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DOE OSTI2025

Reversible control over the distribution of chemical inhomogeneities in multiferroic BiFeO3

Abstract Despite the appeal of flawless order, semiconductor technology has demonstrated that implanting inhomogeneities into single-crystalline materials is pivotal for modern electronics. However, the influence of the local arrangement of chemical inhomogeneities on the material’s functionalities is underexplored. In this work, we control the distribution of chemical inhomogeneities in La 3+ -substituted ferroelectric BiFeO 3 thin films. By means of a stress- and composition-driven phase transition, we trigger the formation of a lattice of La 3+ -rich and La 3+ -poor layers. This ordering correlates with the emergence of an antipolar phase. An electric field restores the original ferroelectric phase and re-randomizes the distribution of the La 3+ inhomogeneities. Leveraging these insights, we tune the polar/antipolar phase coexistence to set the net polarization of La 0.15 Bi 0.85 FeO 3 to any desired value between its saturation limits. Finally, we control the net polarization response in device-compliant capacitor heterostructures to show that inhomogeneity-distribution control is a valuable tool in the design of functional oxide electronics.

Science & Technology - Other Topics↗

DOE OSTI2025

Atomic lift-off of epitaxial membranes for cooling-free infrared detection

Recent breakthroughs in ultrathin, single-crystalline, freestanding complex oxide systems have sparked industry interest in their potential for next-generation commercial devices. However, the mass production of these ultrathin complex oxide membranes has been hindered by the challenging requirement of inserting an artificial release layer between the epilayers and substrates. Here we introduce a technique that achieves atomic precision lift-off of ultrathin membranes without artificial release layers to facilitate the high-throughput production of scalable, ultrathin, freestanding perovskite systems. Leveraging both theoretical insights and empirical evidence, we have identified the pivotal role of lead in weakening the interface. This insight has led to the creation of a universal exfoliation strategy that enables the production of diverse ultrathin perovskite membranes less than 10 nm. Our pyroelectric membranes demonstrate a record-high pyroelectric coefficient of 1.76 × 10 −2 C m −2 K −1 , attributed to their exceptionally low thickness and freestanding nature. Moreover, this method offers an approach to manufacturing cooling-free detectors that can cover the full far-infrared spectrum, marking a notable advancement in detector technology.

nanoscale materials↗

DOE OSTI2026

Vibrational and electronic properties of Np 2 O 5 from experimental spectroscopy and first principles calculations

High-valence actinide oxides are critical to understanding the behavior of 5f-electrons, yet their structural and electronic properties remain poorly understood due to challenges in synthesis and handling. We report the first Raman spectroscopic study of single-crystalline Np 2 O 5 and the first scanning tunneling spectroscopy (STS) measurement on any neptunium-containing material. Hydrothermally synthesized crystals were structurally verified by X-ray diffraction. Raman spectra revealed sharply resolved vibrational features, including previously unreported low-frequency modes. STS measurements revealed a band gap of 1.5 eV. Density functional theory (DFT) enables vibrational mode assignments, reveals neptunium-dominated low-frequency phonons, oxygen-dominated high-frequency modes, and predicts an indirect band gap of 1.68 eV. This predicted value is in excellent agreement with the experimentally measured STS gap. This combined Raman, DFT, and STS approach provides a robust framework for correlating lattice dynamics and electronic structure in actinide materials, providing benchmark data for Np 2 O 5 , and opening new avenues for probing structure–property relationships in complex f-electron materials.

36 - MATERIALS SCIENCE↗

DOE OSTI2025

Growth of tetragonal PtO by molecular-beam epitaxy and its integration into β-Ga 2 O 3 Schottky diodes

We demonstrate the epitaxial growth of tetragonal platinum monoxide (PtO) on MgO, TiO 2 , and β-Ga 2 O 3 single-crystalline substrates by ozone molecular-beam epitaxy. We provide synthesis routes and derive a growth diagram under which PtO films can be synthesized by physical vapor deposition. A combination of electrical transport and photoemission spectroscopy measurements, in conjunction with density functional theory calculations, reveal PtO to be a degenerately doped p-type semiconductor with a bandgap of E g ≈ 1.6 eV. Spectroscopic ellipsometry measurements are used to extract the complex dielectric function spectra, indicating a transition from free-carrier absorption to higher photon energy transitions at E ≈ 1.6 eV. Using tetragonal PtO as an anode contact, we fabricate prototype Schottky diodes on n-type Sn-doped β-Ga 2 O 3 substrates and extract Schottky barrier heights of ϕ B > 2.2 eV.

