Isotropic Negative Thermal Expansion Research Articles

Optical temperature sensing properties realized by isotropic negative thermal expansion in ScF3:Tb3+/Eu3+ phosphor ceramics

The anomalous luminescence thermal quenching performance caused by negative thermal expansion has attracted much attention due to the potential application in optical fields. However, the downshifting emissions with abnormal thermal quenching achieved by isotropic negative thermal expansion for optical temperature sensing applications are still lacking. Herein, a large enhancement of red emission and a high temperature sensing performance are realized by isotropic negative thermal expansion in ScF3:Tb3+/Eu3+ phosphors ceramics. Specially, a selectively thermal enhanced red emission of Eu3+ from 5D0→7F2 with hypersensitive transition characteristics could be obtained due to the thermal stimulated lattice distortion. Attributing to the shortening of cation spacing, the energy transfer efficiency between Tb3+ and Eu3+ is largely enhanced with the increasing of the temperature from 303 to 473 K. The enhanced energy transfer leads to that the emission of Tb3+ firstly increases and then slightly decreases, whereas the emission from Eu3+ has been largely improved. Finally, an optical temperature sensing strategy based on the fluorescence intensity ratio of the sensitizer Tb3+ (signal ions) and the activator Eu3+ (referring ions) is designed, attributing to the distinguishable luminescence response to the temperature. The obtained maximum relative sensitivity is 1.04 % K−1 (@303 K). Besides, the sensing strategy based on lifetime mode also suggests a maximum relative sensitivity of 1.00 % K−1 at 343 K. It provides a feasible strategy to obtain an optical temperature sensing material with high emission efficiency at a high temperature, which sheds light on the design of luminescence materials keeping high luminescence stability in a wide temperature range in the fields of optical temperature sensing.

Reduced Expansion and Strain to Boost Performance and Safety of LiNi0.8Co0.1Mn0.1O2 by Cubic ZrMo2O8 Nanorods with Isotropic Negative Thermal Expansion

Reduced Expansion and Strain to Boost Performance and Safety of LiNi_0.8Co_0.1Mn_0.1O₂ by Cubic ZrMo₂O₈ Nanorods with Isotropic Negative Thermal Expansion

Isotropic negative thermal expansion in ZrW2O8 and HfW2O8 from 1100 to 1275°C

AbstractZrW2O8 (ZrO2•2WO3) and HfW2O8 (HfO2•2WO3) have been the focus of thermal expansion studies due to their isotropic negative thermal expansion (NTE) measured previously at temperatures below 775°C. This work presents measurements of these materials at their thermodynamically stable temperature ranges of 1105 and 1257°C for ZrW2O8 and 1105–1276°C for HfW2O8, where they were characterized with in situ, powder X‐ray diffraction. The linear coefficients of thermal expansion were measured to be −5.52 × 10−6 and −4.87 × 10−6°C−1 for ZrW2O8 and HfW2O8, respectively. The mechanism leading to this NTE is discussed. Powder samples were synthesized by a solution‐based process called the organic–inorganic steric entrapment method. In situ characterization in air was carried out at the National Synchrotron Light Source II using a hexapole lamp, optical furnace and the Advanced Photon Source using a quadrupole lamp, optical furnace to achieve elevated temperatures.

Simple chemical synthesis and isotropic negative thermal expansion in MHfF6 (M = Ca, Mn, Fe, and Co)

Simple chemical synthesis and isotropic negative thermal expansion in MHfF6 (M = Ca, Mn, Fe, and Co)

Synthesis, thermal expansion and optical properties of ZrV2O7 thin films

Cubic ZrV2O7 thin films have been synthesized by sol-gel spin-coating method. The influences of annealing temperatures on the phase composition and morphology of ZrV2O7 thin films were investigated using XRD, SEM, and EDX. Negative thermal expansion (NTE) and optical performances of cubic ZrV2O7 thin films were analyzed using variable temperature XRD and UV–Vis spectroscopy. Results indicate that as-deposited ZrV2O7 thin films have an amorphous structure with smooth and dense surface. Cubic ZrV2O7 thin films were prepared after heat treatment at 720 °C for 1 h. It was found that the thin films contained V2O5 impurity with the Zr: V = 1:2 precursor solution. Pure cubic ZrV2O7 thin films were fabricated with the Zr: V = 1.75:2 precursor solution. Cubic ZrV2O7 thin films show isotropic NTE in the temperature range of 100–700 °C. The coefficients of thermal expansion (CTEs) of ZrV2O7 films along the a, b, and c axes are −6.88 × 10−6 °C−1, and the volumetric and linear CTEs are −20.56 × 10−6 °C−1 and -6.85 × 10−6 °C−1, respectively. The transmittance of cubic ZrV2O7 thin film is approximately 80 %.

