Negative Thermal Expansion Properties Research Articles

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.

Effects of (KMn)3+ co-doping on the negative thermal expansion property of In2W3O12

At room temperature, monoclinic In2W3O12 ceramics exhibits positive thermal expansion. However, it transforms into an orthorhombic phase above 253 ℃, and then stably exhibits negative thermal expansion (NTE). In this work, to improve the NTE performance and extend the NTE temperature range of In2W3O12, the KxMnxIn2-xW3O12(0≤x≤0.5) ceramics were synthesized via the solid-state reaction method. The effects of (KMn)3+ double cation co-doping on the composition, microstructure, and thermal expansion behaviors of In2W3O12 ceramics were studied using XRD, Raman, XPS, SEM, and TMA. The results show that (KMn)3+ cations can replace In3+ in In2W3O12 ceramics. As the (KMn)3+ doping amount increases, monoclinic In2W3O12 gradually changed into monoclinic KxMnxIn2-xW3O12. Meanwhile, the grains grow up and the density of KxMnxIn2-xW3O12 ceramics was increased. Pure monoclinic KxMnxIn2-xW3O12 ceramics were prepared when x rises to 0.25 and 0.4. Among them, the thermal expansion coefficient of K0.4Mn0.4In1.6W3O12 ceramics in 100–700 ℃ is as high as -17.83×10-6 ℃-1, which was significantly improved compared to In2W3O12 ceramics. In addition, the structural phase transition of In2W3O12 ceramics around 253 ℃ was gradually eliminated and the NTE temperature range was widened. Double cation (KMn)3+ co-doping effectively improves the NTE performance of In2W3O12.

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.

Effects of (KMg)3+ co-doping and sintering temperature on the negative thermal expansion property of Sc2W3O12 ceramics

(KMg)3+ co-doped Sc2W3O12 ceramics have been prepared via co-precipitation method. Effects of (KMg)3+ co-doping amount and sintering temperature on the phase constitution, microstructure, morphology, and negative thermal expansion (NTE) performance of KxMgxSc2-xW3O12 (0 ≤ x ≤ 1.25) ceramics were studied. Results indicate that: Sc3+ cations can be substituted by (KMg)3+ dual-cations and a composition-induced structural phase transition was observed in KxMgxSc2-xW3O12. For x ≤ 0.25, orthorhombic Sc2W3O12 gradually changed into hexagonal KxMgxSc2-xW3O12 and coexisted. Single phase KxMgxSc2-xW3O12 with hexagonal symmetry can be prepared for 0.25 < x ≤ 1. When x ≥ 1.25, (KMg)3+ substitution reaches its solid solution limit in Sc2W3O12, and impurity MgWO4 formed in the samples. As co-doping amount x increased, the NTE performance of the KxMgxSc2-xW3O12 (0 ≤ x ≤ 1) ceramics gradually enhanced. The coefficient of thermal expansion (CTE) of KxMgxSc2-xW3O12 (0 ≤ x ≤ 1) ceramics enhanced from −2.14 × 10−6 °C−1 to −19.68 × 10−6 °C−1 in 30–700 °C. With the increase of sintering temperature from 800 to 1100 °C, the grains grew up and the density of the K0.75Mg0.75Sc1.25W3O12 ceramics increased as well, and the NTE performance was also improved. The linear CTE of K0.75Mg0.75Sc1.25W3O12 ceramics enhances from −2.15 × 10−6 °C−1 to −14.70 × 10−6 °C−1 in 30–700 °C.

The Negative Thermal Expansion Property of NdMnO3 Based on Pores Effect and Phase Transition

The Negative Thermal Expansion Property of NdMnO3 Based on Pores Effect and Phase Transition

Simultaneously tuning the luminescent color and realizing an optical temperature sensor by negative thermal expansion in Sc2(WO4)3:Tb/Eu phosphors.

At present, many researchers are focusing on trivalent lanthanide (Ln3+)-doped thermally enhanced upconversion luminescent (UCL) materials with negative thermal expansion (NTE) properties. However, selective anti-thermal quenching downshifting emissions of the activator and thermal quenching of the sensitizer in a phosphor with NTE properties are not implemented. Herein, Tb3+/Eu3+ co-doped Sc2(WO4)3 phosphors synthesized by the solid-state method are explored in selectively enhanced red emission (Eu3+:5D0 → 7F2) due to the energy-transfer efficiency from Tb3+ to Eu3+ and the promoted radiative transition probability. The selective thermally quenched green emission (Tb3+:5D4 → 7F5) is owing to the change of energy transfer from Tb3+ to Eu3+ as the temperature increased. Moreover, under ultraviolet 365 nm excitation, the thermally stimulated color emission tuned from yellow to red with the increase in temperature. Based on the radically different thermal response downshifting the luminescence of the activator and sensitizer, the luminescence intensity ratio (LIR) of non-thermally coupled levels (NTCLs) for 5D0 (Eu3+) and 5D4 (Tb3+) is adopted for optical temperature sensing. The optimal relative sensitivity of temperature sensing in the Sc2(WO4)3:25%Tb3+/3%Eu3+ sample could reach 2.94% K-1 at 347 K. All these indicate that this Sc2(WO4)3:Tb3+/Eu3+ material is a promising candidate for high-sensitivity optical temperature sensing.

