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The Al 2 W 3 O 12 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 Al 2 W 3 O 12. This work focuses on optimising the material processing—powder synthesis, calcination, milling, and sintering—to prepare dense polycrystalline Al 2 W 3 O 12 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, Al 2 W 3 O 12 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. [ABSTRACT FROM AUTHOR]

Near-zero thermal expansion (NZTE) materials have important scientific significance and several potential applications. In this work, a NZTE GeNb 18 O 47 ceramic has been successfully synthesized by the solid-state method, and its phase, structure, expansion properties, and NZTE mechanism were investigated. Results show that the pure phase GeNb 18 O 47 ceramic is successfully obtained, and the crystal structure is composed of NbO 6 octahedron and Nb/GeO 4 tetrahedron. GeNb 18 O 47 shows a near-zero linear coefficient of thermal expansion (CTE) of 1.23 × 10−6 °C−1 (−100–400 °C), which is caused by negative thermal expansion (NTE) originating from the rotational coupling of NbO 6 octahedron and Nb/GeO 4 tetrahedron. In addition, GeNb 18 O 47 is a NZTE semiconductor with a band gap of 3.05 eV, which has great application value in integrated circuits, and chip manufacturing. [ABSTRACT FROM AUTHOR]

Novel BaMg 2 Al 6 Si 9 O 30 -based ceramics were prepared using the traditional solid-phase reaction method, and this paper presents the fabrication procedure, crystal structure, microstructure, microwave dielectric properties and temperature coefficient of thermal expansion of BaMg 2 Al 6 Si 9 O 30 -based ceramics. BaMg 2 Al 6 Si 9 O 30 -based ceramics were found to possess a hexagonal crystal structure with the P 6/ mcc space group. The BaAl 2 Si 2 O 8 and BaMg 2 Al 6 Si 9 O 30 phases coexisted in BaMg 2 Al 6 Si 9 O 30 ceramic given that raw MgO material reacted easily with water vapour in the air, and the BaMg 2 Al 6 Si 9 O 30 single-phase ceramic could be synthesized with calcined raw MgO material. The BaMg 2 Al 6 Si 9 O 30 single-phase ceramic exhibited ultralow ε r (5.68 at 14.05 GHz), moderate Q × f value (28534 GHz at 14.05 GHz), a self near-zero τ f value (7.35 ppm/°C), a near-zero average temperature coefficient of thermal expansion (+1.89 ppm/°C) at 30 °C 1000 °C and a rare negative temperature coefficient of thermal expansion (9.43 ppm/°C) at 655 °C 710 °C. The rare near-zero and negative thermal expansions of the BaMg 2 Al 6 Si 9 O 30 single-phase ceramic were mainly related to the strong Si/Al-O bonds with high relative covalency and 2 coordinate O(1) allowing longitudinal vibrations. [ABSTRACT FROM AUTHOR]

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 Mn 3 Zn 1-x Sn x N (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. [ABSTRACT FROM AUTHOR]

Thermal expansion is inevitable for space structures under the alternating temperature of outer space around the earth. This may lead to the thermal stress and deformation due to the mismatch of the coefficient of thermal expansion. Near-zero thermal expansion (Near-ZTE) is a vitally essential demand for large-scale space telescopes or antennas to preserve their spatial precision and resolution. Recently, mechanical metamaterials with superior and tailorable properties have attracted significant interest with regard to developing negative materials or ultra-property materials. In this paper, the near-ZTE space structure architected by a dual-hourglass bi-material lattice is achieved by the structural optimization method with the gradient-based algorithm. First, an hourglass lattice with adjustable structural parameters is optimized to seek the design of effective negative thermal expansion (NTE) in the thickness direction. Then, two building blocks with both NTE and legacy positive thermal expansion (PTE) are combined as a dual-layered lattice to obtain the near-ZTE. Finally, a structure with near-ZTE of about ~10−9 m/(m·K) is obtained. Furthermore, the various lattice configurations, such as the hexagonal pyramid and triangle pyramid, are investigated in detail. Finally, the natural frequencies of two near-ZTE lattices are calculated by the modal analysis method, and the stiffness is discussed for the optimal solution of space applications. This work demonstrates that the near-ZTE structure can be achieved by utilizing the negative metamaterial and structural optimization method. It provides a novel solution to design the large-scale space structures with the near-zero thermal induced deformation, and may be constructed and assembled by the on-orbit fabrication technology. [ABSTRACT FROM AUTHOR]

