Near-zero Thermal Expansion Research Articles

Enhanced toughness of KZr2(PO4)3 ceramics via hydrothermal incorporation of multi-walled carbon nanotubes

The multi-walled carbon nanotubes/KZr₂(PO₄)₃ (MWCNTs/KZP) composite ceramics were successfully prepared by introducing MWCNTs during the hydrothermal process. The impact of MWCNTs addition on the crystal structure, morphology, mechanical strength, and thermal expansion properties of KZP ceramics was investigated. XRD and SEM analyses revealed that the introduction of MWCNTs did not alter the phase and crystal structure of KZP. It was observed that the MWCNTs formed a strong interfacial bond with the KZP matrix and were uniformly dispersed. Mechanical testing showed that the composite ceramic with 0.3 wt% MWCNTs exhibited significantly improved flexural strength and fracture toughness, measuring 125.08 MPa and 2.57 MPa m1/2, respectively, compared to the KZP ceramic. This enhancement was attributed to the refinement of KZP grain size and the formation of a high-strength bonding interface between MWCNTs and the KZP matrix. Moreover, the incorporation of MWCNTs not only improved the toughness of KZP ceramics but also imparted exceptional thermal properties, with a thermal expansion coefficient (TEC) ranging from −0.30 to 0.49 × 10−6/K, demonstrating outstanding near-zero low thermal expansion characteristics.

High-Entropy Magnet Enabling Distinctive Thermal Expansions in Intermetallic Compounds.

The high-entropy strategy has gained increasing popularity in the design of functional materials due to its four core effects. In this study, we introduce the concept of a "high-entropy magnet (HEM)", which integrates diverse magnetic compounds within a single phase and is anticipated to demonstrate unique magnetism-related properties beyond that of its individual components. This concept is exemplified in AB2-type layered Kagome intermetallic compounds (Ti,Zr,Hf,Nb,Fe)Fe2. It is revealed that the competition among individual magnetic states and the presence of magnetic Fe in originally nonmagnetic high-entropy sites lead to intricate magnetic transitions with temperature. Consequently, unusual transformations in thermal expansion property (from positive to zero, negative, and back to near zero) are observed. Specifically, a near-zero thermal expansion is achieved over a wide temperature range (10-360 K, αv = -0.62 × 10-6 K-1) in the A-site equal-atomic ratio (Ti1/5Zr1/5Hf1/5Nb1/5Fe1/5)Fe2 compound, which is associated with successive deflection of average Fe moments. The HEM strategy holds promise for discovering new functionalities in solid materials.

Negative and near-zero thermal expansion driven by cooperative Jahn–Teller effect in Fe2P2O7

Negative and near-zero thermal expansion driven by cooperative Jahn–Teller effect in Fe2P2O7

Zero thermal expansion in KxMnxIn2-x(MoO4)3 based materials

Zero thermal expansion (ZTE) materials can solve problems such as device failure and cracking caused by mismatched coefficient of thermal expansion. However, ZTE material is rare in nature. NaZr2(PO4)3 is a framework compound with near-zero thermal expansion due to coupled rotations of rigid ZrO6 and PO4 polyhedra in the structure, and several studies have been devoted to obtaining more ZTE compounds by chemical substitution of Na or Zr. Inspired by the AAV concept we proposed, in this work, the PO4 tetrahedra with a small volume has been replaced by the large volume MoO4 tetrahedra in KxMnxIn2-x(MoO4)3 (x = 0.4, 0.6, 0.8, and 1.0) compounds to provide more space for the coupling rotation of the polyhedron, and reduce the coefficient of thermal expansion. On the other hand, the flexibility of the framework structure has been modulated by the content of K+ to achieve new ZTE materials, and the effects of K+ content on crystal structure and thermal expansion have been analyzed in detail by combining variable temperature XRD and Raman. These findings not only provide more ZTE materials, but also suggest a promising design method for ZTE materials.

