Doctoral student Petruša Borštnar from the Department for Advanced Materials at Jožef Stefan Institute, under the mentorship of Assoc. Prof. Dr. Nina Daneu, and in collaboration with colleagues from the National Institute of Chemistry and Cheng Kung University in Taiwan, published a paper Transient Ruddlesden–Popper-Type Defects and Their Influence on Grain Growth and Properties of Lithium Lanthanum Titanate Solid Electrolyte in the journal ACS Nano. The research describes the development of a coarse-grained microstructure in lithium lanthanum titanate (LLTO) ceramics under the influence of Ruddlesden-Popper-type planar defects. Based on quantitative high-resolution scanning transmission electron microscopy (HAADF-STEM) analyses, the authors explain the process from the formation of defects in the initial grain growth stage to the exaggerated growth of grains with RP-type defects and finally, to recrystallization of the RP-type sequences to LLTO perovskite. The results are a contribution to the development of solid electrolytes for applications in lithium-ion batteries, where the total ionic conductivity is directly related to the number of highly resistive grain boundaries.