stabilization of Metastable 3C BaRuO 3 Thin Film with Ferromagnetic Non-Fermi Liquid Phase

Thin films of perovskite ruthenates of the general formula ARuO 3 (A = Ca and Sr) are versatile electrical conductors for viable oxide electronics. They are also scientifically intriguing, as they exhibit nontrivial electromagnetic ground states depending on the A-site element. Among them, realization of the cubic perovskite (3C) BaRuO 3 in thin film form has been a challenge so far, because the 3C phase is metastable with the largest formation energy among the various polymorph phases of BaRuO 3 . In this study, 3C BaRuO 3 thin films are successfully prepared employing epitaxial stabilization. Here the 3C BaRuO 3 thin films show itinerant ferromagnetism with a transition temperature of ≈48 K and a non-Fermi liquid phase. The epitaxial stabilization of the 3C BaRuO 3 further enables to make a standard comparison of perovskite ruthenates, thereby establishing the importance of the Ru-O orbital hybridization in understanding the itinerant magnetic system.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Structures of honeybee-infecting Lake Sinai virus reveal domain functions and capsid assembly with dynamic motions

Understanding the structural diversity of honeybee-infecting viruses is critical to maintain pollinator health and manage the spread of diseases in ecology and agriculture. We determine cryo-EM structures of $T$ = 4 and $T$ = 3 capsids of virus-like particles (VLPs) of Lake Sinai virus (LSV) 2 and delta-N48 LSV1, belonging to tetraviruses, at resolutions of 2.3–2.6 Å in various pH environments. Structural analysis shows that the LSV2 capsid protein (CP) structural features, particularly the protruding domain and C-arm, differ from those of other tetraviruses. The anchor loop on the central β-barrel domain interacts with the neighboring subunit to stabilize homo-trimeric capsomeres during assembly. Delta-N48 LSV1 CP interacts with ssRNA via the rigid helix α1’, α1’–α1 loop, β-barrel domain, and C-arm. Cryo-EM reconstructions, combined with X-ray crystallographic and small-angle scattering analyses, indicate that pH affects capsid conformations by regulating reversible dynamic particle motions and sizes of LSV2 VLPs. C-arms exist in all LSV2 and delta-N48 LSV1 VLPs across varied pH conditions, indicating that autoproteolysis cleavage is not required for LSV maturation. The observed linear domino-scaffold structures of various lengths, made up of trapezoid-shape capsomeres, provide a basis for icosahedral $T$ = 4 and $T$ = 3 architecture assemblies. These findings advance understanding of honeybee-infecting viruses that can cause Colony Collapse Disorder.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2022

Predicting third-body collision efficiencies for water and other polyatomic baths

Low-pressure-limit microcanonical (collisional activation) and thermal rate constants are predicted using a combination of automated ab initio potential energy surface construction, classical trajectories, transition state theory, and a detailed energy- and angular-momentum-resolved collision kernel. Several systems are considered, including CH 4 (+M) and HO 2 (+M), with an emphasis on systems where experimental information is available for comparison. The a priori approach involves no adjustable parameters, and we show that the predicted thermal rate constants are in excellent agreement with experiments, with average deviations of less than 25%. Notably, the a priori approach is shown to perform equally well for atomic, diatomic, and polyatomic baths, including M = H 2 O, CO 2 , and “fuel” baths like M = CH 4 and NH 3 . Additionally, the utility of microcanonical rate constants for interpreting trends and inferring mechanistic details in the thermal kinetics is demonstrated.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1997

Laboratory Studies of Chemical and Photochemical Processes Relevant to Stratospheric Ozone

The purpose of this project is to reduce the uncertainty in several key gas-phase kinetic processes which impact our understanding of stratospheric ozone. The main emphasis of this work is on measuring rate coefficients and product channels for reactions of HO(x) and NO(x) species in the temperature range 200 K to 240 K relevant to the lower stratosphere. The results of these studies will improve models of stratospheric ozone chemistry and predictions of perturbations due to human influences. The second year's effort has focussed the design and construction of the proposed high pressure flow reactor on three separate areas: (1) the construction of the high pressure flow reactor; (2) characterization of the turbulent flow profile; and (3) demonstration of the instrument by measuring HO2 + NO2 and HO2 + NO reaction rate coefficients.

