Large Negative Thermal Expansion Coefficient Research Articles

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.

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.

Program multi-directional thermal expansion in a series of bending dominated mechanical metamaterials

Most metamaterials based on the bi-material curved beam (BC) were designed through hinge joints and presented only a unidirectional programmable coefficient of thermal expansion (CTE). Here, by contrast, a series of mechanical metamaterials based on the beam BC are originally devised with fixed joints. Moreover, by integrating the triangular, quadrilateral and hexagon configurations with rotational symmetry, these metamaterials could exclusively program the CTE in multiple directions. The explicit expressions of the relative densities are theoretically established. It is shown that increasing the parameter L1/h and reduction of the angle θ is beneficial to achieve light weight performance in these metamaterials. Besides, the closed-form expressions of the CTE are also theoretically derived and verified through numerical modeling. The analysis confirms that the CTE of the metamaterial in multiple directions can be well programmed to be either positive or negative values by rationally selecting the material combination and geometrical parameters. The CTEs vary linearly with the parameters L1 and θ, while show the parabolic variation with parameter m. In addition, the coupling relationships between the CTE and relative density are revealed and provide a guideline to achieve the large positive or large negative CTEs as well as light weight simultaneously. This work originally devises and analyzes a series of metamaterials of light weight and multi-directional customized CTE for engineering applications.

Giant Negative Thermal Expansion in Antiferromagnetic CrAs -Based Compounds

Materials featuring negative thermal expansion (NTE) attract attention due to their numerous applications in printed circuit boards, machinery, optical-fiber reflective grating devices, and high-precision mirrors. Unfortunately, most large samples of NTE material are very sensitive to external magnetic fields. To address this stumbling block, the authors chemically modify CrAs, which can turn antiferromagnetic and thus field-insensitive, and obtain a large NTE coefficient across a large range that includes room temperature. Electrons in $3d$ orbitals are responsible for NTE, accompanied by a first-order antiferromagnetic-paramagnetic transition.

Exploration of the high temperature phase evolution of electrochemically modified Sc2(WO4)3via potassium discharge

Electrochemical discharge followed by thermal treatment produces K2WO4 and other phases. K2WO4 features a large negative thermal expansion coefficient between 923–1023 K.

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.

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.

Effect of sintering technology in β-eucryptite ceramics: Influence on fatigue life and effect of microcracks

β-eucryptite ceramics with low negative or near-zero coefficient of thermal expansion (CTE) with excellent mechanical properties, such as Young's modulus ≥100GPa, have attracted attention for many important industrial applications. The extremely anisotropic thermal expansion behavior of this material leads to thermal residual stresses, and causes spontaneous microcracking. These microcracks cause large negative CTE with mechanical weaknesses. The appearance of microcracks is due to different factors. The most important are prolonged sintering time and heating source used.The present work shows experimentally the evolution of grain microcracks and residual stresses of the sintered β-eucryptite material going through many thermal fatigue cycles (∼3600). The effect of stresses applied on β-eucryptite crystals due to the thermal cycling could be considered for explaining the small change observed of β-eucryptite to β-spodumene phase, which is higher in the samples obtained by microwave sintering. Therefore, the study of residual stresses has suggested that the heating source employed, such as conventional or microwave, has a great influence on thermal fatigue life and the final mechanical and thermal properties. The microwave heating has a significant impact on β-eucryptite materials lifetime.

Negative thermal expansion in hybrid improper ferroelectric Ruddlesden-Popper perovskites by symmetry trapping.

We present new results on the microscopic nature of the ferroelectricity mechanisms in Ca3 Mn2O7 and Ca3Ti2O7. To the first approximation, we confirm the hybrid improper ferroelectric mechanism recently proposed by Benedek and Fennie for these Ruddlesden-Popper compounds. However, in Ca3Mn2O7 we find that there is a complex competition between lattice modes of different symmetry which leads to a phase coexistence over a large temperature range and the "symmetry trapping" of a soft mode. This trapping of the soft mode leads to a large uniaxial negative thermal expansion (NTE) reaching a maximum between 250 and 350 K (3.6×10^(-6) K^{-1}) representing the only sizable NTE reported for these and related perovskite materials to date. Our results suggest a systematic strategy for designing and searching for ceramics with large NTE coefficients.

Designing Microstructural Architectures With Thermally Actuated Properties Using Freedom, Actuation, and Constraint Topologies

In this paper, we demonstrate how the principles of the freedom, actuation, and constraint topologies (FACT) approach may be applied to the synthesis, analysis, and optimization of microstructural architectures that possess extreme or unusual thermal expansion properties (e.g., zero or large negative-thermal expansion coefficients). FACT provides designers with a comprehensive library of geometric shapes, which may be used to visualize the regions wherein various microstructural elements can be placed for achieving desired bulk material properties. In this way, designers can rapidly consider and compare a multiplicity of microstructural concepts that satisfy the desired design requirements before selecting the final concept. A complementary analytical tool is also provided to help designers rapidly calculate and optimize the desired thermal properties of the microstructural concepts that are generated using FACT. As a case study, this tool is used to calculate the negative-thermal expansion coefficient of a microstructural architecture synthesized using FACT. The result of this calculation is verified using a finite element analysis (FEA) package called ale3d.

