Negative Thermal Expansion Materials Research Articles

Unrevealing the wetting behavior and mechanism of AgCuTi filler on negative thermal expansion Sc2W3O12 materials: Experiments and First-principles calculations

Improving understanding of wetting behavior and mechanism between negative thermal expansion materials and filler metals was critical for the application of negative thermal expansion materials in the aerospace, precise instrument, etc. However, there is a lack of research on the wettability of negative thermal expansion materials. In this work, we employed experimental studies and First-principles calculations to investigate the wetting behavior, interfacial microstructure, and interfacial bonding characteristic between AgCuTi filler and Sc2W3O12 materials. The sessile drop method experiment investigated the influence of Ti content on the wettability of AgCuTi filler. When the Ti content was 4.6 wt%, the minimum contact angle of 15° was achieved. The XRD and TEM results indicated that active Ti reacted with Sc2W3O12 to form Cu3Ti3O, Ti3O5, and Cu0.4W0.6 compound. Furthermore, we investigated the interfacial bonding characteristics of Sc2W3O12 (010)/Ti (001) interface and Ti3O5 (001)/Ti (001) interface by First-principles calculations. According to the calculations results, the work of adhesion of Ti3O5/Ti interface system was higher than that of Sc2W3O12/Ti interface system, which suggested that the formed Ti3O5 reaction layer was conducive to improve the wettability of AgCuTi filler on the Sc2W3O12 materials. This work provided a new vision for the wetting mechanism between metal filler and negative thermal expansion materials, and was expected to provide guidance for the design of new material systems.

Exploring negative thermal expansion materials with bulk framework structures and their relevant scaling relationships through multi-step machine learning.

Discovering new negative thermal expansion (NTE) materials is a great challenge in experiment. Meanwhile, the machine learning (ML) method can be another approach to explore NTE materials using the existing material databases. Herein, we adopt the multi-step ML method with efficient data augmentation and cross-validation to identify around 1000 materials, including oxides, fluorides, and cyanides, with bulk framework structures as new potential NTE candidate materials from ICSD and other databases. Their corresponding coefficients of negative thermal expansion (CNTE) and temperature ranges are also well predicted. Among them, about 57 materials are predicted to have an NTE probability of 100%. Some predicted NTE materials were tested by the first-principles calculations with quasi-harmonic approximation (QHA), which indicates that the ML results are in good agreement with the first principles calculation results. Based on the comprehensive analysis of the existing and predicted NTE materials, we established three universal relationships of CNTE with an average electronegativity, porosity, and temperature range. From these, we also identified some important critical values characterizing the NTE property, which can serve as an important criterion for designing new NTE materials.

Mixed anion control of enhanced negative thermal expansion in the oxysulfide of PbTiO3.

The rare physical property of negative thermal expansion (NTE) is intriguing because materials with a large NTE over a wide temperature range can serve as high-performance thermal expansion compensators. However, the applications of NTE are hindered by the fact that most of the available NTE materials show small magnitudes of NTE, and/or NTE occurs only in a narrow temperature range. Herein, for the first time, we investigated the effect of anion substitution instead of general Pb/Ti-site substitutions on the thermal expansion properties of a typical ferroelectric NTE material, PbTiO3. Intriguingly, the substitution of S for O in PbTiO3 further increases the tetragonality of PbTiO3. Consequently, an unusually enhanced NTE with an average volumetric coefficient of thermal expansion of V = -2.50 × 10-5 K-1 was achieved over a wide temperature range (300-790 K), which is in contrast to that of pristine PbTiO3 (V = -1.99 × 10-5 K-1, RT-763 K). The intensified NTE is attributed to the enhanced hybridization between Pb/Ti and O/S atoms by the substitution of S, as evidenced by our theoretical investigations. We therefore demonstrate a new technique for introducing mixed anions to achieve a large NTE over a wide temperature range in PbTiO3-based ferroelectrics.

