Large Negative Thermal Expansion Research Articles

Density Functional Studies Revealing Anomalous Lattice Behavior in Metal Cyanide, AgC8N5

We have investigated anomalous lattice behavior of metal–organic framework compound AgC8N5 on application of pressure and temperature using ab initio density functional theory calculations. The van der Waals dispersion interactions are found to play an important role in structural optimization and stabilization of this compound. Our ab initio calculations show negative linear compressibility (NLC) along the c-axis of the unit cell. The ab initio lattice dynamics and molecular dynamics simulations show large negative thermal expansion (NTE) along the c-axis. The mechanism of NLC and NTE along the c-axis of the structure is governed by the dynamics of Ag atoms in the a–b plane. The NLC along the c-axis drives the NTE along that direction.

Three dimensional lightweight lattice structures with large positive, zero and negative thermal expansion

Tailoring thermal expansion of structures is in urgent need in engineering applications where the structures are susceptible to suffer large temperature fluctuation. Here, a method to reconstruct 3D truss structures is developed to obtain large positive, zero and even negative coefficient of thermal expansion (CTE). As the basis, theoretical analysis and numerical verification of the bi-material pyramid and tetrahedron lattice cells explicitly reveal that with thick members, the influence of the cross section on the CTEs should be well considered, and the CTEs should be accurately calculated by the solid model. Furthermore, two kinds of 3D lattice structures with isotropic tailorable CTEs are originally devised. Moreover, bi-pyramid and bi-tetrahedron units are devised, and a reconstruction method, which can reconstruct an arbitrary 3D truss structures to obtain specific target CTE, is originally developed. Typical supporting structure and platform used in satellites are reconstructed by the proposed method, and near zero thermal expansion, which is urgent needed in satellite, can be flexibly obtained. The analysis and proposal of three dimensional lattice structures and reconstruction method provide a new approach to develop structures with light weight and tailorable CTEs.

Giant negative thermal expansion in Fe-doped layered ruthenate ceramics

The effects of iron doping on the giant negative thermal expansion (NTE) of Ca2RuO4−y ceramics are investigated. Fe-doped ruthenate ceramics exhibit a large NTE even though the crystallographic unit-cell volume shows no NTE. The anisotropic thermal strain of crystal grains consumes open spaces in the sintered body and causes giant bulk volume contraction on heating. This giant NTE is reproducible against repeated thermal cycling, indicating a tough microstructure. The thermal expansion of epoxy resin is fully suppressed below 400 K by the 56 vol % loading of the Fe-doped ruthenate ceramic powder, demonstrating tough microstructures and the capability of thermal expansion compensation of the ruthenate sintered body.

Colossal Volume Contraction in Strong Polar Perovskites of Pb(Ti,V)O3.

The unique physical property of negative thermal expansion (NTE) is not only interesting for scientific research but also important for practical applications. Chemical modification generally tends to weaken NTE. It remains a challenge to obtain enhanced NTE from currently available materials. Herein, we successfully achieve enhanced NTE in Pb(Ti1-xVx)O3 by improving its ferroelectricity. With the chemical substitution of vanadium, lattice tetragonality (c/a) is highly promoted, which is attributed to strong spontaneous polarization, evidenced by the enhanced covalent interaction in the V/Ti-O and Pb-O2 bonds from first-principles calculations. As a consequence, Pb(Ti0.9V0.1)O3 exhibits a nonlinear and much stronger NTE over a wide temperature range with a volumetric coefficient of thermal expansion αV = -3.76 × 10-5/°C (25-550 °C). Interestingly, an intrinsic giant volume contraction (∼3.7%) was obtained at the composition of Pb(Ti0.7V0.3)O3 during the ferroelectric-to-paraelectric phase transition, which represents the highest value ever reported. Such volume contraction is well correlated to the effect of spontaneous volume ferroelectrostriction. The present study extends the scope of the NTE family and provides an effective approach to explore new materials with large NTE, such as through adjusting the NTE-related ferroelectric property in the family of ferroelectrics.