Villalta, Peter W.↗

DOE OSTI2020

Mineralogy of the deep lower mantle in the presence of H 2 O

Understanding the mineralogy of the Earth's interior is a prerequisite for unravelling the evolution and dynamics of our planet. Here, we conducted high pressure-temperature experiments mimicking the conditions of the deep lower mantle (DLM, 1800–2890 km in depth) and observed surprising mineralogical transformations in the presence of water. Ferropericlase, (Mg, Fe)O, which is the most abundant oxide mineral in Earth, reacts with H 2 O to form a previously unknown (Mg, Fe)O 2 H x (x ≤ 1) phase. The (Mg, Fe)O 2 H x has a pyrite structure and it coexists with the dominant silicate phases, bridgmanite and post-perovskite. Depending on Mg content and geotherm temperatures, the transformation may occur at 1800 km for (Mg 0.6 Fe 0.4 )O or beyond 2300 km for (Mg 0.7 Fe 0.3 )O. The (Mg, Fe)O 2 H x is an oxygen excess phase that stores an excessive amount of oxygen beyond the charge balance of maximum cation valences (Mg 2+ , Fe 3+ and H + ). This important phase has a number of far-reaching implications including extreme redox inhomogeneity, deep-oxygen reservoirs in the DLM and an internal source for modulating oxygen in the atmosphere.

58 GEOSCIENCES↗

DOE OSTI2026

Coupled Chemical and Mechanical Control of Phase Stability in Lanthanide-Substituted BiVO 4

Doping is widely used to enhance the photoelectrochemical performance of BiVO 4 , yet solubility limits and polymorphic stability constrain compositional tuning. Here, in this study, the role of trivalent cation substitution (Ln = La, Nd, Dy, Ho, Y) on pressure-induced phase transformations in Bi 1–x Ln x VO 4 (x ≤ 0.5) is described. Powder X-ray and neutron diffraction reveal that increasing Ln content stabilizes the tetragonal zircon-type polymorph under ambient conditions, while applied pressures of up to ∼5 GPa promote conversion to the monoclinic fergusonite-type polymorph. In-situ neutron diffraction on Bi 0.8 La 0.2 VO 4 shows a reversible monoclinic to tetragonal transition near 2–3 GPa with a bulk modulus of 147 GPa. The extent of conversion depends strongly on dopant identity, concentration, and synthetic route, with mixed-phase solid-state samples converting more efficiently than phase-pure coprecipitated materials. These results demonstrate pressure as a viable pathway to access metastable, doped BiVO 4 compositions beyond conventional solubility limits.

Sypkes, Kathryn I. [University of Sydney, NSW (Aus↗

NASA NTRS2009

High Repetition Rate Pulsed 2-Micron Laser Transmitter for Coherent CO2 DIAL Measurement

A high repetition rate, highly efficient, Q-switched 2-micron laser system as the transmitter of a coherent differential absorption lidar for CO2 measurement has been developed at NASA Langley Research Center. Such a laser transmitter is a master-slave laser system. The master laser operates in a single frequency, either on-line or off-line of a selected CO2 absorption line. The slave laser is a Q-switched ring-cavity Ho:YLF laser which is pumped by a Tm:fiber laser. The repetition rate can be adjusted from a few hundred Hz to 10 kHz. The injection seeding success rate is from 99.4% to 99.95%. For 1 kHz operation, the output pulse energy is 5.5mJ with the pulse length of approximately 50 ns. The optical-to-optical efficiency is 39% when the pump power is 14.5W. The measured standard deviation of the laser frequency jitter is about 3 MHz.

