Effects of Y doping on the (Hg,Re)-1212 superconductor properties C.A.C. Passos * , J.L. Passamai Jr., M.T.D. Orlando High Pressure Laboratory, Departamento de Fı ´sica, Universidade Federal do Espı ´rito Santo, Vito ´ ria - ES, 29060-900, Brazil Available online 28 March 2007 Abstract Hg 0.82 Re 0.18 Ba 2 Ca x1 Y x Cu 2 O 6+d samples were prepared with different yttrium (Y) content (0.05 < x < 0.55). The X-ray diffraction analysis has revealed that there is no Y-precursor precipitation, however, the n = 3 phase has appeared for x < 0.15. The ac magnetic susceptibility measurements have shown that T c was reduced with increasing the Y content. Moreover, the T c values can be fitted as an approaching parabolic dependence on yttrium content. In our opinion, this behavior is understood according to the phenomenolog- ical model charge-transfer, i.e., the Y doping changed the carrier in the inner layer and induced an overdoped, which reduced the T c value. Ó 2007 Elsevier B.V. All rights reserved. Keywords: (Hg,Re)-1212 samples; High-T c ; Yttrium doping 1. Introduction The synthesis of the HgBa 2 Ca n1 Cu n O 2n+2+d or Hg- 12(n  1)n compound has been optimized in the last years [1]. Some authors have used the partial substituting Hg by cations with a higher-valence [2–6], for instance, the rhe- nium (Re) oxide [7], which stabilizes the structure. In addi- tion, these compounds are increasing the possibility for applications to electronic devices operating at temperatures higher than liquid nitrogen temperature (77 K). We have here reported an investigation about the Y doping on the (Hg,Re)-1212 superconductor sample. In this study we report ceramic precursor preparations to obtain a homogeneous distribution on final samples. 2. Experimental Initially, the Ba 2 Ca x1 Y x Cu 2 O 6 compound was pre- pared from the monophasic precursor Y 2 Cu 2 O 5 or Y 1.4 BaCu 1.6 O 5 , CaCu 2 O 3 , and BaCuO 1.997 . The yttrium content was chosen x = 0.10, 0.20, 0.30, and 0.50. Sec- ondly, ReO 2 (99.0% Aldrich) and Ba 2 Ca x1 Y x Cu 2 O 6 in a powder form were prepared with the molar relationship of 0.18:1. The precursors were heated at 850 °C in a flow of oxygen for 15 h. The obtained precursor was crushed, homogenized, and compacted again before being heated a second time at 920 °C for 12 h in a flow of oxygen. The later procedure was repeated for seven more times [8]. Finally, the precursors were blended with HgO at the molar relationship of 1:0.82, pelletized with a uniaxial pres- sure of 1 GPa and introduced into a sealed quartz tube with 8 mm inner diameter. The synthesis of the samples were done at 865 °C for 72 h [7,8]. All details of the synthe- sis process and susceptibility measurements were reported elsewhere [7]. The X-ray diffraction (XRD) measurements were performed using laboratory diffractometer models Rigaku Multiflex and D-MAX with CuKa radiation. 3. Results and discussions The main (Hg,Re)-1212 phase was very crystalline as considering small broadening of their peaks. In all the case, there is no precipitation of yttrium, however, the n =3 phase is present for x < 15, as shown in Fig. 1. The param- eters of (Hg,Re)-1212 phase were calculated from the XRD spectra and considering the P4/mmm space-group symme- try. The increment of the Y concentration has caused a 0921-4534/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2007.03.153 * Corresponding author. E-mail address: cacpassos@yahoo.com (C.A.C. Passos). www.elsevier.com/locate/physc Physica C 460–462 (2007) 728–729