The formation energy, phase transition, and negative thermal expansion of Fe2-xScxW3O12.

Tungstates with a molecular formula A2W3O12 exhibits a wider negative thermal expansion (NTE) temperature range than molybdates but are challenging to synthesize, especially when A = Fe or Cr with metastable structures. To enhance the structural stability of Fe2W3O12, Sc with lower electronegativity is adopted to substitute Fe according to Fe2-xScxW3O12, considering the thermodynamic stability of Sc2W3O12. It is shown that the solid solutions can be easily synthesized and the phase transition temperature (PTT) can be tuned to well below room temperature (RT). Theoretical calculations and experimental results show that the formation energy decreases and the W-O bond in Fe-O-W gradually strengthens as the substitution of Sc in Fe2-xScxW3O12 increases, indicating an increase in structural stability. NTE is enhanced after phase transition with an increase in the Sc content. The reduction in PTT and the enhancement in NTE properties of Fe2W3O12 could result in a decrease in the effective electronegativity of the Fe-site elements, resulting in a low formation energy and strengthened W-O bond in Fe-O-W, which corresponds to a more stable structure.

Multi-dimensional tailoring of the thermometric behaviors of Er3+/Yb3+-codoped Y2W3O12 polychromatic upconverting microparticles for multi-mode visual optical thermometry

To combat the thermal quenching and inadequate sensitivities of luminous materials, the Y1.98–2xW3O12:0.02Er3+/2xYb3+ (YWO:Er3+/2xYb3+; 0.01 ≤ x ≤ 0.11) microparticles with splendid negative thermal expansion (NTE) effect were designed. Excited at 980 nm, the produced samples emit polychromatic upconversion (UC) emissions triggered by the energy back transfer from Er3+ to Yb3+ and it has been systematically discussed via steady-state rate theory. The thermally enhanced UC emissions are accomplished in YWO:Er3+/2xYb3+ microparticles due to the distinctive NTE properties. Moreover, according to the temperature-associated UC emissions of Er3+ arising from its thermally coupled levels (TCLs) and non-thermally coupled levels (non-TCLs), the thermometric properties of synthesized microparticles are investigated. When non-TCLs are adopted, the absolute and relative sensitivities of resultant microparticles are 0.0129% and 1.7875% K−1, respectively. Furthermore, through manipulating doping content and spatial mode, the temperature sensing capacities of YWO:Er3+/2xYb3+ microparticles are multi-dimensionally regulated. In addition, contactless temperature recognition can also be realized through analyzing the thermochromic features of final products and its relative sensitivity is 2.1604% K−1. Ultimately, visual optical temperature detection is obtained in designed microparticles via its temperature-related emitting colour. Our findings may provide an important insight into the design of luminescent materials with high sensitivities for multi-mode visual optical thermometry.

Interplay of Consecutive Energy Transfer and Negative Thermal Expansion Property for Achieving Superior Anti‐Thermal Quenching Luminescence

AbstractLuminescence thermal quenching (TQ) is one of the most critical problems to be solved for further improvement of phosphors’ applications in lighting and many other fields. Herein, a novel strategy is demonstrated to achieve outstanding anti‐TQ performance with a substantial enhancement of Eu3+ red emission at 613 nm from Sc2MO3O12:Tb3+,Eu3+ phosphor. Its anti‐TQ performance is endowed by dual energy transfer (ET) pathways and intensified by the negative thermal expansion (NTE) property of the Sc2MO3O12 host. Remarkably, the photoluminescence (PL) emission intensity of Eu3+ from Sc2MO3O12:20%Eu3+,2%Tb3+ phosphor at 648 K reaches 507.3% of the initial intensity taken at 298 K. The lifetime of Eu3+ emission at 613 nm elongates with increasing measurement temperature. The experimental data and density functional theory (DFT) calculations reveal that the host structure shrinkage via NTE leads to the thermally boosted Eu3+ red emission by intensifying the consecutive ET and confinement of the absorption light. The potential of this phosphor as a dual‐mode high temperature thermometer based on both emission lifetime and intensity ratio read‐out modes is realized. This work provides inspiration to combine multiple strategies to achieve broad and dramatic anti‐TQ phosphors with enhanced performance for various optical applications.