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 SE T 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. [Display omitted] • Boron-graphene composite was high-efficiently fabricated by SPS. • Boron plays a role as binders and promotes the graphitization of graphene. • The resultant composite demonstrates excellent EMI shielding effectiveness. • The resultant composite also shows outstanding multifunctional properties. • Density functional theory elucidates the evolution mechanism of boron in graphene. [ABSTRACT FROM AUTHOR]

The influence of extra-framework cations on the intrinsic negative thermal expansion (NTE) of calcined ultrastable and lanthanum-exchanged zeolites Y was analysed. High-temperature thermal behaviour, cationic migration and dealumination were examined by in situ high temperature X-ray powder diffraction and thermogravimetric (TG) analyses. We analysed protonated ultrastable zeolite Y and zeolite Y containing 13% La2O3 (LaY), and investigated how the presence of La3+ influences thermal behaviour of zeolite Y. Uncalcined LaY was also analysed to observe the La3+ migration before calcination. Mass loss up to 990°C was accompanied by TG analyses. X-ray powder diffraction data were analysed by Rietveld method. Our data show that lanthanum migration from supercages to sodalitic cavities is not reversible. However, some La3+ migration occurs above 400°C and we observe emptying of site I ′, migration to site I and to some extent to site II ′. Furthermore, we examined the dealumination process as well. Both samples show two distinct thermal behaviours, positive or near-zero thermal expansion up to 500°C and NTE above this temperature. Together with intrinsic NTE in faujasite type zeolites, the dealumination process is largely responsible for NTE at high temperatures. [ABSTRACT FROM AUTHOR]

Abstract In the study, Zr 0.5 Hf 0.5 V 2−x P x O 7 (0 ≤ x ≤ 1.2) was prepared by solid state method and then the microstructure of synthesized samples was investigated. The microstructure, coefficient of thermal expansion (CTE) and phase transition of Zr 0.5 Hf 0.5 V 2−x P x O 7 (0 ≤ x ≤ 1.2) were investigated with thermal dilatometry, x-ray diffraction (XRD) and Raman spectroscopy. The results showed that the samples were single cubic phase with the space group of Pa 3 ¯ in the crystal structure. When the substitution rate of P5+ was higher than 0.6, the 3 × 3 × 3 superstructure disappeared. The expansion coefficient of Zr 0.5 Hf 0.5 V 1.2 P 0.8 O 7 was calculated to be −0.53 × 10−6 K−1 under the linear thermal expansion in a very wide temperature range from 300 to 573 K. With the increase of P5+ content, the temperatures of positive-to-negative thermal expansion of Zr 0.5 Hf 0.5 V 2−x P x O 7 firstly even decreased below room temperature and then increased. The synthesized Zr 0.5 Hf 0.5 V 2−x P x O 7 exhibited near zero thermal expansion behavior in a wide temperature range around room temperature. Highlights • Near-zero thermal expansion behavior over a wide temperature range. • The samples are of single-phase cubic type with space group Pa 3 ¯ at RT. • The samples have low phase change temperature. • From superstructure to ideal crystal structure between 310 and 323 K. • CTE was measured by dilatometer to be 0.59 × 10−6 K−1 (310 ∼ 673 K). [ABSTRACT FROM AUTHOR]

The effects of Zn2+ incorporation on the phase formation, thermal expansion, phase transition, and vibrational properties of HfMg1−xZnxMo3O12 are investigated by XRD, dilatometry, and Raman spectroscopy. The results show that (i) single phase formation is only possible for x ≤ 0.5, otherwise, additional phases of HfMo2O8 and ZnMoO4 appear; (ii) The phase transition temperature from monoclinic to orthorhombic structure of the single phase HfMg1−xZnxMo3O12 can be well-tailored, which increases with the content of Zn2+; (iii) The incorporation of Zn2+ leads to an pronounced reduction in the positive expansion of the b-axis and an enhanced negative thermal expansion (NTE) in the c-axes, leading to a near-zero thermal expansion (ZTE) property with lower anisotropy over a wide temperature range; (iv) Replacement of Mg2+ by Zn2+ weakens the Mo–O bonds as revealed by obvious red shifts of all the Mo–O stretching modes with increasing the content of Zn2+ and improves the sintering performance of the samples which is observed by SEM. The mechanisms of the negative and near-ZTE are discussed.

