Negative Thermal Expansion Effect Research Articles

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.

Regulating the upconversion luminescence properties of Tm3+/Yb3+-codoped ZrScW2PO12 microparticles with a negative thermal expansion effect through thermal stimulation for optical thermometry.

Tm3+/Yb3+-codoped ZrScW2PO12 microparticles were prepared in order to solve the problems of the severe thermal quenching and unsatisfactory thermometric properties of most luminescent materials. The synthesized materials exhibit a rarely observed negative thermal expansion (NTE) effect, which was verified by in situ X-ray diffraction experiments, performed under high temperature conditions. Upon excitation with a 980 nm laser, bright blue upconversion (UC) emissions originating from Tm3+ were observed. Moreover, owing to the promoted energy transfer, cross-relaxation and non-radiative decay processes at high temperatures triggered by the NTE effect, the observed UC emissions arising from 1G4 and 3F2,3 levels show non-monotonic responses to temperature. By analysing the temperature-dependent luminescence intensity ratio of these UC emissions originating from the non-thermally coupled levels of Tm3+ (1G4 and 3F2,3), the thermometric properties of the prepared microparticles were investigated in detail. Interestingly, the maximum absolute and relative sensitivities of the synthesized compounds are 0.09 and 1.45% K-1, respectively, which are independent of Yb3+ content, but they can be manipulated by employing different sensing modes. Our results manifest that the exploitation of the NTE effect is an efficient way to control the UC luminescence features of rare earth ions and to realize high performance optical thermometry.

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.

Spin-orbital mechanisms for negative thermal expansion in Ca2RuO4

The phenomenon of negative thermal expansion (NTE) deals with the increase of the lattice parameters and the volume of the unit cell when the material is thermally cooled. The NTE is typically associated with thermal phonons and anomalous spin-lattice coupling at low temperatures. However, the underlying mechanisms in the presence of strong electron correlations in multiorbital systems are not yet fully established. Here, we investigate the role of Coulomb interaction in the presence of lattice distortions in setting out the NTE effect, by focusing on the physical case of layered ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{4}$ with the ${d}^{4}$ configuration at each Ru ion site. We employ the Slater-Koster parametrization to describe the electron-lattice coupling through the dependence of the d-p hybridization on the Ru-O-Ru bond angle. The evaluation of the minimum of the free energy at finite temperature by fully solving the multiorbital many-body problem on a finite-size cluster allows us to identify the regime for which the system is prone to exhibit NTE effects. The analysis shows that the nature of the spin-orbital correlations is relevant to drive the reduction of the bond angle by cooling, and in turn the tendency toward a NTE. This is confirmed by the fact that a changeover of the electronic and orbital configuration from ${d}^{4}$ to ${d}^{3}$ by transition metal substitution is shown to favor the occurrence of a NTE in ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{4}$. This finding is in agreement with the experimental observations of a NTE effect which is significantly dependent on the transition metal substitution in the ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{4}$ compound.

Colossal negative thermal expansion in a cucurbit[8]uril-enabled uranyl-organic polythreading framework via thermally induced relaxation.

It is an ongoing goal to achieve the effective regulation of the thermal expansion properties of materials. In this work, we propose a method for incorporating host-guest complexation into a framework structure and construct a flexible cucurbit[8]uril uranyl-organic polythreading framework, U3(bcbpy)3(CB8). U3(bcbpy)3(CB8) can undergo huge negative thermal expansion (NTE) and has a large volumetric coefficient of -962.9 × 10-6 K-1 within the temperature range of 260 K to 300 K. Crystallographic snapshots of the polythreading framework at various temperatures reveal that, different from the intrinsic transverse vibrations of the subunits of metal-organic frameworks (MOFs) that experience NTE via a well-known hinging model, the remarkable NTE effect observed here is the result of a newly-proposed thermally induced relaxation process. During this process, an extreme spring-like contraction of the flexible CB8-based pseudorotaxane units, with an onset temperature of ∼260 K, follows a period of cumulative expansion. More interestingly, compared with MOFs that commonly have relatively strong coordination bonds, due to the difference in the structural flexibility and adaptivity of the weakly bonded U3(bcbpy)3(CB8) polythreading framework, U3(bcbpy)3(CB8) shows unique time-dependent structural dynamics related to the relaxation process, the first time this has been reported in NTE materials. This work provides a feasible pathway for exploring new NTE mechanisms by using tailored supramolecular host-guest complexes with high structural flexibility and has promise for the design of new kinds of functional metal-organic materials with controllable thermal responsive behaviour.