Structure, Magnetism, and Tunable Negative Thermal Expansion in (Hf,Nb)Fe2 Alloys

Negative thermal expansion (NTE) is one of intriguing properties for solid compounds. Here we report structure and tunable negative thermal expansion in the (Hf1-xNbx)Fe2 magnetic alloys. The NTE mechanism has been investigated by a combined analysis of neutron powder diffraction, synchrotron X-ray diffraction, and macroscopic magnetic measurements. Direct experimental evidence shows that magnetovolume effect is the root of NTE of ferromagnetic phase, while the paramagnetic phase responds to the general positive thermal expansion (PTE). Especially, by adjusting the amount of Nb chemical substitution in (Hf1-xNbx)Fe2, the coexistence of NTE ferromagnetic and PTE paramagnetic phases can tune the large NTE (x = 0.05, αv = -23.13 × 10-6 K-1, 323~398 K) to the relatively low thermal expansion (x = 0.15, αv = -8.28×10-6 K-1, 173~323 K). The present study reveals the direct link between NTE and magnetic structure, and shows that thermal expansion could be tuned by the coexistence of magnetic and paramagnetic phases.

Reversible Thermosalient Effect of N′-2-Propylidene-4-hydroxybenzohydrazide Accompanied by an Immense Negative Compressibility: Structural and Theoretical Arguments Aiming toward the Elucidation of Jumping Phenomenon

The temperature-induced reversible phase transition of N′-2-propylidene-4-hydroxybenzohydrazide from the polymorphic Form II to Form III, and vice versa, is accompanied by the dramatic change of the macroscopic dimensions of the crystal which resulted in the pronounced mechanical motion (jumping) during the phase transition. Prior to the phase transition, the extremely large uniaxial negative thermal expansion along one crystal axis (b axis) was observed, together with the positive thermal expansions along the other two crystal axes. Form III of N′-2-propylidene-4-hydroxybenzohydrazide exhibits the thermal expansion αc = 360 × 10–6 K–1, which is the largest value ever noticed in any organic or metal–organic crystal. From the structural point of view, a thermosalient effect is escorted by the springlike behavior of the zig-zag molecular assemblies along the c axis. First-principles electronic structure calculations show that negative thermal expansion arises from the elastic properties of the crystal which show uniaxial negative compressibilities, NLC. Form III exhibits the negative compressibility along the 001 direction β3 = −28 TPa–1, which is 1 order of magnitude larger than that of any organic compound and, in fact, is comparable to compressibilities of molecular frameworks showing the most pronounced NLC behavior. Elastic properties are also the reason for the reversibility of Form II to Form III transition in contrast to the irreversible Form I to Form II transition. Low energy springlike phonons are easily thermally excited and can assist in the overcoming of the energy barrier between the two phases that precedes thermosalient transition.

First-principles study of elastic mechanical responses to applied deformation of metal-organic frameworks

We use density functional theory to compute the elastic constant tensors of two families of metal-organic frameworks (MOFs) to establish relationships between their structures and mechanical properties. The Zn family consist of Zn4O centers each coordinated by six organic linkers along the ⟨100⟩ directions; we studied three linkers of increasing lengths: 1,4-benzenedicarboxylate (BDC), 4,4’-biphenyl-dicarboxylate (BPDC), and 4,4’’-terphenyl-dicarboxylate. This relatively weak connectivity leads to high anisotropy; in fact, Zn-MOFs exhibit extremely low shear modulus and are near a mechanical instability. In contrast, Zr family studied consists of Zr6O4(OH)4 centers each linked by fumarate, BDC, and BPDC ligands along the twelve ⟨110⟩ directions. The higher structural connectivity results in stiffer frameworks with lower anisotropy. The smallest Zr-MOF exhibits nearly isotropic elasticity with a Zener ratio of 1.06. The stiffest and most compliant directions of both families are directly related to the orientation of the organic linkers. Temperature has a significant effect on elastic moduli; for example, we observed reduction of average Young’s modulus and shear modulus by about 30% from 0 K to 300 K in Zn-BPDC even when it exhibits large negative thermal expansion. We find the effect of temperature to be directionally dependent, leading to an increase in anisotropy upon increasing temperature. The predicted effects of temperature and anisotropy help reconcile a longstanding discrepancy between experiments and first principles calculations.

