Preparation of one to three unit cell thick powders and investigation of their magnetic and microwave properties

Nanocrystalline powders have been prepared by a citrate gel modification of the sol - gel technique. Using a relatively low temperature, , and (i) a process of extracting oxygen and reoxidizing the precursor powder or (ii) a sequence of vacuum annealing and prolonged heating in air, it was possible to avoid sintering of the particles. According to x-ray powder diffraction analysis the particles have orthorhombic structure pertinent to the phase. Measurements made by atomic force microscopy show that they have flat shape with two maxima in the thickness distribution, one at 1.2 nm and the other at 3.8 nm , corresponding to one or three orthorhombic unit cell lengths of the crystal. The average width of the particles is 40 nm. A similar value could be obtained from XRD measurements and the width of microwave absorption line around zero applied field. Superconducting properties of the powders were investigated with magnetization measurements.