Anisotropic thermal expansion based on a novel metamaterial

Metamaterials exhibiting exceptional thermoelastic properties are emerging as promising candidates for scientific and engineering applications. Previous studies on mechanical metamaterials with negative thermal expansion (NTE) have primarily focused on enhancing isotropic NTE, often resulting in a high coefficient of thermal expansion (CTE) but low stiffness that characterizes bending-dominated NTE metamaterials. In this study, we proposed a novel mechanical metamaterial with significant anisotropic thermal expansion behavior and substantial stiffness based on the cross structure, re-entrant structure, and triangular structure with NTE. The programmable CTE and effective elastic modulus were analytically derived using the unit load method and stiffness matrix method, respectively, which were validated by numerical results obtained from finite element analysis (FEA). Drawing inspiration from the body-centered cubic and face-centered cubic strategies, two types of extended three-dimensional metamaterials can be obtained. The results demonstrate that a larger length ratio λ and angle θ3 can enhance the NTE effect, while reducing the Young's modulus. The maximum magnitudes of NTE and positive thermal expansion (PTE) are achieved at approximately θ2 = 90°, resulting in a decreased stiffness and slight negative Poisson's ratio (NPR). By adjusting the angles θ2 of re-entrant structures, six distinct anisotropic thermal expansion behaviors can be obtained in this planar metamaterial. Furthermore, a wider range of isotropic CTE as well as an extended range of anisotropic CTE can be achieved in the present metamaterial compared to its original metamaterials. The proposed metamaterial can be combined with traditional triangle metamaterials to enhance thermoelastic properties. The analysis also provides valuable insights into designing metamaterials with large CTE, optimal stiffness, and lightweight properties simultaneously for engineering applications.

Aluminum-based ceramic/metal composites with tailored thermal expansion fabricated by spark plasma sintering.

We have devised a moderate temperature spark plasma sintering route for preparing aluminum matrix composites which possess tailored coefficients of thermal expansion (CTEs) in combination with tunable electrical and thermal conductivities. Due to its isotropic negative thermal expansion over a wide temperature range, cubic-phase ZrW2-xMoxO8 (x = 0.0, 1.0) is an ideal secondary phase for metal matrix composites with suitable CTEs. In this study, high-density ZrW2O8/Al and ZrWMoO8/Al composites containing 30-70 vol% Al were fabricated using spark plasma sintering. X-ray diffraction analysis indicated that the composites were composed of a thermally-stable cubic phase at temperatures as high as 873 K for ZrW2O8 and 773 K for ZrWMoO8, without any orthorhombic high-pressure phase derived from the large thermal mismatch between the ceramic and metal during sintering. The thermal expansion curves of the ZrW2-xMoxO8/Al composites were consistent with the predictions made using the Rule-of-Mixtures. The CTEs could be controlled from negative to positive and even close to zero by simply varying the volume fraction of aluminum. Similarly, the thermal and electrical conductivity of the ZrW2-xMoxO8/Al composites increases with increasing Al content, which is thought to be mainly related to the contribution of the free electron conduction path of Al in the composites.

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.

A new isotropic negative thermal expansion material of CaSnF6 with facile and low-cost synthesis

A new isotropic negative thermal expansion material of CaSnF6 with facile and low-cost synthesis

Tailoring of thermal expansion and phase transition temperature of ZrW2O8 with phosphorus and enhancement of negative thermal expansion of ZrW1.5P0.5O7.75

ZrW2O8 is a typical isotropic negative thermal expansion material with cubic structure. However, quenching preparation, pressure phase transition and metastable structure influence its practical applications. Adopting P to part-substitute W for ZrW2−x P x O8–0.5x has decreased the sintering temperature and avoided the quenching process. When x = 0.1, ZrW1.9P0.1O7.95 with a stable cubic structure can be obtained at 1150 °C. The thermal expansion coefficient is tailored with the P content, and phase transition temperature is lowered. When x = 0.5, thermal expansion coefficient attains −13.6 × 10−6 °C−1, ZrW1.5P0.5O7.75 exhibits enhance negative thermal expansion property. The difference of electronegativity leads to the decrease of phase transition temperature with the increase of P content. The different radii of ions lead to new structure of materials when P substitutes more. The results suggest that the P atom plays the stabilization role in the crystal structure of ZrW2−x P x O8–0.5x .