Singh, Uprendra N.↗

DOE OSTI2022

Spin relaxation rate for heavy quarks in weakly coupled QCD plasma

We compute the relaxation rate of the spin density of heavy quarks in a perturbative QCD plasma to leading-log order in the coupling constant g. The spin relaxation rate Γ s in spin hydrodynamics is shown to be Γ s ~ g 4 log(1/g)T(T/M) 2 in the heavy-quark limit T/M $\ll$ 1, which is smaller than the relaxation rate of other non- hydrodynamic modes by additional powers of T/M. We demonstrate three different methods to evaluate the spin relaxation rate: 1) the Green-Kubo formula in the spin hydrodynamic regime, 2) the spin density correlation function in the strict hydrodynamic limit, and 3) quantum kinetic theory of the spin distribution function in momentum space. We highlight the interesting differences between these methods, while they are ultimately connected to each other by the underlying Ward-Takahashi identity for the non-conserved spin density.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2024

Effects of drive pulse shape on graded metal pushered single shell capsule implosions on the National Ignition Facility

Graded metal pushered single shells (PSS) are a viable alternative to low-Z capsules (Z is the atomic number) for indirect drive inertial confinement fusion implosions due to enhanced core tamping and radiation trapping, but they can be compromised by the pusher mixing with the fuel. We compare 2-shock and 3-shock laser pulses for Be/Cr PSS capsules filled with deuterium–tritium gas fuel at 6 mg/cc density. 1D radiation-hydrodynamic simulations predict higher core compression and, hence, ∼2× higher fusion yield for the 3-shock drive than for 2-shock. Nevertheless, we observe similar core ion temperatures and fusion yields for both drives. The implosion burn duration is 25% shorter and the core volume is ∼2.5× smaller for the 3-shock drive than for 2-shock, consistent with a higher compression. 1D LASNEX mix simulations using a buoyancy-drag model matching the measured yields also agree with the observed core sizes and burn durations and suggest ∼40% and ∼70% yield degradations for 2-shock and 3-shock drives due to hydrodynamic instabilities and atomic mix at the pusher–fuel interface. At the same time, 2D HYDRA simulations show that mid-mode (2–250) instability degradations are negligible for the 2-shock implosion (9%) and significant (45%) for 3-shock. Subtracting these from the 1D mix simulations, we infer similar degradations from high-mode instabilities and atomic mix for both drives. Due to its robustness to mid-mode instabilities, future pusher–gas mix studies will use the 2-shock drive.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2023

Machine learning guided discovery of superconducting calcium borocarbides

Pursuit of superconductivity in light-element systems at ambient pressure is of great experimental and theoretical interest. In this work, we combine a machine learning (ML) method with first-principles calculations to efficiently search for the energetically favorable ternary Ca-B-C compounds. Three layered borocarbides (stable CaBC 5 and metastable Ca 2 BC 11 and CaB 3 C 3 ) are predicted to be phonon-mediated superconductors at ambient pressure. The stable CaBC 5 and the low-energy metastable Ca 2 BC 11 (with formation energy only 9.5 meV/atom above the convex hull) have a superconducting T c of 5.2 and 8.9 K, respectively. While the hexagonal CaB 3 C 3 possesses a T c of 26.1 K, it is metastable with formation energy of 153 meV/atom above the convex hull. The ML-guided approach opens up a way for greatly accelerating the discovery of new high-T c superconductors.

36 MATERIALS SCIENCE↗

NASA NTRS1999

Highlights of Part I: Propagation Through Mars Environment: Propagation through Mars Environment - Part 1

