Localized anharmonic rattling of Al atoms in VAl<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow /><mml:mrow><mml:mn>10.1</mml:mn></mml:mrow></mml:msub></mml:math>

The inelastic response of AV2Al20 (with A = Al, Ga and Y) was probed by high-resolution inelastic neutron scattering experiments and density functional theory (DFT) based lattice dynamics calculations (LDC). Features characteristic of the dynamics of Al, Ga and Y are established experimentally in the low-energy range of the compounds. In the stereotype 'Einstein-solid' compound AlV2Al20 we identify a unique spectral density extending up to 10 meV at 1.6 K. Its dominating feature is a peak centred at 2 meV at the base temperature. A very similar spectral distribution is established in GaV2Al20 albeit the strong peak is located at 1 meV at 1.6 K. In YV2Al20 signals characteristic of Y dynamics are located above 8 meV. The spectral distributions are reproduced by the DFT-based LDC and identified as a set of phonons. The response to temperature changes between 1.6 and ∼300 K is studied experimentally and the exceptionally vivid renormalization of the A characteristic modes in AlV2Al20 and GaV2Al20 is quantified by following the energy of the strong peak. At about 300 K it is shifted to higher energies by 300% for A = Al and 450% for A = Ga. The dynamics of A = Y in YV2Al20 show a minor temperature effect. This holds in general for modes located above 10 meV in any of the compounds. They are associated with vibrations of the V2Al20 matrix. Atomic potentials derived through DFT calculations indicate the propensity of A = Al and Ga to a strong positive energy shift upon temperature increase by a high quartic component. The effect of the strong phonon renormalization on thermodynamic observables is computed on grounds of the LDC results. It is shown that through the hybridization of A = Al and Ga with the V2Al20 dynamics the matrix vibrations in the low-energy range follow this renormalization.

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“…?? 8. A weak excess of C V (T ) of AlV 2 Al 20 and GaV 2 Al 20 over YV 2 Al 20 and V 2 Al 20 is detected towards low T .…”

Section: E Thermal Displacement Parameters and Heat Capacitymentioning

confidence: 86%

On the microscopic dynamics of the ‘Einstein solids’ AlV₂Al₂₀ and GaV₂Al₂₀, and of YV₂Al₂₀: a benchmark system for ‘rattling’ excitations

Koza

Mutka

Yamaura

et al. 2015

Phys. Chem. Chem. Phys.

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“…In these materials, the phonon glass property is considered to come from weakly bound atoms (rattlers) exhibiting low-energy vibrational modes which scatter the heat-carrying acoustic phonons of the lattice. The precise mechanism by which a rattler scatters phonons is still the subject of research with both resonant scattering [11][12][13] and localized mode coupling 5,6,8,14,15 having been proposed. The distinction between the two mechanisms is perhaps easily understood from the simple (kinetic theory of gases) expression for thermal conductivity:…”

Section: Introductionmentioning

confidence: 99%

Novel K rattling: A new route to thermoelectric materials?

Shoko

Kearley

Peterson

et al. 2014

Journal of Applied Physics

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We have performed ab initio molecular dynamics (MD) simulations to study the alkali-metal dynamics in the Al-doped (KAl0.33W1.67O6 and RbAl0.33W1.67O6) and undoped (KW2O6 and RbW2O6) defect pyrochlore tungstates. The K atoms exhibit novel rattling dynamics in both the doped and undoped tungstates while the Rb atoms do not. The KAl0.33W1.67O6 experimental thermal conductivity curve shows an unusual depression between ~ 50 K and ~ 250 K, coinciding with two crossovers in the K dynamics: the first at ~ 50 K, from oscillatory to diffusive, and the second at ~ 250 K, from diffusive back to oscillatory. We found that the low-temperature crossover is a result of the system transitioning below the activation energy of the diffusive dynamics whereas the high-temperature crossover is driven by a complex reconstruction of the local potential around the K atoms due to the cage dynamics.This leads to a hardening of the K potential with increasing temperature. This unusual reconstruction of the potential may have important implications for the interpretation of finite-temperature dynamics based on zero-temperature potentials in similar materials. The key result is that the novel K rattling, involving local diffusion, leads to a significant reduction in the thermal conductivity. We suggest that this may open a new route in the phonon engineering of cage compounds for thermoelectric materials where the rattlers are specifically selected to reduce the lattice thermal conductivity by the mechanism of local diffusion. a)