Abstract Materials with near-zero thermal expansion are helpful in improving the reliability of devices. One way to synthesize such materials is mixing material showing positive thermal expansion with that displaying negative thermal expansion. Large negative thermal expansion has been widely observed in NaZn 13 -type La(Fe,Si) 13 -based alloys during the magnetic transition. It suggests that these materials have potential applications as thermal-expansion compensators. However, how to compensate the negative thermal expansion and simultaneously improve its strength are two considerable questions. Here, we introduce in-situ precipitated α-Fe phase to compensate the negative thermal expansion of 1:13 phase, and thus achieve a near-zero thermal expansion in La(Fe,Si) 13 /α-Fe in-situ composite. On the other hand, the distributed ductile α-Fe phase greatly enhances the compressive strength, solving the brittleness problem of 1:13 phase. The yield compressive stress of the in-situ composite with near-zero thermal expansion reaches 970 MPa. This work opens up an effective way to the design of materials with both near-zero thermal expansion and improved strength. Graphical abstract Image 1 Highlights • We provide a way to achieve near-zero thermal expansion in La(Fe,Si) 13 -based alloys. • Additional Fe leads to the formation of two-phase La(Fe,Si) 13 /Fe in-situ composite. • Near-zero thermal expansion can be obtained by thermal expansion compensation. • The ductile secondary phase greatly enhances the compressive strength. [ABSTRACT FROM AUTHOR]

Zr x Hf 1- x MgMo 3 O 12 with x  = 0.3, 0.5, 0.7 and 0.8 are developed with a simple solid state method. It is shown that Zr x Hf 1- x MgMo 3 O 12 ( x   =  0–1)crystallizes in an orthorhombic symmetry with space group Pnma and exhibits zero-thermal expansion in a large temperature range, with the value of x ( x  = 0.5, α l  =  −0.363 × 10 −6  K −1 from 80 K to 573 K by X-ray diffraction and α l  =  −0.25 × 10 −6 K −1 from 273 K to 673 K by dilatometer). Zr x Hf 1- x MgMo 3 O 12 with x   =  0.5 remains the orthorhombic structure without phase transition or decomposition at least from 158 K to 673 K and is not hygroscopic. These properties make it an excellent material with near-zero thermal expansion for a variety of applications. [ABSTRACT FROM AUTHOR]

Four types of three-dimensional (3-D) metallic metamaterials with tailorable thermo-mechanical properties are designed. For the first three types, the structure-property relations are studied by adjusting design parameters including two length parameters, one angle parameter and two material combinations. For the fourth type, one additional angle parameter is involved. It is shown that each of the four types of metamaterials designed exhibits the cubic symmetry and thus needs three independent elastic constants to characterize its elastic behavior and one coefficient of thermal expansion to describe its isotropic thermal expansion. The effects of the design parameters on the effective Poisson's ratio (PR), coefficient of thermal expansion (CTE), Young's modulus, shear modulus and the relative density are systematically investigated for each of the four types of designed metamaterials by using unit cell-based finite element simulations that incorporate periodic boundary conditions. It is found that 3-D metallic metamaterials with positive, near-zero or negative PR and CTE can be obtained by tailoring the bi-material lattice structures and material combinations. Also, it is revealed that metamaterial # 1 can achieve both a negative PR and a non-positive CTE while maintaining a high stiffness and a low relative density (and thus a lightweight). The good tunability of thermo-mechanical properties of the four types of metamaterials provides an avenue of enabling the expansion of Ashby's material chart to produce more material options for engineering applications. [ABSTRACT FROM AUTHOR]

A negative thermal expansion (NTE) material In 0.6 (HfMg) 0.7 Mo 3 O 12 with oxygen vacancies was successfully synthesized through He atmosphere annealing. It was found that the introduction of oxygen vacancies enhanced the coefficient of NTE by about an order of magnitude larger. It can be attributed to the increased flexibility of the polyhedra in the framework structure. The introduction of oxygen vacancies also weakened the M O bonds and obviously enhanced the optical absorption in the visible light region. This work provides a promising strategy to effectively improve the NTE and optical properties of traditional NTE materials by introducing oxygen vacancies. [ABSTRACT FROM AUTHOR]

