Strong Local Polarization Fluctuations Enabled High Electrostatic Energy Storage in Pb-Free Relaxors.

Electrostatic energy-storage ceramic capacitors are essential components of modern electrified power systems. However, improving their energy-storage density while maintaining high efficiency to facilitate cutting-edge miniaturized and integrated applications remains an ongoing challenge. Herein, we report a record-high energy-storage density of 20.3 J cm-3 together with a high efficiency of 89.3% achieved by constructing a relaxor ferroelectric state with strongly enhanced local polarization fluctuations. This is realized by incorporating highly polarizable, heterovalent, and large-sized Zn and Nb ions into a Bi0.5Na0.5TiO3-BaTiO3 ferroelectric matrix with very strong tetragonal distortion. Element-specific local structure analysis revealed that the foreign ions strengthen the magnitude of the unit-cell polarization vectors while simultaneously reducing their orientation anisotropy and forming strong fluctuations in both magnitude and orientation within 1-3 nm polar clusters. This leads to a particularly high polarization variation (ΔP) of 72 µC cm-2, low hysteresis, and a high effective polarization coefficient at a high breakdown strength of 80 kV mm-1. This work has surpassed the current energy density limit of 20 J cm-3 in bulk Pb-free ceramics and has demonstrated that controlling the local structure via the chemical composition design can open up new possibilities for exploring relaxors with high energy-storage performance.

Chemical Framework to Design Linear-like Relaxors toward Capacitive Energy Storage.

ABO3-type perovskite relaxor ferroelectrics (RFEs) have emerged as the preferred option for dielectric capacitive energy storage. However, the compositional design of RFEs with high energy density and efficiency poses significant challenges owing to the vast compositional space and the absence of general rules. Here, we present an atomic-level chemical framework that captures inherent characteristics in terms of radius and ferroelectric activity of ions. By categorizing A/B-site ions as host framework, rattling, ferroelectrically active, and blocking ions and assembling these four types of ions with specific criteria, linear-like relaxors with weak locally correlated and highly extendable unit-cell polarization vectors can be constructed. As example, we demonstrate two new compositions of Bi0.5K0.5TiO3-based and BaTiO3-based relaxors, showing extremely high recoverable energy densities of 17.3 and 12.1 J cm-3, respectively, both with a high efficiency of about 90%. Further, the role of different types of ions in forming heterogeneous polar structures is identified through element-specific local structure analysis using neutron total scattering combined with reverse Monte Carlo modeling. Our work not only opens up new avenues toward rational compositional design of high energy storage performance lead-free RFEs but also sheds light on atomic-level manipulation of functional properties in compositionally complex ferroelectrics.

Outstanding Energy-Storage Density Together with Efficiency of above 90% via Local Structure Design.

Dielectric ceramic capacitors with high recoverable energy density (Wrec) and efficiency (η) are of great significance in advanced electronic devices. However, it remains a challenge to achieve high Wrec and η parameters simultaneously. Herein, based on density functional theory calculations and local structure analysis, the feasibility of developing the aforementioned capacitors is demonstrated by considering Bi0.25Na0.25Ba0.5TiO3 (BNT-50BT) as a matrix material with large local polarization and structural distortion. Remarkable Wrec and η of 16.21 J/cm3 and 90.5% have been achieved in Bi0.25Na0.25Ba0.5Ti0.92Hf0.08O3 via simple chemical modification, which is the highest Wrec value among reported bulk ceramics with η greater than 90%. The examination results of local structures at lattice and atomic scales indicate that the disorderly polarization distribution and small nanoregion (∼3 nm) lead to low hysteresis and high efficiency. In turn, the drastic increase in local polarization activated via the ultrahigh electric field (80 kV/mm) leads to large polarization and superior energy storage density. Therefore, this study emphasizes that chemical design should be established on a clear understanding of the performance-related local structure to enable a targeted regulation of high-performance systems.

Local Chemical Clustering Enabled Ultrahigh Capacitive Energy Storage in Pb-Free Relaxors.

