X-ray powder diffraction and transmission electron microscopy were used to investigate the formation characteristics and stability range of the tetragonal modification of a fluorite-type Bi 2 O 3 -Nb 2 O 5 solid solution. The results showed that this tetragonal, commensurately modulated phase forms through the intermediate formation of the incommensurately modulated cubic fluorite phase followed by the incommensurate-commensurate transformation. This transformation can be described as a homogeneous nucleation with a temperature-dependent induction time and growth kinetics, which is determined by a growth rate of the tetragonal domains nucleated during the induction time. The homogeneity range of the tetragonal phase was found to extend between -0.2 e y e 0.04 for the general formula Bi 3-y Nb 1+y O 7+y . The tetragonal Bi 3-y Nb 1+y O 7+y phase is thermally stable up to the transition temperature where it transforms back to the cubic incommensurate phase. The transition temperature increases with Nb concentration from 750 °C for y ) -0.2 to 920 °C for y ) 0.04.
Copper doped sodium titanate nanotubes and nanoribbons were prepared Via two different doping methods called in situ and ex situ. In the applied in situ method, titanate nanotubes were grown from anatase TiO 2 doped with Cu 2+ , while in the ex situ method, titanate nanotubes and nanoribbons were exposed to aqueous solution of Cu 2+ species. By correlating XRD, electron microscopy, magnetic susceptibility, and electron paramagnetic resonance (EPR) measurements, we found that in the samples prepared Via the ex situ doping method, sub-10 nm CuO nanoparticles grow on the inner/outer surface of nanotubes/nanoribbons where the Neel transition temperature is strongly suppressed. In fact, they behave as superparamagnets with a blocking temperature of around 50 K. Strong evidence that Cu 2+ species that form complexes between titanate layers coordinate with Na + ions comes from the pulsed EPR data.
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