JOURNAL OF MATERIALS SCIENCE LETTERS 9 (1990) 1103-1105 Thermal recovery in shock-wave modified copper-oxide superconductors L. E. MURR, C. S. NIOU Department of Metallurgical and Materials Engineering, University of Texas at E1 Paso, El Paso, Texas 799687-0520, USA Murr et al. [1] have recently shown that plane wave shock loading of sintered, superconducting YBa2Cu307 caused the resistance-temperature sig- nature to be changed rather dramatically; the normal state resistance after shock loading exhibits a semi- conducting behaviour, increasing with temperature up to Tc-start (at ~ 90 K) and then exhibiting a broad superconducting transition, intercepting the zero resistivity axis at approximately 45 K. The a.c. sus- ceptibility was also correspondingly degraded. In addition, annealing of the shock-loaded material up to 750°C in oxygen caused the resistance-temperature signature to recover: the normal-state resistivity began to revert to a metallic behaviour while the broadening of the superconducting transition was correspondingly reduced. It was also observed that shock loading at 6 GPa peak pressure did not cause a reduction in the oxygen content, and the To start was unchanged after shock loading or heat treatment from that observed ~(90K) for the unshocked, sintered YBa 2Cu 3 07. We have examined the residual resistance-tempera- ture signature for explosive (shock-wave) fabricated (consolidated), superconducting YBa2Cu307 powder (T~ start ~90K) and BiTPb3Sr~0Ca10Cu150 x super- conducting powder (To start ,-~ll0K) (DOWA Mining, Japan). Samples of these materials consoli- dated at a peak shock pressure of 5 GPa in the same copper tooling matrix [2] were extracted by milling the metal away from the consolidated channels to produce experimental samples measuring approximately 1 to 2cm in length and 0.1 cm × 0.5cm in cross-section. These samples were fitted with four contacts in a 4-probe configuration for resistance-temperature measurements. Specimens of the recovered YBa2Cu30 v and Bi7Pb3Sr~0Ca10CulsOx were also annealed at various temperatures and times in flowing oxygen or air respectively. The annealing of the YBa 2 Cu 3 07 at tem- perature was always followed by a final anneal at 400°C for 12h in flowing oxygen and slow cooling to room temperature to stabilize the orthorhombic phase. Four-probe measurements of resistance- temperature signatures were then made. Fig. 1 compares the resistance-temperature (R-T) signatures for the explosively fabricated and annealed YBa2 Cu 30 7 and Bi7 Pb3 Srl0 Ca10 CUl5 Ox correspond- ing to a peak shock pressure during fabrication of 5GPa. The results shown in Fig. l a are very similar to those obtained for plane-wave shock loaded YBa2 Cu3 07 [1]. The variations in the R-T signatures 0261-8028/90 $03.00 + . 12 © 1990 Chapman and Hall Ltd. with temperature are in fact identical to those previously observed, including the stability of the To start. By comparison with the YBa2Cu307 there is no detectable superconducting transition in the Bi-Pb- Sr-Ca-Cu-O flowing shock fabrication, and this is consistent with observations of shock loaded Bi-Pb- Sr-Ca-Cu-O at much higher pressures (~ 30 GPa) by Yoshimoto et al. [3]. However superconducting tran- sitions become apparent after annealing at 650° C, and the higher-temperature transition (To start l l0K) remains relatively stable up to the annealing tempera- tures where a sharp transition occurs. This is even true of the low-temperature (second phase) transition observed around 80K (Tc start) in Fig. lb. While there are some significant differences in the residual R-T signatures for Y-Ba-Cu-O and Bi-Pb- Sr-Ca-Cu-O explosively fabricated at 5 GPa peak pressure, the corresponding annealing behaviours are similar (Fig. 1): a trend toward metallic behaviour in the normal state and a narrowing of the superconduct- ing transition in the superconducting state with increasing annealing temperature. However, as in the case of YBa2Cu307, the broadening of the supercon- ducting transition also occurs with increasing peak shock pressure (Fig. 2b) as shown for comparison with the annealing temperatures for both Y-Ba- Cu-O and Bi-Pb-Sr-Ca-Cu-O at 5 GPa fabrication pressure in Fig. 2a. In Fig. 2 the half-start temperature is plotted at To (l/2) and corresponds to the tempera- ture mid-way between the resistance at Tc start and R = O (Fig. la). The results shown in Figs 1 and 2 are indica- tive that, as deduced in the case of shock-loaded YBa2Cu307 [1], there is a shock induced alteration in the microstructure which is not easily recovered at low temperatures. This means that simple atomic displace- ments are not involved. Since no oxygen loss was detected by thermogravimetric analysis (TGA) in the Y-Ba-Cu-O, oxygen order-disorder phenomena are not involved. This can also be corroborated by com- paring the R-T signatures of Fig. la with those obtained by Cava et al. [4] for Y-Ba-Cu-O with reduced oxygen, where the To start is reduced with reduced oxygen, while the superconducting transition remains sharp in contrast to the broad transition shown in Fig. l a and Fig. 2. We employed high-resolution transmission electron microscopy to perform a preliminary search of the shock-fabricated microstructures in both the Y-Ba- Cu-O and Bi-Pb-Sr-Ca-Cu-O using a Hitachi H-800 1103