Unusual Thermal Properties Research Articles

Kirigami-Inspired Three-Dimensional Metamaterials with Programmable Isotropic and Orthotropic Thermal Expansion.

Mechanical metamaterials with specifically designed cells can provide unusual thermal expansion properties for diverse applications. Limited by very few available cell topologies and complicated non-linear structural deformation, most existing thermal expansion metamaterials can only achieve orthogonally isotropic negative/zero/positive thermal expansion (NTE/ZTE/PTE) within a mild range, especially the 3D ones. Here, based on one-degree-of-freedom kirigami polyhedrons proposed with a kinematic design strategy, a family of 3D isotropic and orthotropic metamaterials capable of programmable NTE, PTE, and even ZTE over ultra-wide range is developed. Incorporating bi-material strips as creases for isotropic polyhedrons, NTE and PTE metamaterials with coefficients of thermal expansion (CTEs) ranging from -2354.3 to 3006.7ppm/°C are designed and programmed by the theoretical model. Meanwhile, isotropic ZTE metamaterials are constructed by either homogeneous tessellation of ZTE cells or hybrid tessellation of NTE and PTE cells. Furthermore, by allowing distinct geometric parameters in the three orthogonal directions of the kirigami polyhedrons while preserving the kinematic motion, orthotropic metamaterials, in which each of the three directions can be assigned with an independently programmed NTE, ZTE, or PTE, are also achieved. This study paves a novel pathway for the development of thermal expansion metamaterials with potential applications for space optical systems, MEMS, and so on.

Morphological analysis of polydisperse nanoplatelets using SAXS

Two-dimensional materials like graphene and boron nitride find applications in numerous innovations thanks to their high specific surface area and unusual electrical, thermal and optical properties. These materials are often produced via liquid-phase exfoliation, yielding nanoplatelets with a high degree of polydispersity. Unfortunately, methods for the characterization of both lateral dimension and thickness for dispersed polydisperse nanoplatelets are still lacking. In this work, a fast and quantitative method for the characterization of polydisperse nanoplatelets in dispersion is proposed using the example of graphene nanoplatelets (GNPs). The method is benchmarked using well-defined gibbsite nanoplatelets. Synchrotron small-angle X-ray scattering (SAXS) is used to probe the structure of the platelets over a wide range of length scales. The SAXS data are fitted with a polydisperse form factor for discs, which yields size distributions in both thickness and diameter. Benchmarking the procedure with the gibbsite model system shows excellent agreement between the SAXS results and previous transmission electron microscopy and atomic force microscopy data. The method is also successfully applied to GNPs from 1–60 layers in thickness and 20–2000 nm in diameter. We believe that this work brings reliable quantitative in situ characterization, for instance during preparation, of nanoplatelet dispersions within reach.

Insights into a New Multi‐Stimuli‐Responsive Photochromic Metal‐Organic Framework: Highly Sensitive Turn‐On Luminescence in a Lanthanum Phosphonate

AbstractThe new microporous metal organic framework [La2(H2O)5(H2TPPE)]·3H2O (CAU‐54), is obtained in a hydrothermal reaction of the linker 1,1,2,2‐tetrakis(4′‐phosphonophenyl)ethylene (H8TPPE) and La3+ ions. The extensive characterization including temperature‐dependent crystal structures and spectroscopic properties allowed to understand the unique, multi‐responsive material properties. CAU‐54 exhibits rarely observed reversible photochromism as well as turn‐on photoluminescence by various external chemical or physical stimuli including change of pressure, solvent exchange, and temperature variation. These properties can be unequivocally assigned to the presence of tetraphenylethylene (TPE) moieties of the linker molecules within the MOF, i.e., the ordered spatial arrangement of the linker molecules, the presence of accessible pores as well as the coordination flexibility of the phosphonate groups and the rotational freedom of the linker. By temperature‐dependent steady‐state and time‐resolved luminescence studies, it is shown that this compound exhibits a) blue fluorescence that becomes effectively quenched at room temperature, b) green efficient luminescence with thermal stability up to 400 K, and c) red phosphorescence correlated to the observed photochromism. In addition, CAU‐54 shows unusual thermal expansion properties as shown by temperature‐dependent powder X‐ray diffraction measurements with identified transition points that correlate with the observed temperature‐dependent changes in the photoluminescence.

