Direct fabrication and nitridation of a high-quality NaTaO₃ crystal layer onto a tantalum substrate

High-quality nano-/microtextured NaTaO₃ crystal layers were successfully fabricated on Ta substrates at a relatively low temperature using molten NaNO₃ as the starting material. Ta substrates coated with an aqueous NaNO₃ solution were heated at 500 °C in an infrared heating furnace, whereupon Ta reacted with NaNO₃ (which acted as both the Na source and the flux) to afford a layer of densely packed cubic NaTaO₃ crystals that adhered readily onto the substrate. Nitridation of the NaTaO₃ crystal layer by heating at 850 °C under an NH ₃ flow yielded a Ta₃N₅ crystal layer. The crystals retained their original size and shape but became highly porous after nitridation. TEM observations clearly indicated that the porous cubic crystals consisted of highly crystalline nanoparticles.