Grain boundaries (GBs) in metals usually increase electrical resistivity due to their distinct atomic arrangement compared to the grain interior. While the GB structure has a crucial influence on the electrical properties, its relationship with resistivity is poorly understood. Here, we perform a systematic study on the resistivity–structure relationship in Cu tilt GBs, employing high-resolution in situ electrical measurements coupled with atomic structure analysis of the GBs. Excess volume and energies of selected GBs are calculated using molecular dynamics simulations. We find a consistent relation between the coincidence site lattice (CSL) type of the GB and its resistivity. The most resistive GBs are in the high range of low-angle GBs (14°–18°) with twice the resistivity of high angle tilt GBs, due to the high dislocation density and corresponding strain fields. Regarding the atomistic structure, GB resistivity approximately correlates with the GB excess volume. Moreover, we show that GB curvature increases resistivity by ∼80%, while phase variations and defects within the same CSL type do not considerably change it.

Most oxide ceramics are known to be brittle macroscopically at room temperature with little or no dislocation‐based plasticity prior to crack propagation. Here, we demonstrate the size‐dependent brittle to ductile transition in SrTiO ₃ at room temperature using nanoindentation pop‐in events visible as a sudden increase in displacement at nominally constant load. We identify that the indentation pop‐in event in SrTiO ₃ at room temperature, below a critical indenter tip radius, is dominated by dislocation‐mediated plasticity. When the tip radius increases to a critical size, concurrent dislocation activation and crack formation, with the latter being the dominating process, occur during the pop‐in event. Beyond the experimental examination and theoretical justification presented on SrTiO ₃ as a model system, further validation on α‐Al ₂ O ₃ , BaTiO ₃ , and TiO ₂ are briefly presented and discussed. A new indentation size effect, mainly for brittle ceramics, is suggested by the competition between the dislocation‐based plasticity and crack formation at small scale. Our finding complements the deformation mechanism in the nano‐/microscale deformation regime involving plasticity and cracking in ceramics at room temperature to pave the road for dislocation‐based mechanics and functionalities study in these materials.

It is well known that grain boundaries (GBs) increase the electrical resistivity of metals due to their enhanced electron scattering. The resistivity values of GBs are determined by their atomic structure, therefore, assessing local resistivity of GBs is highly significant for understanding structure-property relationships. So far, the local electrical characterization of an individual GB did not receive much attention, mainly due to the limited accuracy of the applied techniques, which were not sensitive enough to detect the subtle differences in electrical resistivity values of highly symmetric GBs. Here, we introduce a detailed methodology to probe in-situ or ex-situ the local resistivity of individual GBs in Cu, a metallic model system we choose due to its low resistance. Both, bulk Cu samples and thin films are investigated and different approaches to obtain reliable and accurate resistivity measurements are described, involving the Van der Pauw technique for macroscopic measurements as well as two different 4-point probe techniques for local in-situ measurements performed inside a scanning electron microscope. The in-situ contacts are realized with needles accurately positioned by piezo driven micromanipulators. Resistivity results obtained on coincidence site lattice GBs (incoherent Σ3 and asymmetric Σ5) are reported and discussed. In addition, the key experimental details as well as pitfalls in the measurement of individual GB resistivity are addressed.

Grain boundaries often exhibit ordered atomic structures. Increasing amounts of evidence have been provided by transmission electron microscopy and atomistic computer simulations that different stable and metastable grain boundary structures can occur. Meanwhile, theories to treat them thermodynamically as grain boundary phases have been developed. Whereas atomic structures were identified at particular grain boundaries for particular materials, it remains an open question if these structures and their thermodynamic excess properties are material specific or generalizable to, e.g., all fcc metals. In order to elucidate that question, we use atomistic simulations with classical interatomic potentials to investigate a range of high-angle $\left[11\overline{1}\right]$ symmetric tilt grain boundaries in Ni, Cu, Pd, Ag, Au, Al, and Pb. We could indeed find two families of grain boundary phases in all of the investigated grain boundaries, which cover most of the standard fcc materials. Where possible, we compared the atomic structures to atomic-resolution electron microscopy images and found that the structures match. This poses the question if the grain boundary phases are simply the result of sphere-packing geometry or if material-specific bonding physics play a role. We tested this using simple model pair potentials and found that medium-ranged interactions are required to reproduce the atomic structures, while the more realistic material models mostly affect the grain boundary (free) energy. In addition to the structural investigation, we also report the thermodynamic excess properties of the grain boundaries, explore how they influence the thermodynamic stability of the grain boundary phases, and detail the commonalities and differences between the materials.