In techniques like spark plasma sintering (SPS) or field assisted sintering technology (FAST), manufacturers apply electrostatic fields to powder compacts to densify ceramic materials. This method has led to debates about whether the applied field affects the materials’ atomic grain boundary structures and macroscopic properties. In response, Hughes et al. systematically changed the atomic structure of grain boundaries in strontium titanate (SrTiO3) with applied electrostatic fields during processing.

In the experiment, they used diffusion bonding to form SrTiO3 bicrystals with a flat interface plane and well-controlled grain boundary misorientation. During diffusion bonding experiments, two single crystals, placed between two insulated electrodes, applied a homogeneous electric field while avoiding current flow. “We were able to fix the misorientation between the two crystals and have systematically studied the effects of the applied electric field,” said author Klaus van Benthem.

The electrostatic field effects in SPS or FAST could help manufacturers make ceramics more quickly and at lower temperatures. Moreover, using an electrostatic field in the absence of current would reduce overall power consumption and costs associated with manufacturing these materials. SrTiO3’s cubic perovskite structure serves as a model system for oxide ceramics used in superconductors, memory devices and photovoltaic cells.

Next, the team will examine the thermodynamic stability of these structures at high temperatures, and test how varying electric field strengths could cause additional changes in grain boundaries. Ultimately, van Benthem identified their driving question as whether they can make a ceramic and change the grain boundary structure in operando.

Source: “Electrostatic fields control grain boundary structure in SrTiO3,” by L. A. Hughes, M. Marple, and K. van Benthem, Applied Physics Letters (2018). The article can be accessed at https://doi.org/10.1063/1.5039646.