In Situ Observation of Electrostatic and Thermal Manipulation of Suspended Graphene Membranes

Graphene is nature's thinnest elastic membrane, and its morphology has important impacts on its electrical, mechanical, and electromechanical properties. Here we report manipulation of the morphology of suspended graphene via electrostatic and thermal control. By measuring the out-of-plane deflection as a function of applied gate voltage and number of layers, we show that graphene adopts a parabolic profile at large gate voltages with inhomogeneous distribution of charge density and strain. Unclamped graphene sheets slide into the trench under tension; for doubly clamped devices, the results are well-accounted for by membrane deflection with effective Young's modulus E = 1.1 TPa. Upon cooling to 100 K, we observe buckling-induced ripples in the central portion and large upward buckling of the free edges, which arises from graphene's large negative thermal expansion coefficient.

Thermal expansion of Cu(II)O nano‐ and micro‐particles and composites at cryogenic temperatures

AbstractA systematic study of the thermal expansion of copper oxide (CuO) nanoparticles and copper oxide‐based composites, prepared by a range of techniques, was performed at cryogenic temperatures in the effort to reproduce recently reported giant negative coefficient of thermal expansion (CTE) of CuO nanoparticles. Chemically synthesized CuO nanoparticles, nanoparticles formed by ball milling of CuO material, CuO nanoparticles with differing surface functionalization, particles subjected to post‐treatments such as electron irradiation, and embedded into various resins or compacted at high pressures were studied by dilatometry and X‐ray diffraction (XRD) at temperatures between 20 and 300 K. None of the samples exhibited large negative CTE in the examined temperature range.

Low-Temperature Sintering of High-Strength β-Eucryptite Ceramics with Low Thermal Expansion Using Li2O-GeO2 as a Sintering Additive

Low-temperature sintering of high-strength β-eucryptite ceramics with low positive coefficient of thermal expansion (CTE) was attained using Li2O–GeO2 sintering additive. High-purity β-eucryptite could be synthesized using high-purity and fine amorphous silica, α-alumina, and lithium carbonate powder mixture at 950°C via the solid-state reaction route. Accordingly, the mixture was calcined at 900°C, pulverized, compacted, and sintered at 1020°C for 2 h with the sintering additive. The sintering temperature could be lowered by about 300°C, compared with the sintering temperature previously reported. The relative density of the sintered sample reached 99% of true density. Its flexural strength and indentation fracture toughness were 214 MPa and 2.5 MPa·m1/2, respectively. Its CTE (from room temperature to 800°C) was 1.2 × 10–6/K. Its dielectric constant was 5.5 with a loss tangent of 7.5 × 10–3. However, prolonged sintering time resulted in large negative CTE and mechanical weakness in the sintered samples. Microcracks were introduced with prolonged sintering time, which caused their large negative CTE with mechanical weakness.

Analytical Solutions to Estimate the Temperature Sensitivity of Arrayed Waveguide Gratings With Stress Plates

Controlling thermal stress is a promising way to reduce the temperature instability of arrayed waveguide gratings (AWGs). A simple method to apply thermal stress is to attach stress plates on the arrayed waveguides. In this paper, a general analytical method to study the temperature sensitivity of the central wavelength in modified AWGs with stress plates is developed. The complete analysis shows that the temperature sensitivity can be controlled effectively by tuning the material parameters and the thickness of the stress plates. To obtain athermal AWGs, a stress plate with large positive thermal expansion coefficient and small Young's modulus should be attached on the bottom of the arrayed waveguides. The material with large negative thermal expansion coefficient suggests another potential scheme.

Origin of the exceptional negative thermal expansion in metal-organic framework-5Zn4O(1,4−benzenedicarboxylate)3

Metal organic framework-5 (MOF-5) was recently suggested to possess an exceptionally large negative thermal-expansion coefficient. Our direct experimental measurement of the thermal expansion of MOF-5 using neutron powder diffraction, in the temperature range of 4 to 600 K, shows that the linear thermal-expansion coefficient is $\ensuremath{\approx}\ensuremath{-}16\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}\text{ }{\text{K}}^{\ensuremath{-}1}$. To understand the origin of this large negative thermal-expansion behavior, we performed first-principles lattice dynamics calculations. The calculated thermal-expansion coefficients within quasiharmonic approximation agree well with the experimental data. We found that almost all low-frequency lattice vibrational modes (below $\ensuremath{\sim}23\text{ }\text{meV}$) involve the motion of the benzene rings and the ${\text{ZnO}}_{4}$ clusters as rigid units and the carboxyl groups as bridges. These so-called ``rigid-unit modes'' exhibit various degrees of phonon softening (i.e., the vibrational energy decreases with contracting crystal lattice) and thus are directly responsible for the large negative thermal expansion in MOF-5. Initial efforts were made to observe the phonon softening experimentally.