Hensling, Felix V. E. [Cornell Univ., Ithaca, NY (↗

DOE OSTI2026

Quantum critical point followed by Kondo-like behavior due to Cu substitution in the itinerant antiferromagnet La 2 ⁢(Cu 𝑥 ⁢Ni 1−𝑥 ) 7

La 2 ⁢Ni 7 is an itinerant magnetic system with a small ordered moment of ∼ 0.1⁢µ 𝐵 /Ni and a series of antiferromagnetic (AFM) transitions at 𝑇 1 = 61.0K, 𝑇 2 = 56.5K, and 𝑇 3 = 42.2K. 𝑀 ⁡(𝐻), and 𝜌 ⁡(𝐻) isotherms as well as constant field 𝑀⁡ (𝑇) and 𝜌 ⁡(𝑇) measurements on single-crystalline samples manifest a complex, anisotropic 𝐻−𝑇 phase diagram with multiple phase lines. Here, in this study, we present the growth and characterization of single crystals of the La 2 ⁢(Cu 𝑥 ⁢Ni 1−𝑥 ) 7 series for 0 ≤ 𝑥 ≤ 0.181. We measured powder x-ray diffraction and composition, as well as anisotropic temperature- and field-dependent resistivity, temperature- and field-dependent magnetization, and temperature-dependent heat capacity on these single crystals. Using the measured data we infer a transition temperature-composition (𝑇−𝑥) phase diagram for this system to study the evolution of the AFM ordering upon Cu substitution. For 0 ≤ 𝑥 ≤ 0.097, the system remains magnetically ordered at base temperature with 𝑥 ≤ 0.012, showing signs of multiple AFM ordering temperatures. For the higher substitution levels 0.125 ≤ 𝑥 ≤ 0.181, there are no signatures of magnetic ordering, but anomalous features in resistance and heat capacity data are observed which are consistent with the Kondo effect in this system. The intermediate 𝑥 = 0.105 sample lies between the magnetic ordered and the Kondo regime and is in the vicinity of the AFM quantum critical point (QCP). Thus, La 2⁢ (Cu 𝑥 ⁢Ni 1−𝑥 ) 7 is an example of a small moment system that can be tuned through a QCP. Given these data combined with the fact that the La 2⁢ Ni 7 structure has kagomelike, Ni sublattices running perpendicular to the crystallographic 𝑐 axis, and a predicted 3⁢𝑑-electron flat band that contributes to the density of states near the Fermi energy, La 2 ⁢(Cu 𝑥 ⁢Ni 1−𝑥 ) 7 becomes a promising system to host and study exotic physics.

Das, Atreyee [Ames Laboratory, and Iowa State Univ↗

DOE OSTI2025

Anisotropic magnetic behavior of Nd 3 ⁢ScBi 5 and Pr 3 ⁡ScBi 5 single crystals

Here, we report an investigation of the magnetic, thermodynamic, and transport properties of single-crystalline Nd 3 ⁢ScBi 5 and Pr 3 ⁡ScBi 5 . Both compounds crystallize in the hexagonal 𝑃⁢6 3 /𝑚⁢𝑐⁢𝑚 space group that is common to related materials with rare-earth atoms that form twisted kagome nets. Nd 3 ⁢ScBi 5 undergoes two successive antiferromagnetic transitions, at 𝑇 𝑁 =5.6K and 𝑇 2 =4.7K. When a magnetic field is applied along [100], both 𝑇 𝑁 and 𝑇 2 are suppressed with increasing field, and multiple metamagnetic transitions are observed; in-plane anisotropy is demonstrated by a slight broadening and movement of the metamagnetic transitions when the field is applied along [110]. For H ∥ [001], 𝑇 𝑁 and 𝑇 2 exhibit only a weak field dependence and metamagnetic transitions are not observed. The magnetoresistance and Hall effect respond strongly to the metamagnetic transitions and further motivate a detailed characterization of the magnetic structures under applied fields. Pr 3 ⁡ScBi 5 , in contrast, undergoes a single antiferromagnetic transition at 𝑇 𝑁 =5.3K and a single metamagnetic transition at higher fields. These findings place Nd 3 ⁢ScBi 5 and Pr 3 ⁡ScBi 5 as promising systems for exploring anisotropic magnetism and field-driven magnetic phase transitions in intermetallic compounds.

