Use of low temperature solvothermal reactions in the synthesis of nanocrystalline tantalum nitrides including nanorods

Abstract

Solvothermal reactions of TaCl₅ with LiNH₂ or Mg₃N₂ lead to amorphous products at temperatures up to 500 °C. Post-reaction annealing under nitrogen yields crystalline products with Ta₃N₅ (LiNH₂) and TaN (Mg₃N₂) structures. When these reactions are carried out with LiNH₂ in refluxing mesitylene, rods of Ta₃N₅-structured material are obtained. Using commercial LiNH₂ these have dimensions of ∼5 × 200 nm but are contaminated with LiTaO₃. With high purity LiNH₂ a black oxide-free but carbon-containing material presents as rods of 20–50 nm length. Higher temperature reactions in an autoclave lead to isotropic nanocrystals of ca. 10 nm diameter of a nitrogen-deficient or carbide-substituted Ta₃N₅-type material. Carbon incorporation is attributed to solvent decomposition at the temperatures required for the reactions. The TaN derived from reactions with Mg₃N₂ consists of nanoparticles of 6–8 nm in diameter.