Thermal Expansion and Phase Formation of ZrW2O8 Aerogels

Aerogels with the nominal composition ZrW 2 O 8 have been prepared by pore solvent exchange with liquid CO 2 followed by supercritical drying. These aerogels are amorphous and can be tailored to have extremely high surface areas. Thermal expansion is measured for the amorphous aerogel as well as the aerogel post thermal treatment. The cubic phase forms at 900 °C in less than 30 s. The cubic phase prepared this way has a large negative thermal expansion coefficient of -10.5 x 10 -6 °C -1 as shown by variable temperature X-ray diffraction.

Pressure-induced volume anomaly of intermediate valence compound Sm 0.9La 0.1S

Thermal expansion of intermediate valence compound Sm 0.9La 0.1S has been measured under high pressure up to 2.1 GPa in the temperature range, 4.2⩽ T⩽300 K. It is found that the thermal expansion shows a smooth variation below 0.5 GPa but an anomalously large expansion, i.e., a large negative thermal expansion coefficient is observed at low temperature above 0.5 GPa. These results are related to the pressure-induced metal–insulator transition. The negative anomaly in the thermal expansion coefficient is suggested to be due to the negative Grüneisen parameter of the energy gap.

Low-thermal-expansion copper composites via negative CTE metallic elements

Thermal management is an important issue in electronic packaging due to the increasing complexity, miniaturization, and high density of components in modern devices. In high-power-dissipation packages, heat sinks are essential for preventing thermal damage to heat-sensitive components on the silicon chip. However, commonly used heat-sink materials (e.g., copper and aluminum alloys) have a much higher coefficient of thermal expansion (CTE) than silicon. CTE mismatch between the various materials in an electronic package can lead to stresses that can trigger complex failure mechanisms like component distortion, stress rupture, thermomechanical fatigue, and creep, thereby seriously degrading device reliability and lifetime. Therefore, it is highly desirable to minimize the CTE mismatch by developing new heat-sink materials having CTEs that are close to the CTE of silicon. In this work, low-thermal-expansion copper composites with CTEs as low as 4 ppm/°C have been fabricated by employing a negative thermal-expansion alloy—equiatomic Ni-Ti, which has a CTE of approximately −21 ppm/°C. The use of negative CTE elements, especially those with very large negative CTE values, offers an attractive route for controlling the thermal-expansion behavior of various metallic and nonmetallic materials.

Activation Volume for Vacancy Motion in Calcium Fluoride

AbstractThe audio frequency complex dielectric constant for sodium doped calcium fluoride is measured at pressures up to 0.4 GPa over the temperature range 240 to 270 K and at zero pressure over the temperature range 5.5 to 400 K. Consequently, the reorientation of a nearest‐neighbor vacancy around a substitutional sodium ion is studied. The activation volume for the motion is found to be (1.73 ± 0.1) cm3/mol. It is argued that this value should be similar to the migration volume for “free” vacancies. The compressibility of the activation volume is found to be forty times the compressibility of the host lattice. Finally, a large negative thermal expansion coefficient is found for the activation volume for vacancy motion.

Studies on Crystallization of Glasses and Properties of Crystallized Glasses of System Li<sub>2</sub>O-MgO-CaO-Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub>-F

Studies on the crystallization of the glasses and the properties of crystallized glasses having the composition {Li2Ca (Mg5-xAlx) (AlxSi8-x) O22F2} were carried out. Those compositions were obtained by the isomorphous substitution of the F-richterite composition {Na⋅NaCa⋅Mg5⋅Si8O22F2}.The results obtained were summarized as follows:1) The crystallized glasses having the compositions of Li2Ca(Mg3Al2)(Al2Si6) O22F2+0.75, 1.0, 2.5mol Li2O heat-treated at 950°C for 2-3 hours had very large negative thermal expansion coefficients and their crystalline phases were mainly β-quartz (ss).2) Accoding to J. Petzoldt, the crystallized glass having the composition of eucryptite (LiAlSiO4) and heat-treated at higher temperatures has a larger negative thermal expansion goefficient (at 900°C α≈-10×10-7/°C at 1000°C α≈-70×10-7/°C). β-quartz (ss) precipitated at higher temperature in the glass having the composition of eucryptite has larger lattice constant chex, so that from the value of lattice constant chexof β-quartz (ss) the value of thermal expansion coefficient of β-quartz (ss) may be presumed. In this investigation, β-quartz (ss) precipitated at 900°C in the glasses containing more than 0.75mol excess Li2O had larger lattice constants chex than that of precipitated at 900°C in the glass having the composition of eucryptite, and β-quartz (ss) precipitated in the glass containing more than 1.0mol excess Li2O had nearly the same value of lattice constant chex as β-eucryptite.3) In the glass having the composition {Li2Ca(Mg4Al)(AlSi7)O22F2}, the crystallization started at the glass surface and the strength of the crystallized glasses, heat-treated at relatively lower temperature, increased with treating time.