Negative Thermal Expansion Coefficient Research Articles

Magnetostriction, piezoelectric effect, and spin-singlet bipolarons in the nonstoichiometric (MnSe)1–х(Tm0.76Se)х compound

The effect of nonstoichiometry in manganese selenide (MnSe)1х(Tm0.76Se)х (0 ≤ x ≤ 0.3) substituted with thulium of variable valence on the magnetic, structural, and magnetoelastic properties of the compound has been studied. The magnetic susceptibility in the temperature range of 801000 K, infrared spectra (IR) in the frequency range of 4007500 cm–1 at temperatures of 80500 K, thermal expansion coefficient, electrostriction, and magnetostriction of the compound have been experimentally determined. The maximum paramagnetic susceptibility, thermal expansion coefficient, and IR absorption frequency shift and the critical temperatures and frequencies at which the IR absorption vanishes have been found above the Néel temperature. A model of bipolarons with vacancies in the anion subsystem has been proposed. Anomalies in the magnetic and structural characteristics of the investigated compound have been explained by the bipolaron dissociation accompanied by a singlettriplet transition and vacancy recombination. The temperatures of the onset of the piezoelectric effect and magnetostriction induced by the loss of inversion in clusters with thulium and the formation of ferromagnetic exchange between thulium and manganese ions have been established. It is shown that the negative thermal expansion coefficient is caused by the competition of the ferro- and antiferromagnetic interactions.

Crystal Growth, Characterization, and Properties of Nonlinear Optical Crystals of Li0.5Ag0.5GaTe2 for Mid-Infrared Applications.

LiGaTe2 is a promising nonlinear optical crystal with a large figure of merit (d362/n3), but it is difficult to grow the LiGaTe2 single crystal due to its extreme instability. In this work, we used Ag to replace Li and successfully grew a Li0.5Ag0.5GaTe2 crystal by the modified Bridgman method for the first time. We found it has thermal stability below 200 °C in an atmospheric environment, and the thermal expansion coefficient is positive. This is different from LiGaTe2 and AgGaTe2 which have a negative thermal expansion coefficient along the c-axis. When the temperature exceeds 200 °C, Li0.5Ag0.5GaTe2 is easily decomposed and oxidized. Under closed vacuum conditions, the melting and solidifying points of Li0.5Ag0.5GaTe2 are measured to be 719 and 694 °C. XPS spectra show that the binding energies of Li, Ga, and Te are higher than LiGaTe2, and the surface is easily oxidized. The A1 vibration modes are found at 117.72 and 135.44 cm-1 by the Raman spectrum which is related to the Te and Ga-Te bond in [GaTe4]5- tetrahedra. Li0.5Ag0.5GaTe2 has a wide transmittance range from 0.94 to 20 μm, and there was two-photon absorption near 16 μm. The phonon spectrum and PDOS were simulated by the DFT calculation to study the phonon vibration modes in the lattice, which shows that the density of the Raman vibration is higher than those of AgGaTe2 and LiGaTe2. The SHG test results showed that the SHG response intensity of Li0.5Ag0.5GaTe2 is 1.5 times that of AgGaS2, which shows its excellent nonlinear optical properties for mid-IR applications.

Design and Modulation of Negative Thermal Expansion for Epoxy Polymers.

Modulating the coefficient of thermal expansion (CTE) and realizing low or negative thermal expansion (NTE) for epoxy polymers are challenging issues. In this study, we developed an effective strategy to prepare epoxy polymers with an NTE performance. A novel motif DBCOD-NH2 based on the dibenzocyclooctadiene (DBCOD) was designed, synthesized, and utilized as a curing agent for several commercial epoxy resins. DBCOD-NH2 suppressed the thermal expansion of the epoxy polymer due to the conformational transition of DBCOD from boat to chair, resulting in low or negative CTE. The AFG90-based polymer showed the most significant thermal contraction behavior (-43.6 ppm/K, 40-80 °C) in the glassy state due to the high DBCOD content, chain rigidity, and cross-link density, which resulted from the high epoxy values, rigidity, and functionality of AFG90 resins. The structure-property interactions were examined and applied to modulate the NTE of epoxy polymers. Our findings are useful for the regulation of thermal expansion and the preparation of materials with desired CTE values.

