Large Negative Thermal Expansion Research Articles

Pressure‐Induced Volumetric Negative Thermal Expansion in CoZr2 Superconductor

AbstractThe study investigates the thermal expansion and superconducting properties of a CuAl2‐type (tetragonal) superconductor CoZr2 under high pressures. High‐pressure synchrotron X‐ray diffraction is performed in a pressure range of 2.9 GPa < P < 10.4 GPa, and it is discovered that CoZr2 exhibits volumetric negative thermal expansion (NTE) under high pressures. Although uniaxial positive thermal expansion (PTE) along the a‐axis is observed under ambient pressure, it is suppressed by pressure, whereas a large uniaxial NTE along the c‐axis is maintained under the pressure regime. Because of the combination of the suppressed uniaxial PTE along the a‐axis and uniaxial NTE along the c‐axis, volumetric NTE is achieved under high pressure in CoZr2. The volumetric NTE mechanism is based on the flexible crystal structure caused by the soft Co–Co bond, as observed in the isostructural compound FeZr2, which exhibits a uniaxial NTE along the c‐axis. High‐pressure electrical resistance measurements of CoZr2 are performed and confirm superconductivity at 0.03 GPa < P < 41.9 GPa. Because of the coexistence of the two phenomena, volumetric NTE and superconductivity, in CoZr2 under high pressure, coexistence can be achieved under ambient pressure by tuning the chemical composition after the present observation.

Fabrication of metal matrix composites with negative thermal expansion zinc pyrophosphate filler

We fabricated Cu matrix composites with low thermal expansion and high thermal conductivity using Zn2P2O7-based negative thermal expansion (NTE) filler. Magnesium and aluminum co-doped Zn2−x−yMgxAlyP2O7 exhibits large NTE over a wide temperature range including room temperature. While achieving high density of the phosphate filler using spark plasma sintering and its uniform dispersion by an ultrasonic process, we reduced thermal expansion of the Cu matrix composites and retained their high thermal conductivity. Particularly, the 30 vol. %-Zn1.70Mg0.25Al0.05P2O7/Cu composite had a linear expansion coefficient as low as 5.1 ppm/K at temperatures of 300–400 K. The results reported herein demonstrate that Zn pyrophosphates, which are superior in terms of environmental impact and cost, are effective for controlling the thermal expansion of metals and are expected to support widely diverse engineering applications in the future.

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.

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

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

Systematic Study on the Role of the Third Zn-Site Element in Zn<sub>2−</sub><i><sub>x</sub></i>Mg<i><sub>x</sub></i>P<sub>2</sub>O<sub>7</sub> Showing Giant Negative Thermal Expansion

For Mg-doped Zn2P2O7, this systematic investigation of co-doping onto Zn sites has elucidated specific effects on negative thermal expansion (NTE). The low-cost and low-environmental-impact NTE material Zn2−xMgxP2O7 shows large NTE in a temperature range including room temperature for x = 0.4. Although Mg doping broadens the operating-temperature window, it remains several dozen degrees wide. Moreover, the total volume change related to NTE becomes less than that of the Zn2P2O7 parent material. Findings obtained from this study demonstrate that co-doping of Mg and of another element onto the Zn site is effective for achieving simultaneous expansion of the operating-temperature window and maintenance of the volume change related to NTE. One illustrative case is that Zn1.64Mg0.30Al0.06P2O7 has a large negative coefficient of linear thermal expansion of about −65 ppm/K at temperatures of 300–375 K. In fact, at temperatures high above room temperature, Zn1.64Mg0.30Al0.06P2O7 powder shows better thermal expansion compensation capability than the composition without Al. The Al-doped phosphates are expected to have broad practical application because of their performance, cost, and environmental load characteristics.

Negative Thermal Expansion of Undulating Coordination Layers through Interlayer Interaction

The negative thermal expansion (NTE) of solid-state materials is of significance in various fields, but a very rare phenomenon. In this study, we carried out a meta-analysis for the anisotropic thermal expansion behavior of fifteen two-dimensional coordination polymers [M(salen)]2[M'(CN)4(solvent)] (M = Mn, Fe; M' = MnN, ReN, Pt, Pt(I2)x; x = 0.18, 0.45, 0.85, 1.0; solvent = H2O, MeOH, MeCN) with a newly synthesized [Fe(salen)]2[MnN(CN)4(MeCN)]. Consequently, we successfully demonstrate the unusual NTE of the undulating coordination layers by an expansion deformation of the layers via strong interlayer interaction within the layer stacking. Notably, the layer volume of [Mn(salen)]2[ReN(CN)4] with its powder form decreases with a large NTE coefficient, αlayer-volume = -27 × 10-6 K-1 (100-500 K). This is a significantly large value despite the increase in layer thickness along the layer contraction based on the anisotropic transformation of undulating layers. Conversely, the analysis demonstrates that the chemical modification of the layers to enhance intralayer interaction rather than interlayer interaction switches a direction of the layer anisotropy, yielding positive thermal expansion materials with the coefficient of the layer volume reaching +92 × 10-6 K-1.

