Effects of Ag, Ag 2 O and AgNO 3 addition on the superconducting properties of Tl 2 Ba 2 CaCu 2 O 8 Faizah M. Salleh a , A.K. Yahya a , H. Imad b , R. Abd-Shukor c, * a Faculty of Applied Sciences, Universiti Teknologi MARA, Shah Alam, Selangor, Malaysia b Faculty of Science and Environmental Studies, Universiti Putra Malaysia, Serdang, Selangor, Malaysia c School of Applied Physics, Universiti Kebangsaan Malaysia, Bangi, Selangor, Malaysia Received 22 April 2002; accepted 24 October 2002 Abstract The effects of 5 wt.% Ag additions in the form of Ag powder, Ag 2 O and AgNO 3 on phase formation and superconductivity of Tl- 2212 is reported. Samples were prepared using two different solid state synthesis routes: (a) addition of 5 wt.% Ag to presynthesized (PS) Tl-2212 powder and (b) premixing (PM) of 5 wt.% Ag to unreacted powders with starting composition of Tl 2 Ba 2 CaCu 2 O 8 . For PS samples, addition of Ag showed little effect on T c values. For PM samples, addition of Ag in the form of Ag powder and AgNO 3 showed a lowering of T c zero to around 70 K. In the case of Ag 2 O the deterioration is severe and the sample was not superconducting down to 10 K. X-ray diffraction patterns of PM samples showed existence of Tl-2212 phase and a substantial amount of unreacted Tl 2 O 3 . We also report results of microstructural investigations using scanning electron microscope and Vickers Microhardness measurements and their variation with the synthesis methods and the different forms of Ag-additives. The different forms of starting silver give rise to varied Tl-2212 properties and the PS AgNO 3 sample showed the best improvement in normal state conductivity compared to metallic silver and silver oxide powders. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Tl 2 Ba 2 CaCu 2 O 8 :silver; Hardness; Microstructure PACS numbers: 74.25.Fy; 74.25.Ld; 74.62.Bf; 74.62.Dh; 74.72.Fq 1. Introduction High-temperature superconductors are ceramic mate- rials in which elements such as yttrium and barium, or lanthanum and strontium, are sandwiched between layers of copper and oxygen atoms. The brittle nature inherent in the ceramics possess one of the most serious difficulties which must be overcome before wider application of the material in a technological environ- ment can be made possible [1]. One way to overcome this difficulty is by packing the ceramic materials or precursor powders into Ag tubes which are extruded and drawn into wires or rolled to form a flat tape before being heat-treated. For RE123 (RE, rare earth) and Bi- based superconductors the addition of Ag which forms a second phase in the superconducting matrix to improve its properties has been reported by several authors [3  /6]. Cankurtaran and Saunders reported that addition of Ag could stiffen the granular ceramic by filling the pores and intergranular spacings [2]. Singh et al. reported that Ag also could increase the resistance to crack propaga- tion by pinning the propagation of cracks [3]. Nishio et al. reported that the presence of Ag enhances the toughness of the ceramic [4] and Moya and Saiz [5] reported that Ag increases water resistance of the superconductor. Amongst high-temperature superconductor families, the Tl-based superconductors are somewhat more difficult to prepare single-phased and is highly porous due to the low melting point of Tl 2 O 3 at atmospheric pressure [6]. Several authors have studied properties of Ag sheathed Tl-based tapes and wires (for e.g. [7  /9]). It is interesting to explore the effects of Ag addition on * Corresponding author. Tel.:  /60-3-89215904; fax:  /60-3- 89213777. E-mail address: ras@pkrisc.cc.ukm.my (R. Abd-Shukor). Materials Science and Engineering B98 (2003) 17  /20 www.elsevier.com/locate/mseb 0921-5107/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0921-5107(02)00575-5