Interlaminar Fracture Toughness Measurement of Multilayered 2D Thermoelectric Materials Bi2Te3 by a Tapered Cantilever Bending Experiment

Multilayered thermoelectric material bismuth telluride (Bi2Te3) is widely used in engineering owing to its exceptional thermoelectric performance at room temperature. However, Bi2Te3 is prone to cracks, voids, or other defects due to its multilayered structure, leading to decreased device lifetime and reliability. This paper aims at stably and precisely measuring the interlaminar fracture toughness (IFT) of multilayered Bi2Te3 for the reliability evaluation of Bi2Te3-based thermoelectric devices. In addition, we seek a method to stably measure the IFT even for very brittle materials. We developed a tapered cantilever bending (TCB) experiment to obtain the IFT. The experimental specimens were fabricated using a focused ion beam (FIB) technique at the micro scale, and the initial interlaminar crack was introduced by the notch method. By performing the TCB experiment, we created an ideally sharp pre-crack and observed stable crack propagation. The critical energy release rate (ERR) for crack propagation obtained in the present paper is around 0.51–0.53 J/m2, which agrees reasonably with theoretical van der Waals (vdW) interlaminar interaction energy. The proposed method can be well-applied in assessing IFTs of multilayered materials, even for very brittle multilayered 2D materials.