Multifunctional single-component organic molecular materials: ferroelectricity, negative thermal expansion, and polymorphism

The evolution of research on ferroelectricity and unusual thermal expansion properties in organic molecular crystals and their existence in polymorphic forms have been highlighted to pinpoint the importance of such materials in organic electronics.

Electronic origin of the unusual thermal properties of copper-based semiconductors: The s-d coupling-induced large phonon anharmonicity

Electronic origin of the unusual thermal properties of copper-based semiconductors: The s-d coupling-induced large phonon anharmonicity

Multihyperuniform long-range order in medium-entropy alloys

Medium-entropy alloys (MEAs) and high-entropy alloys (HEAs) are alloys composed of mixtures of equal or relatively large proportions of three or more elements, and are distinctly different from traditional metallic alloys which contain one or two major components with smaller amounts of other elements. Recently MEAs and HEAs have received extensive research attention because they are found to possess superior mechanical performance, unusual thermal and electronic transport properties, and are resistant to corrosion; however, a fundamental understanding of the atomic structures of these alloys is still largely lacking. In this work, we develop a multihyperuniform (MH) model for disordered medium-entropy alloys (MEAs), in which the normalized infinite-wavelength composition fluctuations for all atomic species are completely suppressed, i.e., a model with hidden long-range order. Using SiGeSn alloy as a representative example, we show that this new type of highly efficient generic computational model results in stable lower-energy states compared to prevailing alloy models with (quasi)random structures, and captures experimentally observed atomic short-range orders in MEAs that are missing in (quasi)random alloy models. The MH model approximately realizes the Vegard’s law, which offers a rule-of-mixture type predictions of the lattice constants and electronic band gap, and thus can be considered as an ideal mixing state. The multihyperuniformity also directly gives rise to enhanced electronic band gaps and superior thermal transport properties at low temperatures compared to (quasi)random structures, which open up novel potential applications in optoelectronics and thermoelectrics. Our MH model can be readily applied and generalized to other medium- and high-entropy alloys (HEAs) with atomic short-range orders, and may account for some of the previously observed major discrepancies between theory and experiment.

Dynamic morphological transformations in soft architected materials via buckling instability encoded heterogeneous magnetization

The geometric reconfigurations in three-dimensional morphable structures have a wide range of applications in flexible electronic devices and smart systems with unusual mechanical, acoustic, and thermal properties. However, achieving the highly controllable anisotropic transformation and dynamic regulation of architected materials crossing different scales remains challenging. Herein, we develop a magnetic regulation approach that provides an enabling technology to achieve the controllable transformation of morphable structures and unveil their dynamic modulation mechanism as well as potential applications. With buckling instability encoded heterogeneous magnetization profiles inside soft architected materials, spatially and temporally programmed magnetic inputs drive the formation of a variety of anisotropic morphological transformations and dynamic geometric reconfiguration. The introduction of magnetic stimulation could help to predetermine the buckling states of soft architected materials, and enable the formation of definite and controllable buckling states without prolonged magnetic stimulation input. The dynamic modulations can be exploited to build systems with switchable fluidic properties and are demonstrated to achieve capabilities of fluidic manipulation, selective particle trapping, sensitivity-enhanced biomedical analysis, and soft robotics. The work provides new insights to harness the programmable and dynamic morphological transformation of soft architected materials and promises benefits in microfluidics, programmable metamaterials, and biomedical applications.

Review on 3D Fabrication at Nanoscale

Abstract Among the different nanostructures that have been demonstrated as promising materials for various applications, three–dimensional (3D) nanostructures have attracted significant attention as building blocks for constructing high-performance nanodevices because of their unusual mechanical, electrical, thermal, optical, and magnetic properties arising from their novel size effects and abundant active catalytic/reactive sites due to the high specific surface area. Considerable research efforts have been devoted to designing, fabricating, and evaluating 3D nanostructures for applications, including structural composites, electronics, photonics, biomedical engineering, and energy. This review provides an overview of the nanofabrication strategies that have been developed to fabricate 3D functional architectures with exquisite control over their morphology at the nanoscale. The pros and cons of the typical synthetic methods and experimental protocols are reviewed and outlined. Future challenges of fabrication of 3D nanostructured materials are also discussed to further advance current nanoscience and nanotechnology.

