An isotropic zero thermal expansion alloy with super-high toughness

Zero thermal expansion (ZTE) alloys with high mechanical response are crucial for their practical usage. Yet, unifying the ZTE behavior and mechanical response in one material is a grand obstacle, especially in multicomponent ZTE alloys. Herein, we report a near isotropic zero thermal expansion (αl = 1.10 × 10-6 K-1, 260-310 K) in the natural heterogeneous LaFe54Co3.5Si3.35 alloy, which exhibits a super-high toughness of 277.8 ± 14.7 J cm-3. Chemical partition, in the dual-phase structure, assumes the role of not only modulating thermal expansion through magnetic interaction but also enhancing mechanical properties via interface bonding. The comprehensive analysis reveals that the hierarchically synergistic enhancement among lattice, phase interface, and heterogeneous structure is significant for strong toughness. Our findings pave the way to tailor thermal expansion and obtain prominent mechanical properties in multicomponent alloys, which is essential to ultra-stable functional materials.

Giant uniaxial negative thermal expansion in FeZr2 alloy over a wide temperature range

Negative thermal expansion (NTE) alloys possess great practical merit as thermal offsets for positive thermal expansion due to its metallic properties. However, achieving a large NTE with a wide temperature range remains a great challenge. Herein, a metallic framework-like material FeZr₂ is found to exhibit a giant uniaxial (1D) NTE with a wide temperature range (93-1078 K, [Formula: see text]). Such uniaxial NTE is the strongest in all metal-based NTE materials. The direct experimental evidence and DFT calculations reveal that the origin of giant NTE is the couple with phonons, flexible framework-like structure, and soft bonds. Interestingly, the present metallic FeZr₂ excites giant 1D NTE mainly driven by high-frequency optical branches. It is unlike the NTE in traditional framework materials, which are generally dominated by low energy acoustic branches. In the present study, a giant uniaxial NTE alloy is reported, and the complex mechanism has been revealed. It is of great significance for understanding the nature of thermal expansion and guiding the regulation of thermal expansion.

Superior zero thermal expansion dual-phase alloy via boron-migration mediated solid-state reaction

Rapid progress in modern technologies demands zero thermal expansion (ZTE) materials with multi-property profiles to withstand harsh service conditions. Thus far, the majority of documented ZTE materials have shortcomings in different aspects that limit their practical utilization. Here, we report on a superior isotropic ZTE alloy with collective properties regarding wide operating temperature windows, high strength-stiffness, and cyclic thermal stability. A boron-migration-mediated solid-state reaction (BMSR) constructs a salient "plum pudding" structure in a dual-phase Er-Fe-B alloy, where the precursor ErFe₁₀ phase reacts with the migrated boron and transforms into the target Er₂Fe₁₄B (pudding) and α-Fe phases (plum). The formation of such microstructure helps to eliminate apparent crystallographic texture, tailor and form isotropic ZTE, and simultaneously enhance the strength and toughness of the alloy. These findings suggest a promising design paradigm for comprehensive performance ZTE alloys.

Significant Zero Thermal Expansion Via Enhanced Magnetoelastic Coupling in Kagome Magnets

Zero-thermal-expansion (ZTE) alloys, as dimensionally stable materials, are urgently required in many fields, particularly in highly advanced modern industries. In this study, high-performance ZTE with a negligible coefficient of thermal expansion a_v as small as 2.4 ppm K^-1 in a broad temperature range of 85-245 K is discovered in Hf_0.85 Ta_0.15 Fe₂ C_0.01 magnet. It is demonstrated that the addition of trace interstitial atom C into Ta-substituted Hf_0.85 Ta_0.15 Fe₂ exhibits significant capability to tune the normal positive thermal expansion into high-performance ZTE via enhanced magnetoelastic coupling in stabilized ferromagnetic structure. Moreover, direct observation of the magnetic transition between ferromagnetic and triangular antiferromagnetic states via Lorentz transmission electron microscopy, along with corresponding theoretical calculations, further uncovers the manipulation mechanism of ZTE and negative thermal expansion. A convenient and effective method to optimize thermal expansion and achieve ZTE with interstitial C addition may result in broadened applications based on the strong correlation between the magnetic properties and crystal structure.

Chemical Diversity for Tailoring Negative Thermal Expansion

Negative thermal expansion (NTE), referring to the lattice contraction upon heating, has been an attractive topic of solid-state chemistry and functional materials. The response of a lattice to the temperature field is deeply rooted in its structural features and is inseparable from the physical properties. For the past 30 years, great efforts have been made to search for NTE compounds and control NTE performance. The demands of different applications give rise to the prominent development of new NTE systems covering multifarious chemical substances and many preparation routes. Even so, the intelligent design of NTE structures and efficient tailoring for lattice thermal expansion are still challenging. However, the diverse chemical routes to synthesize target compounds with featured structures provide a large number of strategies to achieve the desirable NTE behaviors with related properties. The chemical diversity is reflected in the wide regulating scale, flexible ways of introduction, and abundant structure-function insights. It inspires the rapid growth of new functional NTE compounds and understanding of the physical origins. In this review, we provide a systematic overview of the recent progress of chemical diversity in the tailoring of NTE. The efficient control of lattice and deep structural deciphering are carefully discussed. This comprehensive summary and perspective for chemical diversity are helpful to promote the creation of functional zero-thermal-expansion (ZTE) compounds and the practical utilization of NTE.

