Room-Temperature Plastic Deformation of Strontium Titanate Crystals Grown from Different Chemical Compositions
Oxide materials have the potential to exhibit superior mechanical properties in terms of high yield point, high melting point, and high chemical stability. Despite this, they are not widely used as a structural material due to their brittle nature. However, this study shows enhanced room-temperature plasticity of strontium titanate (SrTiO3) crystals through the control of the chemical composition. It is shown that the deformation behavior of SrTiO3 crystals at room temperature depends on the Sr/Ti ratio. It was found that flow stresses in deforming SrTiO3 crystals grown from a powder with the particular ratio of Sr/Ti = 1.04 are almost independent of the strain rate because of the high mobility of dislocations in such crystals. As a result, the SrTiO3 crystals can deform by dislocation slip up to a strain of more than 10%, even at a very high strain rate of 10% per second. It is thus demonstrated that SrTiO3 crystals can exhibit excellent plasticity when chemical composition in the crystal is properly controlled.
Nanoscale to microscale reversal in room-temperature plasticity in SrTiO3 by tuning defect concentration
Abstract Incipient room-temperature plastic deformation in single-crystal SrTiO3 at the nanoscale and the microscale is contrasted by applying a scale-dependent indentation technique. Using nanoindentation pop-in, nanoindentation creep, and an evaluation of dislocation spacing via etch pit study, we demonstrate a reversal of yield stress for crystals with different vacancy concentrations and pre-existing dislocation densities. A competing mechanism between dislocation nucleation and dislocation motion on crystal plasticity at different length scales is highlighted. This finding enables us to complete the understanding of dislocation-mediated plasticity for ceramic oxides at the nanoscale as compared to the microscale and macroscale.
Atomic-scale imaging of individual dopant atoms in a buried interface.
Determining the atomic structure of internal interfaces in materials and devices is critical to understanding their functional properties. Interfacial doping is one promising technique for controlling interfacial properties at the atomic scale, but it is still a major challenge to directly characterize individual dopant atoms within buried crystalline interfaces. Here, we demonstrate atomic-scale plan-view observation of a buried crystalline interface (an yttrium-doped alumina high-angle grain boundary) using aberration-corrected Z-contrast scanning transmission electron microscopy. The focused electron beam transmitted through the off-axis crystals clearly highlights the individual yttrium atoms located on the monoatomic layer interface plane. Not only is their unique two-dimensional ordered positioning directly revealed with atomic precision, but local disordering at the single-atom level, which has never been detected by the conventional approaches, is also uncovered. The ability to directly probe individual atoms within buried interface structures adds new dimensions to the atomic-scale characterization of internal interfaces and other defect structures in many advanced materials and devices.