Tailoring Negative Thermal Expansion via Tunable Induced Strain in La-Fe-Si-Based Multifunctional Material.

Zero thermal expansion (ZTE) composites are typically designed by combining positive thermal expansion (PTE) with negative thermal expansion (NTE) materials acting as compensators and have many diverse applications, including in high-precision instrumentation and biomedical devices. La(Fe1-x,Six)13-based compounds display several remarkable properties, such as giant magnetocaloric effect and very large NTE at room temperature. Both are linked via strong magnetovolume coupling, which leads to sharp magnetic and volume changes occurring simultaneously across first-order phase transitions; the abrupt nature of these changes makes them unsuitable as thermal expansion compensators. To make these materials more useful practically, the mechanisms controlling the temperature over which this transition occurs and the magnitude of contraction need to be controlled. In this work, ball-milling was used to decrease particles and crystallite sizes and increase the strain in LaFe11.9Mn0.27Si1.29Hx alloys. Such size and strain tuning effectively broadened the temperature over which this transition occurs. The material's NTE operational temperature window was expanded, and its peak was suppressed by up to 85%. This work demonstrates that induced strain is the key mechanism controlling these materials' phase transitions. This allows the optimization of their thermal expansion toward room-temperature ZTE applications.

Negative Thermal Expansion Induced in Tri-graphene and T-graphene by the Rigid-Unit Modes.

Materials which contract on heating (negative thermal expansion, NTE) are of significant interest for advanced applications. Graphene has shown NTE up to 1000 K, which motivates further improvements in two-dimensional carbon to attain superior performance. In this Communication, very large negative thermal expansion coefficients (αT) are reported for tri-graphene (TrG) and T-graphene (TG). Quasi-harmonic approximation calculations show that αT remains negative until 4200 K and 2900 K for TrG and TG, respectively. The high NTE for these systems is understood on the basis of the soft phonon modes, which induce rotation of the 3-membered and the 4-membered rings in TrG and TG, respectively, and ab initio molecular dynamics simulations. The local distortions for the 3-12 rings (in TrG) and 4-8 rings (in TG) have structural resemblance with the rigid-unit modes that are usually envisioned for bulk systems.

Insight into the Relationship between Negative Thermal Expansion and Structure Flexibility: The Case of Zn(CN)2-Type Compounds.

High structure flexibility can lead to large negative thermal expansion (NTE), but the reason is not clear. In this work, first-principles calculations have been carried out to investigate the relationship between NTE and structure flexibility in Zn(CN)2-type compounds. Smaller bulk modulus corresponds to larger compressibility, thus making the crystal structure more flexible and more suitable for NTE. It indicated that the ionic nature of the bond and the bond length jointly affect the structural flexibility and then act on the transverse vibration of C and N atoms. The results of lattice dynamic suggested that higher structural flexibility promotes a greater number of low-frequency optical modes with negative Grüneisen parameters, resulting in a larger NTE. This work also gives us new insight into the design of NTE materials.

Designing Geometric Degrees of Freedom in ReO3‐Type Coordination Polymers

AbstractEngineering the interplay of structural degrees of freedom that couple to external stimuli such as temperature and pressure is a powerful approach for material design. New structural degrees of freedom expand the potential of the concept, and coordination polymers as a chemically versatile material platform offer fascinating possibilities to address this challenge. Here, we report a new class of perovskite‐like AB2X6 coordination polymers based on a [BX3] − ReO3‐type host network ([Mn(C2N3)3] −), in which the spatial orientation of divalent A2+ cations ([R3N(CH2)nNR3]2+) with separated charge centers that bridge adjacent ReO3‐cavities is introduced as a new geometric degree of freedom. Herringbone and head‐to‐tail order pattern of [R3N(CH2)nNR3]2+ cations are obtained by varying the separator length n and, together with distortions of the pseudocubic [BX3] − network, they determine the materials’ stimuli‐responsive behavior such as counterintuitive large negative compressibility and uniaxial negative thermal expansion. This new family of coordination polymers highlights the chemists’ capabilities of designing matter on a molecular level to address macroscopic material functionality and underpins the opportunities of the design of structural degrees of freedom as a conceptual framework for rational material synthesis in the future.