Preparation of low thermal expansion, transparent LAS glass-ceramics via simplified heat-treatment method

Li2O–Al2O3–SiO2 (LAS) glass-ceramics are commercially significant due to their unique microstructure and exceptional properties, including near-zero thermal expansion coefficient, making them suitable for a wide range of applications. However, the content of SiO2 and Al2O3 in the composition of LAS glass is very high, which leads to high viscosity and very difficult melting of this type of glasses. In order to reduce the melting temperature of the glass, use of relatively high Na2O in the basic glass composition allows high-quality glass to melt. Employing a simplified heat-treatment method, LAS glass-ceramics are prepared with Australian spodumene as the primary material. By exploring the effect of crystallization temperature on the structures and properties of the resulting LAS glass-ceramics, samples with excellent comprehensive properties are achieved. The prepared glass-ceramics are thoroughly characterized using DSC, XRD, FTIR, SEM, and TEM, along with assessments of their viscosity, thermal, optical, and mechanical properties. Relatively more Na2O is introduced into the glass compositions, which can lower the melting temperature of the glass to below 1600 °C. The basic glass is annealed at 700 °C for 2 h, nucleation phenomenon Nucleation phenomenon can be generated in the LAS glasses. When the microcrystalline temperature of glasses increases from 835 °C to 910 °C, the main crystalline phase of glass-ceramics changes from β-quartz solid solution to β-spodumene solid solution. The change in the main crystal phase has significantly affected the properties of glass-ceramics. When the crystallization temperature is below 860 °C, the glass-ceramics exhibit a low negative expansion coefficient (<-0.5 × 10−6 K−1), high visible light transmittance (>85 %), and excellent average flexural strength (173.3 MPa).

Boron-graphene composite for efficient electromagnetic interference shielding with strong strength and near-zero thermal expansion

The quest for the materials that boast efficient electromagnetic interference (EMI) shielding, strong strength and superb thermal dimensional stability is a burgeoning research area, particularly due to their critical applications in safeguarding sensitive circuits against microwave radiation, especially in the space environments. Graphene-based composites, leveraging the remarkable attributes of individual graphene nanosheets, emerge as prime contenders for fulfilling these sophisticated application requirements. In this study, we prepared boron-graphene composites via spark sintering, combining graphene sheets and boron nanoparticles. This method not only ensures high-performance outcomes but also remains cost-effective and suitable for large-scale production. Boron serves as a binder, facilitating the connection between adjacent graphene sheets and enhancing the graphitization process. The resulting composites demonstrated exceptional electrical conductivity (4.53 × 105 S m−1) and superior EMI shielding effectiveness (average SET 83 dB, with the thickness of 0.25 mm), markedly surpassing previous graphene-based materials in terms of compressive strength (171.3 MPa), and exhibiting low thermal expansion and an ultra-low friction coefficient (0.04). Additionally, to unravel the evolution of boron in the graphene composite and the impact of boron on electrical conductivity, first principles calculations and density functional theory (DFT) were utilized. This investigation underscores the significant promise of boron-graphene composites as high-performance, multifunctional materials across various domains.

Fabrication of flexible (Mg0.2Al0.2Fe0.2Ni0.2Co0.2)2Ti2.8O8 ceramics via compositionally complex ceramics method

A novel compositionally-complex flexible (Mg0.2Al0.2Fe0.2Ni0.2Co0.2)2Ti2.8O8 (abbreviated as CCC) ceramic with pseudobrookite structure was synthesized by solid-state reaction method. As compared to the fabrication process of flexible aluminum titanate ceramic (C. Babelot, 2011), the sintering temperature was significantly reduced from 1600 °C to 1200 °C by co-doping. And, the combinations of displacement (0.11–0.25 mm) and bending strength (10–40 MPa) were achieved by controlling the sintering condition. Among these, the specimen sintered at 1200 °C for 2 h (abbreviated as CCC-1200-2) presents a single-phase crystal structure and uniform elemental distribution. After that, its near-zero thermal expansion coefficient of 0.47 × 10−6 K−1 at low temperature was obtained and the nonlinear thermal expansion behavior was observed. Lastly, the thermal stability of sample CCC-1200-2 was checked out by annealing the samples between 900 °C and 1600 °C for various times up to 100 h. As a result, this study successfully fabricated the flexible CCC ceramics with improved mechanical properties, high thermal stability, and low sintering requirements, providing a new technology strategy for pseudobrookite-type ceramics and compositionally-complex ceramics fabrication.

