Nominally pure nanocrystalline KTaO 3 was thoroughly investigated by micro-Raman and magnetic resonance spectroscopic techniques. In all samples the defect driven ferroelectricity and magnetism are registered. Both ordering states are suggested to appear due to the iron atoms and oxygen vacancies. The concentration of defects was estimated to be 0.04 and 0.06-0.1 mole %, respectively. Note that undoped single crystals of KTaO 3 are nonmagnetic and have never exhibited ferromagnetic properties. The results enable us to refer a nanosized KTa(Fe)O 3 to the class of multiferroics and assume that it could perform the magnetoelectric effect at T<29 K. It was also established that the critical concentration of impurity defects necessary to provoke the appearance of the new phase states in the material strongly correlates with the size of the particle; as the size of the particle decreases, the critical concentration decreases as well.
The surfaces of wire-like silicon crystals grown by self-organization
processes are characterized using electron microscopy of high
resolution, scanning tunnelling microscopy, x-ray microprobe
analysis, secondary-ion mass spectroscopy, and Auger electron
spectroscopy. The results obtained have shown that the upper
layer of each microcrystal
is a nanoporous envelope. The composition of the envelope is in
general similar to the composition of the bulk part of the crystal
but with some differences: the density of the matter - due to the
porous nature of the envelope - is much smaller, and the density of
metal impurities is slightly increased on the external surface.
More striking was the fact that the external surface of the envelope
is passive under exposure to oxygen. In Auger spectra of crystals
stored in open air for several years, only the LVV and KLL peaks
that are specific to the atomically clean silicon surface were
observed.
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