Topology optimization for metamaterials with negative thermal expansion coefficients using energy-based homogenization

Since the existing topology designs of negative thermal expansion metamaterials are primarily based on the asymptotic homogenization theory, this paper conducts a topology optimization method of negative thermal expansion metamaterials based on the computationally efficient energy-based homogenization for the first time. In this research, (1) a new effective thermal stress coefficient equation is pioneeringly proposed using energy-based homogenization frame, where its theoretical derivation process is presented as well as its effectiveness and computational efficiency are verified by comparative cases. Additionally, the matlab code is open-sourced for public learning. (2) A topology optimization design of both 2D and 3D metamaterials with negative thermal expansion properties is established innovatively with Discrete Material Optimization (DMO). Its advantages are illustrated compared with the convectional method and its results are validated by Finite Element Method simulations. The new methods have promising applications in the evaluation and optimization of thermal expansion properties of composites.

Thermal expansion in Prussian Blue analogs M3[Cr(CN)6]2.nH2O (M = Mn, Fe, Co, Ni)

Thermal expansion in Prussian Blue Analogs (PBAs) M3[Cr(CN)6]2.nH2O (M = Mn, Fe, Co, Ni; n = 10–16) was studied using powder X-ray diffraction (XRD) as a function of temperature in the range 123–298 K. Standard chemical precipitation was used to prepare the materials and they were characterized using standard characterization techniques XRD, X-ray fluorescence (XRF), thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. All materials were found to crystallize in the cubic structure with space group Fm3‾m. Strong compositional dependence of thermal expansion is found in this series of PBAs. While Mn3[Cr(CN)6]2.12H2O and Ni3[Cr(CN)6]2.16H2O show positive thermal expansion (PTE) behavior the other two PBAs, Fe3[Cr(CN)6]2.10H2O and Co3[Cr(CN)6]2.14H2O, show strong negative thermal expansion (NTE) behavior with as large coefficient of thermal expansion (CTE) as −19.7 x 10−6 K−1 (for M = Fe) in the temperature range 123–223 K. For the PBAs showing NTE, the magnitude of NTE coefficients can be correlated with the trends for M cation size and cell (or lattice) parameter.

Negative expansion induced anti-abrasive self-cleaning coatings for enhancing output of solar panels

Pollutants on solar panels impede sunlight absorption, leading to a reduction in their output power. Superhydrophilic coatings exhibit effective self-cleaning performance as droplets fully spread on their surfaces. However, one challenge for the commercial development of transparent superhydrophilic coatings is poor abrasion resistance. Frictional heating on the coatings’ surface causes the abrasion force to rise uncontrollably, which in turn causes the coatings to either fracture or wear catastrophically. A promising alternative is utilizing novel adaptive materials with a negative thermal expansion coefficient in the coating. The compressive stress on the surface of the coating with negative expansion will enhance its abrasion resistance. Here, we demonstrate a method to achieve compressive stress in the coating by incorporating halloysite (HNTs) nanotubes due to their negative expansive behavior. Hydrolyzed tetraethyl orthosilicate (TEOS) combines HNTs nanotubes with SiO2 nanoparticles, thus forming a hard nano-composite unit. Meanwhile, amino resin and acrylic resin as adhesives participate in constructing the coating’s three-dimensional network structure. The surfactant sodium alkenyl sulfonate (AOS) endows the coating with superhydrophilicity. As a result, the nano-composite (NC) coating shows superior superhydrophilicity and anti-abrasive properties. The NC coating retains good hydrophilicity and self-cleaning properties after 2000 cycles of Taber abrasion loading 250 g or 1000-line cycles of steel wool friction loading 500 g. The self-cleaning performance of the robust NC coating on solar panels can improve the output power by up to 33.65 % after 296 days. Hence, introducing shrinkage components such as HNTs may provide a general strategy for developing robust superhydrophilic coatings.

