Journal Article 05175J654G 444W947O8O 6I3K30563S Europium Lanthanum Niobium Oxides Research Support, Non-U.S. Gov't Research Support, U.S. Gov't, Non-P.H.S. atomic order electrolyte gating electron energy loss spectroscopy field-effect transistors heterostructures high-temperature tunneling spectroscopy inelastic tunneling spectroscopy interfaces ionic diffusion, nanoionics, tunnel junctions laser heating membranes nanocrystals nanoengineering oxides patterning liquids sapphire scanning transmission electron microscopy surface thin films thin‐film heterostructures