Synthesis and study of high Tc oxide superconductors in the Y-and Bi systems

Abstract

Sine'" t.h•• nj"covFI;ry of hiqh t.empp.rat.ur" superconductivit.y in ceramic materi"ls by Bednarz and MuLler in 1986, extensive research work has been carried out throughout the whole world. Thi.s new family of superconductors are known as high 'I'r sup"l':cnnduct.m:s as their transition temperatur" is in th", range of .liquid nitrogen. FOllr systems of t.he"" high T~oxide Supp.Tconductors viz. I.a-Ba-Cu- 0, Y-Ba-Cu-O, Bi-Sr-Ca-Cu-U and T]-Ba-Cu".O have b",,,n widely investigi'lt.srl. ~-based superconduct.or!>. P1H"ticularly (123) YBalCul01_! compound <lnd Rismut.h blHH,d Ri-Hr-Ca-Cu-O have been selected for 5tlldy in the prflSp.nt work. Present work is divided into two parts. In t.he fin,t pa,rt., Ylla/ellJOHSAmples prepared wling in conventional solid I'tate .reacti.on ,echnlque has been studied. In .the second part. ,Bi-Sr-Ca-Cu-_O of the composit.ion BiJSrica~ul0i and (8]1'1 PbJ) sri' Cal eu; 0y fot" X _ 0, 0.1, 0.2 have been st.udled. Two diff<'!nmt. me .hods of l'ample prep .••.rat.ion called "convent.lonal solid ntat.e rellctjon technique" and "Two Rt.ep technique" have been used to obt.ain t.hene n"mples of Hi-Sr-Ca-Cu-O syst.em. In t.he conventional technique the constitl'ent m"t,eTials wjth appropriate amount. are mixed first and then reacted at elevatAd tf!mpf!rat.ure and then annealed either J.n al.r or in presence of oxygen. In thf! t.wo step techn.ique, 10.11 the cOn!';tihlfmt.8 except Bi,o; were first mjxed and reacted and then HiiO; is ••dried t.O the reactant product to produce the desired specimens. A t.ulmli'lr furnace wit.h Kenthal wi.re waR made. 'l'he furni'lce could be operat.ed to a maxjmumof 1200"C. This furnace was used t.O t.reat the samples in thp. oxygen atmosphere. X-ray diffraction analysis has been used to check the presence of .impurity phaRes J.n the prepared samples. The sl1perconduct.ing properties of this processed materials prepared using both the t.echniques were studied in pallet form. The superconducting t.ransition temperature of the samples were m<'!asur:ed IIsing four prohe ter.hni q"e "nd from the suscept.ibi 1i ty m"asurement. 'rhe present. st.udy shows that. (i ) t.he sup",rconducting transitiosn t.empflrature 'I't fot" YRaiCu,oH (123) Rample is 91..5K. This vCilue is cJose to t.he reported v",luf! of 911<t.o 95K. X-ray d,iffrllct.ion plltt.ern of the specimen "hows the preRenr:e of an ins.ignificant amount of impurity. phases .in the YBapu; OJ.! sample. (ii l IIi1 Sr] elleu] OJ (2212) prep"ren using (':ollventioll"l t.Bchnique ,md two "tel' tp.chnique did not. show any t.Tansition temperature without oxygen treat.ment. When oxygen treated, the sample prep"red using conventiOlll'll technique shows th", t.ransition t.o superconducbng state at liOK, which is higher t.han th"t of the reported value of 99K. Sample prepilr",d using two Eltep technique did not show any tr"nsition temperature. (l:ilIThe sampl •• of Bl1_! PhI SrI CIlJ eUJ 0y (x=O) did not show any transit_ion be for., the sp,"eimen WeT" treated in oxygen. The oxygen treated ,,"mp1e of conventional teohnique 9ave a transition temperature, T~_of 125K lIndfor two step technique it was observed to be 161K. These values lire higher than the report.ed vi'lluE' of 1l0K. With the s'ubstitution of lead for Bi, the trans;;tion t"mperatures were greatly enhanced. '1', for Ph = 1% (K=O.ll waS 161.5K and fur Ph " 2% (1< " 0.2), '1', was 7.04K. X-ray diffrllction pattern shows the presence of signifiC<'lnt amount. of impurity phases .in bot.h (2212) and (2223) "ample". The measurements show that: (i) Oxygen plays an importllnt role in determining t.he transition tp.mperatura in hoth Y~Ha~Ca-Cll-Osyst,em and (Bi_Sr_Ca_Cu_O) Bystem. (il) Substitution of small amount of lead did give a higher value of To hut di.d not stabilized II ",ingle phase for (22J.3). (iii)Two step technique WaR found to give samples of h~gher '1', for (7.7.7.3)compar",d t,o the 5/'1mples of conventirmal technique. 'l'he two step ter:hnique wa" found fruitless, compared to conventiona.J t.echniquf! in prOd1Jcing superconrlucting (2212) phas", (iv) However it appears th"t other than oxygen P''':''s 'In important Tole in determining tha T, Hi-content. also of the system. (v) It looks a major hurdle still need to be overcomfl to prorluce "reliable samples of (Ri-Sr-Ca-Cu-O) system wjth reproducible transition t.emperature.