Negative Thermal Expansion Materials Research Articles

Tuning the thermo-mechanical synergies effect of solid oxide fuel cells with negative thermal expansion NdMnO3 in La0.6Sr0.4Co0.2Fe0.8O3-δ-based symmetric electrode

Solid oxide fuel cells (SOFCs) are efficient and clean energy conversion devices, but one of the major challenges for their marketization is the instability of different component materials under high temperature operating conditions. The existence of a certain internal stress gradient between materials with different thermal expansion characteristics in the process of SOFCs from low temperature assembly to high temperature use is the main reason of this instability, leading to the inability of SOFCs to repeat start-stop and the rapid decay of long-term stability performance. To improve these problems, a creative concept of fuel cell interface overall regulation is proposed, simplifying the complex interface between different components of SOFCs into a unified and adjustable quasi-zero difference thermal expansion interface. The composite of high catalytic activity electrode material and high stability negative thermal expansion material is used for electrolyte support structure symmetrical cell, which makes the whole cell “sandwich” structure thermally and mechanically compatible. As a concept verification, the classic high catalytic performance electrode material La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF), Gd0.2Ce0.8O2-δ (GDC) and NdMnO3 (NM) negative thermal expansion material with high chemical stability and mechanical stability were composited in equal proportions to form LSCF@GDC&NM electrode as the symmetrical electrode. After equal proportion compositing, the thermal expansion curve of LSCF@GDC&NM material can highly coincide with the thermal expansion curve of GDC, making the single cell with LSCF@GDC&NM electrode can withstand 25 power thermal cycles without significant performance decay, achieving 442 mW cm−2 at 800 °C and maintaining stably for 140 h without any degradation. These results show that using negative thermal expansion material to regulate electrode strategy is expected to make a whole zero difference thermal fuel cell configuration.

Negative Thermal Expansion Materials as Anti-Thermal-Quenching Phosphor Matrixes: Status, Opportunities, and Challenges.

Inorganic phosphor materials often face the common phenomenon of luminescence thermal quenching (TQ), which deteriorates their device performance and consequently limits their applicability for broad applications. Thus, exploring thermally stable and even anti-TQ phosphors is viable to meet the urgent requirements of lighting technology and many other luminescence-based applications. One of the emerging approaches devoted to solving the TQ issue of phosphors, especially at elevated temperatures, is to employ negative thermal expansion (NTE) properties occurring in some unique inorganic materials. The present Review focuses on the progress of exploring NTE-based inorganic phosphor materials that have demonstrated unusual negative TQ with enhancing upconversion and downshift luminescence upon elevating temperature. We have also provided a brief history of exploring NTE phosphors for thermally stable and enhanced emission along with the investigation methods and proposed mechanisms of these unusual phenomena. To summarize, we have further discussed some opportunities and challenges that NTE materials face as host matrixes for anti-TQ phosphors. Overall, the aim of this Review is to stimulate the exploration of new NTE-based inorganic phosphors, the correlation of their fundamental structural changes with varying temperature, and the investigation of their potential for broad applications.

Influence of Sn on thermal expansion and dielectric properties of ZrMgMo3O12

Exploring new applications of negative thermal expansion (NTE) materials is a recent research hotspot. In this work, the IV A element Sn was used to tailor the thermal expansion and dielectric properties of NTE material ZrMgMo3O12, and the samples Zr1–xSnxMgMo3O12 (x = 0.05, 0.10, 0.15, 0.20, 0.25) can be used in the field of high-frequency dielectric ceramics. Both the substitution amount of Sn and sintering temperature have a certain effect on the properties of Zr1-xSnxMgMo3O12. The coefficients of thermal expansion (CTE) can be adjusted between near zero thermal expansion (ZTE) (−0.24 × 10−6/K−1) and NTE (−8.16 × 10−6/K−1) and become larger toward negative as the amount of Sn increased under the same sintering temperature. The dielectric constants of Zr1-xSnxMgMo3O12 can be adjusted in the range of 130∼155, which are about 25 times than ZrMgMo3O12. The dissipation factors of Zr1-xSnxMgMo3O12 were adjustable between 4.37 × 10−4 and 5.54 × 10−4, meeting the application requirements of high-frequency dielectric ceramics. This research shows that Sn can adjust the thermal expansion properties and significantly improves the dielectric properties of ZrMgMo3O12, so that Zr1-xSnxMgMo3O12 materials have high value in the field of high-frequency dielectric ceramics.

