A new anatase-type phase in the system Mg–Ta–O–N

Magnesium doped tantalum oxynitrides were prepared by ammonolysis of amorphous mixed oxides. An orange colored anatase-type phase with the composition Mg0.05Ta0.95O1.15N0.85 was found. It is metastable and undergoes a phase transformation to a baddeleyite-type phase between 900 and 1000 °C. X-ray diffraction measurements indicate spacegroup I41/amd   with lattice parameters a=391.986(6)pm and c=1011.19(3)pm. A possible anion ordering was examined by theoretical methods and neutron diffraction experiments. In addition, anosovite-type (Ti3O5) phases MgxTa3−xO3xN5−3x; 0⩽x⩽0.3 were obtained. The electronic spectra of all phases were investigated by UV/vis spectroscopy.

Schematic representation (constant 30 valencies) of all new compounds obtained as single phase samples in the system Mg–Ta–O–N (dark gray symbols).Figure optionsDownload as PowerPoint slide