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

Background: 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. Objective: 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. Methods: 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. Results: 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. Conclusions: The proposed method can be well-applied in assessing IFTs of multilayered materials, even for very brittle multilayered 2D materials.