36 MATERIALS SCIENCE↗

DOE OSTI2026

Low-temperature magnetic structure and lattice response in SmCuAs 2

We investigated the structural and magnetic properties of single-crystalline SmCuAs 2 using high-resolution synchrotron x-ray diffraction and x-ray resonant magnetic scattering (XRMS) at the Sm 𝐿 2 and 𝐿 3 edges. Temperature-dependent diffraction measurements confirm that SmCuAs2 maintains its tetragonal symmetry from room temperature down to 8 K, with lattice parameters showing anomalous behavior below the resistivity minimum (𝑇≈30K). Notably, the c-axis lattice parameter exhibits a plateau and subsequent increase near the Néel temperature, indicating magnetoelastic coupling. XRMS measurements reveal a commensurate antiferromagnetic structure with a propagation vector 𝒒=(0,0,0.5). Our measurement shows that the Sm moments are aligned within the 𝒂𝒃 plane and arranged in a ++−− stacking along the 𝒄 axis. Comparison with related 𝑅⁢𝐸⁢CuAs 2 compounds (RE = Pr, Nd, and Gd) suggests that in-plane moment orientation and associated magnetic frustration play a key role in the emergence of the resistivity minimum. Differences in spin-orbit and magnetoelastic coupling across the series highlight their importance in governing low-temperature transport behavior.

36 MATERIALS SCIENCE↗

DOE OSTI2026

Magnetic order in the van der Waals magnet VCl 3

Here, we investigated the structural and magnetic properties of single-crystalline VCl 3 , a newly synthesized member of the vanadium trihalide family. High-quality single crystals were grown by the chemical vapor transport method, and their behavior was characterized using neutron diffraction and thermodynamic measurements. We show that VCl 3 crystallizes in the BiI 3 -type structure at room temperature and undergoes a structural phase transition at 𝑇 𝑆 = 103.7⁢(5)⁢K that lowers the lattice symmetry, followed by a zigzag antiferromagnetic order with a propagation vector 𝑘 = (0,0.5,1) below 𝑇 𝑁 = 21.8⁢(1)⁢K. Neutron diffraction experiments indicate that the ordered moments are canted by approximately 21° away from the 𝑐 axis toward the 𝑎 axis, yielding a total moment of approximately 1.09⁢(2) ⁢𝜇 B /V 3+ . Field-dependent magnetization along the 𝑐 axis exhibits a half magnetization plateau, indicative of a field-stabilized fractional state. These results establish VCl 3 as a new platform for exploring structural transitions, anisotropic magnetism, and field-induced phases in vanadium-based honeycomb magnets.

Kao, Zeyu [Fudan Univ., Shanghai (China)]↗

DOE OSTI2026

Anisotropic magnetism and Kondo-lattice behavior in the frustrated antiferromagnet Ce 3 ⁢MgBi 5