Negative thermal expansion coefficient and amorphization in defective 4H-SiC

Negative thermal expansion coefficient and amorphization in defective 4H-SiC

Large magnetocaloric effect and negative thermal expansion of Mn-Ni-Si-Fe-Co-Ge high-entropy alloys

Magnetocaloric high-entropy alloys (HEAs) with a vast compositional space have attracted significant interest for some time due to their great potential in multifunctional application. However, magnetocaloric HEAs generally exhibit modest magnet-entropy change as their undergo second-order phase transition. This work focuses on designing MM'X (M, M′ = transition metals, X = main group elements) HEAs undergoing magnerostructural transition to achieve great magnetocaloric response. For this purpose, MnxFe1-xNi0.6Co0.4Si0.62Ge0.38 (x = 0.43, 0.45, 0.48, 0.50) with intriguingly crystallographic texture are successfully synthesized and their magnetocaloric effect and negative thermal expansion (NTE) are investigated. The substitution of Fe for Mn reduces the transition temperature (Tt) so that weakens the first-order transition of MM'X HEAs. Besides, Mn0.55Fe0.45Ni0.6Co0.4Si0.62Ge0.38 undergoing first-order transition from Ni2In-paramagnetic-austenitic phase to TiNiSi-ferromagnetic-martensitic phase exhibits a great magnetic entropy change of 16 J∙kg−1K−1 at 206 K for 2 T. Moreover, an obviously NTE is observed through phase transition with liner NTE coefficient of −6.77×10−6 K−1. In addition, Mn0.55Fe0.5Ni0.6Co0.4Si0.62Ge0.38 displays an intriguing NTE with liner NTE coefficient of −1401.7×10−6 K−1 (220–270 K) along the direction parallel to field in a temperature range from 220 K to 270 K, which is much higher than typical NTE materials. Therefore, the present work demonstrates that MM'X HEAs exhibit potential to achieve some magnetocaloric and NTE multifunctional application.

NASICON-type medium entropy Li1.5Sn1.0Al0.5Zr0.5(PO4)3 electrolyte for solid state Li metal batteries

Developing solid electrolytes for all-solid-state lithium batteries with superior performance is crucial for portable energy storage. This study uses a traditional solid-state reaction technique to fabricate a NASICON-type medium entropy Li1.5Sn1.0Al0.5Zr0.5(PO4)3 (LSAZP) ceramic electrolyte. The Rietveld refinement of room temperature X-ray diffraction (XRD) data confirms a pure rhombohedral phase (R3‾c) for LSAZP ceramic sintered at 1050 °C. Temperature-dependent synchrotron XRD data demonstrates an increase in lattice parameter c with a positive coefficient of thermal expansion (+2.40 × 10−5 K−1) and a negative coefficient of thermal expansion (−1.26 × 10−6 K−1) for the lattice parameter a with increasing temperature. Interestingly, despite the anisotropic thermal expansion, no intergranular cracks, typically observed in rhombohedral NASICON-type phases, are noticeable in the scanning electron micrographs of the LSAZP samples. The sample sintered at 1050 °C (relative density ∼90 %) exhibits an excellent room temperature conductivity of ∼2.95 × 10−4 S cm−1 and activation energy ∼0.39 ± 0.02 eV. The Li-ion transference number is ∼0.99, suggesting that Li-ion is the dominant charge carrier in the sample. During galvanostatic lithium plating-stripping tests, the symmetric Li|LSAZP|Li cell demonstrates excellent lithium plating-stripping stability over 50 h at a current density of 4 μA cm−2.

Negative thermal expansion in hexagonal VF3 predicted by first-principles calculation

Abstract Searching negative thermal expansion (NTE) materials is challenging. Herein, hexagonal VF3 is predicted as a new NTE material for the first time. VF3 displays NTE property in the temperature range from 0 to 380 K, and the minimum NTE coefficient(α) is approximately −4.68 × 10−6 K−1 at 120 K. The NTE mechanism was ascribed to the vibrations of F atom with larger atomic displacement parameters, which dominates the negative Grüneisen parameters. The difference of minimum NTE coefficient between VF3 and TiF3 might be caused by their different chemical bond strength between Ti–F and V–F. This research provides a deeper understanding between NTE and crystal structure.