Regulating the thermal expansion of a [FePt(CN)4] layer by axial coordination and dimensional reduction.

Thermal expansion regulation by chemical decoration at a molecular level is of great technological value for materials science. Herein, we show that the spin crossover active compound Fe(pyz)Pt(CN)4 (pyz = pyrazine) shows a rare 2D negative thermal expansion (NTE) in the ab-plane. By introducing axial coordination iodine ions or reducing the framework dimension from 3D to 2D, the NTE behavior can be effectively switched to positive thermal expansion (PTE) or even zero thermal expansion (ZTE). Moreover, it is found that different spin states of Fe2+ also influence the magnitude of NTE. Compared with the low-spin (LS) sate, the high-spin (HS) state tends to enhance the magnitude of NTE. Combined in situ structural and Raman spectral analyses revealed that the NTE mainly originates from the transverse vibration of a bridging cyano group and the tailorable thermal expansion is closely related to the state of the Fe-CN-Pt linkage. The present study shows how the rational regulation of the building unit and framework dimensions can effectively control thermal expansion behaviors. This insight can serve as guidance for designing and synthesizing novel NTE materials.

Giant enhancement of anti-quenching upconversion luminescence in Sc2W3O12:Er3+/Yb3+ phosphors for temperature sensing

Although negative thermal expansion (NTE) materials provide a new strategy to overcome the thermal-quenching phenomenon in rare earth doped luminescent materials, the overall weak upconversion luminescence still restrict their application...

Visualized real-time flexible high-temperature sensing in Eu3+/Tb3+-doped Y2Mo3O12 negative thermal expansion material films

Visualized real-time flexible high-temperature sensing in Eu3+/Tb3+-doped Y2Mo3O12 negative thermal expansion (NTE) thin films achieved multiple naked-eye color spans that depended on different energy transfer between Eu3+/Tb3+-doped NTE materials.

Mechanism of Negative Thermal Expansion in Monoclinic Cu2P2O7 from First Principles.

Negative thermal expansion (NTE) materials generally have high-symmetry space groups, large average atomic volumes, and corner-sharing octahedral and tetrahedral coordination structures. By contrast, monoclinic α-Cu2P2O7, which has a small average atomic volume and edge-sharing structure, has been reported to exhibit NTE, the detailed mechanism of which is unclear. In this study, we investigate the A2B2O7 polymorphs and analyze the NTE behavior of α-Cu2P2O7 using first-principles lattice-dynamics calculations. From the polymorphism investigation in 20 A2B2O7 compounds using 6 representative crystal structures, small A and B cationic radii are found to stabilize the α-Cu2P2O7-type structure. We then analyze the NTE behavior of α-Cu2P2O7 using quasi-harmonic approximation. Our calculated thermal expansion coefficients and anisotropic atomic displacement parameters were in good agreement with those of the experimental reports at low temperatures. From the mode-Grüneisen parameter distribution plotted over the entire first-Brillouin zone, we found that the phonon contributing most significantly to NTE emerges not into the special points but between them. In this phonon mode, the O connecting two PO4 tetrahedra rotates, and the Cu and O vibrate perpendicular to the bottom of the CuO5 pyramidal unit, which folds the ac lattice plane. This vibration behavior can explain the experimentally reported anisotropic NTE behavior of α-Cu2P2O7. Our results demonstrate that the most negative mode-Grüneisen parameter contributing to NTE behavior is not always located on high-symmetry special points, indicating the importance of lattice vibration analyses for the entire first-Brillouin zone.