Designing Pb-free relaxors with both a high capacitive energy density (Wrec) and high storage efficiency (η) remains a remarkable challenge for cutting-edge pulsed power technologies. Local compositional heterogeneity is crucial for achieving complex polar structure in solid solution relaxors, but its role in optimizing energy storage properties is often overlooked. Here, we report that an exceptionally high Wrec of 15.2 J cm-3 along with an ultrahigh η of 91% can be achieved through designing local chemical clustering in Bi0.5Na0.5TiO3-BaTiO3-based relaxors. A three-dimensional atomistic model derived from neutron/X-ray total scattering combined with reverse Monte Carlo method reveals the presence of subnanometer scale clustering of Bi, Na, and Ba, which host differentiated polar displacements, and confirming the prediction by density functional theory calculations. This leads to a polar state with small polar clusters and strong length and direction fluctuations in unit-cell polar vectors, thus manifesting improved high-field polarizability, steadily reduced hysteresis, and high breakdown strength macroscopically. The favorable polar structure features also result in a unique field-increased η, excellent stability, and superior discharge capacity. Our work demonstrates that the hidden local chemical order exerts a significant impact on the polarization characteristic of relaxors, and can be exploited for accessing superior energy storage performance.

Chemical Design of Pb-Free Relaxors for Giant Capacitive Energy Storage.

Dielectric capacitors have captured substantial attention for advanced electrical and electronic systems. Developing dielectrics with high energy density and high storage efficiency is challenging owing to the high compositional diversity and the lack of general guidelines. Herein, we propose a map that captures the structural distortion (δ) and tolerance factor (t) of perovskites to design Pb-free relaxors with extremely high capacitive energy storage. Our map shows how to select ferroelectric with large δ and paraelectric components to form relaxors with a t value close to 1 and thus obtaining eliminated hysteresis and large polarization under a high electric breakdown. Taking the Bi0.5Na0.5TiO3-based solid solution as an example, we demonstrate that composition-driven predominant order-disorder characteristic of local atomic polar displacements endows the relaxor with a slushlike structure and strong local polar fluctuations at several nanoscale. This leads to a giant recoverable energy density of 13.6 J cm-3, along with an ultrahigh efficiency of 94%, which is far beyond the current performance boundary reported in Pb-free bulk ceramics. Our work provides a solution through rational chemical design for obtaining Pb-free relaxors with outstanding energy-storage properties.

Superior Capacitive Energy-Storage Performance in Pb-Free Relaxors with a Simple Chemical Composition.

Chemical design of lead-free relaxors with simultaneously high energy density (Wrec) and high efficiency (η) for capacitive energy-storage has been a big challenge for advanced electronic systems. The current situation indicates that realizing such superior energy-storage properties requires highly complex chemical components. Herein, we demonstrate that, via local structure design, an ultrahigh Wrec of 10.1 J/cm3, concurrent with a high η of 90%, as well as excellent thermal and frequency stabilities can be achieved in a relaxor with a very simple chemical composition. By introducing 6s2 lone pair stereochemical active Bi into the classical BaTiO3 ferroelectric to generate a mismatch between A- and B-site polar displacements, a relaxor state with strong local polar fluctuations can be formed. Through advanced atomic-resolution displacement mapping and 3D reconstructing the nanoscale structure from neutron/X-ray total scattering, it is revealed that the localized Bi enhances the polar length largely at several perovskite unit cells and disrupts the long-range coherent Ti polar displacements, resulting in a slush-like structure with extremely small size polar clusters and strong local polar fluctuations. This favorable relaxor state exhibits substantially enhanced polarization, and minimized hysteresis at a high breakdown strength. This work offers a feasible avenue to chemically design new relaxors with a simple composition for high-performance capacitive energy-storage.

Understanding the Re-entrant Phase Transition in a Non-magnetic Scheelite.

The stereochemical activity of lone pair electrons plays a central role in determining the structural and electronic properties of both chemically simple materials such as H2O, as well as more complex condensed phases such as photocatalysts or thermoelectrics. TlReO4 is a rare example of a non-magnetic material exhibiting a re-entrant phase transition and emphanitic behavior in the long-range structure. Here, we describe the role of the Tl+ 6s2 lone pair electrons in these unusual phase transitions and illustrate its tunability by chemical doping, which has broad implications for functional materials containing lone pair bearing cations. First-principles density functional calculations clearly show the contribution of the Tl+ 6s2 in the valence band region. Local structure analysis, via neutron total scattering, revealed that changes in the long-range structure of TlReO4 occur due to changes in the correlation length of the Tl+ lone pairs. This has a significant effect on the anion interactions, with long-range ordered lone pairs creating a more densely packed structure. This resulted in a trade-off between anionic repulsions and lone pair correlations that lead to symmetry lowering upon heating in the long-range structure, whereby lattice expansion was necessary for the Tl+ lone pairs to become highly correlated. Similarly, introducing lattice expansion through chemical pressure allowed long-range lone pair correlations to occur over a wider temperature range, demonstrating a method for tuning the energy landscape of lone pair containing functional materials.