Plastic and low-cost axial zero thermal expansion alloy by a natural dual-phase composite

Zero thermal expansion (ZTE) alloys possess unique dimensional stability, high thermal and electrical conductivities. Their practical application under heat and stress is however limited by their inherent brittleness because ZTE and plasticity are generally exclusive in a single-phase material. Besides, the performance of ZTE alloys is highly sensitive to change of compositions, so conventional synthesis methods such as alloying or the design of multiphase to improve its thermal and mechanical properties are usually inapplicable. In this study, by adopting a one-step eutectic reaction method, we overcome this challenge. A natural dual-phase composite with ZTE and plasticity was synthesized by melting 4 atom% holmium with pure iron. The dual-phase alloy shows moderate plasticity and strength, axial zero thermal expansion, and stable thermal cycling performance as well as low cost. By using synchrotron X-ray diffraction, in-situ neutron diffraction and microscopy, the critical mechanism of dual-phase synergy on both thermal expansion regulation and mechanical property enhancement is revealed. These results demonstrate that eutectic reaction is likely to be a universal and effective method for the design of high-performance intermetallic-compound-based ZTE alloys.

Room Temperature Zero Thermal Expansion in a Cubic Cobaltite

Zero thermal expansion (ZTE) materials are highly desired in modern industries where high-precision processing is necessary. However, ZTE materials in pure form are extremely rare. The most widely used are Invar alloys, where the ZTE is intimately associated with spontaneous magnetic ordering, known as the magnetovolume effect (MVE). Despite tremendous studies, there is still no consensus on the microscopic origin of MVE in Invar alloys. Here, we report the discovery of room-temperature isotropic ZTE in a pure-form cobaltite perovskite, A-site disordered La_0.5Ba_0.5CoO_3-x. The temperature window of the anomalous thermal expansion shows large tunability by simply altering the oxygen content, making this material a promising candidate for practical applications. Furthermore, we unveil with compelling experimental evidence that the ZTE originates from an isostructural transition between antiferromagnetic large-volume phase and ferromagnetic small-volume phase, which might shed light on the MVE in Invar alloys.

Adjustable Magnetic Phase Transition Inducing Unusual Zero Thermal Expansion in Cubic RCo2-Based Intermetallic Compounds (R = Rare Earth)

Metallic materials that exhibit negligible thermal expansion or zero thermal expansion (ZTE) have great merit for practical applications, but these materials are rare and their thermal expansions are difficult to control. Here, we successfully tailored the thermal expansion behaviors from strongly but abruptly negative to zero over wide temperature ranges in a series of (Gd,R)(Co,Fe)₂ (R = Dy, Ho, Er) intermetallic compounds by tuning the composition to bring the first-order magnetic phase transition to second-order. Interestingly, an unusual isotropic ZTE property with a coefficient of thermal expansion of α _l = 0.16(0) × 10^-6 K^-1 was achieved in cubic Gd_0.25Dy_0.75Co_1.93Fe_0.07 (GDCF) in the temperature range of 10-275 K. The short-wavelength neutron powder diffraction, synchrotron X-ray diffraction, and magnetic measurement studies evidence that this ZTE behavior was ascribed to the rare-earth-moment-dominated spontaneous volume magnetostriction, which can be controlled by an adjustable magnetic phase transition. The present work extends the scope of the ZTE family and provides an effective approach to exploring ZTE materials, such as by adjusting the magnetism or ferroelectricity-related phase transition in the family of functional materials.

Effect of Si substitution in ferromagnetic Pr2Fe17: a magnetocaloric material with zero thermal expansion operative at high temperature

This article deals with the magnetic and thermal expansion properties of Pr2Fe16Si. This compound has been well characterized from the structural point of view by analysing X-ray diffraction (XRD) patterns. The temperature dependent behaviour of magnetization (M) and the structural parameters (lattice parameters, unit cell volume) suggest that the compound undergoes a second order phase transition from a paramagnetic to a ferromagnetic state at TC = 390 K, driven by an increase in bond length between iron atoms at 6c sites. The field-dependent behaviour of M below TC, and comparatively lower value of coercivity (Hc) have been explained by the role of Si atoms as pinning centres. In the ferromagnetic phase, the system is found to behave like an inhomogenous mean field system. The study of thermal expansion properties establishes that the compound is a zero thermal expansion material (αv = 5.3 × 10-6 K-1) operative in the temperature range T = 200-340 K. As a magnetocaloric material, Pr2Fe16Si possesses high RCP (87 J kg-1 at μ0H = 1.5 T), high operating temperature (390 K) and moderate |ΔSM|max.

Investigation of the kinetics and mechanism of Z-scheme Ag3PO4/WO3 p–n junction photocatalysts with enhanced removal efficiency for RhB

The activity of an Ag₃PO₄/polyhedron-like WO₃ photocatalyst could be enhanced 27 times compared to P25 in the visible light-driven region towards RhB.

Transverse vibration driven large uniaxial negative and zero thermal expansion in boron bridged REPt3B framework materials

In this work anomalous uniaxial thermal expansion behaviour at low temperatures along the c-direction of the tetragonal phase of different members of the antiperovskite REPt3B (RE = Sm, Gd-Tm) compounds is reported. Negative or zero thermal expansion (NTE/ZTE) behaviour in these compounds arises due to the transverse vibration of boron atoms in the linear Pt-B-Pt linkage. The coefficient of thermal expansion along the c-axis tends to become more negative in annealed compounds in comparison to those estimated for as-cast samples. While the as-cast TmPt3B and HoPt3B exhibit essentially ZTE behaviour, the NTE coefficient of annealed GdPt3B (∼-28 ppm K-1) is found to be even larger than that of the well known framework material ZrW2O8 (∼-9 ppm K-1) reported in the literature.