Intergranular properties of uniaxially pressed YBa$_2$Cu$_3$O$_{7-\delta}$ ceramic samples

Abstract

We performed measurements of electrical resistivity as a function of temperature, $\rho(T)$, in polycrystalline samples of YBa$_2$Cu$_3$O$_{7-\delta}$ (Y-123) subjected to different uniaxial compacting pressures. We observed by using X-ray diffractometry that samples have a very similar composition. Most of the identified peaks are related to the superconducting Y-123 phase. Also, from the X-ray diffraction patterns performed, in powder and pellet samples, we estimated the Lotgering factor along the $(00l)$ direction, $F_{(00l)}$. The results indicate that $F_{(00l)}$ increases from 0.13 to 0.16. From electrical resistivity measurements as a function of temperature, we were able to separate contributions arising from both the grain misalignment and microstructural defects. We found appreciable degradation in the normal-state transport properties of samples with an increase in uniaxial compacting pressure. It seems that this type of behavior is associated with an increase in the influence of microstructural defects at the intergranular level. The experimental results are analyzed in the framework of a current conduction model of granular samples.