Investigate the effect of C coating on the wetting and reaction mechanism of Sc2W3O12 and AgCuTi filler

Mitigating the interface reaction between negative thermal expansion materials and filler metals is crucial for enhancing the functionality of negative thermal expansion materials. However, the general approach to mitigate interface reaction, such as minimizing both reaction time and temperature, will result in insufficient metallurgical reactions necessary to establish reliable connections during the brazing process. Through wetting process analysis and first-principles calculations, the effect of C coating on the wetting and reaction mechanism of Sc2W3O12 and AgCuTi filler is revealed. The wetting experiment indicates that the C coating not only improves the wettability but also mitigates the interface reaction. According to the interfacial microstructure, 18 kinds of Ti/Ti3O5 (001) and 3 kinds of Ti/TiC (100) adsorption systems are constructed to calculate the adsorption characteristics. According to the calculations, the Ti/TiC (100) system has lower adsorption energy than Ti/Ti3O5 (001) system, indicating that Ti atoms are more easily adsorbed on the TiC surface. The charge density difference contour shows that the charge repulsion on the TiC surface restricts the entry of Ti atoms. This work provides new insights into the mechanism of how the C coating to reduce interfacial consumption of the negative thermal expansion materials.

High‐Entropy Anti‐Perovskites with Enhanced Negative Thermal Expansion Behavior

AbstractThe negative thermal expansion (NTE) materials, which can act as thermal‐expansion compensators to counteract the positive thermal expansion, have great applications merit in precision engineering. However, the exploration of NTE behavior with a wide temperature range has reached its upper ceiling through traditional doping strategies due to composition limitations. In this paper, the unique sluggish characteristics and extended optimization space in empirically screened high‐entropy anti‐perovskite (HEAP) are utilized to broaden the NTE temperature range. Typically, the NTE temperature range in Mn3Cu0.2Zn0.2Ga0.2Ge0.2Mn0.2N is broadened to ΔT = 235 K (5 K ≤ T ≤ 240 K), which is two or three times wider than that of traditional low‐entropy doping systems. The neutron diffraction analysis reveals a unique sluggish characteristic in magnetic phase transition which survives in an ultra‐wide temperature range of 5 K ≤ T ≤ 350 K (ΔT = 345 K). The sluggish characteristic is further experimentally proved to come from disturbed phase transition dynamics due to distortion in atomic spacing and chemical environmental fluctuation observed by the spherical aberration‐corrected electron microscope. The demonstration provides a unique paradigm for broadening the temperature range of NTE materials through entropy engineering.

Oxide ceramics of A2M3O12 family with negative and close-to-zero thermal expansion coefficients: Machine learning-based modeling of functional characteristics

Ceramic materials with negative and close-to-zero coefficients of thermal expansion may open the avenue to the technologies that have so far been constrained by physical limitations concerned with the thermal stress or with the insufficient structural stability. Two important characteristics of NTE materials which could be used for the evaluation of the possible area and limitations of the sphere of application for negative thermal expansion (NTE) materials are the linear thermal expansion coefficient and the transition temperature from monoclinic to orthorhombic phase. In this study, the machine learning methods were involved in the analysis of experimental data for NTE oxide ceramics of A2M3O12 family (where M is Mo6+, W6+, V5+ or P5+ while A position may be accommodated by the wide range of metal cations). The models are characterized by the following statistical coefficients: the determination coefficient R2 = 0.81 and prediction error RMSE = 1.170 for linear thermal expansion coefficient; the corresponding parameters for the phase transition temperature were assessed as 0.81 and 82.239, respectively. Ionic conductivity in this class of compounds has been discussed as a tandem functional characteristic, emphasizing the role of anharmonicity in both characteristics. The role of synthesis route and defect chemistry in NTE was analyzed. A conclusion on the expected enhancement of NTE resulted from the intentional introduction of cation A vacancies has been made. The principal possibility of combining two functional characteristics, - an ion conductor and a phase with negative thermal expansion, with some compromise in the characteristics of each of them is substantiated.

A novel metamaterial with instantaneously sign-switchable coefficient of thermal expansion and Poisson's ratio

Most materials expand when heated and contract when cooled. In contrast, negative thermal expansion materials exhibit the opposite behavior. In this paper, we present a metamaterial that expands both when heated and cooled. The unit cell configuration is crafted by embedding two isosceles triangular structures composed of high thermal expansion materials within a re-entrant hexagonal honeycomb framework. Initially, the bases of the two isosceles triangles are in contact. The metamaterial exhibits two deformation states under different external loads. Analytical formulas for the equivalent parameters were derived based on classical beam theory within the regime of small deformation. Finite element simulations were conducted to validate the accuracy of these analytical formulas. The influence of geometric parameters on the metamaterial is discussed in detail. The results demonstrate that the metamaterial can exhibit excellent multi-functional properties within a small range of deformation, including instantaneous sign-variable coefficients of thermal expansion and Poisson's ratios, along with significantly distinct tensile and compressive stiffnesses. This metamaterial consistently exhibits expansive characteristics regardless of variations in ambient temperature. Additionally, the material always expands laterally regardless of the sign of uniaxial loads. Based on these properties, the metamaterial can be applied to fasteners in the aerospace industry that require permanent locking, ensuring stability in various temperature and mechanical load conditions.

