Tunable Negative Thermal Expansion Research Articles

Lightweight 3D Graphene Metamaterials with Tunable Negative Thermal Expansion.

In this study, a 3D graphene metamaterial (GM) showing negative thermal expansion is prepared using a strategy of hyperbolically oriented freezing under a dual temperature gradient along orthogonal directions after the π-π stacking-derived assembly of 2D graphene sheets. As the fundamental construction element of the 3D GM, the graphene sheet displays anomalous shrinking deformation with a thermal expansion coefficient of (-6.12 ± 0.28) × 10-6 that is triggered by thermally induced out-of-plane vibrations of the CC bonds. A combination of numerical simulations and experimental investigations validates that anomalous negative thermal expansion (NTE) behavior can be effectively delivered to scalable 3D GM candidates at larger dimensions beyond the basic 2D graphene sheets at the microscale. The multiscale design and optimization of the structural characterization of the 3D GM further realize the desirable regulation of the NTE performance with the NTE coefficient ranging from negative ((-7.5± 0.65) × 10-6 K-1 ) to near-zero values ((-0.8 ± 0.25) × 10-6 K-1 ). This is attributed to the NTE-derived release regulation of the primary stress/strain of the microstructure, and the 3D GM exhibits high thermal stability while preserving the desirable structural robustness and fatigue resistance under thermo-mechanical coupling conditions. Therefore, this 3D GM offers promising potential for applications as protective skin, thermal actuator, smart switcher, and packing filler.

Tunable negative thermal expansion in La(Fe, Si)13/resin composites with high mechanical property and long-term cycle stability

Materials with tunable negative thermal expansion (NTE) are highly demanded in various functional devices. La(Fe, Si)13-based compounds are promising NTE materials due to their outstanding NTE properties. However, their poor mechanical properties and related short service life restrict their practical applications. In this work, epoxy resin with positive thermal expansion is used to synthesize La-Fe-Si/resin composites. The NTE of La-Fe-Si/resin composites can be manipulated by optimizing the La-Fe-Si particle size and resin content, and tailoring resin content could tune the NTE more effectively. The average linear coefficient of thermal expansion of the composites decreases from -275.0 × 10-6 K-1 to -4.9 × 10-6 K-1 over the magnetic transition temperature range as the resin content increases from 3 wt.% to 80 wt.%. In addition, zero thermal expansion is achieved in the La-Fe-Si/resin composite with 20 wt.% resin. The resin would reinforce the binding force by filling the pores between the particles. The La-Fe-Si/resin composite with 80 wt.% resin exhibits highly improved mechanical properties; for example, its compressive strength of 205 MPa is 75% higher than that of the La-Fe-Si/resin composite with 3 wt.% resin. The prepared La-Fe-Si/resin composites can be machined into different shapes for practical applications, such as thin plates, strips, and rods. Furthermore, the La-Fe-Si/resin composites can undergo 1000 thermal cycles without NTE performance degradation and mechanical integrity loss, indicating durable cycle stability. Hence, significantly tunable NTE with high mechanical properties and long-term cycle stability makes La-Fe-Si/resin composites present great application potential as NTE materials.

Enhanced thermal buckling resistance of folded graphene reinforced nanocomposites with negative thermal expansion: From atomistic study to continuum mechanics modelling

Materials with tunable negative thermal expansion (NTE) are of crucial importance in engineering applications. Currently, the route to achieving large tunability for the coefficient of thermal expansion (CTE) in metal matrix composites (MMCs) is very limited. This paper develops folded graphene (FGr) structures to engineering the CTE of MMCs by embedding the FGr into a copper (Cu) matrix through the molecular dynamics (MD) method. Moreover, the present work investigates the thermal buckling resistance capability of the NTE material composite beam using the classical Euler-Bernoulli beam theory and Ritz method. Atomistic studies based on the MD simulations show that the CTE of FGr/Cu nanocomposite can be effectively tuned by mechanical prestress and temperature, especially within the range from 200 K to 400 K. By using the origami-patterned FGr designed herein, the maximum negative and positive CTEs can reach approximately −95.42 × 10−6 K−1 and 56.32 × 10−6 K−1 under the prestress of 1000 MPa at 300 K and 200 K, respectively. More importantly, the quantitative relationship of the temperature- and prestress-dependent material properties of the FGr/Cu composites are built. Based on the built material model, the FGr/Cu composite beam exhibits considerably improved thermal buckling performance than the pristine graphene/Cu beam.