The enhanced negative thermal expansion in less-oxygen-vacancies copper pyrophosphate

For oxides, controlling the concentration of oxygen vacancy is a useful way to optimize their functional properties. However, when it comes to the field of negative thermal expansion (NTE), much less attention has been paid to the effect of oxygen vacancy on NTE, though oxide-typed NTE materials account for more than 40% of the total NTE materials. Here, we report that the linear coefficient of thermal expansion at 250–350 K of copper pyrophosphate (i.e., Cu2P2O7) can be significantly improved from –13.88 to –36.60 ppm/K when the synthesis temperature is raised from 1073 to 1373 K. The combined study including X-ray absorption near edge structure, neutron powder diffraction, and X-ray diffraction has confirmed the selective vacancies in the O1 site for low-temperature synthesized samples, which suppress both the phase-transition and framework-structure driven NTE simultaneously. Our result proposes a new approach for optimizing the NTE effect of oxides.

Illuminating the negative thermal expansion mechanism of YFe(CN)6 via electronic structure and unusual phonon modes

Understanding the negative thermal expansion (NTE) mechanism remains an important and challenging thing. In this work, we selected the case of YFe(CN)6 to investigate the structure-mechanism relation on the base of crystal structure, electronic structure and lattice dynamics. We expanded the NTE of YFe(CN)6 to 150 K, and the temperature dependence of volume and lattice constants was determined by temperature-variable synchrotron X-ray diffraction measurements. A large NTE was found in the system. Our theoretical calculations indicate that the Y–N bond exhibits a strong ionic feature through the calculated electron localization function (ELF), which has a strong influence on the anisotropic vibration of the N atom. The detailed lattice dynamics simulations suggest that the NTE of YFe(CN)6 may be related to the presence of the unusual low-frequency modes of the YN6 triangular prism (tri-prism) units. The optical branches with low frequencies are mainly related to the distortion and twisting modes of the YN6 tri-prism units, which contribute most to the NTE effect in the crystal.

Elastic mechanics solution of thermal expansion of bi-material curved beam and its application to negative thermal expansion metamaterials

Thermal stress impacts various engineering fields significantly, such as aerospace and precision instruments. This adverse effect can be greatly reduced, if not eliminated, by the application of micro-thermal expansion materials, and bi-material beams are widely utilized in the design of micro-thermal expansion structures, thereby exhibiting great application potentials. The elasticity solution of bi-material curved beam under free thermal expansion has been proposed by scholars. Based on this solution, the simplified form is proposed in this paper, and extended to the case where the rotation angles at both ends of the circular arc are constrained under thermal loads. Besides, the geometric parameters and the nonlinear problems of the thermal expansion of bi-material curved beam are analyzed. In addition, a novel type of negative thermal expansion material has been designed by applying the bi-material curved beam to the tetra chiral and anti-tetra chiral materials. The proposed material has greater negative thermal expansion effect than the traditional tetra and anti-tetra chiral materials that are with straight beams.

Releasing the residual stress of Cf/SiC-GH3536 joint by designing an Ag-Cu-Ti + Sc2(WO4)3 composite filler metal

• The work is the first one to introduce Sc 2 (WO 4 ) 3 into brazing process. • The Sc 2 (WO 4 ) 3 maintains its negative thermal expansion effect in Ag-Cu-Ti system. • The residual stress releasing mechanism is revealed by finite element analysis method. • The shear strength improves 2.6 times by introducing Sc 2 (WO 4 ) 3 reinforcing phase. Due to native character of thermal expansion coefficient (CTE) mismatch between C f /SiC and GH3536, achieving high strength joint was a huge challenge for C f /SiC-GH3536 joints. Herein, a composite filler metal of Ag-Cu-Ti + Sc 2 (WO 4 ) 3 was developed to join C f /SiC and GH3536. This work introduced Sc 2 (WO 4 ) 3 to Ag-Cu-Ti system as a negative thermal expansion (NTE) reinforcing phase to release joint residual stress. Sc 2 (WO 4 ) 3 was evenly distributed in the brazing seam and reacted with Ti to form Ti 3 O 5 reaction layer. The results of finite element analysis showed that the residual stress of the joints was effectively released by introducing Sc 2 (WO 4 ) 3 reinforcing phase, and the mises stress was decreased from 447 to 401 MPa. The maximum shear strength of the C f /SiC-GH3536 joint brazed with Ag-Cu-Ti + 6 vol% Sc 2 (WO 4 ) 3 filler alloys was 64 MPa, which was about 2.6 times higher than that of Ag-Cu-Ti alloys. The results of this study provide a promising strategy for the introduction of new Sc 2 (WO 4 ) 3 reinforcing phase in Ag-Cu-Ti system, and improve the reliability and feasibility of composite brazing alloy in brazing filed.