Near-zero thermal expansion ZrW2O8/SiO2f wave-transparent composites: Interfacial anti-debonding structures based on polymeric films

The thermal stability of fiber-optic gyroscopes (FOGs) limits their application in harsh environments. This work utilized the unique water-retention properties of hyaluronic acid and the low-temperature cold sintering process combined to fabricate near-zero thermal expansion ZrW2O8/SiO2f composites with thermal resistance. Based on this novel process, the interface debonding of the composites is effectively suppressed and the mechanical and thermal properties of the composites are significantly improved (flexural strength increased by 69.47 %). Moreover, the interface anti-debonding structure reduces the interfacial polarization and reflection loss of the composites, and enhances the wave-transparent properties in the 2–18 GHz frequency range, with a minimum reflection loss of −0.21 dB. Furthermore, the interface anti-debonding structure of the composite provides creep resistance with enhanced sintering densities (increased by 13.61 %). Simultaneously, the composites achieve a controllable coefficient of thermal expansion (CTE) by regulating the liquid phase content and reach near-zero CTE (−0.246 × 10−6 °C−1 [30–300 °C]). Finally, finite element analysis and thermal shock experiments show that the anti-debonding interfacial structure has excellent thermal resistance, and the densest ZrW2O8/SiO2f composites exhibit the best thermal resistance due to minimal thermal strain during thermal shock, which is expected to meet the requirements of FOGs applications.

High-Energy Laser Protection Performance of Fibrous Felt-Reinforced Aerogels with Hierarchical Porous Architectures.

Continuous-wave lasers can cause irreversible damage to structured materials in a very short time. Modern high-energy laser protection materials are mainly constructed from ceramic, polymer, and metal constitutions. However, these materials are protected by sacrificing their structural integrity under the irradiation of high-energy lasers. In this contribution, we reported multilayer fibrous felt-reinforced aerogels that can sustain the continuous irradiation of a laser at a power density of 120 MW·m-2 without structural damage. It is found that the exceptional high-energy laser protection performance and the comparable mechanical properties of aerogel nanocomposites are attributed to the unique characteristics of hierarchical porous architectures. In comparison with various preparation methods and other aerogel materials, multilayer fibrous felt-reinforced aerogels exhibit the best performance in high-energy laser protection, arising from the gradual interception and the Raman-Rayleigh scattering cycles of a high-energy laser in the porous aerogels. Furthermore, a near-zero thermal expansion coefficient and extremely low thermal conductivity at high temperature allow the lightweight felt-reinforced aerogels to be applied in extreme conditions. The felt-reinforced aerogels reported herein offer an attractive material that can withstand complex thermomechanical stress and retain excellent insulation properties at extremely high temperature.

Zr0.1Fe0.9V1.1Mo0.9O7 as Cathode for Lithium-Ion Battery

Abstract With the development of lithium-ion batteries, high capacity and high cycle stability have been the two main goals being pursued. Recent studies have shown that ZrV2O7 does not perform well in energy storage due to its low electrical conductivity and poor cycling stability. Elemental doping has proven to be an effective strategy for improving electrochemical performance. In this paper, we prepared Zr0.1Fe0.9V1.1Mo0.9O7(ZFVMO) and Zr0.1Fe0.9V1.1Mo0.9O7@c (ZFVMO@c) materials using a simple solid-phase sintering method and a fast microwave sintering method. Double ionic heterovalent substitution of Zr4+/V5+ in ZrV2O7 using Fe3+/Mo6+, Fe3+/Mo6+ gives it near-zero thermal expansion characteristics and excellent conductive properties. In electrochemical tests, the first discharge capacities of ZFVMO and ZFVMO@C are 2261 mA h g−1 and 727 mA h g−1, respectively, and the batteries were finally stabilized for 475 and 500 cycles. Compared to ZrV2O7, the electrochemical properties of ZFVMO are greatly improved.

Rapid densification of low-positive thermal expansion Al2W3O12 ceramics

The Al2W3O12 ceramic with near-zero thermal expansion is a promising candidate for thermal shock resistance applications. However, the often-reported microcracks in the microstructure hinder the practical use of Al2W3O12. This work focuses on optimising the material processing—powder synthesis, calcination, milling, and sintering—to prepare dense polycrystalline Al2W3O12 with fine microcrack-free microstructure. The amorphous powder produced by the co-precipitation method had the highest specific surface area reported for this material, resulting in improved sinterability. Two rapid sintering methods were employed—Rapid Pressure-less Sintering and Spark Plasma Sintering. Both methods led to shorter processing times and lower sintering temperatures. However, Al2W3O12 samples produced by Spark Plasma Sintering were nearly fully dense with a density of ∼98% of theoretical density, the best value reported to date for this phase. The obtained fine crack-free microstructure of the samples led to a superior mechanical response compared to that achieved by Rapid Pressure-less Sintering.