Design optimization of multifunctional metamaterials with tunable thermal expansion and phononic bandgap

Metamaterials have been extensively investigated owing to their unusual properties. However, the design of multifunctional metamaterials requires further investigation. This study focused on the design of three-dimensional (3D) metamaterials to achieve tunable negative thermal expansion and phononic bandgap properties. First, the independent continuous mapping (ICM) topology optimisation method was applied to create metamaterial microstructures with negative thermal expansion properties based on the multi-scale asymptotic homogenisation theory. Secondly, the conceptual structure from the topology optimisation was reconstructed and parameterized to achieve the desired phononic bandgap widths under negative thermal expansion, using a surrogate model-based optimisation method. Both the negative coefficient of thermal expansion and phononic bandgaps were verified through numerical simulations. The results reveal that, by selecting appropriate parameters, the designed metamaterials can have both a negative coefficient of thermal expansion and a maximum bandgap width ratio. The proposed method provides an important reference for the rational design of multifunctional metamaterials.

Large Linear Negative Thermal Expansion in NiAs-type Magnetic Intermetallic Cr-Te-Se Compounds.

A large linear negative thermal expansion (NTE) and expanded NTE temperature range (ΔTNTE) were obtained in magnetoelastic CrTe1-xSex (0 ≤ x ≤ 0.15) compounds. For CrTe compound, its thermal expansion coefficient of volume (αV) was calculated to be -28.8 ppm K-1 with the temperature ranging from 280 to 340 K. Substituting Te with Se atoms, the NTE behavior and magnetic properties can be well manipulated. With increasing Se in CrTe1-xSex (0 ≤ x ≤ 0.15) compounds, the ΔTNTE increases from 60 K (280-340 K for x = 0), to 80 K (240-320 K for x = 0.05), to 95 K (200-295 K for x = 0.1), and finally to 100 K (170-270 K for x = 0.15). Furthermore, a linear NTE remains independent of temperature for samples with x ≤ 0.1. The relationship between tunable NTE and magnetic properties was analyzed in detail, indicating that the NTE in CrTe1-xSex compounds originates from the magnetovolume effect (MVE).

The tunable negative thermal expansion covering a wide temperature range around room temperature in Sn, Mn co-substituted Mn3ZnN

Based on anti-perovskite Mn3ZnN, the negative thermal expansion (NTE) temperature can be effectively broadened via co-substituting Sn, Mn. Using optimized components, the room-temperature NTE effect covering a wide temperature range can be realized. Both the competing ferromagnetic order from Mn and local lattice disorder from Sn should be the reason for the physical origination of the broadening of the NTE temperature. By compositing with epoxy, the low thermal expansion could be achieved around room temperature, which exhibits great potential in the field of electronic packaging.

Large and tunable negative thermal expansion induced by a synergistic effect in M2II[MIV(CN)8] Prussian blue analogues.

Designing negative thermal expansion (NTE) materials with a larger NTE coefficient and a wider temperature window is a great challenge nowadays, leading to the limitation of existing NTE materials such that only about 150 kinds of NTE materials have been discovered since 1996. Here, using first-principles calculations combined with the quasi-harmonic approximation (QHA), we find that the synergistic effect of different vibrational modes can significantly enhance the NTE in open framework compounds. We systematically investigate the NTE properties of the M2IIMIV(CN)8 (MII = Ni, Co, Fe, and Mn; MIV = Mo and W) family, which is the first kind of Prussian blue analogues (PBAs) with a 2D and 3D topology structure, to explore the synergistic enhancement effect in NTE. We reveal that both the optical modes of the rotational motion of [W(CN)8] and [Ni(NC)4] rigid units and the low frequency acoustic modes of the transverse vibration contribute significantly to the NTE. Furthermore, the coefficients of NTE increase monotonously with increasing ionic radius upon substituting Ni in M2IIW(CN)8 with Co, Fe, or Mn, respectively. Analyzing the vibrational modes of the substituted systems indicates that the dramatic changes in NTE originate from a highly synergistic effect, in which all the frequencies of these NTE modes have the same trend, i.e. the lower the frequencies, the larger the coefficient of NTE. This work clearly presents a synergistic mechanism of enhancing NTE in PBA materials, and sheds light on designing new materials with better properties.