Isotropic negative thermal expansion and its mechanism in tetracyanidoborate salt CuB(CN)4

The control of thermal expansion is essential in applications where thermal stability is required from fiber optics coatings, high performance fuel cell cathodes to tooth fillings. Negative thermal expansion (NTE) materials, although rare, are fundamental for this purpose. This work focuses on studying tetracyanidoborate salt CuB(CN)4, an interesting cubic-structure material that displays large isotropic NTE. A joint study of synchrotron x-ray diffraction, temperature-dependent Raman spectroscopy, and lattice dynamics calculations was conducted, showing that not only low-frequency optical modes (transverse thermal vibrations of N and C atoms) but also the acoustic modes (the vibrations of Cu atoms as a collective torsion of the neighboring atoms), contribute to NTE. As a result, new insights were gained into the NTE mechanism of CuB(CN)4 and related framework materials.

Negative Thermal Expansion HfV2O7 Nanostructures for Alleviation of Thermal Stress in Nanocomposite Coatings.

A primary mode of failure of thin-film coatings is the mismatch in thermal expansion coefficients of the substrate and the coating, which results in accumulation of interfacial stresses and ultimately in film delamination. While much attention has been devoted to modulation of interfacial bonding to mitigate delamination, current strategies are constrained in their generalizability and have had limited success in imbuing resistance to prolonged thermal cycling. We demonstrate here the incorporation of rigid thermal expansion compensators within polymeric films as a generalizable strategy for minimizing thermal mismatch with the substrate. Nanostructures of the isotropic negative thermal expansion (NTE) material HfV2O7 have been prepared based on the reaction of nanoparticulate precursors. The NTE behavior, derived from transverse oxygen displacement within the cubic structure, has been examined using temperature-variant powder X-ray diffraction, Raman spectroscopy, electron microscopy, and selected-area electron diffraction measurements. HfV2O7 initially crystallizes in a 3 × 3 × 3 superlattice but undergoes phase transformations to stabilize a cubic structure that exhibits strong and isotropic NTE with a coefficient of thermal expansion (CTE) = -6.7 × 10-6 °C-1 across an extended temperature range of 130-700 °C. Incorporation of HfV2O7 in a high-temperature thermoset polybenzimidazole enables the reduction of compressive stress by 67.3% for a relatively small loading of 26.6 vol % HfV2O7. Based on a composite model, we demonstrate that HfV2O7 can reduce the thermal expansion coefficient of polymer nanocomposite films, even at low volume fractions, as a result of its substantially higher elastic modulus compared to the continuous polymer matrix. By changing the volume fraction of HfV2O7, the overall coefficients of thermal expansion of the film can be tuned to match a range of substrates, thereby mitigating thermal stresses and resolving a fundamental challenge for high-temperature composites and nanocomposite coatings.

Tunable auxeticity and isotropic negative thermal expansion in three-dimensional lattice structures of cubic symmetry

A class of three-dimensional lattice structures of cubic symmetry is designed by spatially assembling and merging a number of two-dimensional re-entrant honeycomb structures. We demonstrate that the effective thermoelastic properties of these structures are widely tunable by tailoring the microstructural geometry and/or constituent materials. Particularly, they possess negative effective Poisson’s ratios. If the inclined and non-inclined walls are of dissimilar thermal expansion coefficients, they can further attain isotropic negative or positive effective thermal expansion coefficients with a magnitude as large as several to dozens of times that of the constituent materials. Owing to these novel properties, they are well suitable as structural or functional components in engineering systems for preventing or harnessing thermal and/or mechanical deformation.

Hot corrosion behavior of YSZ/ZrW2O8 composites exposed to V2O5 at 700 °C and 850 °C in air

The hot corrosion behavior of YSZ/ZrW2O8 composites as a promising thermal barrier coating system exposed to V2O5 at 700 °C and 850 °C was investigated in order to better understand the influence of the incorporated ZrW2O8 with isotropic negative thermal expansion performance on the corrosion resistance. Results indicate that the ZrW2O8 incorporation could retard the degradation of YSZ from V2O5 attack and the corrosion process is significantly related to the inclusion content and the temperature. The corrosion resistance could be determined by the incorporation content, while the reaction products are only temperature dependent. At 700 °C, ZrV2O7, YVO4 and m-ZrO2 were the main corrosion products, while ZrW2O8 recrystallized under the acidic environment provided by V2O5. At 850 °C, ZrW2O8 decomposed and only WO3, YVO4 and m-ZrO2 could be detected as final corrosion products. The corrosion mechanisms of YSZ/ZrW2O8 composites at 700 °C and 850 °C were discussed based on the phase diagrams and Lewis acid-base rule as well as the volume compensation of the positive and negative expansion ceramics.