Large negative thermal expansion in the cubic phase of CaMn7O12

Observations of multiferroicity and giant improper ferroelectricity in ${\mathrm{CaMn}}_{7}{\mathrm{O}}_{12}$ invigorated the research on this material. Delicate structural changes have been reported to cause ferroelectricity in the magnetically ordered state of ${\mathrm{CaMn}}_{7}{\mathrm{O}}_{12}$ as well as high-temperature crystallographic transformations. Through high-resolution synchrotron x-ray diffraction experiments we show for the first time the large negative thermal expansion (NTE) behavior of the cubic phase of ${\mathrm{CaMn}}_{7}{\mathrm{O}}_{12}$. A large NTE coefficient ${\ensuremath{\alpha}}_{L}$ for a temperature window of around 60 K is inferred for the cubic phase in the phase coexistence region during the high-temperature structural transition. It is explained using quasirigid unit modes. We also observe a large phase coexistence region of about 100 K across the high-temperature first-order structural transition, which is different from previous reports.

Abnormal volumetric thermal expansion in the hourglass fermion materials KHgAs and KHgSb

Using first principles density functional theory calculations combined with quasi-harmonic approximation, we demonstrate that the recently reported nonsymmorphic ``hourglass fermion'' materials $\text{KHg}X$ $(X=\mathrm{As}$, Sb) belong to a type of negative thermal expansion (NTE) material with an abnormal volumetric thermal expansion. It is revealed that the NTE is caused by the peculiar layered structures of KHgAs and KHgSb, composed of alternately arranged alkali metal and Hg-$X$ atomic layers with residual tensions. Specifically, the coefficients of negative thermal expansion (CNTE) of KHgAs and KHgSb can reach up to $\ensuremath{-}2.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ and $\ensuremath{-}4.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ along the $a$ axis, respectively, as well as a larger volumetric CNTE of $\ensuremath{-}4.98\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ for KHgSb. The analyses of Gr\uneisen parameters and vibrational modes show that the NTE of $\text{KHg}X$ is driven by the cooperation of membrane and tension effects. It is most likely that the weaker bonds in the Hg-$X$ layer and the smaller mass of alkali metal facilitate the membrane and tension effects, therefore producing a large NTE. Our findings offer insights for understanding the underlying mechanism of NTE behavior in the hourglass fermion materials $\text{KHg}X$.

Colossal negative thermal expansion in reduced layered ruthenate

Large negative thermal expansion (NTE) has been discovered during the last decade in materials of various kinds, particularly materials associated with a magnetic, ferroelectric or charge-transfer phase transition. Such NTE materials have attracted considerable attention for use as thermal-expansion compensators. Here, we report the discovery of giant NTE for reduced layered ruthenate. The total volume change related to NTE reaches 6.7% in dilatometry, a value twice as large as the largest volume change reported to date. We observed a giant negative coefficient of linear thermal expansion α=−115 × 10−6 K−1 over 200 K interval below 345 K. This dilatometric NTE is too large to be attributable to the crystallographic unit-cell volume variation with temperature. The highly anisotropic thermal expansion of the crystal grains might underlie giant bulk NTE via microstructural effects consuming open spaces in the sintered body on heating.

Negative thermal expansion of pure and doped graphene

Graphene and its derivatives distinguish themselves for their large negative thermal expansion even at temperatures as high as 1000 K.

Zero Thermal Expansion Achieved by an Electrolytic Hydriding Method in La(Fe,Si)13 Compounds

The La(Fe,Si)13‐based compounds have been recently developed as promising negative thermal expansion (NTE) materials by elemental substitution, which show large, isotropic and nonhysteretic NTE properties as well as relatively high electrical and thermal conductivities. In this paper, the La(Fe,Si)13 hydrides are prepared by a novel electrolytic hydriding method. Furthermore, the thermal expansion and magnetic properties of La(Fe,Si)13 hydrides are investigated by the variable‐temperature X‐ray diffraction and physical property measurement system. Fascinatingly, it is found that room‐temperature NTE properties and zero thermal expansion (ZTE) properties with broad operation‐temperature window (20–275 K) have been achieved after electrolytic hydriding. The further magnetic properties combined with theoretical analysis reveal that the improvements of NTE and ZTE properties in the La(Fe,Si)13 hydrides are ascribed to the variations of magnetic exchange couplings after hydrogenation. The present results highlight the potential applications of La(Fe,Si)13 hydrides with room‐temperature NTE and broad operation‐temperature window ZTE properties.

