Abstract
To explore the potential for use of the Cr–Al–B borides, Cr
2
AlB
2
, Cr
3
AlB
4
, and Cr
4
AlB
6
as well as hypothetical CrAlB are investigated using density functional theory. In the ...CrAl(CrB
2
)
n
series strong covalent bonding is present between the B and Cr atoms with, significantly, much weaker metallic Cr–Al and B–Al bonds, suggesting similar unusual properties to the MAX phases. The relative stiffness of the weakest and strongest bonds hint at similar unusual properties to the MAX phases with superior damage tolerance expected for hypothetical CrAlB, as evidenced in the lowest Al1–Al2 bond stiffness. The layered nature and metallic bonding are expected to result in high fracture toughness and damage tolerance. Anisotropic compression is demonstrated, with the stiffest axes along the direction of the B–B zigzag‐/hexagonal‐chains and the softest axes determined by an interplay between the soft metallic interlayers and the rigid covalent bonds. In general the elastic moduli in CrAl(CrB
2
)
n
increase as a function of
n
, however, without the price of an increase in density.
Argyrodites with a general chemical formula of A
BX
(A = Cu, Ag; B = Si, Ge, Sn; and X = S, Se, and Te) are known for the intimate interplay among mobile ions, electrons, and phonons, which yields ...rich material physics and materials chemistry phenomena. In particular, the coexistence of fast ionic conduction and promising thermoelectric performance in Ag
GeTe
, Ag
SnSe
, Ag
SiTe
, Ag
SiSe
, and Cu
GeSe
at high temperatures ushered us to their chemical neighbor Ag
GeSe
, whose high-temperature crystal structure and thermoelectric properties are not yet reported. In this work, we have employed a growth-from-the-melt technique followed by hot pressing to prepare polycrystalline Ag
GeSe
samples, on which the crystal structure, micro-morphology, compositional analysis, UV-vis absorption, specific heat, speed of sound, and thermoelectric properties were characterized as a function of the Se-deficiency ratio and temperature. We found that (i) the crystal structure of Ag
GeSe
evolved from orthorhombic at room temperature to face center cubic above 410 K, with a region of phase separations in between; (ii) like other argyrodite 816 phases, Ag
GeSe
exhibited ultralow thermal conductivities over a wide temperature range as the phonon mean free path was down to the order of interatomic spacing; and (iii) varying Se deficiency effectively optimized the carrier concentration and power factor, a figure of merit zT value ∼0.55 was achieved at 923 K in Ag
GeSe
. These results not only fill a knowledge gap of Ag
GeSe
but also contribute to a comprehensive understanding of 816 phase argyrodites at large.
One of the main advantages of lattice structures (a type of porous structures) is their high strength-to-weight ratio. The mechanical properties of lattice structures, including static and dynamic ...properties, are dependent on the type of base repeating unit cell. In this research, we investigate the mechanical properties of lattice structures based on tesseract unit cell. This unit cell is significant due to similarity of its relative density to human bone, especially high-density spongy bone. Up to now, no analytical or homogenization method has been used to analyze the mechanical behavior of this unit cell. In this study, homogenization process based on an Asymptotic method (AH) is used. Then, the accuracy of the homogenization method is evaluated against FE results and experimental tests. We present the analytical solution that relates the geometry of unit cell to normalized Young's modulus, normalized shear modulus, and Poisson's ratio. The mechanical properties of the lattice structures were found to be strongly dependent on the d/l ratio (strut diameter to length ratio). The Young's modulus increased exponentially by increasing the d/l ratio. Compared to the analytical results based on homogenization method, the numerical predictions were higher for the normalized Young's modulus. For instance, for d/l=0.15, the predicted normalized Young's modulus was 0.0316 and 0.0238 for the FE and Homogenization methods, respectively. As a practical application, the range of obtained elastic modulus was 0.13 GPa and 1.23 GPa which is close to the elastic modulus of femur head bone, demonstrating the suitability of the tesseract unit cell to be used as bone replacement biomaterial.
•The mechanical response of Tesseract unit cell is studied analytically for the first time.•Asymptotic Homogenization method (AH) is performed on the unit cell.•Discrete homogenization approach is used to construct an anisotropic micropolar continuum model.•Analytical relative density, Young's modulus, Poisson's ratio, and shear modulus were obtained.•The mechanical properties tesseract was close to the high density femur spongy bone.
The quasi-two-dimensional metal Sr2RuO4 is one of the best characterized unconventional superconductors, yet the nature of its superconducting order parameter is still under debate1–3. This ...information is crucial to determine the pairing mechanism of Cooper pairs. Here we use ultrasound velocity to probe the superconducting state of Sr2RuO4. This thermodynamic probe is sensitive to the symmetry of the material, and therefore, it can help in identifying the symmetry of the superconducting order parameter4,5. Indeed, we observe a sharp jump in the shear elastic constant c66 as the temperature is increased across the superconducting transition. This directly implies that the superconducting order parameter is of a two-component nature. On the basis of symmetry arguments and given the other known properties of Sr2RuO4 (refs. 6–8), we discuss which states are compatible with this requirement and propose that the two-component order parameter {dxz; dyz} is the most likely candidate.Ultrasound experiments show that the superconducting order parameter in strontium ruthenate must have two components.
