A hexagonal phase of BiCuTeO films: Growth, crystal structure, and thermoelectric properties

In this work, a stable metallic phase of BiCuTeO has been identified in c-axis oriented films. Unlike the tetragonal structure observed in BiCuTeO bulks, this film exhibits a unique hexagonal layered structure, consisting of alternating Bi2O2 layers and Cu2Te2 layers along the c-axis, with lattice parameters of c = 12.45 Å and a = b = 4.3 Å. A potential crystal structure model for this hexagonal phase has been constructed using first-principles simulations. Calculations of the phonon spectra and electronic band structures confirm the validity of the hexagonally symmetric structure as well as its metallic nature. Due to its lower resistivity and appropriate Seebeck coefficient, the hexagonal BiCuTeO film achieves a power factor of 3.4–7.7 μW cm−1 K−2 within the temperature range of 300–600 K.