Structure, luminescence properties and anti-thermal quenching of a novel Eu3+-activated red phosphor based on the negative thermal expansion material In0.5Sc1.5(MoO4)3

A new Eu3+-doped phosphor was synthesized by the high-temperature solid-state method based on In0.5Sc1.5(MoO4)3 with negative thermal expansion characteristics in the wide temperature range. The phosphor was pure phase, and the Eu3+ occupied the Sc3+-site. The main emission peak of the phosphor was located at 615 nm, which was attributed to the 5D0-7F2 energy level transition of Eu3+, and the fluorescence lifetime was between 297 and 493 μs. Its quenching concentration was 8 mol%, and the non-radiative energy transfer mechanism between Eu3+ ions was mainly exchange interaction. Under the excitation of 246 nm, the luminous intensity of phosphor was thermically enhanced after 348 K and showed near-zero thermal quenching characteristic. It could be attributed to the positive thermal expansion of phosphor change into two-dimensional negative thermal expansion. At 465 nm excitation, it also exhibited the anti- thermal quenching property and the luminous intensity remained 103.4 % at 423 K of that at the room temperature. The internal quantum efficiency of In0.5Sc1.5(MoO4)3: 8 mol% Eu3+ phosphor was 57.8 %, while the overall color purity was as high as 99.52 %. The LED device packaged it with a commercial LED chip could emit bright red light. Its comprehensive luminous properties were better than the commercial red phosphor Y2O3: Eu3+. The results showed that In0.5Sc1.5(MoO4)3: Eu3+ was a new red phosphor with good luminous performance and anti-thermal quenching characteristic.

Formation of floral microstructures of the refractory negative thermal expansion ceramic MgO-doped Zr2P2WO12 following acid corrosion

Refractory negative thermal expansion (NTE) materials can reduce stress when subjected to drastic temperature changes and therefore have potential applications in fire-fighting field. However, NTE ceramics are susceptible to impact damage due to their poor mechanical properties. We have found that treatment of a ceramic with hydrofluoric acid (HF) generated floral microstructures that enhanced the ceramic's impact resistance. Specifically, pellets of a refractory NTE ceramic, Zr2P2WO12 (ZWP) ceramics, containing various doping ratios of MgO) are fabricated and then treated with hydrofluoric acid (HF) to induce the formation of flower-like microstructures. Structural analyses show that the concentration of MgO in the ZWP pellets affects the morphology of the microstructures. The crystal orientation of ZWP appears after HF acid corrosion, and the formation of floral particles corresponded to the content of MgO. This investigation demonstrates that HF treatment can alter the microstructure of a refractory NTE ceramic and may have wide application for enhancing such ceramics' mechanical properties.

Thermodynamic Origin of Negative Thermal Expansion Based on a Phase Transition-Type Mechanism in the GdF3-TbF3 System.

Multicomponent fluorides of rare earth elements (REEs-R) are phase transition-type negative thermal expansion (NTE-II) materials. NTE-II occurs in RF3-R'F3 systems formed by "mother" single-component dimorphic RF3 (R = Pm, Sm, Eu, and Gd) with a giant NTE-II. There are two structural types of RF3 polymorphic modifications: low-temperature β-YF3 (β-) and high-temperature LaF3 (t-). The change in a structural type is accompanied by a density anomaly: a volume of one formula unit (Vform) Vβ- >Vt-. The empirical signs of volumetric changes ΔV/V of NTE-II materials were considered. For the GdF3-TbF3 model system, an "operating-temperature window ΔT" and a two-phase composition of NTE-II materials follows from the thermodynamics of chemical systems: the phase rule and the principle of continuity. A necessary and sufficient sign of NTE-II is a combination of polymorphism and the density anomaly. Isomorphism in RF3-R'F3 systems modifies RF3 chemically by forming two-component t- and β- type R1-xR'xF3solid solutions (ss). Between the two monovariant curves of ss decay, a two-phase area with ΔTtrans > 0 (the "window ΔT") forms. A two-phase composite (t-ss + β-ss) is an NTE-II material. Its constituent t-ss and β-ss phases have different Vform corresponding to the selected T. According to the lever rule on a conode, Vform is calculated from the t-ss and β-ss compositions, which vary with T along two monovariant curves of ss decay. For the GdF3-TbF3 system, ΔV/V = f(T), ΔV/V = f(ΔT) and the "window ΔT" = f(x) dependencies were calculated.