Dehydration phase transitions in new aluminium arsenate minerals from the Penberthy Croft mine, Cornwall, UK

AbstractBettertonite, [Al6(AsO4)3(OH)9(H2O)5]•11H2O and penberthycroftite, [Al6(AsO4)3(OH)9(H2O)5].8H2O, two new minerals from the Penberthy Croft mine, Cornwall, have flexible layer structures based on corner-connected heteropolyhedral columns. Their response to dehydration on heating was studied using in situ synchrotron powder X-ray diffraction at temperatures in the range -53 to 157°C. The bettertonite sample transforms to penberthycroftite in a narrow temperature range of 67 to 97°C with a large (8%) contraction of the layer separation and a 6 Å sliding of adjacent layers relative to each other. Above 100°C a second phase transition occurs to a DL (displaced layer) phase, involving another 8% inter-layer contraction combined with a rotation of the columns. On heating the penberthycroftite sample the phase transition to the DL phase occurs at a lower temperature of ∼80°C. The DL phase is stable to a temperature of ∼120°C. At higher temperatures, increased rotation of the columns is accompanied by a progressive amorphization of the sample. Bettertonite, penberthycroftite and the DL phase exhibit negative thermal expansion (NTE) along all three axes with large NTE coefficients, of the order of-100 x 10 -6 °C-1.

Structural properties of hypothetical CeBa2Cu3O7 compound from LSDA+DMFT calculations

AbstractThe hypothetical stoichiometric CeBa2Cu3O7 (Ce123) compound, which has not been synthesized as a single phase yet, was studied by the density functional theory (DFT). We utilized a method which merges the local spin density approximation (LSDA) with the dynamical mean-field theory (DMFT) to account for the electronic correlations. The LSDA+DMFT calculations were performed in the high-temperature range. The particular emphasis was put on the pressure-induced changes in the electronic band structure related to strongly correlated 4f states. The computational results indicate the occurrence of a large negative volumetric thermal expansion coefficient near T = 500 K and a trace of a low-volume isostructural metastable state at high temperatures.

Perovskite-Like Polar Lanthanide Formate Frameworks of [NH2NH3][Ln(HCOO)4] (Ln = Tb-Lu and Y): Synthesis, Structures, Magnetism, and Anisotropic Thermal Expansion.

A series of isostructural hydrazinium lanthanide (Ln) formate framework compounds of [NH2NH3][Ln(HCOO)4] for Ln3+ ions from Tb3+ to Lu3+ and Y3+ have been successfully prepared by utilizing NH2NH3+. The compounds crystallize in orthorhombic polar space group Pca21, with cell parameters at 180 K of a = 18.2526(7)-18.1048(5) Å, b = 6.5815(2)-6.5261(2) Å, c = 7.6362(3)-7.5044(2) Å, and V = 917.33(6)-886.67(4) Å3, showing the effect of lanthanide contraction. The compounds possess polar perovskite-like structures incorporating the hydrazinium cations in the cavities of the NaCl-like framework, in which the Ln3+ ions in a bicapped trigonal prism are connected by anti-anti and syn-anti formate groups. The N-H···Oformate hydrogen-bonding interactions are between the hydrazinium cations and the anionic framework. One anti-anti formate group is frustrated by the competitive N-H···Oformate hydrogen-bonding interactions. It thus twists or flips upon warming, resulting in large anisotropic thermal expansion and negative thermal expansion below 180 K. A comparison with the transition metal and magnesium analogues revealed that the structural compactness, tighter binding of the hydrazinium cation by the framework, and symmetrically better match between the framework and ammonium cation for Ln compounds could inhibit the occurrence of phase transition in the series. The IR spectroscopic, thermal, and magnetic properties are investigated.

Lattice dynamics and anharmonicity of CaZrF6 from Raman spectroscopy and ab initio calculations

Very recently it has been found that CaZrF6 exhibits a very large and isotropic negative thermal expansion (NTE), even greater than the current most popular NTE materials. In this work, the vibrational dynamics of CaZrF6 has been investigated by temperature-dependent Raman spectroscopy combined with ab initio calculations. As expected on the basis of the group theory for CaZrF6, three Raman-active modes were identified: the F2g mode peaked at about 236 cm−1, the Eg mode at around 550–555 cm−1, and the Ag mode peaked at about 637 cm−1. The temperature dependence of their frequencies follows an unusual trend: the F2g mode, due to bending vibrations of fluorine atoms in the linear Ca-F-Zr chain, is hardened with increasing temperature, while the Ag mode, corresponding to Ca-F-Zr bond stretching vibrations, is softened. We explain this anomalous behavior by separating implicit and explicit anharmonicity for both F2g and Ag modes. In fact, cubic anharmonicity (three-phonon processes) is observed to dominate the higher-frequency Ag phonon-mode, quartic anharmonicity (four-phonon processes) is found to dominate the lower-frequency F2g phonon-mode. As a result, the large NTE of CaZrF6 cannot be accurately predicted through the quasi-harmonic approximation.