Fluorine atom substituted aromatic polyimides: Unlocking extraordinary dielectric performance and comprehensive advantages

Low-dielectric polymers face prominent development challenges at high frequency. Particularly, the relationship between the high-frequency dielectric loss and polymer structures remains not clear enough. Besides, the strategies for achieving low dielectric loss usually have to scarify other important materials properties, e.g., heat resistance or dimensional stability. Herein, fluorine-containing aromatic polyimides were systematically investigated. Among them, simple fluorine atom (-F) substituted polyimides exhibit remarkable low dielectric loss at high frequency (10 GHz) as well as comprehensive advantages, including near-zero thermal expansion coefficient, extremely high thermal decomposition stability, high optical transmittance and excellent mechanical properties. The fundamental mechanisms of low dielectric loss are fully discussed. Benefiting from the unique electric effect and compact size of -F group, -F substituted polyimides display low dipolar density and strongly restricted dipolar motion, contributing to a reduced permanent dipolar polarization loss. Moreover, the concept of induced dipolar polarization was introduced to illustrate the nontrivial impact of F-substituted effect on conjugated electron cloud polarization loss in aromatic polymer system. This work not only provides valuable insights for understanding the mechanism of dielectric loss at high frequency for aromatic polymers, but also opens up broader application possibilities of polyimides in microelectronic and wireless communications industries.

A series of auxetic metamaterials with negative thermal expansion based on L-shaped microstructures

Mechanical metamaterials are facing various multi-functional requirements. In this study, a series of auxetic metamaterials with enhanced negative thermal expansion and improved stiffness are proposed. These metamaterials consist of four novel L-shaped microstructures connected in various clockwise or counterclockwise directions. Two length ratios and four angle parameters are utilized to define the geometry of these metamaterials. Both analytical analysis and validated numerical homogenization methods are employed to determine their effective thermoelastic properties, including effective Young's modulus, Poisson's ratio, and coefficient of thermal expansion. It is demonstrated that tailoring these microstructural geometries can modulate the effective thermoelastic properties of these metamaterials accordingly. By appropriately tailoring the geometric parameters, these metamaterials exhibit increased effective stiffness as well as more pronounced auxeticity and negative thermal expansion compared to traditional triangle and trapezoid microstructures. Notably, the in-plane effective anisotropic or isotropic Poisson's ratio and coefficient of thermal expansion can be adjustable over a broader range from negative to positive values. High stiffness, High strength, and near-zero thermal expansion can be achieved concurrently in these metamaterials, which is very conducive for structural designing in thermal environments. These metamaterials with a coupled design of stiffness, thermal expansion, and Poisson's ratio hold significant potential for advancing applications in satellite platforms, space structures, composite sandwiches, and precision equipment.

Negative to positive axial thermal expansion switching of an organic crystal: contribution to multistep photoactuation.

Materials displaying negative thermal expansion (NTE), in contrast to typical materials with positive thermal expansion (PTE), are attractive for both fundamental research and practical applications, including the development of composites with near-zero thermal expansion. A recent data mining study revealed that approximately 34% of organic crystals may present NTE, indicating that NTE in organic crystals is much more common than generally believed. However, organic crystals that switch from NTE to PTE or vice versa have rarely been reported. Here, we report the crystal of N-3,5-di-tert-butylsalicylide-3-nitroaniline in the enol form (enol-1) as the first organic crystal in which the axial thermal expansion changes from negative to positive at around room temperature. When heated, the crystal shrinks along the a-axis below 30 °C and then it expands above 30 °C. Geometric calculations revealed that below 30 °C, the decrease in the tilt angle of the molecule exceeds the increase in the interplanar distance, causing NTE, whereas above 30 °C, the increase in the interplanar distance outweighs the decrease in the tilt angle, resulting in PTE. By combining photoisomerisation and the NTE-PTE switching induced by the photothermal effect, multistep crystal photoactuation was achieved. Moreover, actuation switching of the same crystal sample by changing atmosphere temperature was realised by utilising the NTE-PTE change. Such NTE-PTE switching without a thermal phase transition provides not only new insight into organic crystals but also a new strategy for designing crystal actuators.

Fabrication of low thermal expansion coefficient electrodeposited Invar alloy films by hydrogen annealing for OLED fine metal masks

This study unveils the dependence of the Invar effect on grain size. An electrodeposited Invar alloy film was prepared with near-zero inclusions and near-zero thermal expansion, which will advance its application in OLED fine metal masks.

Sintering Temperature Effect of Near-Zero Thermal Expansion Mn3Zn0.8Sn0.2N/Ti Composites.