Interface design and engineering in Al matrix composite with low CTE and high strength reinforced by barium strontium titanate particles

Al matrix composites with both low coefficient of thermal expansion (CTE) and excellent mechanical property has important application value in the fields of aerocraft, precise instruments. However, obtaining both low CTE and high strength simultaneously is still a challenge. In this work, huge negative thermal expansion effect derived from ferroelectric-paraelectric phase transformation of barium strontium titanate (BST) ceramic is designed and utilized in Al matrix. Low CTE is obtained in BST/Al composite at the condition of a low volume fraction of BST particles. Annealing treatment is carried out to improve the interface bonding and to reduce residual stress, therefore the negative thermal expansion effect in the process of phase transformation of the BST particles is more thoroughly brought into play, and then the CTE of BST/Al composite is further decreased. Finally, the average CTE of BST/Al composite annealed at 600 °C for 2 h between room temperature and 250 °C reaches as low as 12.04 × 10−6 °C −1, while achieving a high compressive strength as high as 800 MPa. The microstructure around the interface and the phase transformation behavior are also investigated.

Tolerance Factor Control of Tetragonality and Negative Thermal Expansion in PbTiO3-Based Ferroelectrics

The exploration of materials with large negative thermal expansion (NTE) is highly demanded but remains challenging because chemical substitution generally tends to weaken the NTE effect of currently available NTE materials. Herein, we proposed a tolerance factor (t)-tetragonality (c/a) relationship in order to achieve enhanced NTE in PbTiO3-based ferroelectrics. According to this guidance, we designed a new Pb/Bi-based perovskite of (1 – x)PbTiO3-xBiYO3. The present new system exhibits an unusual increased tetragonality (c/a = 1.073) compared to pristine PbTiO3 (c/a = 1.064). As a result, enhanced NTE with an average volumetric coefficient of thermal expansion of α̅V = −2.34 × 10–5/K has been successfully achieved in an extended temperature range from room temperature (RT) up to 840 K for the 0.90PbTiO3-0.10BiYO3 compound, which is contrasted with that of pristine PbTiO3 (α̅V = −2.11 × 10–5/K, RT to 800 K). The present study not only paves the way for the design of large NTE in PbTiO3-based ferroelectrics, but also has great impact on the understanding of structure–property relationships so as to provide a new design to optimize NTE performance.

Anti-thermal quenching of Eu3+ luminescence in negative thermal expansion Zr(WO4)2

Thermal quenching of luminescence is the most critical problem for rare earth doped phosphors used in light-emitting diodes (LEDs). Herein, we demonstrate that thermal quenching can be considerably suppressed via the negative thermal expansion effect in Zr(WO4)2 that serves as host for Eu3+ red emission. The photoluminescence (PL) intensity is surprisingly enhanced by 130% when the temperature is raised from room temperature to 100 °C. As temperature further increases to 160 °C, the PL intensity turns to reduce, which is still 1.4 times of that at room-temperature. Moreover, Zr(WO4)2:15%Eu phosphor has good durability, which still exhibits strong red luminescence (only 13% loss) after being kept in 85 °C/85% relative humidity chamber for 240 h. The anti-thermal quenching of Eu3+ luminescence can be ascribed mainly to the following two factors: first one is the thermal-enhanced energy transfer between Eu3+ ions induced by the contraction of Zr(WO4)2 unit-cell volume that leads to the strong structural rigidity of host lattice; second one would be electron traps in the host that favors the increase of electrons on the excited energy levels. This important anti-thermal quenching effect induced from the negative thermal expansion of the host matrix may stimulates a novel and efficient approach to design highly thermal stable phosphors for next-generation LEDs.