Cation Short-Range Ordering of MgAl2O4 and NiAl2O4 Spinel Oxides at High Temperatures via In Situ Neutron Total Scattering.

Complex oxides that adopt the isometric spinel structure (AB2O4) are important for numerous technological applications and are relevant for certain geological processes, which involve exposure to extreme environments such as high pressures and temperatures. Recent studies have shown that the changes to the spinel structure caused by these environments are complex and depend on the material length scale under consideration. In this study, we have expanded this approach to the behavior of spinels under high temperatures. In situ neutron total scattering experiments, coupled with pair distribution function analysis, performed on two spinel compositions with various levels of pre-existing disorder (MgAl2O4 and NiAl2O4) revealed that both compositions trend to a state of maximum disorder where the A and B cations are randomly distributed among the two available sites. Temperature-induced cation inversion, conventionally understood as an exchange of cations on the A and B sites, is locally expressed as an atomic rearrangement to a tetragonal symmetry, a correlation that is retained up to the maximum temperature studied (1000 °C). A complex thermal expansion behavior is revealed wherein the oxide materials expand heterogeneously at the level of coordination polyhedra with an apparent dependence on bond strength.

The "good," the "bad," and the "hidden" in neutron scattering and molecular dynamics of ionic aqueous solutions.

We characterize a concentrated 7.3 m CaCl2 solution, combining neutron diffraction with chloride isotopic substitution (Cl-NDIS) in null water and molecular dynamics (MD) simulations. We elucidate the solution structure, thermodynamic properties, and extent of ion pairing previously suggested as concentration-dependent and often not observed at lower concentrations. Our Cl-NDIS measurements designate the solvent-shared ion pairing as dominant and the contact ion pairing (CIP) as insignificant even under conditions close to the solubility limit. The MD models parameterized against neutron diffraction with calcium isotopic substitution (Ca-NDIS) overestimate CIP despite successfully reproducing most of the Cl-NDIS signal. This drawback originates from the fact that Ca2+-Cl- interactions were primarily "hidden" in the Ca-NDIS signal due to overlapping with Ca2+-Ow and Ca2+-Hw contributions to the total scattering. Contrary, MD models with moderate CIP and possessing generally good performance at high concentrations fail to reproduce the NDIS measurements accurately. Therefore, the electronic polarization, introduced in most of the recent MD models via scaling ionic charges, resolves some but not all parameterization drawbacks. We conclude that despite improving the quality of MD models "on average," the question "which model is the best" has not been answered but replaced by the question "which model is better for a given research." An overall "good" model can still be inappropriate or, in some instances, "bad" and, unfortunately, produce erroneous results. The accurate interpretation of several NDIS datasets, complemented by MD simulations, can prevent such mistakes and help identify the strengths, weaknesses, and convenient applications for corresponding computational models.

Observation of Vacancies, Faults, and Superstructures in Ln5Mo2O12 (Ln = La, Y, and Lu) Compounds with Direct Mo-Mo Bonding.

Among oxide compounds with direct metal-metal bonding, the Y5Mo2O12 (A5B2O12) structural family of compounds has a particularly intriguing low-dimensional structure due to the presence of bioctahedral B2O10 dimers arranged in one-dimensional edge-sharing chains along the direction of the metal-metal bonds. Furthermore, these compounds can have a local magnetic moment due to the noninteger oxidation state (+4.5) of the transition metal, in contrast to the conspicuous lack of a local moment that is commonly observed when oxide compounds with direct metal-metal bonding have integer oxidation states resulting from the lifting of orbital degeneracy typically induced by the metal-metal bonding. Although a monoclinic C2/m structure has been previously proposed for Ln5Mo2O12 (Ln = La-Lu and Y) members of this family based on prior single crystal diffraction data, it is found that this structural model misses many important structural features. On the basis of synchrotron powder diffraction data, it is shown that the C2/m monoclinic unit cell represents a superstructure relative to a previously unrecognized orthorhombic Immm subcell and that the superstructure derives from the ordering of interchangeable Mo2O10 and LaO6 building blocks. The superstructure for this reason is typically highly faulted, as evidenced by the increased breadth of superstructure diffraction peaks associated with a coherence length of 1-2 nm in the c* direction. Finally, it is shown that oxygen vacancies can occur when Ln = La, producing an oxygen deficient stoichiometry of La5Mo2O11.55 and an approximately 10-fold reduction in the number of unpaired electrons due to the reduction of the average Mo valence from +4.5 to +4.05, a result confirmed by magnetic susceptibility measurements. This represents the first observation of oxygen vacancies in this family of compounds and provides an important means of continuously tuning the magnetic interactions within the one-dimensional octahedral chains of this system.