We recommend using the dayside Martian ionosphere as a reflector for global communication, because it has a stable density peak and usable critical frequency. This is very crucial for the future Mars ground to ground communication. The dayside ionosphere has been well modeled as a Chapman layer. We suggest performing the Martian nightside ionosphere modeling study. Because the nightside ionosphere has very little measurements available, we propose to drop a digital ionosound instrument into the Mars surface for data collection. Even though the Martian tropospheric radio refractivity had a small value, it still can cause ray bending and multipath effects. We recommend performing an accurate calculation on excess phase and group delays (range and time delays). Other effects, such as range rate errors, appearance angle deviation, defocusing loss on Mars, etc. should be estimated. Ice depolarization effects due to Martian clouds on radio waves are unknown yet, but they are expected to be small, because of lower optical depth and the thinner layer of cloud. Total Martian atmospheric gaseous attenuation is expected to be less than 1 dB on microwaves and, because the Martian atmosphere had very low concentration in uncondensed H2O and O2. An accurate calculation for zenith opacity requires the information about scale heights of H2O and O2 distribution. An accurate water vapor altitude profile at Mars is not available et. Under the normal condition, CO2 and N2 gases ddo not have electric or magnetic dipoles and do not absorb electromagnetic energy from the waves. However, they may generate the dipoles through a collision and interact with waves under a high density condition and absorb electromagnetic waves in the infrared and visible band. Dust storm is the most dominant factor on the radio wave attenuation. Large Martian dust storms can cause at least 3 dB or higher loss to Ka band wave. For a normal dust storm, the attenuation is about 1 dB. The attenuation much depends on dust mass loading, dust size distribution, etc. Most large dust storms occur in the southern hemisphere during later spring and early summer when the southern hemisphere becomes suddenly hot.

Ho, Christian↗

NASA NTRS1999

Radio Wave Propagation for Communication on and around Mars: Highlights: Propagation Through Mars Environment - Part 1

We recommend to use the dayside Martian ionosphere as a reflector for global communication, because the dayside ionosphere has stable density peak and usable critic frequency. This is very crucial for the future Mars ground to around communication. The dayside ionosphere has been well modeled as a Chapman layer. We suggest to perform the Martian nightside ionospheric modeling study. Because the nightside ionosphere has very little measurements available, we propose to drop a digital ionosond instrument into the Mars surface for data collection. Even though the Martian tropospheric radio refractivity has small value, it still can cause the ray bending and multipath effects. We recommend to perform an accurate calculation on excess phase and group delays (range and time delays). Other effects, such as range rate errors, appearance angle deviation, defocusing loss on Mars, etc. are also needed to be estimated. Ice depolarization effects due to Martian clouds on radio waves is unknown yet, which is expected to be small, because lower optical depth and thinner layer of cloud: Total Martian atmospheric gaseous attenuation is expected to be less than 1 dB on microwaves band, because the Martian atmosphere has very low concentration in uncondensed H2O and O2. An accurate calculation for zenith opacity requires the information about scale heights of H2O and O2 distribution. An accurate water vapor altitude profile at Mars is not available yet. Under the normal condition, CO2 and N2 gases do not have electric or magnetic dipoles and do not absorb electromagnetic energy from the waves. However, they may generate the dipoles through a collision and interact with waves under a high density condition and absorb electromagnetic waves in the infrared and visible band. Dust storm is most dominant factor to the radio wave attenuation. Large Martian dust storm can cause at least 3 dB or higher loss to Ka band wave. For a normal dust storm, the attenuation is about 1 dB. The attenuation much depends on dust mass loading, dust size distribution, etc. Most large dust storm occur in the southern hemisphere during later spring and early summer when the southern hemisphere become suddenly hot.