Hoberman-sphere-inspired lattice metamaterials with tunable negative thermal expansion

Materials with engineered thermal expansion coefficients, capable of avoiding failure or irreversible destruction of structures and devices, are important for aerospace, civil, biomedical, optics, and semiconductor applications. In natural materials, thermal expansion usually cannot be adjusted easily and a negative thermal expansion coefficient is still uncommon. Here we propose a novel architected lattice bi-material system, inspired by the Hoberman sphere, showing a wide range of tunable thermal expansion coefficient from negative to positive, −1.04 × 10−3 °C−1 to 1.0 × 10−5 °C−1. Numerical simulations and analytical formulations are implemented to quantify the evolution of the thermal expansion coefficients and reveal the underlying mechanisms responsible for this unusual behavior. We show that the thermal expansion coefficient of the proposed metamaterials depends on the thermal expansion coefficient ratio and the axial stiffness ratio of the constituent materials, as well as the bending stiffness and the topological arrangement of the constitutive elements. The finding reported here provides a new routine to design architected metamaterial systems with tunable negative thermal expansion for a wide range of potential applications.

Auxetic and Negative Thermal Expansion Structure Based on Interconnected Array of Rings and Sliding Rods

An exploration by analytical method has been made herein for a mechanism‐based structure that involves a two‐dimensional array of rings and a three‐dimensional array of double‐rings, with short fixed rods and long sliding rods attached at the outer and inner surfaces of the rings, respectively. Based on the theory of thin rings, effective Poisson's ratio and effective coefficient of thermal expansion (CTE) models have been obtained for single‐ring structures, pole‐loaded double‐ring structures, and equator‐loaded double‐ring structures. Results establish a very strong correlation between these effective properties with the ring radius and rod lengths. In addition, the analysis of four of the double‐ring structures reveals that the sign of Poisson's ratio is dependent on the direction of loading. An example application is demonstrated herein in which positive thermal expansion rings, used in conjunction with rigid rods, enable the design of an overall zero thermal expansion structure (i.e., minimal thermal stress) with tunable negative thermal expansion internal microstructure for use as sieve. Finally, it is herein shown that, by judicious positioning of the short fixed rods and/or long sliding rods, one may possibly obtain various combinations of positive and negative CTEs with positive and negative Poisson's ratio.

Structure, Magnetism, and Tunable Negative Thermal Expansion in (Hf,Nb)Fe2 Alloys

Negative thermal expansion (NTE) is one of intriguing properties for solid compounds. Here we report structure and tunable negative thermal expansion in the (Hf1-xNbx)Fe2 magnetic alloys. The NTE mechanism has been investigated by a combined analysis of neutron powder diffraction, synchrotron X-ray diffraction, and macroscopic magnetic measurements. Direct experimental evidence shows that magnetovolume effect is the root of NTE of ferromagnetic phase, while the paramagnetic phase responds to the general positive thermal expansion (PTE). Especially, by adjusting the amount of Nb chemical substitution in (Hf1-xNbx)Fe2, the coexistence of NTE ferromagnetic and PTE paramagnetic phases can tune the large NTE (x = 0.05, αv = -23.13 × 10-6 K-1, 323~398 K) to the relatively low thermal expansion (x = 0.15, αv = -8.28×10-6 K-1, 173~323 K). The present study reveals the direct link between NTE and magnetic structure, and shows that thermal expansion could be tuned by the coexistence of magnetic and paramagnetic phases.