Bi4TaO8Cl Nano-Photocatalyst: Influence of Local, Average, and Band Structure.

The average structure, local structure, and band structure of nanoparticles of photocatalyst Bi4TaO8Cl, an Aurivillius-Sillen layered material, has been studied by powder neutron Rietveld refinement, neutron pair distribution function technique, Raman scattering, and density functional theory calculations. A significant local structural deviation of nano-Bi4TaO8Cl was established in contrast to the local structure of bulk-Bi4TaO8Cl. Local structure was further supported by Raman scattering measurements. Through DFT calculations, we identify specific features in the electronic band structure that correlate lower secondary structural distortions in nano-Bi4TaO8Cl. Increased distortion of TaO6, decreased Ta-O-Ta bond angle, and increased octahedral tilt in the local structure of nano-Bi4TaO8Cl influence the band structure and the electron hole pair migration. Therefore, in addition to morphology and size, the local structure of a nanomaterial contributes to the photocatalytic performance. Trapping experiments confirm the role of superoxide radical in the photocatalysis mechanism of this material. Such studies help in developing new functional materials with better photocatalytic efficiency to address energy and environmental issues.

Structural relaxation, viscosity, and network connectivity in a hydrogen bonding liquid.

In liquids, the ability of neighboring molecules to rearrange and jostle past each other is directly related to viscosity, the property which describes the propensity to flow. The presence of hydrogen bonds (H-bonds) complicates the molecular scale picture of viscosity. H-Bonds are attractive, directional interactions between molecules which, in some cases, result in transient network structures. In this work, we use experimental and computational methods to demonstrate that the timescale of H-bond network reorganization is the dominant dynamical timescale associated with viscosity for the case of the model H-bonding liquid n-methylacetamide (NMA). This molecule is a peptide analog which forms a transient linear H-bond network. Individual H-bond lifetimes and dynamical fluctuations were observed on the timescale of 1.5 ps, while collective motions and the longest lived population of H-bond partner lifetimes were observed on the order of 20 ps, in agreement with the Maxwell relaxation time. This identifies a mechanism which may aid in understanding the emergence of various complex phenomena arising from transient molecular structures, with implications ranging from the internal dynamics of proteins, to the glass transition, to better understanding the origins of the unique properties of H-bonding liquids.

A new molybdenum nitride catalyst with rhombohedral MoS2 structure for hydrogenation applications.

Nitrogen-rich transition-metal nitrides hold great promise to be the next-generation catalysts for clean and renewable energy applications. However, incorporation of nitrogen into the crystalline lattices of transition metals is thermodynamically unfavorable at atmospheric pressure; most of the known transition metal nitrides are nitrogen-deficient with molar ratios of N:metal less than a unity. In this work, we have formulated a high-pressure route for the synthesis of a nitrogen-rich molybdenum nitride through a solid-state ion-exchange reaction. The newly discovered nitride, 3R-MoN2, adopts a rhombohedral R3m structure, isotypic with MoS2. This new nitride exhibits catalytic activities that are three times more active than the traditional catalyst MoS2 for the hydrodesulfurization of dibenzothiophene and more than twice as high in the selectivity to hydrogenation. The nitride is also catalytically active in sour methanation of syngas with >80% CO and H2 conversion at 723 K. Our formulated route for the synthesis of 3R-MoN2 is at a moderate pressure of 3.5 GPa and, thus, is feasible for industrial-scale catalyst production.

Average and Local Crystal Structures of (Ga(1-x)Znx)(N(1-x)Ox) Solid Solution Nanoparticles.

