Inorganic Crystals with Glass‐Like and Ultralow Thermal Conductivities†

Abstract

The ability to control the transport of thermal energy is critical in a wide variety of technologies. At the same time, understanding the underlying microscopic mechanisms of thermal transport in solids continues to be a central goal of condensed matter and materials physics, with many persistent challenges and unanswered questions. One of the remarkable findings has been the observation that some crystalline materials have very low, glass-like thermal conductivities despite long-range order in the arrangement of the atoms in their structure. Although examples with such unusual behavior were initially rare, the number of crystalline materials known to have glass-like thermal conductivities has grown significantly in the past two decades. Moreover, some fully dense inorganic solids have recently been discovered that possess ultralow thermal conductivities below the so-called glass limit. In this review, we use several specific examples to highlight the salient structural and lattice dynamical features of these intriguing "glass-like crystals," focusing on current understanding of the microscopic mechanisms that cause these crystals to conduct heat like a glass. The study of such materials continues to push our understanding of heat transport in solids and the roles that chemical bonding and structural order and disorder play in thermal transport processes.

Thermal expansion performance and intrinsic lattice thermal conductivity of ferroelastic RETaO4 ceramics

“…The contribution of C V to thermal conductivity was limited, as C V of each atom approached 3k B at temperature beyond Debye temperature . Therefore, Λ could be obtained based on Equation and:…”

Charge‐Induced Disorder Controls the Thermal Conductivity of Entropy‐Stabilized Oxides

“…For macroscale applications in which films inevitably become large enough that grains of varying orientations form, thermal conductivity reduction in one crystallographic direction does not have significant benefit. Thus, for isotropic crystals, such reduction is typically achieved via increasing compositional disorder, which can lead to mass mismatch, atomic radii mismatch, and local atomic strain that results in additional phonon scattering. For example, mixed crystals with controlled disorder were shown to have thermal conductivities that approach their minimum limit .…”

Advanced Materials for High‐Temperature Thermal Transport

“…Dense materials have shown the lowest κ in the range of 1 to 2 W m −1 K −1 at high temperature, as represented by the amorphous limit discussed in Section 2. Κ lower than the amorphous limit, commonly referred to as "ultralow" κ, [106] has also been observed in a few classes of fully dense materials, for instance, in multilayer with nanoscale interfaces or nanolaminates, disordered layered crystals of WSe 2 , [107] and thin films of MoSe 2 , [108] and layered heterostructures. [109] For these materials, κ is still higher than that of air (e.g., 0.026 W m −1 K −1 at 25 °C and 1 atm).…”