Physica C 2 18 ( 1993) 63-68 North-Holland Effect of pelletization pressure on texturing of a YBa2Cu307_-6 sample P. Barat, SK. Bandyopadhyay, P. Dasgupta, Pintu Sen and Udayan De zyxwvutsrqponmlkjihgfedcbaZ Variable Energy Cyclotron Centre, l/AF Bidhan Nagar, Calcutta, PIN 700064, India S.K. Kar, P.K. Mukhopaclhyay and C.K. Majumdar S.N. Bose National Centre for BasicSciences, DB-I 7 Bidhan Nagar, Calcutta, PIN 700064, India Received 26 August 1993 Texturing in YBa&us07_dpellets has been studied as a function of pelletixation pressureapplied before fmal oxygen annealing. X-ray diffraction, scanning electron microscopy, oxygen estimation, as well as resistivity measurements along and perpendicular to the direction of pelletixation pressure have been carried out to investigate this texturing. Such measurements of both the resistivity components for textured samples have not been reported earlier. Our observations are that ( 1) the texturing progresses through two different mechanisms, viz grain growth and slip-plane movement, depending on the applied pressurerange, and (2) at high enough pressure, the grains break up, inhibiting attempts at higher texturing by still higher pressure. 1. Introduction One of the characteristics of ceramic cuprates is the anisotropy of the transport properties. This is primarily manifest in single crystals, where anisot- ropies in resistivity and critical current density have been observed by many groups [ l-31. Polycrystal- line samples have randomly oriented grains. Hence they do not show anisotropy. One of the ways of achieving anisotropy is through texturing, i.e. ori- entation of grains along a certain direction. Textur- ing can be achieved in various ways like melting with directional solidification [ 41, by changing oxygen vacancy ordering [ 51 or by the action of uniaxial pressure [ 6,7] used for making pellets. In this work, an attempt has been made to inves- tigate texturing in YBa2Cu907_d (YBCO) pellets due to different pelletizing pressures up to 1000 MPa, with respect to a “random” sample (in powdered form). The samples have been characterized in de- tail; their bulk oxygen content has been measured. Enhancement of X-ray reflection from the (001) planes as compared to other planes, is taken as a manifestation of the degree of texturing. Scanning electron microscopic (SEM) studied have been car- ried out to observe grain orientation and other pos- sible effects due to the pelletizing pressure. The re- sistivities pZand pxy,have been measured parallel and perpendicular to the direction of the application of pressure, to study the anisotropy electrically as a function of the pelletization pressure. To the best of our knowledge such measurements have not been re- ported earlier, and these resistivity results are found to be more complex than those expected from simple texturing alone. 2. Experimental Samples have been prepared starting from Y203, BaC03 and CuO by usual a solid-state reaction. Ini- tially during two sintering stages, the pressures for making the pellets were kept low (80 MPa). Pres- sures employed before the final annealing in oxygen were 400,600,800 and 1000 MPa. The pelletization of the powder was done in a dry condition. A small portion of the sintered sample pelletized at 80 MPa, which is termed random in this paper, was powdered and oxygen annealed along with the other samples. X-ray diffraction (XRD) patterns have been re- 0921.4534/93/$06.00 0 1993 Elsevier Science Publishers B.V. All rights reserved.