Here, we report the synthesis and physical characterization of single-crystalline Ce 3 ⁢MgBi 5 , a previously unexplored member of the Ce 3 ⁢𝑀⁢𝑃⁢𝑛 5 family. This compound crystallizes in the hexagonal 𝑃⁢6 3 /𝑚⁢𝑐⁢𝑚 structure, featuring an anisotropic Ce sublattice composed of zigzag chains along the 𝑐 axis and a distorted kagome-like network in the basal plane. Magnetization measurements reveal antiferromagnetic order below 𝑇 𝑁 ≈ 4.2K with strong magnetic anisotropy and multiple field-induced metamagnetic transitions for fields applied perpendicular to [001], leading to a dome-shaped 𝐻–𝑇 phase diagram. Electrical transport exhibits characteristic signatures of a Ce-based Kondo lattice, including broad resistivity maxima and pronounced field-dependent anomalies in the magnetoresistance and Hall response that track the magnetic phase boundaries. Specific-heat measurements confirm the magnetic transition and show that the full R ⁢ln⁡ 2 entropy expected for a Ce 3+ Kramers doublet is recovered by 20 K, indicating an extended temperature range of magnetic fluctuations consistent with Kondo correlations. Our results establish Ce 3 ⁢MgBi 5 as a platform within the Ce 3 ⁢𝑀⁢𝑃⁢𝑛 5 family for exploring the interplay of geometric frustration, magnetic anisotropy, and Kondo-lattice physics under applied magnetic fields.

Kondo effect↗

DOE OSTI2025

Anisotropic Thermal Transport in Quasi-2D Ruddlesden-Popper Hybrid Perovskite Superlattices

Two-dimensional hybrid metal-halide perovskites (2D-MHPs) have emerged as important solution-processed semiconductors with favorable optical and electronic properties for diverse applications in photovoltaics, optoelectronics, and spintronics. The quasi-2D layered structures, featuring large acoustic impedance mismatches between the organic and inorganic sublattices, are expected to result in distinct and anisotropic thermal transport properties along the cross-plane and in-plane directions. Here, we introduce transducer-free vibrational-pump-visible-probe (VPVP) approaches that enable accurate quantification of anisotropic thermal transport properties in various archetypical single-crystalline 2D-MHPs. Specifically, using VPVP spectroscopy and VPVP microscopy, we measure the anisotropic thermal diffusivities of 2D-MHPs with systematically varied Pb-I octahedral layer thicknesses, as well as organic spacer types and lengths, revealing how these structural parameters alter the cross-plane and in-plane thermal transport properties in distinct ways. While diffuse interface scattering plays an important role in dictating cross-plane thermal transport, in-plane thermal transport is primarily determined by phonon transport within interconnected inorganic layers. Density functional theory incorporating four-phonon scatterings provides further insight into the low thermal conductivity and modest thermal conduction anisotropy in 2D-MHPs. Our work demonstrates a new all-optical and noncontact method, which requires minimal sample preparation and allows direct visualization of cross-plane and in-plane thermal transport, potentially compatible with sample environments. The demonstrated VPVP approaches can advance understanding of thermal transport in 2D-MHPs as well as wide-ranging hybrid and polymeric semiconductors beyond 2D-MHPs.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Tuning the structure and superconductivity of SrNi 2⁢ P 2 by Rh substitution

The compound SrNi 2⁢ P 2 is unique among the ThCr 2 ⁢Si 2 class since it exhibits a temperature-induced transition upon cooling from an uncollapsed tetragonal (ucT) state to a one-third-collapsed orthorhombic (tcO) state where one out of every three P-rows bond across the Sr layers. This compound is also known for exhibiting bulk superconductivity below 1.4 K at ambient pressure. Here, in this paper, we report on the effects of Rh substitution in Sr⁢(Ni 1-x ⁢Rh x ) 2 ⁢P 2 on the structural and superconducting properties. We studied the variation of the nearest P-P distances as a function of the Rh fraction at room temperature, as well as its temperature dependence for selected compositions. We find that increasing the Rh fraction leads to a decrease in the transition temperature between the ucT and tcO states, until a full suppression of the tcO state for x ≥ 0.166. The superconducting transition first remains nearly insensitive to the Rh fraction, and then it increases to 2.3 K after the tcO state is fully suppressed. These results are summarized in a phase diagram, built upon the characterization by energy dispersive x-ray spectroscopy, x-ray diffraction, resistance, magnetization, and specific heat measurements done on crystalline samples with varying Rh content. The relationship between band structure, crystal structure, and superconductivity is discussed based on previously reported band structure calculations on SrRh 2 ⁢P 2 . Moreover, the effect of Rh fraction on the stress-induced structural transitions is also addressed by means of strain-stress studies done by uniaxial compression of single-crystalline micropillars of Sr⁢(Ni 1-x ⁢Rh x ) 2 ⁢P 2 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2025

