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Thermoelectric (TE) conversion technology, capable of transforming heat into electricity, is critical for sustainable energy solutions. Many promising TE materials contain rare or toxic elements, so the development of cost-effective and eco-friendly high-performance TE materials is highly urgent. Herein, we explore the thermal transport and TE properties of transition metal vanadate CuVO3 by using first-principles calculation. On the basis of unified theory of heat conduction, we uncover the hierarchical thermal transport feature in CuVO3, where wave-like tunneling makes a significant contribution to the lattice thermal conductivity (\k{appa}l) and result in the anomalously weak temperature dependence of \k{appa}l. This is primarily attributable to the complex phononic band structure caused by the heterogeneity of Cu-O and V-O bonds. Simultaneously, we report a high power factor of 5.45 mW K-2 m-1 realized in hole-doped CuVO3, which arises from a high electrical conductivity and a large Seebeck coefficient enabled by the multiple valleys and large electronic density of states near the valence band edge. Impressively, the low \k{appa}l and the high power factor make p-typed CuVO3 have ZT of up to 1.39, with the excellent average ZT above 1.0 from 300 to 600 K, which is superior to most reported Cu-based TE materials. Our findings suggest that CuVO3 compound is promising candidate for energy conversion applications in innovative TE devices.

Three-dimensional obstructed atomic insulators (OAIs) are characterized by the appearance of floating surface states (FSSs) at specific surfaces. Benefiting from this feature, our study here shows the presence of abundant surface-semimetal phases in 3D OAIs. The symmetries of obstructed Wannier charge centers ensure the degeneracy of such FSSs at high-symmetry points or invariant lines in the surface Brillouin zone. Utilizing topological quantum chemistry theory, we identify a carbon allotrope with a body-centered tetragonal structure, named bct-C20, as an ideal candidate for realizing different kinds of surface-semimetal phases. For the (001)surface of bct-C20, there are four in-gap FSSs, and these four FSSs form two kinds of surface Dirac cones, i.e., topological Dirac cones with linear dispersion and symmetry-enforced quadratic Dirac cones. The band topology of a surface Dirac cone is captured by the effective surface Hamiltonian and the emergence of hinge states. Moreover, the existence of the surface-nodal-line state is also discussed. This work reports an approach to obtain d-dimensional semimetal phases from the surface states of (d + 1)-dimensional systems, which is of great significance for the studies in revealing topological states and their practical applications in high-dimensional crystals., Comment: 6 pages, 4 figures

Topological phonon states in crystalline materials have attracted significant research interests due to their importance for fundamental physical phenomena, yet their implication on phonon thermal transport remains largely unexplored. Here, we use density functional theory calculations and symmetry analyses to explore topological phonon phase transitions under uniaxial strains and their tuning effects on thermal transport in titanium monoxide (TiO). Our calculation shows that application of 10% tension significantly diminishes lattice thermal conductivity of TiO by 77% and 66% along the a and c axes, respectively, at room temperature. This suppression is found to result largely from the breaking of symmetry protected degeneracy of acoustic branches, which induces a substantial enhancement of phonon scattering phase space due to the easier fulfillment of scattering selection rules. Our study provides evidence for the importance of phononic band topology in modulating thermal conductivity and offers a promising route towards controlling solid-state heat transport.