Design and preparation of high-content Sc2W3O12 dispersed interlayer: alleviating the high residual stress of Cf/SiC and GH3536 joint

Negative thermal expansion (NTE) materials were utilized to alleviate the high residual stress of brazed joints by regulating the coefficient of thermal expansion (CTE) of metal composite filler. However, the confined addition amount of NTE materials restricted their ability to control the CTE of metal composite filler. In this study, the physical properties of the brazing seam were investigated by finite element analysis to understand their influence on the stress distribution of brazed joint. Based on theoretical analysis, a new method of preparation a high-content Sc2W3O12 dispersed interlayer by cold-pressing sintering method was proposed. This method increased the optimal addition amount of Sc2W3O12 materials from 10 vol.% to 40 vol.%. When the content of Sc2W3O12 materials was 40 vol.%, the CTE of Sc2W3O12 dispersed interlayer decreased from 16.5 (the CTE of AgCuTi) to 10.9 × 10−6 K−1, achieving a gradient transition of CTE from the Cf/SiC composite material/brazing seam/GH3536. The maximum shear strength of the Cf/SiC-GH3536 joint using Sc2W3O12 dispersed interlayer is 141 MPa, which was 5.9 times higher than that of AgCuTi filler. This study highlights the potential of proposed method for preparing brazed interlayer with high-content reinforcements, which may find practical applications in other metal composites.

Bridging the Gap between Zeolites and Dense Silica Polymorphs: Formation of All-Silica Zeolite with High Framework Density from Natural Layered Silicate Magadiite.

A silica zeolite (RWZ-1) with a very high framework density (FD) was synthesized from highly crystalline natural layered silicate magadiite, bridging the gap between the two research areas of zeolites and dense silica polymorphs. Magadiite was topotactically converted into a 3D framework through two-step heat treatment. The resulting structure had a 1D micropore system of channel-like cavities with an FD of 22.1 Si atoms/1000 Å3 . This value is higher than those of all other silica zeolites reported so far, approaching those of silica polymorphs (tridymite (22.6) and α-quartz (26.5)). RWZ-1 is a slight negative thermal expansion material with thermal properties approaching those of dense silica polymorphs. It contributes to the creation of a new field on microporous high-density silica/silicates. Synergistic interactions are expected between the micropores with molecular sieving properties and the dense layer-like building units with different topologies which provide thermal and mechanical stabilities.

Preparation and Properties of Negative Thermal Expansion Snow Melting and Ice Suppression Materials

To investigate the potential utilization of materials exhibiting negative thermal expansion in snow melting and ice suppression applications, an orthogonal test was conducted to ascertain the optimal ratio of effective constituents in said materials. The thermal expansion coefficient of the porous carrier for negative thermal expansion materials was examined, and modifications were made to the material used for snow melting and ice suppression. In conclusion, the researchers successfully developed snow melting and ice suppression materials with low thermal expansion that met the desired performance criteria. Furthermore, they conducted an analysis of the precipitation rate, as well as the snow melting and ice suppression effectiveness of these materials across various temperature ranges. According to the results, the thermal expansion coefficient of the carrier Z1 is positive and varies slightly in the temperature range of −30 °C~−10 °C. In the temperature range of −10 °C~0 °C, the thermal expansion coefficient is negative, and it has negative thermal expansion characteristics. At 0 °C~60 °C, its thermal expansion coefficient first increases and then decreases. In the low temperature stage, the amount of salt precipitation decreases with the decrease of temperature. In the conductivity test, the conductivity at 0 °C is greater than that at −5 °C, and much greater than that at 10 °C, the presence of a negative thermal expansion coefficient has been observed to exert a specific influence on the precipitation of materials used for snow melting and ice suppression. In addition, with the increase of temperature, the amount of salt precipitation increases. Whereas, when the temperature is higher than 35 °C, due to the thermal expansion characteristics of the carrier, the expansion of the volume of snow melting and ice suppression materials is comparatively limited, which results in a not greatly increased precipitation rate of the snow melting and ice suppression components compared with that at 35 °C.

