Positive Thermal Expansion Research Articles

Balancing negative and positive thermal expansion effect in dual-phase La(Fe,Si)13/α-Fe in-situ composite with improved compressive strength

Materials with near-zero thermal expansion are helpful in improving the reliability of devices. One way to synthesize such materials is mixing material showing positive thermal expansion with that displaying negative thermal expansion. Large negative thermal expansion has been widely observed in NaZn13-type La(Fe,Si)13-based alloys during the magnetic transition. It suggests that these materials have potential applications as thermal-expansion compensators. However, how to compensate the negative thermal expansion and simultaneously improve its strength are two considerable questions. Here, we introduce in-situ precipitated α-Fe phase to compensate the negative thermal expansion of 1:13 phase, and thus achieve a near-zero thermal expansion in La(Fe,Si)13/α-Fe in-situ composite. On the other hand, the distributed ductile α-Fe phase greatly enhances the compressive strength, solving the brittleness problem of 1:13 phase. The yield compressive stress of the in-situ composite with near-zero thermal expansion reaches 970 MPa. This work opens up an effective way to the design of materials with both near-zero thermal expansion and improved strength.

Controlling Thermal Expansion Behaviors of Fence-Like Metal-Organic Frameworks by Varying/Mixing Metal Ions.

Solvothermal reactions of 3-(4-pyridyl)-benzoic acid (Hpba) with a series of transition metal ions yielded isostructral metal-organic frameworks [M(pba)2]·2DMA (MCF-52; M = Ni2+, Co2+, Zn2+, Cd2+, or mixed Zn2+/Cd2+; DMA = N,N-dimethylacetamide) possessing two-dimensional fence-like coordination networks based on mononuclear 4-connected metal nodes and 2-connected organic ligands. Variable-temperature single-crystal X-ray diffraction studies of these materials revealed huge positive and negative thermal expansions with |α| > 150 × 10−6 K−1, in which the larger metal ions give the larger thermal expansion coefficients, because the increased space not only enhance the ligand vibrational motion and hinged-fence effect, but also allow larger changes of steric hindrance between the layers. In addition, the solid-solution crystal with mixed metal ions further validates the abundant thermal expansion mechanisms of these metal-organic layers.

Twin Crystal Induced near Zero Thermal Expansion in SnO2 Nanowires.

Knowledge of controllable thermal expansion is a fundamental issue in the field of materials science and engineering. Direct blocking of the thermal expansions in positive thermal expansion materials is a challenging but fascinating task. Here we report a near zero thermal expansion (ZTE) of SnO2 achieved from twin crystal nanowires, which is highly correlated to the twin boundaries. Local structural evolutions followed by pair distribution function revealed a remarkable thermal local distortion along the twin boundary. Lattice dynamics investigated by Raman scattering evidenced the hardening of phonon frequency induced by the twin crystal compressing, giving rise to the ZTE of SnO2 nanowires. Further DFT calculation of Grüneisen parameters confirms the key role of compressive stress on ZTE. Our results provide an insight into the thermal expansion behavior regarding to twin crystal boundaries, which could be beneficial to the applications.

Mesopores induced zero thermal expansion in single-crystal ferroelectrics

For many decades, zero thermal expansion materials have been the focus of numerous investigations because of their intriguing physical properties and potential applications in high-precision instruments. Different strategies, such as composites, solid solution and doping, have been developed as promising approaches to obtain zero thermal expansion materials. However, microstructure controlled zero thermal expansion behavior via interface or surface has not been realized. Here we report the observation of an impressive zero thermal expansion (volumetric thermal expansion coefficient, −1.41 × 10−6 K−1, 293–623 K) in single-crystal ferroelectric PbTiO3 fibers with large-scale faceted and enclosed mesopores. The zero thermal expansion behavior is attributed to a synergetic effect of positive thermal expansion near the mesopores due to the oxygen-based polarization screening and negative thermal expansion from an intrinsic ferroelectricity. Our results show that a fascinating surface construction in negative thermal expansion ferroelectric materials could be a promising strategy to realize zero thermal expansion.

