Dislocation-induced ultra-low lattice thermal conductivity in rare earth doped β-Zn₄Sb₃

Defect engineering in thermoelectric materials leads to the formation of exotic transport properties. Specifically, reduction in lattice thermal conductivity (к_L) can be realized through scattering of low and high-frequency phonons by interfacial and point defects respectively. Herein we explore such phenomena by inducing dense dislocations through doping of rare earth (RE) impurities in β-(Zn_1−xRE_x)₄Sb₃ [x = 0.3–0.5 at.%] as phonon scattering source of all frequencies. Lattice anharmonicity created results in an ultra-low к_L of ~0.15 W/mK for β-(Zn_0.997 Yb_0.003)₄Sb₃. Vibrational properties and phonon scattering altered by the lattice anharmonicity are studied in detail through terahertz and infrared spectroscopies.