Discovery of Ternary Silicon Titanium Nitride with Spinel-Type Structure

Here we report on the discovery of a ternary silicon titanium nitride with the general composition (Si_1-x,Ti_x)₃N₄ with x = 0 < x < 1 and spinel-type crystal structure. The novel nitride is formed from an amorphous silicon titanium nitride (SiTiN) precursor under high-pressure/high-temperature conditions in a large volume high-pressure device. Under the conditions of 15-20 GPa and 1800-2000 °C, spinel-type γ-Si₃N₄ and rock salt-type c-TiN are formed. In addition, crystals of the discovered nano-sized ternary phase (Si_1-x,Ti_x)₃N₄ embedded in γ-Si₃N₄ are identified. The ternary compound is formed due to kinetically-controlled synthesis conditions and is analyzed to exhibit the spinel-type structure with ca. 8 atom% of Ti. The Ti atoms occur in both Ti³⁺ and Ti⁴⁺ oxidation states and are located on the Si sites. The ternary nano-crystals have to be described as (Si,Ti)₃N₄ with N-vacancies resulting in the general composition (Si⁴⁺_1-x Ti⁴⁺_x-δTi³⁺_δ)₃N_4-δ.