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.

Large negative thermal expansion in GdFe(CN)6 driven by unusual low-frequency modes

Understanding the negative thermal expansion (NTE) mechanism is of great importance. In this work, we consider the new NTE compound GdFe(CN)6 (αv = −34.2×10-6 K-1) as a case study to investigate the NTE mechanism from the perspective of the lattice vibrational dynamics. The atomic mean-square displacements suggest that the NTE of GdFe(CN)6 comes from the strong tension effect induced by the transverse vibrations of the atomic –Fe–CN–Gd– linkages, with the largest contribution given by N atoms. Lattice dynamics calculations show that three low-frequency optical modes at about 50 cm-1 show the largest negative Grüneisen parameters thus providing the largest contribution to the NTE. The existence of these unusual low-frequency vibrational modes can be ascribed to the presence of GdN6 trigonal prisms in the framework structure of GdFe(CN)6.

Large negative thermal expansion induced by cation dimerization in ilmenite-type vanadate ceramic

A significant negative thermal expansion (NTE) in an ilmenite-type MgVO3 ceramic is reported in this paper. MgVO3 undergoes V–V dimerization at 500–550 K accompanied by a structural phase transition from the triclinic (low-temperature) to rhombohedral (high-temperature) phase. This transition induces a large anisotropic crystal structure deformation and results in a large NTE in the ceramic sample, which is caused by the microstructural effect. The NTE was observed over a temperature range of 450–630 K, and the total volume shrinkage reached approximately −0.7%. This study demonstrates that controlling the chemical bonding is a promising method for the creation of NTE materials.

Understanding Large Negative Thermal Expansion of NdFe(CN)6 through the Electronic Structure and Lattice Dynamics.

A large negative thermal expansion (NTE) (αv = -4.1 × 10-5 K-1, 100-525 K) has been discovered in NdFe(CN)6. Here, the synchrotron X-ray diffraction and lattice dynamics calculations using the density functional theory were conducted to understand the NTE in NdFe(CN)6. The information obtained on the bond nature of the Nd-N≡C-Fe linkage and on the atomic thermal vibrations suggests that the transverse vibrations of the -N≡C- group, in particular from N atoms, produced the NTE in NdFe(CN)6. This is corroborated by the calculated Grüneisen parameters, which confirm the relationship between NTE and CN atomic vibrations. The results provide a helpful contribution toward the realization of new materials with negative or controllable thermal expansion.

Transformation of Thermal Expansion from Large Volume Contraction to Nonlinear Strong Negative Thermal Expansion in PbTiO3-Bi(Co1-xFex)O3 Perovskites.

Controlling negative thermal expansion (NTE) is an important topic in the study of NTE materials. Generally, a large magnitude of NTE with a wide NTE operation temperature window is preferable for applications of NTE materials, as a stronger NTE can be used to tailor the coefficient of thermal expansion (CTE) of materials with positive thermal expansion by forming composites more efficiently. However, controlling the NTE in single-phase materials is still a significant challenge. In present study, we proposed a promising method to control the thermal expansion from large volume contraction in a limited temperature widow (x = 0, ΔV = -4.8%, 675-700 °C) to a nonlinear strong NTE over a wider temperature range (x = 0.8, α̅V = -6.12 × 10-5/°C, RT to 600 °C) by means of adjusting the proportion of cations with different ferroelectric activities in 0.5PbTiO3-0.5Bi(Co1-xFex)O3 ferroelectrics. The obtained NTE was stronger than many of the currently available NTE materials, and the operation window of NTE was also in an extended temperature range. The unusual transformation is well explained by the spontaneous volume ferroelectrostriction effect, which was evidenced by joint experimental and theoretical studies. The present work not only may pave the way for controllable large NTE in PbTiO3-based ferroelectrics but also could be extended to magnetic NTE materials, whose NTE is coupled with magnetism.

Negative thermal expansion of (Al1/3Fe1/3Cr1/3)2(Mo1/2W1/2)3O12 (AFCMW) and low thermal expansion of AFCMW-(Co1/2Ni1/2)(Mo1/2W1/2)O4 with high entropy

A2Mo3O12 (A-Al, Fe, Cr) have large negative thermal expansion (NTE) coefficients and structural stability but high phase-transition temperatures (PTTs). Herein, we prepared (Al1/3Fe1/3Cr1/3)2(Mo1/2W1/2)3O12 (AFCMW), and found it to have a low NTE coefficient and a low PTT. Furthermore, combination of AFCMW with (Co1/2Ni1/2)(Mo1/2W1/2)O4 (CNMW) afforded an AFCMW–CNMW composite with a low thermal expansion (LTE). We determined that the PTT reductions in A2Mo3O12 are largely due to the high-entropy effect resulting from the introduction of different ions into its A and M sites. Moreover, we found that the low LTE of the AFCMW–CNMW composite is attributable to the opposite thermal expansion behaviours of AFCMW and CNMW. We suggest that the suppressed thermal expansion during the phase transition process of the AFCMW–CNMW composite could be derived from the high-entropy effect resulting from its increased diversity of polyhedra, the influence of Co2+ and Ni2+ dopants, and CNMW-induced lattice distortion.

