Structural and thermal confinement of Schwarz crystals

Huang, D.*; Fu, H.*; Lyu, M.*; Feng, Y.*; 梶本 亮一  ; 中村 充孝   ; 本田 孝志*; Liu, E.*; Li, B.*; Li, X.*; Lu, K.*

Huang, D.*; Fu, H.*; Lyu, M.*; Feng, Y.*; Kajimoto, Ryoichi; Nakamura, Mitsutaka; Honda, Takashi*; Liu, E.*; Li, B.*; Li, X.*; Lu, K.*

As a nontrivial state of solid, Schwarz crystal manifests itself in extremely refined nanograins and triply periodic minimal surface (TPMS) grain boundaries, and therefore exceptional thermal and mechanical stability. However, it remains unexploited how the structural units interact and thermal transport is influenced by such complex atomic structures. Here, we investigate Schwarz crystals of Cu and Pt using neutron scattering and thermal transport measurements. Pair distribution function analysis reveals the coexistence of compressed grains and expanded TPMS grain-boundary regions, forming a spatially confined atomic environment. This leads to an unusual phonon hardening suggested by inelastic neutron scattering. As bulk materials, Schwarz crystals exhibit a quasilinear temperature dependence of thermal conductivity, which was previously only observed in low-dimensional materials. This contrast indicates that the spatial confinement of the Schwarz crystals plays a crucial role in determining the unique thermal conductivity, which also provides an emergent route to regulate thermal properties in bulk materials.