Physical properties of intergrowth compound Eu 2 CuZn 2 P 3

Here, the physical properties of single-crystalline Eu 2 ⁢CuZn 2 ⁢P 3 were inspected via thermodynamic, transport, and neutron diffraction measurements. Eu 2 ⁢ CuZn 2⁢ P 3 is composed of EuCuP and EuZn 2 ⁢ P 2 motifs stacked in a one-to-one ratio. The magnetic response of Eu 2 ⁢ CuZn 2 ⁢ P 3 is similar to that of EuZn 2 ⁢ P 2 in its A-type antiferromagnetic (semiconducting) state. A Néel temperature of T N = 40.3K is obtained from the specific heat capacity. Single-crystal neutron diffraction reveals a (001) magnetic propagation vector, with primarily in-plane moments coupled along [001] in an up-up-down-down pattern. This spin structure retains the ferromagnetic EuCuP motifs and antiferromagnetic coupling across the EuZn 2 ⁢P 2 motifs. The electrical resistivity is characterized by metallic behavior above 100 K, an increase in ρ upon cooling below ≈ 75K, and a large negative magnetoresistance below T N . First principles calculations evidence a narrow band gap for antiferromagnetic ordering and semimetallic behavior for the ferromagnetic state. This is consistent with the observed effect of magnetic field on the electrical resistivity. Hall effect measurements reveal a field-induced, negative anomalous Hall effect that increases on cooling down to 2 K. Also, an unconventional contribution to the Hall effect dominates the low-field Hall signal, particularly near T N , and is similar in appearance to a topological Hall effect. However, further work is necessary to understand if any of the transport properties have topological origins or if magnetism-induced modifications to the Fermi surface induce these unusual Hall effect signals in this and related materials.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Type-II Weyl nodes, flat bands, and evidence for a topological Hall-effect in the new ferromagnet FeCr 3 Te 6

The interplay between linearly dispersing, or Dirac-like, and flat electronic bands, for instance, in the kagome ferromagnets, has attracted attention due to a possible interplay between topology and electronic correlations. Here, we report the synthesis, structural, electrical, and magnetic properties of a single-crystalline ferromagnetic compound, namely Fe 1/3 ⁢CrTe 2 or FeCr 3 ⁢Te 6 , which crystallizes in the 𝑃$\overline{3}$⁢𝑚⁢1 space group instead of the 𝐼⁢2/𝑚 previously reported for FeCr 2 ⁢Te 4 . Electronic band structure calculations reveal type-II Dirac nodes and relatively flat bands near the Fermi level (ε 𝐹 ). This compound shows onset Curie temperature 𝑇 c ≃ 120K, followed by an additional ferromagnetic transition near 𝑇 c2 ∼ 92.5K. Below 𝑇 c , FeCr 3 ⁢Te 6 displays a pronounced anomalous Hall effect, as well as sizable coercive fields that exceed 𝜇 0 ⁢𝐻=1 T at low 𝑇⁢s. However, a scaling analysis indicates that the anomalous Hall effect results from a significant intrinsic contribution, as expected from the calculations, and also from the extrinsic mechanism, i.e., scattering. The extrinsic contribution probably results from occupational disorder at the 1b Fe-site within the van der Waals gap of the CrTe 2 host. We also observe evidence for a topological Hall component superimposed onto the overall Hall response, suggesting the presence of chiral spin textures akin to skyrmions in this centrosymmetric system. Their possible presence will require experimental confirmation.

36 MATERIALS SCIENCE↗

NASA NTRS1976

Oxidation of metals and alloys in controlled atmospheres using in situ transmission electron microscopy and Auger spectrography

Single-crystalline thin films of copper were oxidized at an isothermal temperature of 425 C and at an oxygen partial pressure of .005 Torr in situ in a high-resolution electron microscope. The specimens were prepared by epitaxial vapor deposition onto polished 100 and 110 faces of rocksalt and mounted in a hot stage inside an ultra-high-vacuum specimen chamber of the microscope. Large amounts of sulfur, carbon, and oxygen were detected by Auger electron spectroscopy on the surface of the as-received films and were removed in situ by ion-sputter etching immediately prior to the oxidation. The nucleation and growth characteristics of Cu2O on Cu were studied. Results show that neither stacking faults nor dislocations are associated with the Cu2O nucleation sites. The growth of Cu2O nuclei is linear with time. The experimental findings, including results from oxygen dissolution experiments and from repetitive oxidation-reduction-oxidation sequences, fit well into the framework of an oxidation process involving (a) the formation of a surface-charge layer, (b) oxygen saturation in the metal and (c) nucleation, followed by surface diffusion of oxygen and bulk diffusion of copper for lateral and vertical oxide growth, respectively.