We report a comprehensive study of the crystal structure of (Ga(1-x)Znx)(N(1-x)Ox) solid solution nanoparticles by means of neutron and synchrotron X-ray scattering. In our study, we used four different types of (Ga(1-x)Znx)(N(1-x)Ox) nanoparticles, with diameters of 10-27 nm and x = 0.075-0.51, which show energy band gaps from 2.21 to 2.61 eV. Rietveld analysis of the neutron diffraction data revealed that the average crystal structure is hexagonal wurtzite (space group P63mc) for the larger nanoparticles, while the crystal structure of smaller nanoparticles is disordered hexagonal. Pair-distribution-function analysis found that the intermediate crystal structure retains a "motif" of the average one; however, the local structure is more disordered. The implications of disorder on the reduced energy band gap are discussed.

Molybdenum nitrides as oxygen reduction reaction catalysts: structural and electrochemical studies.

Monometallic (δ-MoN, Mo5N6, and Mo2N) and bimetallic molybdenum nitrides (Co0.6Mo1.4N2) were investigated as electrocatalysts for the oxygen reduction reaction (ORR), which is a key half-reaction in hydrogen fuel cells. Monometallic hexagonal molybdenum nitrides are found to exhibit improved activities over rock salt type molybdenum nitride (γ-Mo2N), suggesting that improvements are due to either the higher molybdenum valence or a more favorable coordination environment in the hexagonal structures. Further enhancements in activity were found for hexagonal bimetallic cobalt molybdenum nitride (Co0.6Mo1.4N2), resulting in a modest onset potential of 0.713 V versus reversible hydrogen electrode (RHE). Co0.6Mo1.4N2 exhibits good stability in acidic environments, and in the potential range lower than 0.5 V versus RHE, the ORR appears to proceed via a four-electron mechanism based on the analysis of rotating disc electrode results. A redetermination of the structures of the binary molybdenum nitrides was carried out using neutron diffraction data, which is far more sensitive to nitrogen site positions than X-ray diffraction data. The revised monometallic hexagonal nitride structures all share many common features with the Co0.6Mo1.4N2 structure, which has alternating layers of cations in octahedral and trigonal prismatic coordination, and are thus not limited to only trigonal prismatic Mo environments (as was originally postulated for δ-MoN).

Mixed close-packed cobalt molybdenum nitrides as non-noble metal electrocatalysts for the hydrogen evolution reaction.

A two-step solid-state reaction for preparing cobalt molybdenum nitride with a nanoscale morphology has been used to produce a highly active and stable electrocatalyst for the hydrogen evolution reaction (HER) under acidic conditions that achieves an iR-corrected current density of 10 mA cm(-2) at -0.20 V vs RHE at low catalyst loadings of 0.24 mg/cm(2) in rotating disk experiments under a H2 atmosphere. Neutron powder diffraction and pair distribution function (PDF) studies have been used to overcome the insensitivity of X-ray diffraction data to different transition-metal nitride structural polytypes and show that this cobalt molybdenum nitride crystallizes in space group P63/mmc with lattice parameters of a = 2.85176(2) Å and c = 10.9862(3) Å and a formula of Co0.6Mo1.4N2. This space group results from the four-layered stacking sequence of a mixed close-packed structure with alternating layers of transition metals in octahedral and trigonal prismatic coordination and is a structure type for which HER activity has not previously been reported. Based on the accurate bond distances obtained from time-of-flight neutron diffraction data, it is determined that the octahedral sites contain a mixture of divalent Co and trivalent Mo, while the trigonal prismatic sites contain Mo in a higher oxidation state. X-ray photoelectron spectroscopy (XPS) studies confirm that at the sample surface nitrogen is present and N-H moieties are abundant.

Crystal and magnetic structures and physical properties of a new pyroxene NaMnGe2O6 synthesized under high pressure.

A new pyroxene compound, NaMnGe(2)O(6), has been synthesized at 3 GPa and 800 °C and fully characterized by X-ray single-crystal diffraction, neutron powder diffraction, and measurements of magnetization and specific heat. NaMnGe(2)O(6) crystallizes into a monoclinic C2/c structure with unit-cell parameters a = 9.859(2) Å, b = 8.7507(18) Å, c = 5.5724(11) Å, and ß = 105.64(3)° at 153 K. A cooperative Jahn-Teller distortion is formed by an ordering of the longest Mn-O bonds between two neighboring octahedra along the chain direction. This feature distinguishes NaMnGe(2)O(6) from other pyroxene compounds without Jahn-Teller active cations and suggests that the Jahn-Teller distortion competes with the intrinsic local distortion in the pyroxene structure. No orbital order-disorder transition has been found up to 750 K. Like other alkali-metal pyroxenes with S > (1)/(2), NaMnGe(2)O(6) (S = 2) was found to undergo a long-range antiferromagnetic (AF) ordering at T(N) = 7 K due to intrachain and interchain exchange interactions. Due to the peculiar structural features and the corresponding magnetic coupling, the weak AF spin ordering gives way to a ferromagnetic-like state at a sufficiently high magnetic field. Specific-heat measurements demonstrated that a large portion of the magnetic entropy, >60%, has been removed above T(N) as a result of strong spin correlations within the quasi-one-dimensional Mn(3+)-spin chains. The Reitveld refinement of neutron powder diffraction data gives a commensurate magnetic structure defined by k = [0 0 0.5] with Mn moments aligned mainly along the c-axis with a small component along both a- and b-axes.

