Nanoparticles of Ni/NiO embedded in TiO2 synthesized by the complex-polymer sol-gel method

Ni-doped TiO2 nanoparticles were synthesized by the non-hydrous complex-polymer sol-gel method. Titanium isopropoxide was used as precursor and acetyl acetone (AcAc) and citric acid were used as polymer and complex agent, respectively. A series of Nix: Ti1-xO2 samples with x=0.01, 0.03, 0.05 and 0.10 were prepared and subsequently annealed at 400, 600 and 800 0C. The structural and magnetic properties of Nix: Ti1-xO2 were studied by means of x-ray diffraction (XRD) and dc magnetometery. Samples annealed at 400 0C attained a particle size of 12 nm with structural phases of anatase, rutile and cubic NiO. From the blocking temperatures of the zero-field-cooled and field-cooled measurements, similar particle sizes (as from XRD) were obtained. The presence of ferro- and antiferromagnetic (AFM) interactions further confirms that the particles have different structural compositions. At 800 0C the particles have grown to about 30 nm with either a rutile or NiTiO3-type structure. The presence of NiTiO3 is also seen in the magnetic measurements, which show the characteristic AFM peak at 23 K.