ГЕНОТОКСИЧНОСТЬ МЕТАЛЛСОДЕРЖАЩИХ НАНОЧАСТИЦ

No more than 100 nm large, nanoparticles (NPs) are distinguished by unusual mechanical, electrical, optical, thermal and magnetic properties. They are used in biology, pharmacology, medicine, chemistry, physics, materials technology and engineering industry. Nanoparticles penetrate in organism through the skin, GIT and airways. Their genotoxicity depends on size, form, mode of action and composition. Two principal mechanisms of NPs genotoxicity are primary and secondary. The primary mechanism is realized in direct interaction with the genome; the secondary mechanism is achieved through mediation of the active forms of oxygen. NPs can modulate the epigenome by altering the gene functions and do not change the DNA sequence directly. Consequences of prolonged exposure to low NPs doses on the human organism still remain uninvestigated.

Reduced lattice thermal conductivity of perovskite-type high-entropy (Ca0.25Sr0.25Ba0.25RE0.25)TiO3 ceramics by phonon engineering for thermoelectric applications

The high-entropy effect suggests the possibility of unusual thermal transport properties that may be favorable for thermoelectrics. Novel perovskite-type high-entropy (Ca0.25Sr0.25Ba0.25La0.25)TiO3 (4La) and (Ca0.25Sr0.25Ba0.25Ce0.25)TiO3 (4Ce) ceramics were successfully prepared through a conventional solid-state reaction method. XRD, SEM-EDS, and HRTEM were performed to confirm that the chosen multi-component cations can be introduced into A-site to form a single cubic phase with Pm-3m space group. Introduce high-entropy engineering, constituent elements competing inter into the A-site creating lattice distortion and strain fields, which results in extensive structural defects including dislocations which contributed to the phonons scattering of mid wavelength. Grain boundaries and intrinsic oxygen vacancies respectively scatter phonons of high and low wavelengths. The enhanced effective scattering of phonons through the multi-scale defects gives rise to a low lattice thermal conductivity of 2.5 W·m−1·K−1 at 1073 K for the 4La ceramics, much lower than that of SrTiO3-based perovskite thermoelectric ceramics. The high-entropy 4La ceramics possess the maximum power factor of 420 μW·m−1·K−2. This work provides a strategy of compositional design for thermoelectric oxides with decreased intrinsic thermal conductivity for thermoelectric applications.

Design and additive manufacturing of thermal metamaterial with high thermal resistance and cooling capability

Abstract Metamaterials are defined as artificially designed micro-architectures with unusual physical properties, including optical, electromagnetic, mechanical, and thermal properties. This study proposes a thermal metamaterial that provides an efficient thermal cycle with two conflicting objectives: (i) high thermal resistance as a thermal insulator and (ii) high cooling capability as a heat exchanger. To enable these conflicting objectives, we used cellular lattice structures fabricated by additive manufacturing (AM). An efficient design method based on a finite element (FE) mesh was developed to obtain boundary-conformal lattices for arbitrary 3D shapes. FE analyses were then conducted to evaluate the structural and thermal behaviors of the lattice structures. The designed lattice structures were fabricated by powder-bed fusion (PBF) type AM using Ti-6Al-4V powders. Heat conduction tests were then performed to evaluate the thermal resistance of the lattices with various strut diameters, and the resulting thermal resistance increased five to fifteen times in comparison with that of the pure material. Cooling tests were also conducted to evaluate the cooling capability of the lattices, which showed that the lattice structures could act not only as a thermal insulator but also as a heat exchanger. Consequently, the developed lattice structures can be regarded as a thermal metamaterial that is useful in various applications that require a high thermal cycle of heating and cooling.

Impact of surface conditions changes on changes in thermodynamic properties of quasi 2D crystals

In continuation of our research regarding the phonon-induced properties of the low dimensional structures, we are investigating the impact of changes in boundary parameters onto the thermodynamic properties of the quasi 2D crystals (ultrathin films). Internal energy and thermal capacitance of the ultrathin film are theoretically analyzed and numerically and graphically presented for the various combinations of boundary surface parameters. This research is motivated by efforts to explain many unusual thermal properties of novel two-dimensional materials. The obtained results are also of great significance for the heat removal and other important physical properties and processes in ultrathin films, with special emphasis to the improvement of the superconducting properties towards the high TC superconductivity.

Designing Mechanical Metamaterials with Kirigami-Inspired, Hierarchical Constructions for Giant Positive and Negative Thermal Expansion.

