Segregation and properties at curved vs straight (000) inversion boundaries in piezotronic ZnO bicrystals

Abstract

TEM and SEM investigations of ZnO bicrystal interfaces were undertaken with an aim to study the correlation of local grain‐boundary structure, segregation, and electrical transport perpendicular to the interface. To this end, varistor‐like ZnO bicrystals with piezotronic characteristics were chosen with (0001¯)║(0001¯) tail‐to‐tail orientation with respect to the c‐axis. In order to contrast different local grain‐boundary structures with different coherency and segregation of bismuth, but identical macroscopic polarization state, two complementary processing techniques were applied. A diffusion‐bonded bicrystal with an intermediate thin film containing Zn–Bi–Co–O provided a straight interface as reference. In contrast, a ZnO bicrystal prepared by epitaxial solid‐state transformation was manufactured by bonding two ZnO single crystals with a 100 µm thick polycrystalline ZnO varistor material with a typical dopant composition including bismuth and cobalt. This structure was annealed to the point that a bicrystal was formed with the varistor concentration at the boundary, which was strongly curved due to the polycrystalline microstructure still providing a shadow image at the interface. The results highlight a distinct correlation between local interfacial morphology, degree of segregation of bismuth, and degree of nonlinearity of the electrical transport across the interface.

TEM and DFT study of basal-plane inversion boundaries in SnO2-doped ZnO

“…On the other hand, Zn 2+ located in very uncommon octahedral sites, would modify the bandgap, and possibly also enhance the in-plane conductivity of carriers. Theoretical studies of IBs have recently shown a great potential in studying potential barriers in ZnO [79,80]. To study the long-range ordering of cations in the Sn-rich IBs, molecular dynamic calculations on larger scale should be performed.…”