Effect of magnetic field on thermal strain, thermal expansion and negative thermal expansion property in a polycrystalline Ni55Mn18Ga27 alloy

The magnetic field effect on phase transition and thermal expansion properties were investigated in Ni55Mn18Ga27 alloy. The results show that the alloy has an excellent isotropy, reproducibility and thermostability in thermal strain and exhibits a large negative thermal expansion (NTE) effect in the direct and reverse martensitic transformations (MTs). For the direct MT, the average linear expansion coefficient α is about −225.21 ppm/K and the corresponding temperature span is around 8.2 K. Additionally, the sensitivities of the transformation strain and peak temperatures to field are about 88.5 ppm/T and 1.31 K/T, respectively. The rates of α and temperature spans of NTE to magnetic field are about 8.88 ppm/K T and 0.82 K/T, indicating that the magnetic field can improve the NTE property of the Ni–Mn-Ga alloy. Finally, the NTE mechanism has also been discussed. Our findings are beneficial to improving the thermal expansion and NTE properties of Ni–Mn-Ga alloys.

Understanding the Origin of the Particularly Small and Anisotropic Thermal Expansion of MOF‐74

AbstractMetal–organic frameworks often display large positive or negative thermal expansion coefficients. MOF‐74, a material envisioned for many applications, shows a different behavior. Temperature‐dependent X‐ray diffraction reveals particularly small negative (positive) thermal expansion coefficients perpendicular (parallel) to the hexagonally arranged pores. These trends are explained by combining density‐functional theory calculations with the Grüneisen theory of thermal expansion, which allows tracing back thermal expansion to contributions of individual phonons. On the macroscopic level, the small thermal expansion coefficients arise from compensation effects caused by the large coupling between perpendicular stress and strain and by the small magnitudes of the mean Grüneisen tensor elements, 〈γ〉. These provide information on how strains impact phonon frequencies. To understand the small value of 〈〉, the individual mode contributions are analyzed using the corresponding atomic motions. This reveals that only the lowest frequency modes up to ≈3 THz provide non‐negligible contributions, such that 〈〉 drops sharply at higher temperatures. These considerations reveal, how the details of the anharmonic properties of specific phonon bands determine the magnitude and sign of thermal expansion in a prototypical material like MOF‐74. Beyond that, the authors also discuss, how the choice of the theoretical methodology impacts the obtained results.

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.

Low-melting metal bonded MM′X/In composite with largely enhanced mechanical property and anisotropic negative thermal expansion

MM′X (M, M′ = transition metals, X = carbon or boron group elements) compounds experiencing magnetostructural transition have great potential in multifunctional applications due to the various magnetoresponsive effects. However, the poor mechanical properties hinder their practical applications. In the present work, the low-melting metal bonded MM′X/In composites are fabricated. The dense structure with low porosity, formed due to the high ductility of In, greatly improves the machinability and thermal conductivity. The thermal cycling tests prove the excellent integrality and stability of MM′X/In composites. The introduction of ductile In reduces the constraints of structural transition so that weakens the first-order magnetostructural transition of MM′X compounds, thus lowering the hysteresis loss. Besides, the MM′X/In composite with 30 wt.% In (In30) exhibits a larger magnetocaloric effect than that of the benchmark magnetocaloric material Gd. In addition, zero thermal expansion (ZTE) property is achieved in In30 composite over a wide temperature range. Moreover, magnetic oriented In30 composite displays a strongly anisotropic thermal expansion performance. An obvious positive thermal expansion (PTE) with linear PTE coefficient of 5.2 × 10−6 K−1 is observed along the direction parallel to pressure, while large negative thermal expansion (NTE) can be obtained along the directions perpendicular and parallel to field. The NTE in the direction parallel to field is as high as −40.6 × 10−6 K−1, which is comparable to those of some typical NTE materials. Consequently, the present result highlights the potential multifunctional applications of low-melting metal bonded MM′X/In composites, especially as magnetic refrigerants and NTE materials around room temperature.