Realization of zero thermal expansion in La(Fe,Si)13-based system with high mechanical stability

A stable, zero thermal expansion material with enhanced mechanical properties was achieved by introducing in-situ secondary phases into a La(Fe,Si)13 matrix. In the Cu-doped LaFe10.6-xCuxSi2.4 system, a large amount of 1:1:1 and α-Fe phases are also clearly found, except for cubic 1:13 phase. With the increase of Cu-content, the number of precipitated phases increased gradually. Due to the positive thermal expansion of the secondary phases, the effect of the negative thermal expansion was compensated for in the composites. For the LaFe10.1Cu0.5Si2.4 sample, a low thermal expansion coefficient, about 2.8×10−7K−1, was achieved between 185 and 250K. This near-zero thermal expansion effect also showed high reversibility with the temperature variation because of the characteristics of second-order transitions. Moreover, the compressive yield strengths of the composites were improved, owing to the strengthening mechanism of the secondary phases. The enhancement of the mechanical properties impeded the degradation of geometric integrity and promoted the mechanical stability during cyclic thermal measurements. This work supports the design of Invar-type materials with low structural fatigue for technological application.

Giant Thermal Expansion in 2D and 3D Cellular Materials.

When temperature increases, the volume of an object changes. This property was quantified as the coefficient of thermal expansion only a few hundred years ago. Part of the reason is that the change of volume due to the variation of temperature is in general extremely small and imperceptible. Here, abnormal giant linear thermal expansions in different types of two-ingredient microstructured hierarchical and self-similar cellular materials are reported. The cellular materials can be 2D or 3D, and isotropic or anisotropic, with a positive or negative thermal expansion due to the convex or/and concave shape in their representative volume elements respectively. The magnitude of the thermal expansion coefficient can be several times larger than the highest value reported in the literature. This study suggests an innovative approach to develop temperature-sensitive functional materials and devices.

Thermal expansion coefficient measurement from electron diffraction of amorphous films in a TEM

We measured the linear thermal expansion coefficients of amorphous 5–30 nm thick SiN and 17 nm thick Formvar/Carbon (F/C) films using electron diffraction in a transmission electron microscope. Positive thermal expansion coefficient (TEC) was observed in SiN but negative coefficients in the F/C films. In case of amorphous carbon (aC) films, we could not measure TEC because the diffraction radii required several hours to stabilize at a fixed temperature.

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.

Joint Experimental and Computational Investigation of the Flexibility of a Diacetylene‐Based Mixed‐Linker MOF: Revealing the Existence of Two Low‐Temperature Phase Transitions and the Presence of Colossal Positive and Giant Negative Thermal Expansions

Solvothermal reaction in N,N-dimethylformamide (DMF) between 1,6-bis(1-imidazolyl)-2,4-hexadiyne monohydrate (L1⋅H2 O), isophthalic acid (H2 L2), and Zn(NO3 )2 ⋅6 H2 O gives the diacetylene-based mixed-ligand coordination polymer {[Zn(L1)(L2)](DMF)2 }n (UMON-44) in 38 % yield. Combination of DSC with variable-temperature single-crystal X-ray diffraction revealed the occurrence of two phase transitions spanning the ranges 129-144 K and 158-188 K. Furthermore, the three structurally similar phases of UMON-44 show giant negative and/or colossal positive thermal expansions. These unusual phenomena exist without any change in the contents of the unit cell. DFT calculations using the PBE+D3 dispersion scheme were able to distinguish between these polymorphs by accurately reproducing their salient structural features, although corrections in the size of the unit cell turned out to be necessary for the high-temperature phase to account for its large thermal expansion. In addition, the infrared spectra (vibration frequencies and peak intensities) of these theoretical models were calculated, allowing for univocal identification of the corresponding polymorphs. Last, the limits of our computational method were tested by calculating the phase transition temperatures and their associated enthalpies, and the derived figures compare favorably with the values determined experimentally.

Correction: A combined stretching-tilting mechanism produces negative, zero and positive linear thermal expansion in a semi-flexible Cd(ii)-MOF.

Correction for 'A combined stretching-tilting mechanism produces negative, zero and positive linear thermal expansion in a semi-flexible Cd(ii)-MOF' by Prem Lama et al., Chem. Commun., 2014, 50, 6464-6467.

Negative/zero thermal expansion in black phosphorus nanotubes.

Black phosphorus nanotubes (BPNTs) as new 1D materials have very promising prospects in nanoelectronic devices. Taking into account that the effect of finite temperature on nanoelectronic devices is indispensable, we perform a comprehensive first-principles study of thermal expansion of BPNTs. It is surprisingly found that the thermal expansion can be tuned from positive thermal expansion (PTE) to zero thermal expansion (ZTE) and even to negative thermal expansion (NTE) by changing the diameter and bonding in the unique configurations of armchair and zigzag BPNTs. The thermal expansion of zigzag BPNTs is diameter independent, in contrast, the size effect of thermal expansion is evidently presented in the armchair BPNTs. Accordingly, it is more manageable to adjust the coefficient of thermal expansion (CTE) in the armchair BPNTs. Unusual phonon hardening with the increase of temperature can be detected in both types of nanotubes. The unique dynamical modes and different vibrational amplitudes are analyzed. Underlying physical mechanisms have been explored. This work can provide some inspiration for exploring the abnormal thermal expansion in nanotubes and how to regulate these properties.