Large isotropic negative thermal expansion in water-free Prussian blue analogues of ScCo(CN)6

We first found that ScCo(CN)6 of Prussian blue analogues has a large isotropic negative thermal expansion which occurs in a wide temperature range from 25K to 600K. More intriguingly, the present material of ScCo(CN)6 exhibits the merits of the facile fabrication via chemical coprecipitation and the good environment stability of water-free, which are very important for the applications. The transverse vibration of C and N atoms is critical for the occurrence of negative thermal expansion, which is confirmed by the atomic mean square relative displacements. The present new material of ScCo(CN)6 will be promising for the applications.

Realizing isotropic negative thermal expansion covering room temperature by breaking the superstructure of ZrV2O7

ZrV2O7 is a well-known isotropic negative thermal expansion (NTE) material. However, the NTE property of ZrV2O7 can only be observed in high temperatures above 375 K. In this paper, we report a facile method to break the superstructure of ZrV2O7 for realizing the NTE property of ZrV2O7 to room temperature by partial substitution of Mo for V atoms. The detailed structure information and the phase transition process are revealed by high-resolution synchrotron x-ray diffraction, neutron powder diffraction, and high pressure Raman spectral analyses. It is found that the incorporation of Mo prompts the V-O2-V/Mo angles to expand from 160° to 180°, which enables the NTE property at room temperature. Different from most open framework structures where NTE is dominated by low energy phonons, here several high energy phonon modes are found to have negative Grüneisen parameters and contribute to the negative thermal expansion.

Discovering Large Isotropic Negative Thermal Expansion in Framework Compound AgB(CN)4 via the Concept of Average Atomic Volume.

Exploring isotropic negative thermal expansion (NTE) compounds is interesting, but remains challenging. Here, a new concept of "average atomic volume" is proposed to find new NTE open-framework materials. According to this guidance, two NTE compounds, AgB(CN)4 and CuB(CN)4, have been discovered, of which AgB(CN)4 exhibits a large NTE over a wide temperature range (αv = -40 × 10-6 K-1, 100-600 K). The analysis by extended X-ray absorption fine structure spectroscopy and first-principles calculation indicate that (i) the NTE driving force comes from the transverse vibrations of bridge chain atoms of C and N, corresponding to the low-frequency phonon modes; and (ii) the same transverse vibration direction of C and N atoms is a key factor for the occurrence of strong NTE in AgB(CN)4. The present concept of "average atomic volume" can be a simple parameter to explore new NTE compounds especially in those open-framework materials.

Kondo-Induced Giant Isotropic Negative Thermal Expansion.

Negative thermal expansion is an unusual phenomenon appearing in only a handful of materials, but pursuit and mastery of the phenomenon holds great promise for applications across disciplines and industries. Here we report use of x-ray spectroscopy and diffraction to investigate the 4f-electronic properties in Y-doped SmS and employ the Kondo volume collapse model to interpret the results. Our measurements reveal an unparalleled decrease of the bulk Sm valence by over 20% at low temperatures in the mixed-valent golden phase, which we show is caused by a strong coupling between an emergent Kondo lattice state and a large isotropic volume change. The amplitude and temperature range of the negative thermal expansion appear strongly dependent on the Y concentration and the associated chemical disorder, providing control over the observed effect. This finding opens avenues for the design of Kondo lattice materials with tunable, giant, and isotropic negative thermal expansion.

Micro-structured medium with large isotropic negative thermal expansion.

A challenge in nano- and micro-mechanics is the realization of innovative materials exploiting auxetic behaviour to tailor thermal expansion properties. For this purpose, a new class of micro-structured media possessing an extremely wide range of tunable (positive, negative or even zero) thermal expansion is proposed and analytically and experimentally assessed. For this class of isotropic Mechanical-Auxetic Thermal-Shrinking media, the effective coefficient of thermal expansion is explicitly linked to two microstructural variables via a simple relation, allowing the design with desired values. The theoretical predictions for the negative thermal properties are fully validated by the experimental and numerical outcomes. The simplicity of the proposed structure makes the design useful for the production of a new generation of advanced media, with applications ranging from micromechanical devices to large civil and space structures.

Infrared lattice dynamics in negative thermal expansion material in single-crystal ScF3

Simple cubic ‘open’ perovskite ScF3 stands out among trifluoride materials in its large, isotropic negative thermal expansion (NTE), but also its proximity of its zero-temperature state to a structural phase transition. Here we report a temperature- and frequency-dependent lattice dynamical study of Brillouin zone center lattice excitations of single crystals of ScF3 using infrared reflectivity measurements. In addition to quantifying the mode strengths and energies in single crystals of this interesting material, we also find strong evidence for multiphonon absorption processes which excite the zone-edge incipient soft modes associated with NTE and the structural quantum phase transition. In this way, we identify an optically-allowed pathway to excite soft modes provides a means to athermally populate modes associated with NTE in ScF3.