Tunable negative thermal expansion and structural evolution in antiperovskite Mn3Ga1−xGexN (0 ≤ x ≤ 1.0)

AbstractThe negative thermal expansion (NTE) and structural evolution of antiperovskite compounds Mn3Ga1−xGexN (0 ≤ x ≤ 1.0) were systematically investigated. Our results indicate the crystal structure of Mn3Ga1−xGexN changes from cubic (C) to tetragonal (T4) with increasing Ge content by X‐ray diffraction (XRD).The negative thermal expansion from x = 0 (operation‐temperature range ▵T = 20 K) to x = 0.4 (▵T = 60 K) becomes broad and shifts to higher temperature, and then it became positive from x = 0.5 in Mn3Ga1−xGexN. Typically, Mn3Ga0.5Ge0.5N shows low thermal expansion behavior between 300 and 450 K (∆T = 150 K), and thermal expansion coefficient α is estimated to be 2 × 10−6 K−1. Furthermore, variable temperature XRD was measured to reveal the origin of NTE. The cubic I ‐ cubic II phases coexistence (x = 0.2) and cubic I ‐ tetragonal coexistence (x = 0.5, 0.6) was observed at low temperature. The tunable NTE is highly valuable for practical applications in precision devices.

Lightweight Mechanical Metamaterials with Tunable Negative Thermal Expansion.

Ice floating on water is a great manifestation of negative thermal expansion (NTE) in nature. The limited examples of natural materials possessing NTE have stimulated research on engineered structures. Previous studies on NTE structures were mostly focused on theoretical design with limited experimental demonstration in two-dimensional planar geometries. In this work, aided with multimaterial projection microstereolithography, we experimentally fabricate lightweight multimaterial lattices that exhibit significant negative thermal expansion in three directions and over a temperature range of 170degrees. Such NTE is induced by the structural interaction of material components with distinct thermal expansion coefficients. The NTE can be tuned over a large range by varying the thermal expansion coefficient difference between constituent beams and geometrical arrangements. Our experimental results match qualitatively with a simple scaling law and quantitatively with computational models.

Tunable Negative Thermal Expansion in Layered Perovskites from Quasi-Two-Dimensional Vibrations.

We identify a quasi-two-dimensional (quasi-2D) phonon mode in the layered-perovskite Ca_{3}Ti_{2}O_{7}, which exhibits an acoustic branch with quadratic dispersion. Using first-principles methods, we show this mode exhibits atomic displacements perpendicular to the layered [CaTiO_{3}]_{2} blocks comprising the structure and a negative Grüneisen parameter. Owing to these quasi-2D structural and dynamical features, we find that the mode can be utilized to realize unusual membrane effects, including a tunable negative thermal expansion (NTE) and a rare pressure-independent thermal softening of the bulk modulus. Detailed microscopic analysis shows that the NTE relies on strong intralayer Ti-O covalent bonding and weaker interlayer interactions, which is in contrast to conventional NTE mechanisms for perovskites, such as rigid-unit modes, structural transitions, and electronic or magnetic ordering. The general application of the quasi-2D lattice dynamics opens exciting avenues for the control of lattice dynamical and thermodynamic responses of other complex layered compounds through rational chemical substitution, as we show in A_{3}Zr_{2}O_{7} (A=Ca, Sr), and by heterostructuring.

Isotropic Negative Thermal Expansion Metamaterials.

Negative thermal expansion materials are important and desirable in science and engineering applications. However, natural materials with isotropic negative thermal expansion are rare and usually unsatisfied in performance. Here, we propose a novel method to achieve two- and three-dimensional negative thermal expansion metamaterials via antichiral structures. The two-dimensional metamaterial is constructed with unit cells that combine bimaterial strips and antichiral structures, while the three-dimensional metamaterial is fabricated by a multimaterial 3D printing process. Both experimental and simulation results display isotropic negative thermal expansion property of the samples. The effective coefficient of negative thermal expansion of the proposed models is demonstrated to be dependent on the difference between the thermal expansion coefficient of the component materials, as well as on the circular node radius and the ligament length in the antichiral structures. The measured value of the linear negative thermal expansion coefficient of the three-dimensional sample is among the largest achieved in experiments to date. Our findings provide an easy and practical approach to obtaining materials with tunable negative thermal expansion on any scale.