Experimental study of Double-Elliptic-Ring-based thermomechanical metamaterials’ behaviour

In recent years there has been increased interest in 3D thermomechanical metamaterials. The current work reports the design, fabrication and testing of a novel anisotropic anepectic metamaterial obtained by grafting inserts of a second material into a known auxetic structure, the Double Elliptic Ring (DER). While auxetics have a Negative Poisson's Ratio (NPR), anepectics combine this with a negative coefficient of thermal expansion (NTE). To avoid unnecessary time and material expenditure during the additive manufacturing (AM) stage, mechanical and thermal finite element simulations (FEA) were used as a tool to screen the multitude of possible design variants under consideration, thus aiding in rapidly determining the more promising geometries. To further increase the efficiency during AM, the selected structures were then assembled from planar elements, joined together with an adhesive. In the end, through the combination of two conventional materials – PVA and Nylon – of positive Poisson's ratio (PR) and coefficient of thermal expansion (CTE) organized in the DER architecture, it was possible to achieve the desired NPR and CTE behaviour along some directions, coupled with positive values in other directions. Experimental results revealed a correlation between PR values and the number of cells in the structure and showed that, while NPR values are essentially determined by the metamaterial's geometry, the induction of NTE results from a subtle interaction of geometry and the properties mismatch between the constitutive materials.

Metalite, a new class of composite laminates with unique properties

Metalite is a new class of antisymmetric composite laminates composed of angle-plies, 0-degree, and 90-degree plies, presenting unique properties. These include extremely thin laminates suitable for minimum gauge applications, remarkable weight savings compared to conventional quads, adjustable zero and negative coefficients of thermal expansion (CTE), ease of manufacturing, excellent ability to adjust mode frequency, change sound radiation characteristics, and high tunability. In this study, Metalite laminates ranging from 3 to 8 plies are described using their feasible spaces and compared with quads, detailing the weight savings achieved for hard, soft, and neutral laminates. Through an experimental study, the CTE value of a hybrid Metalite is correlated with theory, demonstrating how to tune zero and negative CTE values. The proposed work offers significant benefits through practical solutions for designing and manufacturing lightweight composite laminates with unique properties.

Hamiltonian limited valence model for liquid polyamorphism

Liquid-liquid phase transitions have been found experimentally or by computer simulations in many compounds such as water, hydrogen, sulfur, phosphorus, carbon, silica, and silicon. Limited valence model implemented via event-driven molecular dynamics algorithm provides a simple generic mechanism for the liquid-liquid phase transitions in all these diverse cases. Here, we introduce a variant of the limited valence model with a well defined Hamiltonian, i.e., a unique algorithm by which the potential energy of the system of particles can be computed solely from the coordinates of the particles and is thus equivalent to a complex multi-body potential. We present several examples of the model which can be used to reproduce liquid--liquid phase transition in systems with maximum valence z = 1 (hydrogen), z = 2 (sulfur) and z = 4 (water), where z is the maximum number of bonds an atom is allowed to have. For z = 1, we find a set of parameters for which the system has a liquid-liquid and an isostructural solid-solid critical points. For z = 4, we find a set of parameters for which the phase diagram resembles that of water with a wide region of negative thermal expansion coefficient (density anomaly) extending into the metastable region of negative pressures. The limited valence model can be modified to forbid not only too large valences but also too low valences. In the case of sulfur, we forbid the formation of monomers, thus restricting the valence v of an atom to be within an interval 1 = vmin ≤ v ≤ vmax ≡ z = 2.

Exploring VAE-driven implicit parametric unit cells for multiscale topology optimization

The simulation and optimization of metamaterial, known for their engineered properties in various applications, encounter intricate challenges due to complex microstructure interactions, extensive design spaces, and substantial computational requirements. To address these challenges, our research introduces a novel data-driven framework utilizing deep generative modeling to enhance the design process of metamaterials.Focusing on composite metamaterial with double negative coefficients of thermal expansion and Poisson's ratio, we apply an Alternative Active Phase and Objective functions (AAPO) method for deciding the initial metamaterial dataset. To enhance dataset diversity, a distortion filter is applied, broadening the range of design possibilities. Subsequently, we utilize a Variational Autoencoder (VAE), integrated with a regressor, to train on this diversified database. This training effectively maps complex unit cell geometries to a coherent latent space, simultaneously correlating them with continuous material properties.Our approach demonstrates robustness in multi-phase and multi-physics optimization as well as efficiency in generating specialized databases of unit cells. This framework is pivotal in systematically designing unit cells and multiscale systems, specifically aiming for distinct thermo-mechanical behavior targets.To mitigate the computational demands encountered during multiple design meta-materials via gradient-based topology optimization, we have integrated high-performance methods and automatic differentiation. This integration marks a significant advancement in the data-driven design of metamaterials, offering substantial practical and theoretical benefits in the field.

