Solvothermal synthesis of hierarchically structured pyrochlore ammonium tungstate nanospheres

Nanospheres of pyrochlore ammonium tungstate with an average diameter of 80 nm are formed quantitatively via the one-step solvothermal reaction of ammonium metatungstate in the presence of an organic amine. The key solvothermal reaction parameters for pyrochlore formation are outlined. Morphology control is exerted over two length scales: the nanospheres are composed of nanorods with diameters around 2 nm and lengths in the 10 nm range. The spherical pyrochlore particles are thermally resistant up to 400 °C, and they are finally transferred into nanoscale monoclinic WO3 upon heating to 850 °C.