Preparation and negative thermal expansion in medium-entropy ceramics (Zr1/3Hf1/3Ti1/3)V2O7

The negative thermal expansion material ZrV2O7 exhibits superior performance and holds significant potential for applications. In this study, the medium entropy concept was employed to successfully synthesize (Zr1/3Hf1/3Ti1/3)V2O7, with metal atoms (Ti, Zr, and Hf) occupying the position of Zr in ZrV2O7. The material shows a negative thermal expansion coefficient of 4.2 × 10-6K-1, which is essentially consistent with the crystal structure and expansion performance of ZrV2O7. However, (Zr1/3Hf1/3Ti1/3)V2O7 demonstrates higher softening temperature and thermal stability. This study simplified the complex preparation process of the material, broadening its negative thermal expansion range and enhancing its high-temperature stability. Furthermore, the material possesses a significant dielectric constant of 2.24 × 108 (log f <1) and a high hardness of 187.7 HV0.5, making it a new type of dielectric ceramic material. It has great potential for applications in the fields of energy storage and electronic packaging.

Fluorescent probe effect of super-sensitive transition Dy3+ ions in the negative thermal expansion materials Sc2W3O12

Negative thermal expansion (NTE) materials have attracted significant attention for their distinctive thermal expansion properties and potential applications in various fields such as micro-electronic packaging, aerospace engineering, optics, and sensors. Despite significant advancements, the field continues to face numerous challenges, including scarcities in material types, unclear mechanisms underlying thermal shrinkage, response temperature far from room temperature, as well as limited potential for industrialization. In our work, we report a type of Sc2W3O12:Dy3+ luminescent material whereby the doped super-sensitizing rare earth ion Dy3+ can form luminescent centers within a specific crystal field environment, thereby extending the optical properties of NTE materials. With the temperature increasing, the emission of WO42− undergoes a red shift, and the yellow-to-blue (Y/B) ratio resulting from Dy3+ transitions increase, effectively illustrate the W–O bond spacing decreases. The effect of lattice shrinkage with increasing temperature is proved by the optical performance of luminescent ions in the NTE materials, gives rare earth ions the role of fluorescent probes in the process of negative thermal expansion. This also provides a novel strategy for the dynamic monitoring of lattice environments that vary with temperature.

Giant Negative Thermal Expansion in Ultralight NaB(CN)4.

Negative thermal expansion (NTE) is crucial for controlling the thermomechanical properties of functional materials, albeit being relatively rare. This study reports a giant NTE (αV ∼-9.2 ⋅ 10-5 K-1 , 100-200 K; αV ∼-3.7 ⋅ 10-5 K-1 , 200-650 K) observed in NaB(CN)4 , showcasing interesting ultralight properties. A comprehensive investigation involving synchrotron X-ray diffraction, Raman spectroscopy, and first-principles calculations has been conducted to explore the thermal expansion mechanism. The findings indicate that the low-frequency phonon modes play a primary role in NTE, and non-rigid vibration modes with most negative Grüneisen parameters are the key contributing factor to the giant NTE observed in NaB(CN)4 . This work presents a new material with giant NTE and ultralight mass density, providing insights for the understanding and design of novel NTE materials.

A high-performance composite cathode based on thermal expansion complementation for SOFC

The discrepancy in thermal expansion coefficients (TECs) between the cobalt-based cathode and the electrolyte presents a notable obstacle in attaining optimal performance levels for solid oxide fuel cells (SOFCs). Here we propose to introduce negative thermal expansion (NTE) component Sm0.85Zn0.15MnO3 (SZM) to SrNb0.1Co0.9O3−δ (SNC) cathode to prepare SNC-xSZM (x = 0, 10, 20 and 30 %) composite cathode materials. The impact of incorporating negative thermal expansion material on the composition and properties of the matrix materials were examined by X-ray diffraction, thermal dilatometer, high-resolution transmission electron microscopy, and electrochemical workstation. The results show that SNC-xSZM can achieve more ideal thermal matching with Ce0.8Gd0.2O1.9 (GDC), and the thermal expansion coefficient decreases observably from 25.47 × 10−6 K−1 for x = 0 to 13.74 × 10−6 K−1 for x = 30 %. The optimal comprehensive electrochemical performance is obtained for SNC-20SZM, which possesses the minimum polarization resistance (Rp) of 0.012 Ω cm2 at 700 °C. The SNC-20SZM-based cell shows a maximum peak power density (PPD) of 1.22 W cm−2 while exhibiting stable operation for a continuous duration of 120 h at a constant current of 0.8 A cm−2, with performance remaining optimal. Moreover, SNC-20SZM demonstrates exceptional durability and stability over prolonged durations even in high CO2 atmospheres. An innovative approach for enhancing the development of intermediate-temperature solid oxide fuel cells (IT-SOFCs) involves incorporating SZM in the SNC cathode, thereby augmenting electrochemical performance and narrowing the gap in the thermal expansion coefficient among SOFC modules.

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.

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.