Dual arrowhead-shaped re-entrant auxetic hybrid metamaterial with adjustable thermal expansion

The lightweight metamaterial with the adjustable coefficient of thermal expansion (CTE) and Poisson's ratio (PR) has aroused great interest in potential engineering applications. However, the bifunctional metamaterials with dual negative properties exhibit relatively narrow ranges of CTE and PR, only considering one direction. In this work, a dual arrowhead-shaped re-entrant auxetic (DARA) hybrid metamaterial with controllable CTE is designed by combining a star-shaped re-entrant structure and a dual arrowhead inclined triangle structure. A theoretical model of the DARA unit cell is established to obtain CTE and PR solutions using the stiffness matrix method, which is verified by the finite element method (FEM). The theoretical model is used to further study the effect of geometric parameters, configuration, and base material on the thermal and mechanical properties. The DARA metamaterial can simultaneously realize the adjustable CTE and PR, especially a wide range of CTE under two directions, from negative to positive values. Furthermore, the 3D-printed DARA samples are fabricated to validate the CTE and PR values of the unit cell, which are in line with the FEM and theoretical values. The bi-metamaterial unit cell exhibits positive, quasi-zero, or negative CTE and PR owing to the synergistic effect of re-entrant and dual arrowhead structure. The deformation mechanism is proposed based on the structure's stretch-bending coupling and stretch-dominated design.

Synthesis and crystal structure of 2,9-diamino-5,6,11,12-tetrahydrodibenzo[a,e]cyclooctene

The cis- form of diaminodibenzocyclooctane (DADBCO, C16H18N2) is of interest as a negative coefficient of thermal expansion (CTE) material. The crystal structure was determined through single-crystal X-ray diffraction at 100 K and is presented herein.

Evolution of structure and spectroscopic properties of a new 1,3-diacetylpyrene polymorph with temperature and pressure.

A new polymorph of 1,3-diacetylpyrene has been obtained from its melt and thoroughly characterized using single-crystal X-ray diffraction, steady-state UV-Vis spectroscopy and periodic density functional theory calculations. Experimental studies covered the temperature range from 90 to 390 K and the pressure range from atmospheric to 4.08 GPa. Optimal sample placement in a diamond anvil cell according to our previously presented methodology ensured over 80% data coverage up to 0.8 Å for a monoclinic sample. Unrestrained Hirshfeld atom refinement of the high-pressure crystal structures was successful and anharmonic behavior of carbonyl oxygen atoms was observed. Unlike the previously characterized polymorph, the structure of 2°AP-β is based on infinite π-stacks of antiparallel 2°AP molecules. 2°AP-β displays piezochromism and piezofluorochromism which are directly related to the variation in interplanar distances within the π-stacking. The importance of weak intermolecular interactions is reflected in the substantial negative thermal expansion coefficient of -55.8 (57) MK-1 in the direction of C-H...O interactions.

Impact resistance analysis of a dual-constituent negative Poisson’s ratio lattice metamaterial with tailorable coefficient of thermal expansion

The combination of parameters such as negative Poisson’s ratio (NPR) and negative coefficient of thermal expansion (NCTE) can result in novel materials with specialized functions to meet the requirements of multifunctional and multipurpose devices. However, the additional structural design to meet NCTE requires a re-examination of its impact resistance. In this paper, the deformation modes and impact resistance of dual-constituent re-entrant hexagonal lattice metamaterial (DRHLM) with both NPR and NCTE are investigated under different impact velocities, and the nominal stress–strain curves and energy absorption characteristics of DRHLM structures with different arch heights, chord lengths, and angles of the bottom edge ribs and the diagonal ribs are discussed. The results show that the bi-material bending ribs affect the energy absorption of the structure, and in most cases the DRHLM structure has a better energy absorption capacity than the traditional concave hexagonal structure, but too much or too little curvature of the bi-material portion reduces the energy absorption characteristics of the DRHLM structure. In addition, the increase in the pinch angle of the ribs leads to the weakening of the negative Poisson’s ratio effect, which is also detrimental to the energy absorption of the structure. The work done can provide guidance for finding the dimensional parameters of DRHLM structures with optimal energy absorption performance.

