Microwave absorption enhancement and electron microscopy characterization of BaTiO₃ nano-torus.

Uniform BaTiO(3) nano-torus with either concave or epicenter holes were synthesized by a hydrothermal method. Experimental observations indicated that the BaTiO(3) nano-torus with an average diameter ranging from 50 to 100 nm was of tetragonal phases at room temperature. The morphology of the BaTiO(3) nano-torus depends on the shape of the original titanium dioxide precursor and reaction time. The microwave absorption properties of both the BaTiO(3) nano-torus and the BaTiO(3) solid nanoparticles were examined between 2-18 GHz microwave frequency bands. The maximum reflection loss of the BaTiO(3) nano-torus reached -28.38 dB at 11.36 GHz, compared to that of -12.87 dB at 16.32 GHz of the BaTiO(3) solid nanoparticles. The nearly 120% enhancement of the reflection loss in the range of 8-12 GHz was probably attributed to the hollow volume inside the BaTiO(3) nano-torus which might contribute more dissipation and scattering effects of the microwave. Growth mechanisms of the BaTiO(3) nano-torus were also investigated by changing both the reaction time from 0.5 h to 48 h and the reactants concentration ratio between Ba(OH)(2)·8H(2)O and titanium dioxide. Both an "in situ transformation" mechanism and a "dissolution-precipitation" growth mode were proposed.