Sintering Temperature Effect of Near-Zero Thermal Expansion Mn3Zn0.8Sn0.2N/Ti Composites.

Metal matrix composites with near-zero thermal expansion (NZTE) have gained significant popularity in high-precision industries due to their excellent thermal stability and mechanical properties. The incorporation of Mn3Zn0.8Sn0.2N, which possesses outstanding negative thermal expansion properties, effectively suppressed the thermal expansion of titanium. Highly dense Mn3Zn0.8Sn0.2N/Ti composites were obtained by adjusting the fabrication temperature. Both composites fabricated at 650 °C and 700 °C exhibited NZTE. Furthermore, finite element analysis was employed to investigate the effects of thermal stress within the composites on their thermal expansion performance.

Building Negative-Thermal-Expansion Protective Layers on the Grain Boundary of Ni-rich Cathodes Enables Safe and Durable High Voltage Lithium-Ion Batteries.

Ni-rich layered oxide cathode materials demonstrate high energy densities for Li-ion batteries, but the electrochemically driven thermal runaway and mechanical degradation remain their long-standing challenges in practical applications. Herein, it presents a novel ZrV2 O7 (ZVO) coating with negative thermal expansion properties along the secondary particles and primary particle grain boundaries (GBs), to simultaneously enhance the structural and thermal stability of LiNi0.8 Co0.1 Mn0.1 O2 (NCM811). It unveils that, such an architecture can significantly enhance the electronic conductivity, suppress the microcracks of GBs, alleviate the layered to spinel/rock-salt phase transformation, and meanwhile relieve the lattice oxygen loss by increasing the oxygen vacancy formation energy increased (1.43 vs 1.90eV). Consequently, the ZVO-coatedNCM811 material demonstrates a remarkable cyclability with 86.5% capacity retention after 100 cycles, and an outstanding rate performance of 30C under a high-voltage of 4.6V, outperforming the state-of-the-art literature. More importantly, the Li+ transportation can be readily blocked at 120°C by the negative-thermal-expansion ZVO coating, thus avoiding the high-temperature thermal runaway.

Novel metamaterial structures with negative thermal expansion and tunable mechanical properties

The thermal expansion and stiffness characteristics are significant in determining the responses of lightweight mechanical metamaterials in a thermal environment. This paper proposed a novel trapezoid unit with negative thermal expansion (NTE) by three conventional materials with positive thermal expansion, and constructed a series of lightweight metamaterials by sharing edges and sharing vertexes. The effective linear coefficients of thermal expansion (CTE) of these metamaterial structures are theoretically explored by considering axial and bending deformations. Based on Euler beam theory, the effective linear elastic stiffnesses of these metamaterials are given accurately by the stiffness matrix method. The accuracy of the theoretical effective CTE and stiffness is well verified by numerical modeling. The effective linear CTE, elastic stiffness, and Poisson's ratio of these metamaterials can be programmable by controlling geometrical parameters and material properties. The NTE effect can be achieved in ET, EQ, EH, and VT metamaterials due to the presence of re-entrant structures, in which the ET metamaterial can fulfill the maximum magnitude NTE. The NTE and negative Poisson's ratio can simultaneously be realized in EQ metamaterial. Significantly, a broader range of CTE from negative to positive values can be fulfilled in these metamaterials compared with the conventional triangle unit. Furthermore, the high specific stiffness with extremely low thermal stress can be obtained in EQ, VT, and VH metamaterials, which benefits the stability controlling and enhancing natural frequencies of structures in a thermal environment.

A cobalt(II) hydrogen-bonded organic framework exhibiting uniaxial negative thermal expansion and field-induced slow magnetic relaxation

The magnetic and thermal expansion properties of a cobalt(II) hydrogen-bonded organic framework (CoHOF), [Co(H2O)6](NPS)2 (1, HNPS = naphthalene-2-sulphonic acid), constructed by hexaaquacobalt(II) and organsulfonate were reported. Single-crystal X-ray diffraction reveals a porous 2D hydrogen-bonded framework of 1 sustained by multiple and charge-assisted intermolecular hydrogen bonding interactions. Variable-temperature single-crystal combined with powder X-ray diffraction and thermal gravimetric analyses confirms the high thermal stability of the CoHOF. The dynamic changes of the crystal lattice indicate uniaxial negative thermal expansion (NTE) behavior along the c-axis direction through a possible slippage motion. Magnetic measurements indicate the Co2+ ions show uniaxial magnetic anisotropy with D = −92.5 cm−1. A.C. susceptibility measurements reveal field-driven slow magnetic relaxation of 1. These results provide a rare cobalt(II) hydrogen-bonded organic framework showing single-ion magnetism and negative thermal expansion properties.