Giant negative thermal expansion in a textured MnCoSi alloy

In the present work, textured stoichiometric MnCoSi alloys were fabricated by slow-cooling thermal treatment. Microstructure and crystallographic characterization revealed that the textured MnCoSi alloy consists of three different oriented orthorhombic TiNiSi-type martensite variants with their aOrth-axis lying in the cross-section of the rod-like MnCoSi alloy. A giant reversible linear negative thermal expansion (NTE) as much as 9350 ppm was achieved along the aOrth-axis of the textured MnCoSi alloy at a wide operation temperature span from 50 K to 400 K, owing to the antiferromagnetic arrangement. The linear NTE value slightly decreases from 9350 ppm to 9200 ppm with increasing the external magnetic field up to 2 T, which indicates that the present MnCoSi alloy demonstrates a stable NTE effect under external magnetic field. Moreover, during the martensitic transformation, the linear NTE along the aOrth-axis of the textured MnCoSi alloy could be up to 70,000 ppm at about 1200 K.

A study of physical effects in magnetic-phase-transition materials

<p indent=0mm>Magnetic-phase-transition materials possess abundant physical properties and exhibit magnetocaloric, magnetostrictive, elastocaloric, and negative thermal expansion effects under magnetic, stress or temperature fields. They show promising applications in many fields, including refrigeration, sensor, and energy conversion. As a new class of functional magnetic materials, research fields and contents based on the magnetic-phase-transition materials are becoming enriched. In this paper, we first introduce the phase transition types of magnetic materials and present some emphatic descriptions of the first-order magnetic-phase-transition materials. Thereafter, we review recent research progress on the related effects of the first-order magnetic-phase-transition materials driven by magnetic, stress, and temperature fields.

Ultrafast photoinduced strain in super-tetragonal PbTiO3 ferroelectric films

The ultrafast photoinduced strain (UPS) resulting from the coupling of piezoelectric and photovoltaic effects in ferroelectric has been focused in the last decade, endowing them with extensive applications including ultrafast optical memories, sensors and actuators with strain engineering. The mechanism of screening of the depolarization field by photoinduced carriers is generally accepted for UPS in ferroelectrics, while the thermal component of the strain is usually diluted as the offset and has not been systematically confronted, leading to unnecessary confusion. Herein, both the positive and negative thermal expansion effects in composite ferroelectric epitaxial films are investigated by use of high-repetition-rate ultrafast X-ray diffraction, along with the piezoelectric and photovoltaic effects. The coupling of the positive/negative thermal effects and the piezoelectric/photovoltaic effects in ultrafast strain is evidenced and can be regulated. The opposite lattice responses due to different thermal effects of the samples with different axial ratios are observed. The maximum UPS is up to 0.24%, comparable to that of conventional ferroelectric. The interaction between the thermal and ferroelectric effects in the induced strain could promote the diversified applications with the coupling of light, heat and electricity.

Large anisotropic negative thermal expansion in Cu-TDPAT metal-organic framework: A combined in situ X-ray diffraction and DRIFTS study

Cu-TDPAT (H6TDPAT = 2,4,6-tris(3,5-dicarboxylphenylamino)-1,3,5-triazine), a stable nanoporous metal-organic framework with rht topology, has sparked broad interest as an adsorbent for several chemical separation processes. In this work, in situ synchrotron diffraction experiments followed by sequential LeBail refinements reveal that Cu-TDPAT shows unusually large anisotropic negative thermal expansion (NTE). The PASCal crystallography tool, used to analyze the magnitude of the NTE, reveals an average volumetric thermal expansion coefficient αv = −20.3 MK−1. This value is significantly higher than the one reported for Cu-BTC (also known as HKUST-1), which contains the same Cu-paddlewheel building unit, αv ≈ −12 MK−1. In situ synchrotron single crystal X-ray diffraction and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were employed to shed light on the NTE mechanism. Using these two methods, we were able to elucidate the three main structural motions that are responsible for the NTE effect. The more pronounced NTE behavior of Cu-TDPAT is attributed to the lower symmetry combined with the more complex ligand structure when compared to Cu-BTC. The knowledge obtained in this work is important for understanding the behavior of the adsorbent under transient variable temperature conditions in fixed adsorption beds.

Analysis of Antichiral Thermomechanical Metamaterials with Continuous Negative Thermal Expansion Properties.