Advanced mechanical metamaterials with unusual thermal expansion properties represent an area of growing interest, due to their promising potential for use in a broad range of areas. In spite of previous work on metamaterials with large or ultralow coefficient of thermal expansion (CTE), achieving a broad range of CTE values with access to large thermally induced dimensional changes in structures with high filling ratios remains a key challenge. Here, design concepts and fabrication strategies for a kirigami-inspired class of 2D hierarchical metamaterials that can effectively convert the thermal mismatch between two closely packed constituent materials into giant levels of biaxial/uniaxial thermal expansion/shrinkage are presented. At large filling ratios (>50%), these systems offer not only unprecedented negative and positive biaxial CTE (i.e., -5950 and 10 710ppm K-1 ), but also large biaxial thermal expansion properties (e.g., >21% for 20 K temperature increase). Theoretical modeling of thermal deformations provides a clear understanding of the microstructure-property relationships and serves as a basis for design choices for desired CTE values. An Ashby plot of the CTE versus density serves as a quantitative comparison of the hierarchical metamaterials presented here to previously reported systems, indicating the capability for substantially enlarging the accessible range of CTE.

Microscopic Mechanisms of Glasslike Lattice Thermal Transport in Cubic Cu_{12}Sb_{4}S_{13} Tetrahedrites.

Materials based on cubic tetrahedrites (Cu_{12}Sb_{4}S_{13}) are useful thermoelectrics with unusual thermal and electrical transport properties, such as very low and nearly temperature-independent lattice thermal conductivity (κ_{L}). We explain the microscopic origin of the glasslike κ_{L} in Cu_{12}Sb_{4}S_{13} by explicitly treating anharmonicity up to quartic terms for both phonon energies and phonon scattering rates. We show that the strongly unstable phonon modes associated with trigonally coordinated Cu atoms are anharmonically stabilized above approximately 100K and continue hardening with increasing temperature in accord with experimental data. This temperature-induced hardening effect reduces scattering of heat carrying acoustic modes by reducing the available phase space for three-phonon processes, thereby balancing the conventional ∝T increase in scattering due to phonon population and yielding nearly temperature-independent κ_{L}. Furthermore, we find that very strong phonon broadening leads to a qualitative breakdown of the conventional phonon-gas model and modify the dominant heat transport mechanism from the particlelike phonon wave packet propagation to incoherent contributions described by the off-diagonal terms in the heat-flux operator, which are typically prevailing in glasses and disordered crystals. Our work paves the way to a deeper understanding of glasslike thermal conductivity in complex crystals with strong anharmonicity.

Magnetically driven giant negative thermal expansion covering room temperature in Hf0.875Ta0·125Fe2

Abstract Neutron diffraction is used to reveal the origin of the unusual thermal expansion properties of the itinerant-electron system Hf0.875Ta0.125Fe2. Hf0.875Ta0.125Fe2 shows temperature-induced magnetic transitions from ferromagnetic (FM) to antiferromagnetic (AFM) order and then to the paramagnetic (PM) state upon heating. The FM-AFM transition proceeds in a stepwise fashion, as a first-order phase transition, and is accompanied by an extremely anisotropic lattice collapse. The unit cell volume shrinks abruptly, but only in the basal plane; the dimension along the c-axis varies almost continuously. Hf0.875Ta0.125Fe2 exhibits a 0.37 % spontaneous volume contraction across the FM-AFM transition, where a giant negative thermal expansion (NTE), with a volumetric thermal expansion coefficient -74×10-6 K-1, is observed over a temperature interval of ΔT∼50 K around room temperature.

Unusual anisotropic thermal expansion in multilayer SnSe leads to positive-to-negative crossover of Poisson's ratio

Monolayer SnSe has been predicted to exhibit an unusual anisotropic thermal expansion—when heated, the long lattice parameter contracts, while the short one expands, resulting in a rectangular-to-square-lattice phase transformation at a critical temperature (Tc). Here, we employ density-functional-theory calculations to demonstrate an even more notable thermal-expansion behavior of SnSe from monolayer to bulk. We find that the unusual thermal expansion persists in multilayers, while the coefficients of thermal expansion of different numbers of layers are almost identical. This behavior results from a delicate interplay between the elastic stiffness coefficient and Grüneisen parameters. Finally, we find that the Poisson's ratio of multilayer SnSe, which is positive at T=0 K, gets smaller with increasing temperature and even turns negative, signaling a zero Poisson's ratio at a particular temperature. Overall, the present results provide another perspective in understanding the unusual thermal properties of monochalcogenides.