Macroscopic negative differential thermal resistance in the overlapping graphene homojunction structure

As one of the most potential ways to manipulate heat, thermal functional devices have achieved several breakthroughs in recent years, but are still limited to theoretical simulations. One of its theoretical bases is the existence of the negative differential thermal resistance (NDTR). However, most of the existing systems where the phenomenon of NDTR is found are atomic-level systems. In order to realize the macroscopic NDTR and provide effective theoretical guidance and support for the practical realization of thermal functional devices, we construct the overlapping graphene homojunction model, using the negative thermal expansion property of graphene to modify the overlapping area, and thus regulating the heat flow. The COMSOL-MATLAB co-simulation is used to perform calculations through negative feedback loops. It is found that the NDTR phenomenon exists under certain parameter conditions, which can provide new ideas and bring more opportunities for the experimental realization of nonlinear thermal functional devices.

Preparation of In0.5Sc1.5Mo3O12 nanofibers and its negative thermal expansion property

Orthorhombic In0.5Sc1.5Mo3O12 nanofibers were prepared by electrospinning followed by a heat treatment. The effects of post-annealing temperatures on the phase composition, microstructure and morphology were investigated by XRD, SEM, HRTEM and XPS. Negative thermal expansion (NTE) behaviors of the In0.5Sc1.5Mo3O12 nanofibers were analyzed by high-temperature XRD. Results indicate that the as-prepared In0.5Sc1.5Mo3O12 nanofibers show an amorphous structure with smooth and homogeneous shape. The average diameter of the as-prepared In0.5Sc1.5Mo3O12 nanofibers is around 515 nm. Well crystallized orthorhombic In0.5Sc1.5Mo3O12 nanofibers could be prepared after post-annealing at 550 °C for 2 h with an average diameter of about 192 nm. The crystallinity of In0.5Sc1.5Mo3O12 nanofibers gradually improved with the increase of annealing temperature. However, too high post-annealing temperature leads to a damage of sample's fiber structure. The high-temperature XRD results reveal that In0.5Sc1.5Mo3O12 nanofibers show an anisotropic NTE, and the coefficients of thermal expansion (CTEs) along a-axis and c-axis were −5.95 × 10−6 °C−1 and -3.54 × 10−6 °C−1, while the one along b-axis is 5.61 × 10−6 °C−1. The volumetric CTE of In0.5Sc1.5Mo3O12 nanofibers is −3.90 × 10−6 °C−1 and the linear one is 1.3 × 10−6 °C−1 in 25–700 °C.

Structure, phase transition, and tailoring thermal expansion in Cu2-xMnxP2O7

Among the A2P2O7 (A = divalent metal) series compounds, Cu2P2O7 has attracted a lot of attention because of its unique negative thermal expansion properties. In this work, we have synthesized a series of Cu2-xMnxP2O7 (0 ≤ x ≤ 2) compounds by solid state reaction method. The crystal structure of the Cu2-xMnxP2O7 (0 ≤ x ≤ 2) experiences three changes from α-Cu2P2O7 to β-Cu2P2O7 and then to Mn2P2O7 structure. The thermal expansion in Cu2-xMnxP2O7 is gradually regulated from strong negative (αl = −12.5 × 10−6 K−1, 173–373 K) to near zero (αl = 1.17 × 10−6 K−1, 173–273 K), and then to positive with increasing Mn content. The first-principles calculation has revealed that the Mn substitution diminishes structural flexibility and depress the NTE of Cu2-xMnxP2O7 (0 ≤ x ≤ 2). The present work not only achieves controlled thermal expansion, but also deepens the understanding of the correlation between structure and properties of frame-structured negative thermal expansion compounds.

Ultralow lattice thermal conductivity, negative thermal expansion, elastic and thermoelectric properties of Lanthanum Nitride: Insights from first-principle calculations

Ultralow lattice thermal conductivity, negative thermal expansion and thermoelectric properties for the face centered cubic phase of lanthanum nitride (LaN) have been explored for the first time from first-principle density functional theory and ab-initio molecular dynamics calculations. The elastic constants, phonon dispersion relations, mode Grüneisen parameter, phonon group velocity and phonon-phonon scattering rates have been studied to unveil the ultralow lattice thermal conductivity ( = 1.08 Wm−1K−1) of the compound at room temperature (T = 300 K). The negative thermal expansion of LaN has been estimated from the mode Grüneisen parameter. The electronic band structure, hole-electron effective masses and the thermoelectric properties including the Seebeck coefficient, electrical conductivity, electronic thermal conductivity and thermoelectric power factor have been investigated to estimate the high thermoelectric figure of merit (ZT ∼ 0.98) of the system at room temperature. We believe that the present study will help to unfold LaN for its applications in thermoelectric power generators, fibre-optic communications, fuel cells and in clean and global energy conservation.

