SECONDARY-PHASE ORIENTATION PROBED BY EPR - Y2BACUO5 IN YBA2CU3O7-X

Textured YBa2CU3O7-x samples have been studied by electronic paramagne tic resonance. EPR spectroscopy allows us to analyze the Y2BaCuO5 seco nd phase present as inclusions in the YBa2Cu3O6 textured matrix. All s amples were deoxygenated in order to limit the skin effect due to cond uctivity. This is applied to samples textured according to different t echniques. Preferential orientation of these particles according to th e 123 matrix can be observed. For instance, if texturing under a magne tic field, the particular Y2BaCuO5 orientation is observed of the b(21 1) axis (b = 7.132 Angstrom) parallel to c(123) and to the magnetic fi eld direction. By appropriate calculations from initial spectra, the f raction of preferred orientation of these Y2BaCuO5 grains can be quant ified. This orientation comprises 16 +/- 2 % of the Y2BaCuO5 weight fo r texturing under a magnetic field, presently one of the highest value s obtained. It involves the longest size of Y2BaCuO5 elongated grains lying in YBa2CU3O6 planes, facilitating the texturation process. Textu ring on Y2O3 by the modified melt textured growth method leads to a pr eferential orientation of Y2BaCuO5 grains too, but in another directio n, i.e., b(211) perpendicular to c(123) There is no Y2BaCuO5 preferent ial orientation if texturing with a thermal gradient or on a monocryst alline MgO substrate. This type of analysis can be applied easily to o ther systems (nanocomposites, dispersoids, etc.), providing that the s ignal of the secondary phase can be clearly separated from the signal of the primary one.