Four metallic metamaterials with tailorable mechanical properties are designed using bi-material star-shaped re-entrant planar lattice structures, which do not involve pins, adhesive, welding or pressure-fit joints and can be fabricated through laser-based additive manufacturing. Three length parameters, one angle parameter and three material combinations are used as adjustable design parameters to explore structure-property relations. For each of the four designed metamaterials, the effects of the design parameters on the Poisson’s ratio (PR), coefficient of thermal expansion (CTE), Young’s modulus and relative density are systematically investigated using unit cell-based finite element simulations that incorporate periodic boundary conditions. It is found that the bi-material lattice structures can be tailored to obtain 3-D printable metallic metamaterials with positive, near-zero or negative PR and CTE together with an uncompromised Young’s modulus. In particular, it is shown that metamaterial # 1 can exhibit both a negative PR and a non-positive CTE simultaneously. These metallic metamaterials can find applications in structures or devices such as antennas and precision instruments to reduce thermomechanical stresses and extend service lives. [ABSTRACT FROM AUTHOR]

ZrFeMo 2 VO 12 material was successfully synthesized by solid-state method. The structure, phase transformation and thermal expansion of such material were studied by X-ray powder diffraction (XRD), Raman spectra and thermal dilatometry. It crystallizes in monoclinic structure at room temperature (RT). The monoclinic structure transforms to orthorhombic structure at the temperature between 298 and 312 K. The coefficient of thermal expansion (CTE) was measured by dilatometer to be ( 0.36 ± 0.02 ) × 10 − 6 K − 1 ( 401 ∼ 573 K ) and calculated by XRD data to be ( 0.68 ± 0.17 ) × 10 − 6 K − 1 ( 423 ∼ 573 K ). Both the values of intrinsic (XRD) and extrinsic (dilatometric) thermal expansion are near zero. [ABSTRACT FROM AUTHOR]

An orthorhombic AlMoVO 7 was synthesized by solid-state method. Its phase, expansion property, and Raman spectra were analyzed in detail. Analysis showed that AlMoVO 7 has near-zero expansion in 173–673 K. With increasing temperature, the librational and translational vibrations of [AlO 6 ] and [MoO 4 ] caused the Al-O-Mo chain bending. The thermal expansion of AlMoVO 7 unit cell has an anisotropic and near-zero expansion. The thermal expansion performance of AlMoVO 7 block depends on its unit cell structure and microstructure. Therefore, near-zero expansion in 173–673 K is shown. [Display omitted] • AlMoVO 7 always maintains an orthogonal structure at 153–673 K. • AlMoVO 7 exhibits near-zero expansion in the temperature range of 173–673 K. • With the change of the a , b and c , AlMoVO 7 unit cell expansion is anisotropic. An orthorhombic AlMoVO 7 was synthesized by solid-state method. Its phase, expansion property, and Raman spectra were analyzed in detail. Analysis showed that AlMoVO 7 has near-zero expansion in 173–673 K. With increasing temperature, the librational and translational vibrations of [AlO 6 ] and [MoO 4 ] caused the Al-O-Mo chain bending. The thermal expansion of AlMoVO 7 unit cell has an anisotropic and near-zero expansion. The thermal expansion performance of AlMoVO 7 block depends on its unit cell structure and microstructure. Therefore, near-zero expansion in 173–673 K is shown. [ABSTRACT FROM AUTHOR]

Negative thermal expansion (NTE) materials can compensate high thermal expansion of metal materials, showing great potential use in precision instruments and microelectronics field. We developed a near-zero thermal expansion ZrW 2 O 8 /Al–Si composites with three dimensional mutually interpenetrated structure. Pressure infiltration ensured dense structure and mild interface reaction. The resulting composite has ultra-low thermal expansion (1.09 × 10−6 K−1) in a broad temperature range of −50 to 120 °C (ΔT = 170 °C). The content of high pressure phase (γ-ZrW 2 O 8) drops dramatically from 71.4% for the particle reinforced composite to 18.7% for the interpenetrating composite. Raman tests and numerical computational results indicated that the residual stress can be effectively released in the interpenetrating composites. This low dense and ultralow thermal expansion results in ideal materials for precision instruments and microelectronics component such as optical communication and gyroscope. [ABSTRACT FROM AUTHOR]