Controllable Technology for Thermal Expansion Coefficient of Commercial Materials for Solid Oxide Electrolytic Cells.

Solid oxide electrolysis cell (SOEC) industrialization has been developing for many years. Commercial materials such as 8 mol% Y2O3-stabilized zirconia (YSZ), Gd0.1Ce0.9O1.95 (GDC), La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF), La0.6Sr0.4CoO3-δ (LSC), etc., have been used for many years, but the problem of mismatched thermal expansion coefficients of various materials between cells has not been fundamentally solved, which affects the lifetime of SOECs and restricts their industry development. Currently, various solutions have been reported, such as element doping, manufacturing defects, and introducing negative thermal expansion coefficient materials. To promote the development of the SOEC industry, a direct treatment method for commercial materials-quenching and doping-is reported to achieve the controllable preparation of the thermal expansion coefficient of commercial materials. The quenching process only involves the micro-treatment of raw materials and does not have any negative impact on preparation processes such as powder slurry and sintering. It is a simple, low-cost, and universal research strategy to achieve the controllable preparation of the thermal expansion coefficient of the commercial material La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) through a quenching process by doping elements and increasing oxygen vacancies in the material. Commercial LSCF materials are heated to 800 °C in a muffle furnace, quickly removed, and cooled and quenched in 3.4 mol/L of prepared Y(NO3)3. The thermal expansion coefficient of the treated material can be reduced to 13.6 × 10-6 K-1, and the blank sample is 14.1 × 10-6 K-1. In the future, it may be possible to use the quenching process to select appropriate doping elements in order to achieve similar thermal expansion coefficients in SOECs.

Effect of Ti4+ and Pb2+ on negative thermal expansion and polarization behaviors of KSr2Nb5O15: First-principles investigation

The utilization of both negative and positive thermal expansion coefficients presents a potential means of mitigating internal stress in high-temperature materials, hence offering a novel approach to enhance the impact strength of those materials. The investigation of the thermal expansion coefficient and polarization characteristics of KSr2Nb5O15 doped with Ti4+ and Pb2+ was conducted by the utilization of first-principles calculations. The introduction of Ti4+ and Pb2+ into the KSr2Nb5O15 lattice resulted in an increase in lattice distortion. This effect was particularly pronounced when Ti4+ and Pb2+ were co-doped, leading to the largest lattice distortion observed in KSr2Nb5O15. Furthermore, the negative thermal expansion coefficient of KSr2Nb5O15 was also found to be the highest under these co-doping conditions, with a value of −0.560×10−5 K−1 compared to the original value of −0.011×10−5 K−1. Conversely, when Ti4+ was doped individually, the lattice distortion and negative thermal expansion coefficient of KSr2Nb5O15 were found to be the smallest. Furthermore, the inclusion of Ti4+ and Pb2+ leads to an enhancement in the dielectric constant. This effect is particularly pronounced when Ti4+ and Pb2+ are simultaneously incorporated into the KSr2Nb5O15 lattice. Consequently, the dielectric constant of the material exhibits a substantial improvement. The greatest polarization intensity is achieved when KSr2Nb5O15 is co-doped with Ti4+ and Pb2+, resulting in a polarization intensity of 38.61 μC/cm2. The dense ceramics comprising of KSr2Nb5O15, with the addition of Ti4+ and Pb2+ dopants, were synthesized using the solid-state reaction method. Subsequently, the thermal expansion coefficients and dielectric characteristics of these ceramics were evaluated. The experimental results are not in good agreement with the calculated results, but qualitatively, the trend predicted by the theory is confirmed by experiment. This study establishes the groundwork for the synthesis of KSr2Nb5O15 materials exhibiting pronounced negative thermal expansion characteristics.