Switching from positive to negative axial thermal expansion in two organic crystalline compounds with similar packing.

Switching from positive to negative axial thermal expansion in pure organic materials is reported for the first time. This rare phenomenon has been rationalized based on the packing of molecules in crystal structures and transverse thermal vibrations of atoms in the molecule. Unique packing of the molecules in the crystal structure contributes to the restricted movement of molecules along the c axis. Subsequently, contraction of molecular dimensions with increasing temperature, due to transverse vibrations of some atoms, assists with the switch from Positive Thermal Expansion (PTE) to Negative Thermal Expansion (NTE).

Designing anisotropic cyanometallate coordination polymers with unidirectional thermal expansion (TE): 2D zero and 1D colossal positive TE.

Oxidative addition of halogens to tetracyanoplatinate results in the formation of a Pt(iv)-building block that, combined with Cu(ii), forms coordination polymers Cu(H2O)2[PtX2(CN)4] (X = Br, Cl). These materials exhibit directional anisotropic thermal expansion: nearly zero expansion within the cyanometallate sheets and positive thermal expansion in the third dimension.

Experimental and theoretical evidence of a supercritical-like transition in an organic semiconductor presenting colossal uniaxial negative thermal expansion.

Thermal expansion coefficients of most materials are usually small, typically up to 50 parts per million per kelvin, and positive, i.e. materials expand when heated. Some materials show an atypical shrinking behavior in one or more crystallographic directions when heated. Here we show that a high mobility thiophene-based organic semiconductor, BHH-BTBT, has an exceptionally large negative expansion between 95 and 295 K (-216 < α2 = αb < -333 MK-1), being compensated by an even larger positive expansion in the perpendicular direction (287 < α1 < 634 MK-1). It is shown that these anomalous expansivities are completely absent in C8-BTBT, a much studied organic semiconductor with a closely related molecular formula and 3D crystallographic structure. Complete theoretical characterization of BHH-BTBT using ab initio molecular dynamics shows that below ∼200 K two different α and β domains exist of which one is dominant but which dynamically exchange around and above 210 K. A supercritical-like transition from an α dominated phase to a β dominated phase is observed using DSC measurements, UV-VIS spectroscopy, and X-ray diffraction. The origin of the extreme negative and positive thermal expansion is related to steric hindrance between adjacent tilted thiophene units and strongly enhanced by attractive S···S and S···C interactions within the highly anharmonic mixed-domain phase. This material could trigger the tailoring of optoelectronic devices highly sensitive to strain and temperature.

Magnetic layered perovskites of [CH3C(NH2)2]2[M(HCOO)4] (M = Co2+ and Ni2+): synthesis, structures and properties.

We present two layered perovskites of the formula [CH3C(NH2)2]2[M(HCOO)4] (M = Co and Ni). The two materials are isostructural and crystallize in the orthorhombic space group Pccn. The structures consist of anionic 100-oriented perovskite or square metal-formate layers and interlayer [CH3C(NH2)2]+ cations. In each layer octahedral M2+ ions are linked by equatorial anti-anti HCOO- bridges and are further coordinated by apical monodentate HCOO- groups. The interlayer acetamidinium cations form N-HO H-bonds with the anionic layers to support the 3D structure. As the directions of most vibrations of the interlayer atoms are approximately along the a-axis, the two materials exhibit nearly zero thermal expansion (a few (MK)-1) along the b-direction perpendicularly to the layers and positive thermal expansion along the a- (∼40 (MK)-1) and c- (∼20 (MK)-1) axes parallel to the layers. They are both weak ferromagnets, and the Néel temperatures are 6.0 K and 17.0 K for M = Co and Ni, respectively. The Co compound exhibited high spontaneous magnetization of 444 cm3 G mol-1 under a field of 10 Oe and an unusually low coercive field of 38 Oe at 2 K. IR spectroscopic, thermal and dielectric properties were investigated.

