Transition from Crystal-like to Amorphous-like Heat Conduction in Structurally-Complex Crystals

Abstract

<pre>The physics of heat conduction puts practical </pre><pre>limits on many technological fields such as </pre><pre>energy production, storage, and conversion, as</pre><pre>well as high-power and high-frequency </pre><pre>electronics. Heat conduction in simple, </pre><pre>defect-free crystals is generally well </pre><pre>understood and seems to be well described by </pre><pre>the phonon-gas model (PGM), where phonon </pre><pre>wave-packets are viewed as heat carrying</pre><pre>particles which propagate their mean free </pre><pre>path before being scattered. It is widely</pre><pre>appreciated that the PGM does not describe </pre><pre>the full vibrational spectrum in amorphous </pre><pre>materials, since this picture likely breaks </pre><pre>down at higher frequencies. Furthermore, it </pre><pre>has been shown that the PGM also breaks down </pre><pre>in certain defective and anharmonic crystals,</pre><pre>not only in the amorphous limit. In this work, </pre><pre>in an attempt to bridge our understanding </pre><pre>between crystal-like (described by the PGM)</pre><pre>and amorphous-like heat conduction, we study </pre><pre>structurally-complex crystalline YB<sub>14</sub>(Mn,Mg)SB<sub>11</sub> </pre><pre>experimentally using inelastic neutron </pre><pre>scattering and computationally using a </pre><pre>two-channel lattice dynamical approach. </pre><pre>One channel is the commonly considered PGM, </pre><pre>and the second we call the diffuson-channel </pre><pre>since it is mathematically the same mechanism </pre><pre>through which diffusons were defined. Our </pre><pre>results show that the diffuson-channel </pre><pre>dominates in YB<sub>14</sub>MnSb<sub>11</sub> above 300 K, which is </pre><pre>a champion thermoelectric material above 800 K. </pre><pre>We demonstrate a method for the rational </pre><pre>design of amorphous-like heat conduction by </pre><pre>considering the energetic proximity phonon modes </pre><pre>and modifying them through chemical means.</pre>

High‐Density Frenkel Defects as Origin of N‐Type Thermoelectric Performance and Low Thermal Conductivity in Mg3Sb2‐Based Materials

“…We analyze the thermal conductivity κ of Mg 3 Sb 2 using a two-channel model, [30,38] and confirm excellent agreement when we include phonon scattering by the strain field (red solid line in Figure 2). The thermal conductivity is given by κ = κ P + κ C , where κ P is a phonon-like propagon term typically showing T −1 dependence at high temperature and κ C is a loss-of-coherence diffuson term that corresponds to inter-mode coupling and increases with temperature.…”

Symmetric Bloch oscillations of matter waves

“…It can be seen in Fig. 5(a) that the total specific heats C(T ) of all three compounds are nearly equal over the interval 2-300 K. This implies that the phonons, which make the major contribution to the total specific heat, are essentially identical in all three materials [52]. In Fig.…”

Diffuson-mediated thermal and ionic transport in superionic conductors

“…13 Given the computational cost of third and fourth order force constants, an analytical scattering model was implemented to describe the temperature dependence of the phonon lifetimes (details in Supplemental Note 9). 13 The analytical model considers phonon-phonon scattering (& ! '( ) and boundary scattering (& ) '( ) resulting in a total scattering rate of…”

“…10,11 In contrast to the phonon-gas model, diffusons correspond to heat transport via local (atomic) scale random walk. 12,13 This diffusive walk of heat 14 means that non-propagating vibrations in a solid transfer thermal energy between adjacent diffuson modes, 11,12 at a much smaller length scale compared to typical propagating modes (shown schematically in Figure 1 a, b).…”