Phonon, thermal, and thermo-optical properties of halide perovskites.

Metal halide perovskites are semiconductors with many fascinating characteristics and their widespread use in optoelectronic devices has been expected. High-quality thin films and single crystals can be fabricated by simple chemical solution processes and their fundamental electrical, optical, and thermal properties can be changed significantly by compositional substitution, in particular halogen ions. In this perspective, we provide an overview of phonon and thermal properties of metal halide perovskites, which play a decisive role in determining device performance. After a brief introduction to fundamental material properties, longitudinal-optical phonons and unusual thermal properties of metal halide perovskites are discussed. Remarkably, they possess very low thermal conductivities and very large thermal expansion coefficients despite their crystalline nature. In line with these discussions, we present optical properties governed by the strong electron-phonon interactions and the unusual thermal properties. By showing their unique thermo-optic responses and novel application examples, we highlight some aspects of the unusual thermal properties.

Independently Tunable Thermal Conductance and Phononic Band Gaps of 3D Lattice Materials

Lattice materials provide unusual thermal and vibrational properties but not within the same structure. Thermal and vibrational multifunctionality is, however, crucial for thermomechanical applications such as automotive, aerospace, building, transportation, and energy infrastructure. In applications involving mobility, both high heat transfer and low mass are desired. Although there have been various efforts to design multifunctional lattice materials, the focus has largely remained on quasi‐static mechanical and thermal properties or mechanical and vibrational properties. Herein, designs of realizable lattice materials are reported, which are inherently thermally resistive, with vastly improved thermal conductance and omnidirectional phononic band gaps. By redesigning the truss structures to serve as interconnected heat pipes, a three‐order‐of‐magnitude improvement in the specific thermal conductance is found. Nodal masses at truss junctions are further used to obtain full vibrational band gaps. It is shown that it is possible to independently tune vibrational and thermal properties within the same structure. This work provides background for the design and fabrication of multifunctional lattice materials that simultaneously prevent structural vibrations and enhance heat conduction.

Unusual Thermal Boundary Resistance in Halide Perovskites: A Way To Tune Ultralow Thermal Conductivity for Thermoelectrics.

Halide perovskites have emerged as promising candidates as the active material in photovoltaics and light-emitting diodes. They possess unusual bulk thermal transport properties that have been the focus of a number of studies, but there is much less understanding of thermal transport in thin films where a diverse range of structures and morphologies are accessible. Here, we report on the tuning of in-plane thermal conductivity in methylammonium lead iodide thin films by morphological control. Using 3-ω measurements, we find that the room temperature thermal conductivity of thermally evaporated methylammonium lead iodide perovskite films ranges from 0.31 to 0.59 W/(m K). We measure a discontinuity in thermal conductivity at the orthorhombic-tetragonal phase transition and explore this using density functional theory and attributing it to a collapse in the phonon group velocity along the c-axis of the tetragonal crystal. Moreover, we have quantified the thermal boundary resistance (Kapitza resistance) for thermally evaporated films, allowing us to estimate the Kapitza length, which is 36 ± 2 nm at room temperature and 15 ± 2 nm at 100 K. Curiously, the Kapitza resistance has a strong temperature dependence which we also explore using density functional theory, with these results suggesting an important role of methylammonium rotational modes in scattering phonons at the crystallite boundaries.

First-principles study of the electronic, magnetic and optical properties of Fe3Se4 in its monoclinic phase

In the present work, we have gained fundamental understanding of the physical properties of ferric selenide (Fe3Se4), an emerging ferrimagnetic material, via a systematic study of its structural, electronic, magnetic, optical and transport properties based on first-principles calculations. The analysis of the electronic band structure (with spin-orbit coupling taken into account) and density of states confirms its metallic behavior and reveals considerable hybridization of Fe-3d and Se-4p states near/at the Fermi level. With the predominant spin polarization on Fe sites, Fe3Se4 in its monoclinic phase favors a type-II ferrimagnetic ordering resulting in a total magnetic moment of 4.25μB per unit cell. The symmetry and charge analysis further suggests the tilting of Fe sub-lattice and the existence of interesting orbital-ordering due to the Jahn-Teller (JT) distortion. In addition, electron plasmonic peaks in the optical absorption spectra and unusual electrical and thermal transport properties are observed. These findings make Fe3Se4 as a potential candidate for a wide variety of applications in magnetism, spintronics, optoelectronics, and thermoelectrics.