Properties of CMAs: Theory and Experiments

Maciá, Enrique; Boissieu, M. de

doi:10.1002/9783527632718.ch2

Cited by 6 publications

(6 citation statements)

References 182 publications

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“…Finally, it is worth noticing that the dynamics we find here is also completely different from what is observed in cage compounds such as clathrates or skutterudites [31][32][33][34][35], where an atom or a group of atoms is weakly bonded to a surrounding cage.…”

Section: Discussion: An Exceptional Dynamical Flexibilitycontrasting

confidence: 68%

Ordering and dynamics of the central tetrahedron in the 1/1 Zn₆Sc periodic approximant to quasicrystal

Euchner

Yamada

Schober

et al. 2012

J. Phys.: Condens. Matter

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Periodic approximants to quasicrystals offer a unique opportunity to better understand the structure, physical properties and stabilizing mechanisms of their quasicrystal counterparts. We present a detailed study of the order-disorder phase transition occurring at about 160 K in the Zn(6)Sc cubic approximant to the icosahedral quasicrystal i-MgZnSc. This transition goes along with an anti-parallel ordering of the tetrahedra located at the centres of large atomic clusters, which are packed on a bcc lattice. Single crystal x-ray diffuse scattering shows that the tetrahedra display pre-transitional short range ordering above T(c) (Yamada et al 2012 in preparation). Using quasielastic neutron scattering (QENS) we clearly evidence this short range order to be dynamical in nature above T(c). The QENS data are consistent with a model of tetrahedra 'jumping' between almost equivalent positions, which is supported by molecular dynamics simulations. This demonstrates a unique dynamical flexibility of the Zn(6)Sc structure even at room temperature.

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Section: Discussion: An Exceptional Dynamical Flexibilitycontrasting

confidence: 68%

Ordering and dynamics of the central tetrahedron in the 1/1 Zn₆Sc periodic approximant to quasicrystal

Euchner

Yamada

Schober

et al. 2012

J. Phys.: Condens. Matter

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show abstract

“…Thus, the microscopic origin for the low κ remains elusive. In particular the respective roles played by guest atoms and unit cell complexity are ambiguous [18].…”

mentioning

confidence: 99%

Phononic filter effect of rattling phonons in the thermoelectric clathrate Ba8Ge40+xNi
Euchner
¹
,
Pailhés
²
,
Nguyen
³

et al. 2012
Phys. Rev. B
90
9
63
0
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One of the key requirements for good thermoelectric materials is a low lattice thermal conductivity. Here we present a combined neutron scattering and theoretical investigation of the lattice dynamics in the type I clathrate system Ba-Ge-Ni, which fulfills this requirement. We observe a strong hybridization between phonons of the Ba guest atoms and acoustic phonons of the Ge-Ni host structure over a wide region of the Brillouin zone which is in contrast with the frequently adopted picture of isolated Ba atoms in Ge-Ni host cages. It occurs without a strong decrease of the acoustic phonon lifetime which contradicts the usual assumption of strong anharmonic phononphonon scattering processes. Within the framework of ab-intio density functional theory calculations we interpret these hybridizations as a series of anti-crossings which act as a low pass filter, preventing the propagation of acoustic phonons. To highlight the effect of such a phononic low pass filter on the thermal transport, we compute the contribution of acoustic phonons to the thermal conductivity of Ba8Ge40Ni6 and compare it to those of pure Ge and a Ge46 empty-cage model system.A central issue in thermoelectrics research is to find materials that generate a high electromotive force under a small applied thermal gradient. The best thermoelectric materials (TE) should therefore combine a low lattice thermal conductivity with high electrical conductivity and thermopower. An efficient and economic way to reduce the thermal conductivity of bulk TE materials, without degrading their electronic properties, is to take advantage of inelastic resonant scattering between heatcarrying acoustic and non-propagative phonons, arising from isolated impurities with internal oscillator degrees of freedom. The librational vibration of molecules incorporated in crystal structures is a well-known example of such scattering centers and was formerly observed in KCl ionic crystals, doped with anionic molecules [1], or in the filled water nanocages of clathrate hydrates [2,3]. In TE clathrates and skutterudites, in which the phonon dispersions were recently investigated by means of inelastic neutrons scattering (INS) [4][5][6]10], the localized resonators are so-called rattling phonon modes of loosely bonded guest atoms in oversized atomic cages. The effect of inelastic resonant scattering [11,12] was described theoretically, using the relaxation-time approximation of the Boltzmann equation, in which the lattice thermal conductivity, κ L , for a cubic crystal can be expressed asHere C v (ω) is the phonon specific heat per unit volume and unit frequency, v(ω) is the mean group velocity for phonon frequency ω, τ (ω) is the mean time between collisions that destroy the heat current for all phonons of frequency ω and ρ 0 (ω) is the normalized vibrational density of states. The most common approach to evaluate the scattering of acoustic phonons by a resonator with frequency ω 0 is to add a phenomenological relaxation rate, τ −1where C is a constant proportional to the concentrat...

