Ž . Physica C 333 2000 1–12 www.elsevier.nlrlocaterphysc Reaction of YBa Cu O with Br : oxidation and formation of 2 3 6 2 nanoscale YBa Cu O 2 3 7 D.G. Hinks a, ) , O. Chmaissem b,c , L. Ely b,d , C. Scott b,d , J.D Jorgensen a , J.K. Akujieze b,d a Materials Science DiÕision, Argonne National Laboratory, Bldg. 223, 9700 S. Cass AÕenue, Argonne, IL 60439, USA b Science and Technology Center for SuperconductiÕity, Argonne National Laboratory, Argonne, IL 60439, USA c Department of Physics, Northern Illinois UniÕersity, Dekalb, IL 60115, USA d Chemistry and Physics Department, Chicago State UniÕersity, Chicago, IL 60628, USA Received 2 June 1999; received in revised form 13 January 2000; accepted 20 January 2000 Abstract We have investigated the products of the reaction of reduced YBa Cu O with bromine using thermal analysis and 2 3 6qx neutron powder diffraction. We find that bromine is not intercalated into the 123 structure. The reaction reduces the particle size of the 123 material allowing the oxygen formed at the reacting surface to diffuse into the material in a reasonable time scale at the low reaction temperatures. q 2000 Elsevier Science B.V. PACS: 74.72.Bk.Y; 74.62.Dh; 82.40.g; 66.30.yh Keywords: Br intercalation; O diffusion; YBa Cu O Br 2 3 6 1. Introduction Ž . Soon after the discovery of YBa Cu O 123 , 2 3 6qx it was found that treatment of the reduced material Ž . Ž . i.e., x f 0 with halogen Cl , Br or I gas at low 2 2 2 temperatures would reoxidize the material and rein- w x troduce superconductivity 1–7 . This reaction was Ž done at low temperature at approximately 2508C, . 2208C and 1208C for I , Br and Cl , respectively 2 2 2 in order to avoid secondary reactions leading to other wx phases 6 . The temperature for this oxidization is much below the temperature then thought to be ) Corresponding author. Tel.: q 1-630-252-5471; fax: q 1-630- 252-7777. Ž . E-mail address: hinks@anl.gov D.G. Hinks . necessary for diffusion of O into the lattice by 2 wx conventional methods. Radousky et al. 7 estimated that the diffusion constant for Br into 123 at 2608C 2 was four orders of magnitude greater than for oxy- gen at the same temperature. The low reaction tem- perature and the estimate of a faster diffusion con- stant than would be expected for oxygen at these temperatures led to the belief that halogens interca- late into the 123 lattice. An alternative explanation, other than intercala- tion, for the results of such experiments is that a surface reaction of the halogen gas occurs to yield oxygen that subsequently diffuses into the lattice. wx Olesh et al. 9 investigated the chlorination of 123 using X-ray diffraction and Auger Electron Spec- Ž . troscopy AES . After chlorination, they found sec- ondary phases by X-ray diffraction that included 0921-4534r00r$ - see front matter q 2000 Elsevier Science B.V. Ž . PII: S0921-4534 00 00094-0