Thermal and Gas Dual-Responsive Behaviors of an Expanded UiO-66-Type Porous Coordination Polymer.

Through a modified solvothermal reaction using benzoic acid as an additive, the fcu-type framework [Zr6 O4 (OH)4 (edba)6 ] (H2 edba=4,4'-(ethyne-1,2-diyl)dibenzoic acid), an expanded version of UiO-66, is synthesized as high-quality single crystals, which can retain their single-crystallinity after solvent exchange and degas treatments. In situ variable-temperature single-crystal X-ray diffraction measurements show that the guest-free framework exhibits a remarkably large isotropic negative thermal expansion (α=-11.0×10-6 K-1 ) as a result of the transverse vibrational bending of the long organic ligand. By virtue of the relatively large π-conjugation system of the organic ligand, [Zr6 O4 (OH)4 (edba)6 ] also exhibits bright blue luminescence, which can be quenched efficiently by gaseous O2 (Ksv =2.4 bar-1 ).

Magnetocaloric and negative thermal expansion effects for Ni55.5Mn19.5Ga25 Heusler alloy with magneto-structural transition

In the present work, the crystal structure, transforming property, magnetocaloric and negative thermal expansion effects were investigated in polycrystalline Ni55.5Mn19.5Ga25 alloy, respectively. The structure measurement indicates that it possesses unmodulated martensitic structure (L10) at room temperature. Here, the present alloy shows a first-order magneto-structural transformation from paramagnetic (PM) austenite to ferromagnetic (FM) martensite on cooling. Benefiting from this transformation, a considerable refrigerant capacity (RC) with a value of about 55 J/kg K was obtained around room temperature for the magnetic field change of 3 T. Moreover, the unique negative thermal expansion (NTE) effect was observed not only for the transforming range, but also for the pure martensitic state of the studied alloy. As distinct from a large NTE effect caused by magneto-structural transformation, such an effect at martensite is not accompanied by any thermal hysteresis, performing an excellently linear feature with a coefficient over 8 × 10−6/K within a broad temperature range (from 250 K to 50 K).

Ab initio molecular dynamics simulations of the Sc K-edge EXAFS of scandium trifluoride

Scandium fluoride ScF3 has a simple cubic structure and attracts attention due to its large negative thermal expansion (NTE) over a wide range of temperatures (0-1100 K). In this study we present ab initio molecular dynamics (AIMD) simulations of ScF3 and their validation using the Sc K-edge EXAFS spectra in the temperature range from 300 K to 1000 K measured at the XAFS beamline of ELETTRA. The obtained results allow an assessement of the employed AIMD model and provide insight into the local structure and the lattice dynamics of ScF3 beyond the harmonic approximation. A strong anisotropy of the fluorine atom vibrations in the direction orthogonal to the -Sc-F-Sc- chain is observed. An expansion of the ScF6 octahedra is found upon increasing temperature despite of the overall NTE of the crystal.

Negative thermal expansion and magnetostriction in the frustrated spinel ZnCr2(Se1−xSx)4 (0 ≤ x ≤ 0.1)

The bond-frustrated ZnCr2Se4 displays strong spin-lattice coupling characterized by large magnetostriction and negative thermal expansion. Here, we report on systematic investigations on the magnetization, heat capacity, thermal expansion and magnetostriction of single crystalline ZnCr2(Se1−xSx)4 (0 ⩽ x ⩽ 0.1) to study the evolution of its spin-lattice coupling with sulfur substitution. We show that with increasing sulfur content, the antiferromagnetic ordering is gradually replaced by a spin-glass state, the temperature region of the negative thermal expansion expands, and the magnetostriction is gradually suppressed. These phenomena are explained qualitatively by taking into account the enhancement of the antiferromagnetic interactions and bond disorder introduced by sulfur substitution.