IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 27, NO. 4, JUNE 2017 7200403 Interrelation Between Structural and Electrical Properties in RuSr 2 GdCu 2 O 8±Z Prepared Under Different Annealing Conditions Valentin Garcia-Vazquez, Mohamed Abatal, Outmane Oubrame, Ismeli Alfonzo, Hussain Alazki, Jose O. Flores-Flores, Adolfo Quiroz, Jose C. Flores-Garcia, and Gonzalo Gonzalez Abstract—The effect of annealing in flowing oxygen on the structural and electrical properties of the rutheno-cuprate RuSr 2 GdCu 2 O 8 ±z (Ru-1212) was investigated. The solid-state re- action method was used to synthesize the Ru-1212 compound at ambient pressure using temperatures between 960 and 1000 °C in air. Pure-phase samples were obtained and then annealed in flow- ing oxygen at 1060 °C for 0, 48, 72, or 168 hrs. The structural data of each sample were refined by the Rietveld method. Cell pa- rameters, a and c, as well as the Cu-O(1) interatomic distances increase as the annealing time in flowing oxygen increases. The temperature-dependent electrical resistance of the sample that was not annealed in flowing oxygen shows semiconducting behavior. In contrast, samples annealed in flowing oxygen show superconduct- ing transitions. All these results indicate that the structural and electrical properties of the Ru-1212 compound are related. Index Terms—Electrical resistance measurement, granular su- perconductors, magnetic materials, ruthenium, X-ray diffraction. I. INTRODUCTION S UPERCONDUCTIVITY and magnetism are two ordered states into which materials can condense at low temper- Manuscript received September 7, 2016; accepted January 26, 2017. Date of publication February 6, 2017; date of current version February 17, 2017. This work was supported in part by CONACyT under Grant 169133 and Grant INFR-230530 and in part by SEP and VIEP-BUAP. V. Garcia-Vazquez is with the Instituto de F´ ısica Luis Rivera Terrazas, Benem´ erita Universidad Aut´ onoma de Puebla, Puebla 72570, Mexico (e-mail: lema@ifuap.buap.mx). M. Abatal, H. Alazki, and A. Quiroz are with the Facultad de In- genier´ ıa, Universidad Aut´ onoma del Carmen, Ciudad del Carmen 24180, Mexico (e-mail: mabatal@pampano.unacar.mx; halazki@pampano.unacar.mx; adquiroz@hotmail.com). O. Oubrame is with the Facultad de Ciencias Qu´ ımicas e Ingenier´ ıa, Univer- sidad Autonoma del Estado de Morelos, Cuernavaca 62209, Mexico (e-mail: oubram@uaem.mx). I. Alfonzo is with the Instituto de Investigaciones en Materiales, Unidad Morelia, Universidad Nacional Aut´ onoma de M´ exico, Morelia 58190, Mexico (e-mail: ialfonso@iim.unam.mx). J. O. Flores-Flores is with the Centro de Ciencias Aplicadas y Desarrollo Tecnol´ ogico, Universidad Nacional Aut´ onoma de M´ exico, M´ exico D.F. 04510, Mexico (e-mail: ocotlan.flores@ccadet.unam.mx). J. C. Flores-Garcia is with the Facultad de Ciencias de la Electr´ onica, Benem´ erita Universidad Aut´ onoma de Puebla, Puebla 72570, Mexico (e-mail: jocafg@gmail.com). G. Gonzalez is with the Instituto de Investigaciones en Materiales, Univer- sidad Nacional Aut´ onoma de M´ exico, M´ exico D.F. 04510, Mexico (e-mail: joseggr.iim@gmail.com). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TASC.2017.2664420 atures. These two states, in general, are detrimental to one another. Tremendous interest has been devoted to study com- pounds in which magnetism and superconductivity coexist. Examples of compounds that exhibit this exotic behavior are the copper-ruthenium oxides RuSr 2 LnCu 2 O 8 (Ru-1212) and RuSr 2 (Ln 1+x Ce x )Cu 2 O 10 (Ru-1222) with Ln = Sm, Eu, and Gd, synthesized for the first time by Bauernfeind et al. [1]. The crystal structure of the Ru-1212 layered cuprate is derived from the YBa 2 Cu 3 O 7 system, where the Cu–O chains in the charge reservoir block are replaced by RuO 2 planes [2], [3]. The in- fluence of cation substitution on the physical properties in the Ru-1212 system has been reported in the literature [4]–[10]. The superconducting transition Tc in Ru-1212 occurs at tem- peratures far below the ferromagnetic transition. Several values of Tc have been reported in the literature. The superconducting transition seems to depend on the sample synthesis and anneal- ing conditions [11], [12]. Furthermore, several authors report the formation of a small amount of ferromagnetic SrRuO3 impurity. Some of them indicate the sintering method used to remove this impurity [13]–[17]. In the studies that use a sintering step with flowing oxygen, the annealing time may vary from 10 hours up to 7 days. So far, there is no report that presents precise time of oxygenation that is needed to obtain a pure-phase Ru-1212 superconductor. We have obtained a pure phase of superconducting Ru-1212 compound without performing a reaction with N 2 . The impor- tance of this paper is to present a detailed study of the pre- cise time of oxygenation for obtaining the superconducting phase. In the present contribution, we report the relationship be- tween structural and electrical properties of the rutheno-cuprate Ru 2 Sr 2 GdCu 2 O 8±z annealed at different times in flowing oxygen. II. EXPERIMENT RuSr 2 GdCu 2 O 8±z samples were sintered by the solid state reaction method from high purity ( 99.9%) starting powders of RuO 2 , SrCO 3 , Gd 2 O 3 , and CuO. The stoichiometric mixture of powders was ground in an agate mortar, homogenized, and heat treated at temperatures ranging from 960 to 1000 °C for 3 days in air. The process was repeated five times. The powders were then pelletized and annealed in oxygen flowing at 1060 °C for 0, 48, 72, or 168 hrs., followed by a slow cooling down to room temperature at 50 °C/hr. 1051-8223 © 2017 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications standards/publications/rights/index.html for more information.