The Young modulus of partially and fully sintered alumina ceramics, obtained by firing to different temperatures (range 1200–1600°C), has been determined via impulse excitation, and the evolution of ...Young’s modulus of partially sintered alumina with temperature has been monitored from room temperature to 1600°C. As expected, the room-temperature Young modulus of the partially sintered materials is lower than all theoretical predictions. With increasing temperature Young’s modulus decreases, until the original firing temperature is exceeded and sintering (densification) continues, resulting in a steep Young’s modulus increase. During heating and cooling the temperature dependence obeys a master curve for alumina, unless the temperature of the original firing is excessively low.
Structural composites and electrochemical energy storage underpin electrification of transportation, but advances in electric vehicles are shackled by parasitic battery mass. The emergence of ...structural power composites, multifunctional materials that simultaneously carry structural loads whilst storing electrical energy, promises dramatic improvements in effective performance Here, we assess the literature on structural supercapacitors, not only providing a comprehensive and critical review of the constituent (i.e., structural electrode, structural electrolyte and structural separator) developments, but also considering manufacture, characterisation, scale-up, modelling and design/demonstration. We provide a rigorous analysis of the multifunctional performance data reported in the literature, providing the reader with a detailed comparison between the different structural supercapacitor developments. We conclude with insights into the future research and adoption challenges for structural supercapacitors. There are several significant hurdles which must be addressed to mature this technology. These include development of a processable structural electrolyte; optimisation of current collection to facilitate device scale-up; identification of load-transmitting encapsulation solutions; standard protocols for characterisation and ranking of structural supercapacitors and; predictive multiphysics models for structural supercapacitors. Through addressing such issues, these emerging multifunctional materials will deliver a novel lightweighting strategy that can contribute to managing the ongoing climate crisis.
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Nanoscale Mechanical Softening of Morphotropic BiFeO3 Heo, Yooun; Jang, Byong‐Kweon; Kim, Seung Jin ...
Advanced materials (Weinheim),
December 3, 2014, 2014-Dec-03, 20141203, Letnik:
26, Številka:
45
Journal Article
Recenzirano
Mechanical switching can be used to form phase‐transformed areas in mixed‐phase bismuth ferrite thin films, which might be exploited to yield various soft elastic areas with greatly reduced Young's ...modulus on the nanoscale. Due to the mechanically susceptible nature of morphotropic phase boundaries in multiferroics, combined elastic control of electronic, magnetic, and ferroelectric properties becomes possible.
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Mechanical metamaterials are man-made structures with counterintuitive mechanical properties that originate in the geometry of their unit cell instead of the properties of each ...component. The typical mechanical metamaterials are generally associated with the four elastic constants, the Young's modulus E, shear modulus G, bulk modulus K and Poisson's ratio υ, the former three of which correspond to the stiffness, rigidity, and compressibility of a material from an engineering point of view. Here we review the important advancements in structural topology optimisation of the underlying design principles, coupled with experimental fabrication, thereby to obtain various counterintuitive mechanical properties. Further, a clear classification of mechanical metamaterials have been established based on the fundamental material mechanics. Consequently, mechanical metamaterials can be divide into strong-lightweight (E/ρ), pattern transformation with tunable stiffness, negative compressibility (−4G/3 < K < 0), Pentamode metamaterials (G ≪ K) and auxetic metamaterials (G ≫ K), simultaneously using topology optimisation to share various fancy but feasible mechanical properties, ultralight, ultra-stiffness, well-controllable stiffness, vanishing shear modulus, negative compressibility and negative Poisson’s ratio. We provide here a broad overview of significant potential mechanical metamaterials together with the upcoming challenges in the intriguing and promising research field.
Spatial stiffness modulations defined by the sampling of a two-dimensional surface provide one-dimensional elastic lattices with topological properties that are usually attributed to two-dimensional ...crystals. The cyclic modulation of the stiffness defines a family of lattices whose Bloch eigenmodes accumulate a phase quantified by integer valued Chern numbers. Nontrivial gaps are spanned by edge modes in finite lattices whose location is determined by the phase of the stiffness modulation. These observations drive the implementation of a topological pump in the form of an array of continuous elastic beams coupled through a distributed stiffness. Adiabatic stiffness modulations along the beams' length lead to the transition of localized states from one boundary, to the bulk and, finally, to the opposite boundary. The first demonstration of topological pumping in a continuous elastic system opens new possibilities for its implementation on elastic substrates supporting surface acoustic waves, or to structural components designed to steer waves or isolate vibrations.
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