Metal matrix composites with near-zero thermal expansion (NZTE) have gained significant popularity in high-precision industries due to their excellent thermal stability and mechanical properties. The incorporation of Mn3Zn0.8Sn0.2N, which possesses outstanding negative thermal expansion properties, effectively suppressed the thermal expansion of titanium. Highly dense Mn3Zn0.8Sn0.2N/Ti composites were obtained by adjusting the fabrication temperature. Both composites fabricated at 650 °C and 700 °C exhibited NZTE. Furthermore, finite element analysis was employed to investigate the effects of thermal stress within the composites on their thermal expansion performance.

Near-zero thermal expansion in a wide temperature range of lightweight mMnZnSnN/AlSi with high thermal conductivity

Lightweight materials with near-zero thermal expansion (NZTE) and high thermal conductivity have potential applications in precision instruments, aerospace industry and electronic packaging due to their high thermal stability. In this study, multiphase Mn3Zn1-xSnxN (MnZnSnN) with abnormal negative thermal expansion (NTE) were used to inhibit the positive thermal expansion of AlSi. The resulting composites multiphase-MnZnSnN/AlSi (mMnZnSnN/AlSi) achieved NZTE (0.40 × 10-6 °C-1) in a wide temperature range (-5–60 °C, ΔT = 65 °C). Compared with other NZTE materials, mMnZnSnN/AlSi exhibits high thermal conductivity of 60 W·m-1·K-1 and high bending strength of 211 MPa. The density of the composite is only 4.46 g/cm3, 45% lower than invar alloy. This work provides guidance for designing and fabrication of aluminum matrix materials with combined advantages of wide temperature range zero thermal expansion behavior, high thermal conductivity and high mechanical properties.

Observation of near-zero thermal expansion in CrVMoO7

Materials with zero thermal expansion (ZTE) are important for many high-performance applications but are very rare. Here we report the discovery and characterization of near-ZTE in CrVMoO7. CrVMoO7 shows near-ZTE in a wide range of working temperatures (av ∼ -1.92 × 10−6 K−1, 100–240 K and 2.28 × 10−6 K−1, 240–473 K). This material shows small thermal expansion along two axes, with negative thermal expansion along the third axis that nearly cancels the small positive expansion along the other two axes. Through the joint characterizations, the transverse vibrations of O6 and O4 atoms contribute more to the NTE. In this work, CrVMoO7 provides a new option in the ZTE field as an undoped single-phase material.

Design of near-zero thermal expansion composites with superior mechanical properties in a wide temperature region

Materials that exhibit very small dimensional changes with temperature, i.e., near-zero thermal expansion (NZTE) properties, find attractive prospects in fields such as precision instrumentation and aerospace. However, how to manually design and synthesize NZTE materials with high performance instead of laboriously exploring composition has been a long-standing challenge. In this study, based on the excellent bonding and forming abilities of metallic glass (MG), a composite with continuous regulation of thermal expansion was obtained by combining different volume ratios of MG with beta-LiAlSiO4 (beta-LAS) possessing negative thermal expansion (NTE). Interestingly, excellent NZTE performance of 0.693 and 1.587 ppm/K was achieved over the 150–700 K temperature range when the volume ratio of MG was 40% and 50%, respectively. In addition, the compressive strength of the NZTE composite reached 320 and 436 MPa for the above two ratios, respectively. The thermal shock resistance results show that the composite can withstand thermal cycling tests of not less than 80 times. The proposed strategy not only provides new NZTE materials with high performance but also facilitates a shift in the preparation of high-performance NZTE composites from laborious search to customizable design.

Sintering pressure effect on the performances of near-zero thermal expansion xLFCS/Cu metal matrix composites

Metal-matrix materials exhibiting near-zero thermal expansion (NZTE) behavior are urgently required in electronic packaging and precision instruments. However, the practical application of this material faces some challenges, such as a narrow operating temperature, low thermal conductivity, and weak mechanical properties. This study investigates the effect of sintering pressure on the microstructural evolution of multicomponent negative-thermal-expansion La(Fe, Co, Si)13 reinforced Cu composites via spark plasma sintering (SPS). Near-zero thermal expansion was obtained over a wide range of temperature between 200 and 320 K by using multicomponent reinforcements. The porosity decreased from 4.7% to 0.6% when the sintering pressure increased from 50 to 150 MPa. As the sintering pressure increases, the agglomerated Cu particles gradually transform into continuous Cu networks. The combination of a dense structure and continuous Cu networks leads to a large maximum compressive strength of 758 MPa and a high thermal conductivity of 56.2 Wm−1K−1, which are the best comprehensive properties of wide-temperature-range NZTE composites ever reported. This study provides an effective method for resolving the tradeoff between low thermal expansion and high strength in most NZTE materials.