Rao, D. B.↗

NASA NTRS1976

Direct observation of small cluster mobility and ripening

Direct evidence is reported for the simultaneous occurrence of Ostwald ripening and short-distance cluster mobility during annealing of discontinuous metal films on clean amorphous substrates. The annealing characteristics of very thin particulate deposits of silver on amorphized clean surfaces of single-crystalline thin graphite substrates have been studied by in situ transmission electron microscopy (TEM) under controlled environmental conditions in the temperature range from 25 to 450 C. It was possible to monitor all stages of the experiments by TEM observation of the same specimen area. Slow Ostwald ripening was found to occur over the entire temperature range, but the overriding surface transport mechanism was short-distance cluster mobility. This was concluded from in situ observations of individual particles during annealing and from measurements of cluster size distributions, cluster number densities, area coverages, and mean cluster diameters.

Heinemann, K.↗

NASA NTRS1984

Amorphous metallic films in silicon metallization systems

The general objective was to determine the potential of amorphous metallic thin films as a means of improving the stability of metallic contacts to a silicon substrate. The specific objective pursued was to determine the role of nitrogen in the formation and the resulting properties of amorphous thin-film diffusion barriers. Amorphous metallic films are attractive as diffusion barriers because of the low atomic diffusivity in these materials. Previous investigations revealed that in meeting this condition alone, good diffusion barriers are not necessarily obtained, because amorphous films can react with an adjacent medium (e.g., Si, Al) before they recrystallize. In the case of a silicon single-crystalline substrate, correlation exists between the temperature at which an amorphous metallic binary thin film reacts and the temperatures at which the films made of the same two metallic elements react individually. Amorphous binary films made of Zr and W were investigated. Both react with Si individually only at elevated temperatures. It was confirmed that such films react with Si only above 700 C when annealed in vacuum for 30 min. Amorphous W-N films were also investigated. They are more stable as barriers between Al and Si than polycrystalline W. Nitrogen effectively prevents the W-Al reaction that sets in at 500 C with polycrystalline W.

Nicolet, M. A.↗

NASA NTRS1986

Initial observations of GeSe-xenon transport experiments performed on the D1 space flight

GeSe-xenon experiments performed aboard the D1 mission at xenon pressures of 2 and 6 atm confirm the crystal growth pattern, sizes, and surface morphology of crystals previously grown aboard STS-7 for different pressures. Besides the deposition and growth of GeSe crystals on the ampoule wall, several large single-crystalline GeSe platelets with lateral dimensions much greater than those of crystals on the wall and obtained on the ground are found. The present results reemphasize the question concerning the nucleation phenomena in microgravity.

Wiedemeier, H.↗

NASA NTRS1990

Si-Ge-metal ternary phase diagram calculations

Solution crystal growth and doping conditions of Si-Ge alloys used for high-temperature thermoelectric generation are determined here. Liquid-phase epitaxy (LPE) has been successfully employed recently to obtain single-crystalline homogeneous layers of Si-Ge solid solutions from a liquid metal solvent. Knowledge of Si-Ge-metallic solvent ternary phase diagrams is essential for further single-crystal growth development. Consequently, a thermodynamic equilibrium model was used to calculate the phase diagrams of the Si-Ge-M systems, including solid solubilities, where M is Al, Ga, In, Sn, Pb, Sb, or Bi. Good agreement between calculated liquidus and solidus data and experimental DTA and microprobe results was obtained. The results are used to compare the suitability of the different systems for crystal growth (by LPE-type process).

Fleurial, J. P.↗