Equation of state predictions for ScF3 and CaZrF6 with neural network-driven molecular dynamics.

In silico property prediction based on density functional theory (DFT) is increasingly performed for crystalline materials. Whether quantitative agreement with experiment can be achieved with current methods is often an unresolved question, and may require detailed examination of physical effects such as electron correlation, reciprocal space sampling, phonon anharmonicity, and nuclear quantum effects (NQE), among others. In this work, we attempt first-principles equation of state prediction for the crystalline materials ScF3 and CaZrF6, which are known to exhibit negative thermal expansion (NTE) over a broad temperature range. We develop neural network (NN) potentials for both ScF3 and CaZrF6 trained to extensive DFT data, and conduct direct molecular dynamics prediction of the equation(s) of state over a broad temperature/pressure range. The NN potentials serve as surrogates of the DFT Hamiltonian with enhanced computational efficiency allowing for simulations with larger supercells and inclusion of NQE utilizing path integral approaches. The conclusion of the study is mixed: while some equation of state behavior is predicted in semiquantitative agreement with experiment, the pressure-induced softening phenomenon observed for ScF3 is not captured in our simulations. We show that NQE have a moderate effect on NTE at low temperature but does not significantly contribute to equation of state predictions at increasing temperature. Overall, while the NN potentials are valuable for property prediction of these NTE (and related) materials, we infer that a higher level of electron correlation, beyond the generalized gradient approximation density functional employed here, is necessary for achieving quantitative agreement with experiment.

Influence of A/B Element Substitution on Negative Thermal Expansion in AB(CN)6 (A = Al, Ga, In; B = Co, Fe, Mn, Cr, V, Ti): A Density Functional Theory Study.

Negative thermal expansion as an abnormal physical behavior of materials has promising applications in a high sophisticated equipment field, but the materials are rare. Here, we use the first-principles calculations based on density functional theory combined with the recently developed average atomic volume (AAV = V/N, where V is unit cell volume and N is the number of atoms in the unit) rule to predict the large isotropic negative thermal expansion materials of Prussian blue analogues AB(CN)6 (A = Al, Ga, In; B = Co, Fe, Mn, Cr, V, Ti) in a wide temperature range. Our results clearly show that the coefficient of negative thermal expansion has a near-linear relationship with the average atomic volume of the systems and is also influenced by the element substitution at the A or B site. Lattice dynamic simulations indicate that the main contribution to the negative thermal expansion comes from the low-frequency transverse vibration of the (B)-C≡N-(A) groups, especially the transverse vibration of the N atoms. Thus, the element substitution at the A site (binding to N) can tune the negative thermal expansion behavior of the systems more effectively than that at the B site (binding to C), indicating the different roles of bonds on the negative thermal expansion. Our present work not only expands the kinds of isotropic materials but also gives some insights into the relationship between the average atomic volume and negative thermal expansion.

Zero thermal expansion, high specific thermal conductivity, and good machinability of Cu2P2O7/2024Al composite

Negative thermal expansion (NTE) materials can be applied to suppress thermal expansion of other materials, forming composites with zero thermal expansion (ZTE). However, the shortcomings (e.g., high density, narrow working temperature window) inherited from various NTE materials hinder the applications of corresponding ZTE composites. The modified Cu2P2O7 by reducing oxygen deficiencies has a relatively low density and strong NTE over a wide temperature range, which therefore was used to composite with 2024Al. When the volume content of modified Cu2P2O7 is about 50%, the composite Cu2P2O7/2024Al shows ZTE effect, and the linear coefficient of thermal expansion is about −0.014 ppm/K at 273–333 K. The ZTE composite also exhibits a high specific thermal conductivity, significantly superior to other existing ZTE materials. Furthermore, due to the matched moduli between Cu2P2O7 and 2024Al, the ZTE composite displays good machinability. The current ZTE composite may have great potential applications in the fields of high-precision electronics and optics.