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“…CeT 2 Al 20 (T = Ti, V, Cr) are found to exhibit Pauli paramagnetism, consistent with a nonmagnetic tetravalent configuration of the Ce atom [29,30]. PrT 2 Al 20 (T = Ti, V) are exotic superconductors in which the superconducting state coexists with quadrupolar order [13][14][15][16], while PrCr 2 Al 20 was described as a paramagnetic Kondo lattice [30]. NdTi 2 Al 20 is an antiferromagnet (AFM) with the Néel temperature T N = 1.45 K [35], NdV 2 Al 20 and NdCr 2 Al 20 in turn are ferromagnets (FM) with the Curie temperature T C = 1.8 K and 1.7 K, respectively [35].…”

Section: Introductionmentioning

confidence: 88%

“…in suppression of the lattice thermal conductivity [3,5,9] that can lead to an increase in the thermoelectric figure of merit (ZT) [3,5]. The presence of 'rattling' phonons is also found to enhance the superconducting critical temperature in hexa-and dodecaborides [1,10,11], β-pyrochlores [8,12], and CeCr 2 Al 20 -type compounds: Al x V 2 Al 20 [13][14][15], Ga x V 2 Al 20 [14,16], and RV 2 Al 20 (R = Sc, Y, Lu) [17]. The contribution of 'rattling' phonons to the specific heat are usually well described using the Einstein model with a low characteristic (Einstein) temperature Θ E .…”

Section: Introductionmentioning

confidence: 99%

Crystal structure and low-energy Einstein mode in ErV 2 Al 20 intermetallic cage compound

Winiarski

Klimczuk

2017

Journal of Solid State Chemistry

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Single crystals of a new ternary aluminide ErV 2 Al 20 were grown using a self-flux method. The crystal structure was determined by powder X-ray diffraction measurements and Rietveld refinement, and physical properties were studied by means of electrical resistivity, magnetic susceptibility and specific heat measurements. These measurements reveal that ErV 2 Al 20 is a Curie-Weiss paramagnet down to 1.95 K with an effective magnetic moment μ eff = 9.27(1) μ B and Curie-Weiss temperature Θ CW = -0.55(4) K. The heat capacity measurements show a broad anomaly at low temperatures that is attributed to the presence of a low-energy Einstein mode with characteristic temperature Θ E = 44 K, approximately twice as high as in the isostructural 'Einstein solid' VAl 10.1 .

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Localized anharmonic rattling of Al atoms in VAl10.1

Cited by 50 publications

References 71 publications

On the microscopic dynamics of the ‘Einstein solids’ AlV₂Al₂₀ and GaV₂Al₂₀, and of YV₂Al₂₀: a benchmark system for ‘rattling’ excitations

On the microscopic dynamics of the ‘Einstein solids’ AlV₂Al₂₀ and GaV₂Al₂₀, and of YV₂Al₂₀: a benchmark system for ‘rattling’ excitations

Novel K rattling: A new route to thermoelectric materials?

Crystal structure and low-energy Einstein mode in ErV 2 Al 20 intermetallic cage compound

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Localized anharmonic rattling of Al atoms in VAl10.1

Cited by 50 publications

References 71 publications

On the microscopic dynamics of the ‘Einstein solids’ AlV2Al20 and GaV2Al20, and of YV2Al20: a benchmark system for ‘rattling’ excitations

On the microscopic dynamics of the ‘Einstein solids’ AlV2Al20 and GaV2Al20, and of YV2Al20: a benchmark system for ‘rattling’ excitations

Novel K rattling: A new route to thermoelectric materials?

Crystal structure and low-energy Einstein mode in ErV 2 Al 20 intermetallic cage compound

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Product

Resources

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On the microscopic dynamics of the ‘Einstein solids’ AlV₂Al₂₀ and GaV₂Al₂₀, and of YV₂Al₂₀: a benchmark system for ‘rattling’ excitations

On the microscopic dynamics of the ‘Einstein solids’ AlV₂Al₂₀ and GaV₂Al₂₀, and of YV₂Al₂₀: a benchmark system for ‘rattling’ excitations