Hydrothermal synthesis of flower-like Sc2Mo3O12 and its investigation into negative thermal expansion property

Orthorhombic Sc2Mo3O12 samples have been synthesized using ethylene glycol (EG)-assisted hydrothermal reaction. The influences of hydrothermal temperature, hydrothermal time and additive content of EG on the preparation and negative thermal expansion (NTE) behavior of Sc2Mo3O12 samples were characterized using XRD, SEM, HRTEM, EDX, TMA and HTXRD. Results indicate that flower-like Sc2Mo3O12 with a uniform particle size of 1–2 μm can be synthesized at 120 °C for 2 h by adding 60 ml EG. Hydrothermal temperature, time and additive content of EG have strong influences on the growth and morphology of the Sc2Mo3O12. The average coefficients of thermal expansion (CTEs) of the Sc2Mo3O12 prepared at 120 °C for 2 h and 200 °C for 24 h are tested to be −6.94 × 10−6 °C−1 and -7.18 × 10−6 °C−1 in 25–700 °C using TMA. HTXRD results indicate that the flower-like Sc2Mo3O12 exhibits anisotropic NTE, and the corresponding CTEs along the a, b and c axes are −6.73 × 10−6 °C−1, 4.98 × 10−6 °C−1 and -4.78 × 10−6 °C−1 in 25–700 °C, respectively, and the corresponding linear CTE is −2.21 × 10−6 °C−1.

Thermochromic Upconversion Emission in Tm3+/Yb3+-Codoped La2Mo3O12 Microparticles via Negative Thermal Expansion Engineering for Ultrahigh Sensitivity Optical Thermometry

To develop high-sensitivity optical thermometers, Yb3+/Tm3+-codoped La2Mo3O12 microparticles were synthesized by the sol–gel method. With the aid of in situ X-ray diffraction, the resultant microparticles are verified to possess negative thermal expansion (NTE) properties. When excited at 980 nm, the upconversion (UC) emission properties of final products are investigated, in which their strongest fluorescence intensities are reached at x = 0.07. Due to the coexistence of the increased energy transfer, cross-relaxation, and nonradiative relaxation procedures, the as-prepared microparticles present thermochromic UC emissions. Moreover, the intensity of UC emission arising from the 3F2,3 excited level at 583 K is 21 times higher than its starting value at 303 K, resulting in thermally enhanced luminescence in resultant microparticles. By employing the fluorescence intensity ratio technique to investigate the temperature-related intensities of UC emissions from 1G4 and 3F2,3 levels, the thermometric characterization of designed compounds is explored, where its highest absolute and relative sensitivities are 0.44 K–1 and 7.37% K–1, respectively. Furthermore, according to the temperature-related lifetimes of 1G4 and 3F2,3 levels of Tm3+, the relative sensitivities of developed microparticles are 0.36% and 0.23% K–1, respectively. Ultimately, visual optical thermometry is also realized by the studied samples owing to their thermochromic UC emissions. Our findings propose a facile strategy by employing NTE to regulate the UC emission behaviors of rare-earth ions so as to obtain high-sensitive luminescent materials.

Polar–Nonpolar Transition-Type Negative Thermal Expansion with 11.1% Volume Shrinkage by Design

Chemical substitution for the tuning of the working temperature of phase-transition-type negative thermal expansion (NTE) materials generally reduces the volume shrinkage during the transition. We have investigated the effects of electron doping and reduction of 6s2 lone-pair activity in PbVO3 with a large polar distortion (c/a = 1.23) and found that the combination of Bi and Sr substitutions for Pb enables a temperature-induced polar to non-polar transition with 11% volume shrinkage, even larger than the pressure-induced volume collapse of PbVO3 (∼10.6%), and is the largest value among the NTE materials reported so far. The domain structure of the coexisting cubic and tetragonal phases with such a huge volume difference was successfully observed by high-angle annular dark-field scanning transmission electron microscopy and the spatial distribution of domains by Bragg coherent X-ray diffraction imaging. The temperature hysteresis is reduced by repeated heating/cooling cycles, suggesting that the changes in the domain structure dominate the NTE properties.