Ho, Christian↗

DOE OSTI2020

Materials Data on Ho2Cu(WO4)4 by Materials Project

Ho2Cu(WO4)4 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. Ho3+ is bonded to seven O2- atoms to form distorted HoO7 pentagonal bipyramids that share corners with seven WO6 octahedra, an edgeedge with one WO6 octahedra, an edgeedge with one CuO6 octahedra, and an edgeedge with one HoO7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 30–58°. There are a spread of Ho–O bond distances ranging from 2.22–2.49 Å. There are two inequivalent W6+ sites. In the first W6+ site, W6+ is bonded to six O2- atoms to form distorted WO6 octahedra that share a cornercorner with one CuO6 octahedra, corners with two equivalent WO6 octahedra, corners with three equivalent HoO7 pentagonal bipyramids, an edgeedge with one WO6 octahedra, and an edgeedge with one HoO7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 12–54°. There are a spread of W–O bond distances ranging from 1.82–2.19 Å. In the second W6+ site, W6+ is bonded to six O2- atoms to form distorted WO6 octahedra that share corners with three equivalent CuO6 octahedra, corners with four equivalent HoO7 pentagonal bipyramids, and edges with two WO6 octahedra. The corner-sharing octahedra tilt angles range from 51–54°. There are a spread of W–O bond distances ranging from 1.79–2.15 Å. Cu2+ is bonded to six O2- atoms to form CuO6 octahedra that share corners with eight WO6 octahedra and edges with two equivalent HoO7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 51–54°. There are a spread of Cu–O bond distances ranging from 2.07–2.35 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two equivalent Ho3+ and one W6+ atom. In the second O2- site, O2- is bonded in a 3-coordinate geometry to one Ho3+, one W6+, and one Cu2+ atom. In the third O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent W6+ and one Cu2+ atom. In the fourth O2- site, O2- is bonded in a bent 150 degrees geometry to one Ho3+ and one W6+ atom. In the fifth O2- site, O2- is bonded in a 3-coordinate geometry to one Ho3+, one W6+, and one Cu2+ atom. In the sixth O2- site, O2- is bonded in a distorted linear geometry to two equivalent W6+ atoms. In the seventh O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to one Ho3+ and two W6+ atoms. In the eighth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ho3+ and two W6+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Probing Ice-Rule-Breaking Transition in Dy 2 Ti 2 O 7 Thin Film by Proximitized Transport and Magnetic Torque

While the spin-ice state of bulk pyrochlores such as Dy 2⁢ Ti 2 ⁢O 7 and Ho 2⁢ Ti 2 ⁢O 7 has been extensively studied in the past several decades due to its unique degenerate ground state and emergent monopole excitation, whether it survives in the thin-film form remains a mystery. The limited volume of the thin-film sample makes it challenging to study the intrinsic magnetic properties. Here, we synthesized 18-nm-thick Dy 2⁢ Ti 2 ⁢O 7 thin film on yttria-stabilized zirconia with 9.5 mol% Y 2 ⁢O 3 substrate and capped it by a thin conductive Bi 2 ⁢Ir 2 ⁢O 7 layer and performed the proximitized magnetoresistance measurements. Our Letter found that the ice-rule-breaking phase transition survives but with a modified effective nearest-neighbor interaction (𝐽 eff =1.054 K) and distorted Ising spin axes (𝜀 = +0.051) compared to the bulk crystal. Furthermore, the results are supported by the simultaneously measured capacitive torque magnetometry. Our Letter demonstrates that proximitized transport is an effective tool for thin films of insulating frustrated magnets.

Magnetic interactions↗

DOE OSTI2024

Electronic-grade epitaxial (111) KTaO 3 heterostructures

KTaO 3 heterostructures have recently attracted attention as model systems to study the interplay of quantum paraelectricity, spin-orbit coupling, and superconductivity. However, the high and low vapor pressures of potassium and tantalum present processing challenges to creating heterostructure interfaces clean enough to reveal the intrinsic quantum properties. Here, we report superconducting heterostructures based on high-quality epitaxial (111) KTaO 3 thin films using an adsorption-controlled hybrid PLD to overcome the vapor pressure mismatch. Electrical and structural characterizations reveal that the higher-quality heterostructure interface between amorphous LaAlO 3 and KTaO 3 thin films supports a two-dimensional electron gas with substantially higher electron mobility, superconducting transition temperature, and critical current density than that in bulk single-crystal KTaO 3 -based heterostructures. Our hybrid approach may enable epitaxial growth of other alkali metal–based oxides that lie beyond the capabilities of conventional methods.

36 MATERIALS SCIENCE↗