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“…Accordingly, η can be regarded as a control design parameter able to determine the overall FDM optical behavior, varying from that corresponding to a selective filter (T = 1) to that proper of a reflective coating (T min ). In fact, plugging (15) we see that, when η = R/2 or η = 3R/2, the transmittance attains an extreme value, which should be a minimum or a maximum depending on the parity of the Fibonacci number F j −2 : when F j −2 is even we obtain T N = 1, while for odd values we have T N = T min . Since the parity of the Fibonacci numbers exhibits the recurrence odd-odd-even, the transmittances corresponding to consecutive S j FDMs should alternate accordingly, as it is illustrated in figure 8 for FDMs corresponding to F j −2 = 2, F j −2 = 3 and F j −2 = 5.…”

Section: Transfer Matrix Techniquesmentioning

confidence: 91%

“…During the last decade we have come to realize that ordered matter domains can be suitably expanded to embrace not only periodic arrangements but aperiodic ones as well [1][2][3][4][5][6][7][8][9][10][11]. In this way, the very notion of aperiodic order, that is, order without periodicity, has been used to properly describe a growing number of physical systems, including quasiperiodic crystal (QC) alloys [12][13][14][15], semiconductor heterostructures, metallic and dielectric multilayers, or both synthetic and biological DNA macromolecules [16]. The gradual awakening of aperiodic thinking in condensed matter and materials science communities alike has naturally given rise to a novel approach in the quest for more efficient optical devices, focusing on the design of aperiodic structures able to achieve a better performance than periodic ones for certain specific optical applications.…”

Section: The Rise Of Aperiodic Thinkingmentioning

confidence: 99%

Exploiting aperiodic designs in nanophotonic devices

2012

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In this work we consider the role of aperiodic order-order without periodicity-in the design of different optical devices in one, two and three dimensions. To this end, we will first study devices based on aperiodic multilayered structures. In many instances the recourse to Fibonacci, Thue-Morse or fractal arrangements of layers results in improved optical properties compared with their periodic counterparts. On this basis, the possibility of constructing optical devices based on a modular design of the multilayered structure, where periodic and quasiperiodic subunits are properly mixed, is analyzed, illustrating how this additional degree of freedom enhances the optical performance in some specific applications. This line of thought can be naturally extended to aperiodic arrangements of optical elements, such as nanospheres or dielectric rods in the plane, as well as to three-dimensional photonic quasicrystals based on polymer materials. In this way, plentiful possibilities for new tailored materials naturally appear, generally following suitable optimization algorithms. Then, we present a detailed discussion on the physical properties supporting the preferential use of aperiodic devices in a number of optical applications, opening new avenues for technological innovation. Finally we suggest some related emerging topics that deserve some attention in the years to come.

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Properties of CMAs: Theory and Experiments

Cited by 6 publications

References 182 publications

Ordering and dynamics of the central tetrahedron in the 1/1 Zn₆Sc periodic approximant to quasicrystal

Ordering and dynamics of the central tetrahedron in the 1/1 Zn₆Sc periodic approximant to quasicrystal

Phononic filter effect of rattling phonons in the thermoelectric clathrate Ba8Ge40+xNi
Euchner
¹
,
Pailhés
²
,
Nguyen
³

et al. 2012
Phys. Rev. B
90
9
63
0
View full text Add to dashboard Cite

Exploiting aperiodic designs in nanophotonic devices

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Properties of CMAs: Theory and Experiments

Cited by 6 publications

References 182 publications

Ordering and dynamics of the central tetrahedron in the 1/1 Zn6Sc periodic approximant to quasicrystal

Ordering and dynamics of the central tetrahedron in the 1/1 Zn6Sc periodic approximant to quasicrystal

Phononic filter effect of rattling phonons in the thermoelectric clathrate Ba8Ge40+xNiEuchner1, Pailhés2, Nguyen3 et al. 2012Phys. Rev. B909630View full textAdd to dashboardCite

Exploiting aperiodic designs in nanophotonic devices

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Product

Resources

About

Ordering and dynamics of the central tetrahedron in the 1/1 Zn₆Sc periodic approximant to quasicrystal

Ordering and dynamics of the central tetrahedron in the 1/1 Zn₆Sc periodic approximant to quasicrystal

Phononic filter effect of rattling phonons in the thermoelectric clathrate Ba8Ge40+xNi
Euchner
¹
,
Pailhés
²
,
Nguyen
³

et al. 2012
Phys. Rev. B
90
9
63
0
View full text Add to dashboard Cite