Negative thermal expansion is an interesting and appealing phenomenon for various scientific and engineering applications, while rarely occurring in natural materials. Here, using a universal antichiral metamaterial model with bimetal beams or strips, a generic theory has been developed to predict magnitude of the negative thermal expansion effect from model parameters. Thermal expansivity of the metamaterial is written as an explicit function of temperature and only three design parameters: relative node size, chirality angle, and a bimetal constant. Experimental measurements follow theoretical predictions well, where thermal expansivity in the range of negative 0.0006–0.0041 °C−1 has been seen.

Using negative thermal expansion effect to grow spiny NiS/C architecture and its application in sodium-ion batteries

Negative thermal expansion of nickel sulfide (NiS) is an underlying cause for the self-explosion of toughened glass in practical use. In this work, this undesired thermal property is rationally used to produce spiny NiS/C architectures. By liquid-nitrogen quenching NiS/C microspheres for 120 min, one can obtain a full-grown spiny structure with a well-defined NiS/C core and dense NiS prickles with large slenderness ratios. Using this architecture as an anode material in sodium-ion batteries, a relatively high specific capacity of 504.3 mAh g−1 (ca. 85.4% of its theoretical capacity value) is achieved at a current density of 200 mA g−1 after the 1000th charge-discharge cycle. Moreover, rate performance test of the 1000th-cycled cell illustrates a capacity drop from 504.3 to 445.6, then to 384.7, 319.4, and finally to 245.2 mAh g−1 as increasing the current density from 200 to 500, then to 1000, 2000, and finally to 5000 mA g−1, respectively. More detailed TEM characterization, cyclic voltammetry and electrochemical impedance measurements are conducted after the rate performance test, and the result shows that high current density can alter the contact interface between NiS architecture and electrolyte, or even change its microstructure.

Ultrafast Photoinduced Strain in Super-Tetragonal PbTiO3 Ferroelectric Films

The ultrafast photoinduced strain in ferroelectric coupling of piezoelectric and photovoltaic effects have been focused in the last decade, making them extend numerous applications including ultrafast optical memories, sensors and actuators with strain engineering. The mechanism of screening of the depolarization field by photoinduced carriers is generally accepted for ultrafast photoinduced strain in ferroelectric, while the thermal component of the strain is usually diluted as the offset and have not been systematically confronted, leading to unnecessary confusion. Herein, both the positive and negative thermal expansion effect in composite ferroelectric epitaxial films have been investigated by use of high repetition rate ultrafast X-ray diffraction, along with the piezoelectric and photovoltaic effects. The coupling of the positive/negative thermal effects and the piezoelectric/photovoltaic effects in ultrafast strain have been evidenced and regulated. The opposite lattice response due to different thermal effect of the different axial ratio samples have been observed. The maximum ultrafast photoinduced strain is up to 0.24%, comparable to that of conventional ferroelectric. The interaction of thermal and ferroelectric effect in the induced strain could promote the diversified application with the coupling of light, heat and electricity.

Anomalous thermal expansion properties in perovskite Sm0.85Zn0.15MnO3

The multiple sintering compounds of perovskite Sm0.85Zn0.15MnO3, which are denoted as S1, S2, S3, S4, and S5, have been synthesized by a solid-state method. The analysis of their crystal structure and microstructure were conducted by X-ray diffractometer and scanning electron microscopy, respectively. The average particle size and porosity were counted by microscopic image analysis. The thermal-expansion behavior of the compounds was studied by a dilatometer and high-temperature XRD. Experimental results indicated that the once sintering sample (S1) of Sm0.85Zn0.15MnO3 possesses the negative thermal expansion (NTE) properties with a coefficient of thermal expansion of −8.40 × 10−6 K−1 in the range of 519–1023 K. By contrast, the thermal expansion behavior for the multiple sintering samples (S2–S5) is not same as that of S1. The porosity of the samples dramatically affects their thermal expansion behavior. The samples S1 and S2 exhibit the NTE characteristics as their porosity was larger than 9.5%, but the samples S3, S4, and S5 exhibit positive thermal expansion characteristics, as their porosity is less than 9.5%. In addition, anisotropy of thermal expansion plays a crucial role in the NTE mechanism. The mechanism underlying the NTE of Sm0.85Zn0.15MnO3 (S1) involves the coupling effect of the high porosity and the microstructural NTE effect caused by crystal grains with anisotropic thermal expansion and intercrystalline pores.