Emergence of high piezoelectricity from competing local polar order-disorder in relaxor ferroelectrics.

Relaxor ferroelectrics are known for outstanding piezoelectric properties, finding a broad range of applications in advanced electromechanical devices. Decoding the origins of the enhanced properties, however, have long been complicated by the heterogeneous local structures. Here, we employ the advanced big-box refinement method by fitting neutron-, X-ray-based total scattering, and X-ray absorption spectrum simultaneously, to extract local atomic polar displacements and construct 3D polar configurations in the classical relaxor ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3. Our results demonstrate that prevailing order-disorder character accompanied by the continuous rotation of local polar displacements commands the composition-driven global structure evolution. The omnidirectional local polar disordering appears as an indication of macroscopic relaxor characteristics. Combined with phase-field simulations, it demonstrates that the competing local polar order-disorder between different states with balanced local polar length and direction randomness leads to a flattening free-energy profile over a wide polar length, thus giving rise to high piezoelectricity. Our work clarifies that the critical structural feature required for high piezoelectricity is the competition states of local polar rather than relaxor.

The nano- and meso-scale structure of amorphous calcium carbonate.

Understanding the underlying processes of biomineralization is crucial to a range of disciplines allowing us to quantify the effects of climate change on marine organisms, decipher the details of paleoclimate records and advance the development of biomimetic materials. Many biological minerals form via intermediate amorphous phases, which are hard to characterize due to their transient nature and a lack of long-range order. Here, using Monte Carlo simulations constrained by X-ray and neutron scattering data together with model building, we demonstrate a method for determining the structure of these intermediates with a study of amorphous calcium carbonate (ACC) which is a precursor in the bio-formation of crystalline calcium carbonates. We find that ACC consists of highly ordered anhydrous nano-domains of approx. 2 nm that can be described as nanocrystalline. These nano-domains are held together by an interstitial net-like matrix of water molecules which generate, on the mesoscale, a heterogeneous and gel-like structure of ACC. We probed the structural stability and dynamics of our model on the nanosecond timescale by molecular dynamics simulations. These simulations revealed a gel-like and glassy nature of ACC due to the water molecules and carbonate ions in the interstitial matrix featuring pronounced orientational and translational flexibility. This allows for viscous mobility with diffusion constants four to five orders of magnitude lower than those observed in solutions. Small and ultra-small angle neutron scattering indicates a hierarchically-ordered organization of ACC across length scales that allow us, based on our nano-domain model, to build a comprehensive picture of ACC formation by cluster assembly from solution. This contribution provides a new atomic-scale understanding of ACC and provides a framework for the general exploration of biomineralization and biomimetic processes.

Superior High-Temperature Strength in a Supersaturated Refractory High-Entropy Alloy.

Refractory high-entropy alloys (RHEAs) show promising applications at high temperatures. However, achieving high strengths at elevated temperatures above 1173K is still challenging due to heat softening. Using intrinsic material characteristics as the alloy-design principles, a single-phase body-centered-cubic (BCC) CrMoNbV RHEA with high-temperature strengths (beyond 1000 MPa at 1273 K) is designed, superior to other reported RHEAs as well as conventional superalloys. The origin of the high-temperature strength is revealed by in situ neutron scattering, transmission-electron microscopy, and first-principles calculations. The CrMoNbV's elevated-temperature strength retention up to 1273 K arises from its large atomic-size and elastic-modulus mismatches, the insensitive temperature dependence of elastic constants, and the dominance of non-screw character dislocations caused by the strong solute pinning, which makes the solid-solution strengthening pronounced. The alloy-design principles and the insights in this study pave the way to design RHEAs with outstanding high-temperature strength.