Excellent high-pressure-sustainable thermoelectric performance driven by metal-insulator topological phase transition in semimetal CaCdGe

Recent advances in thermoelectric research have shed light on the promising properties of topological semimetals, which exhibit superior carrier mobility and electrical conductivity compared to traditional thermoelectric materials. Herein, we employ a first -principles method and semiclassical Boltzmann transport theory to investigate the electronic structures, lattice dynamics, and thermoelectric performance of CaCdGe, a representative nodal -line semimetal, along with their response to pressure. Our findings reveal that CaCdGe possesses an ultralow lattice thermal conductivity at room temperature (0.765 Wm-1K-1) and exhibits excellent n -type thermoelectric behavior in a wide temperature range. Specifically, we identify in -plane (out -of -plane) maximum thermoelectric figures of merit, ZTmax, reaching 1.02 (0.65) at 700 K(1100 K). Remarkably, even under extreme conditions of high pressure (up to 50 GPa), CaCdGe maintains its structural stability without undergoing any structural phase transition. Moreover, we explore the impact of spin -orbit coupling and observe a pressure -driven Lifshitz transition of the Fermi surface around 40 GPa. This transition results in CaCdGe undergoing an electronic phase transition from a charge -compensated semimetal to a topological insulator. Intriguingly, the thermoelectric parameters exhibit unconventional pressure response, embodied by the insensitivity to high pressure after electronic phase transition. Notably, even at 50 GPa, the in -plane (out -of -plane) ZTmax reaches 1.2 (0.7) at 1500 K(500 K). Our comprehensive theoretical study demonstrates the immense potential of CaCdGe and related topological semimetals for thermoelectric applications, even in extreme conditions of high pressure and high temperature.