Giant Negative Thermal Expansion Materials: Progress of Research and Future Prospects

Giant Negative Thermal Expansion Materials: Progress of Research and Future Prospects

Morphology controlled synthesis and sensitive temperature sensing performance of Gd2(WO4)3: Er3+, Yb3+

Rare-earth ion doped negative thermal expansion materials as fluorescent thermosensitive materials have attracted significant attention due to their natural advantage in achieving high resolution fluorescence. Herein, Er3+/Yb3+-codoped Gd2(WO4)3 microparticles were developed. Their morphology and size can be finely controlled by manipulating the additives, pH values, and reaction rates. Under near-infrared (NIR) excitation, the compounds evince green and red UC emissions. With regards to the thermal coupling level of 2H11/2/4S3/2 of Er3+ ions, the maximum absolute sensitivity (Sa) and relative sensitivity (Sr) were established to be 1.39 % K−1 (at 300 K) and 1.18 % K−1 (at 293 K), respectively. Ultimately, the utilization of synthesized microparticles and a 940 nm NIR chip facilitated the development of a proficient green-emitting light-emitting diode device. The aforementioned characteristics indicate that Er3+/Yb3+ co-doped Gd2(WO4)3 microparticles possess potential applications in the fields of non-contact optical temperature sensing as well as solid-state lighting.

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

Negative thermal expansion (NTE) alloys possess great practical merit as thermal offsets for positive thermal expansion due to its metallic properties. However, achieving a large NTE with a wide temperature range remains a great challenge. Herein, a metallic framework-like material FeZr2 is found to exhibit a giant uniaxial (1D) NTE with a wide temperature range (93-1078 K, {bar{alpha }}_{l}=-34.01times {10}^{-6},{{{{{{rm{K}}}}}}}^{-1}). Such uniaxial NTE is the strongest in all metal-based NTE materials. The direct experimental evidence and DFT calculations reveal that the origin of giant NTE is the couple with phonons, flexible framework-like structure, and soft bonds. Interestingly, the present metallic FeZr2 excites giant 1D NTE mainly driven by high-frequency optical branches. It is unlike the NTE in traditional framework materials, which are generally dominated by low energy acoustic branches. In the present study, a giant uniaxial NTE alloy is reported, and the complex mechanism has been revealed. It is of great significance for understanding the nature of thermal expansion and guiding the regulation of thermal expansion.

Application of Ba0.5Sr0.5FeO3−δ-NdMnO3−δ Composite Cathode in Proton-Conducting Solid Oxide Fuel Cells

Ba0.5Sr0.5FeO3−δ (BSF) nanofibers are prepared via electrospinning and sintering at a temperature of 800 °C for 2 h to produce a pure cubic perovskite phase, with the aim of finding a high-performance cathode material suitable for proton-conducting solid oxide fuel cells (PCFCs) operating at medium temperatures. The results of SEM analysis showed that the BSF nanofibers are alternately stacked, presenting fluffy and uniform high porosity, which is favorable to the cathode polarization reaction of PCFCs. To balance the excessive coefficient of thermal expansion of the BSF cathode, it is combined with a negative thermal expansion (NTE) material NdMnO3−δ (NM). At 700 °C, the peak power density (PPD) of the BSF–NM cathode cell is 1170 mW cm−2, and the open-circuit voltage (OCV) of the single cell is 1.04 V. The corresponding polarization impedance (Rp) of the BSF–NM is 0.037 Ω cm2. This result is significantly better than the previously reported powder cathode BSF, indicating that the performance of PCFC can be further optimized by transforming the BSF cathode into a nanofiber state and compounding it with the NTE material NM.