Neutron diffraction studies on the thermal expansion and anomalous mechanics in the perovskite-type [C(ND2)3]Me2+(DCOO)3 [Me = Cu, Mn, Co

The thermomechanical characteristics of [C(ND2)3]Me2+(DCOO)3 [Me = Cu, Co, Mn] have been evaluated by single-crystal and powder neutron diffraction. [C(ND2)3]Cu2+(DCOO)3, presenting with the polar space group Pna21, exhibits lattice expansion along the a and c axes, while the b-axis shows a crossover from negative to positive thermal expansion. The relative change in lattice parameters is independent in all directions, resulting in anisotropic thermal characteristics. The thermomechanical response is a collective effect of hingeing and deformation, with the former as the dominant factor. In this study, every individual hinge and strut are evaluated, unlike the conventional averaging of the mechanical units. The Mn cousin displays a higher magnitude of octahedral tilting than the Co-twin. Such an effect has direct consequences on higher expansivity for manganese guanidinium formate along all directions. Hingeing is the dominant factor in both Mn and Co-twins, with their relative values much closer than reported earlier.

Auxetics and Other Systems of Anomalous Characteristics

Auxetics and Other Systems of Anomalous Characteristics

Auxetic and Negative Thermal Expansion Structure Based on Interconnected Array of Rings and Sliding Rods

An exploration by analytical method has been made herein for a mechanism‐based structure that involves a two‐dimensional array of rings and a three‐dimensional array of double‐rings, with short fixed rods and long sliding rods attached at the outer and inner surfaces of the rings, respectively. Based on the theory of thin rings, effective Poisson's ratio and effective coefficient of thermal expansion (CTE) models have been obtained for single‐ring structures, pole‐loaded double‐ring structures, and equator‐loaded double‐ring structures. Results establish a very strong correlation between these effective properties with the ring radius and rod lengths. In addition, the analysis of four of the double‐ring structures reveals that the sign of Poisson's ratio is dependent on the direction of loading. An example application is demonstrated herein in which positive thermal expansion rings, used in conjunction with rigid rods, enable the design of an overall zero thermal expansion structure (i.e., minimal thermal stress) with tunable negative thermal expansion internal microstructure for use as sieve. Finally, it is herein shown that, by judicious positioning of the short fixed rods and/or long sliding rods, one may possibly obtain various combinations of positive and negative CTEs with positive and negative Poisson's ratio.

Crystal chemistry and thermal behavior of La doped (U, Th)O2

X-ray diffraction, chemical and thermal studies of [(U0.2Th0.8)1-yLay]O2+x (LUTL) and [(U0.3Th0.7)1-yLay]O2+x (UTL); compounds (where y ≤ 0.4) were carried out. These compounds were synthesized by gel combustion method followed by heating in reduced atmospheres at 1673 K. To co-relate lattice parameters with metal and oxygen concentrations, reduced oxides were heated in Ar, CO2 and air atmospheres. Retention of FCC phase was confirmed in all mixed oxides with y ≤ 0.4. The cubic lattice parameters could be expressed in a linear equation of x and y as:a (Ǻ) = 5.5709 − 0.187 x + 0.032 y; [x < 0 and 0 ≤ y ≤ 0.40] for LUTL anda (Ǻ) = 5.5580 − 0.26 x + 0.015 y; [x < 0 and 0 ≤ y ≤ 0.36] for UTL.Oxidation studies and simple ionic model calculations suggested that uranium is predominantly present as a mixture of +5 and + 6 states when La/U ratio ∼2. Oxidation kinetics of mixed oxides was studied by non-isothermal method using thermogravimetry and was found to be a diffusion controlled reaction. High temperature X-ray diffraction studies of LUTL and UTL mixed oxides showed positive thermal expansion in the temperature range of 298–1273 K and % expansion increases with La concentration.

Spin crossover-induced colossal positive and negative thermal expansion in a nanoporous coordination framework material

External control over the mechanical function of materials is paramount in the development of nanoscale machines. Yet, exploiting changes in atomic behaviour to produce controlled scalable motion is a formidable challenge. Here, we present an ultra-flexible coordination framework material in which a cooperative electronic transition induces an extreme abrupt change in the crystal lattice conformation. This arises due to a change in the preferred coordination character of Fe(II) sites at different spin states, generating scissor-type flexing of the crystal lattice. Diluting the framework with transition-inactive Ni(II) sites disrupts long-range communication of spin state through the lattice, producing a more gradual transition and continuous lattice movement, thus generating colossal positive and negative linear thermal expansion behaviour, with coefficients of thermal expansion an order of magnitude greater than previously reported. This study has wider implications in the development of advanced responsive structures, demonstrating electronic control over mechanical motion.