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Obrvation of superconductivity in Y 2PdGe 3,structurally same as MgB 2E.V.Sampathkumaran †and Subham Majumdar Tata Institute of Fundamental Rearch,Homi Bhabha Road,Colaba,Mumbai-400005,India The results of electrical resistance (1.4-300K),magneti-zation (2-300K)and heat-capacity (2-50K)measurements in Y 2PdGe 3,found to crystallize in a AlB 2-derived hexag-onal structure,are reported 1.The results establish that this compound is superconducting below 3K.This oberva-tion is interesting considering that this compound is the first superconductor among the ternary members derived from the hexagonal AlB 2structure.With superconductivity being un-common even among binary alloys derived from AlB 2struc-ture and with recent excitement on the obrvation of high temperature superconductivity in Mg B 2,this finding gains importance.Recent obrvation [1]of superconductivity with T c clo to 40K in MgB 2has caud considerable excitement among condend matter physicists.[2,3]This compound crystallizes in the hexagonal AlB 2-type structure,which is made up of alternating of hexagonal layers of Al and graphit
e-like honeycomb layers of B atoms.This obr-vation of superconductivity is further fascinating,par-ticularly when one notes that this structure is generally unfavorable for superconductivity.Thus,for instance,among the rare-earth disilides and germanides having the same electron concentration (YSi 2,YGe 2,LaSi 2and LaGe 2),only tho with the α-ThSi 2structure (YGe 2,LaSi 2and LaGe 2,structurally slightly different from that of AlB 2)have been found to be superconducting;[4–6]even for ThSi 2,the α-tetragonal form exhibits a higher T c (3.16K)than the β-form which is of AlB 2-type (2.4K).[7,8]Thus,it is of interest to arch for supercon-ductors among compounds crystallizing in the AlB 2-type structure,particularly to look for the ones not containing B in view of a proposal that B,being a light atom,plays a vital role to favor superconductivity in this structure.During last few years,we have been actively involved in synthesizing new compounds of the type R 2XY 3,with
crystal structures derived from that of AlB 2(Ref.9).Though we noticed veral interesting magnetic anoma-lies,[10–20]in particular relevant to the fields of Kondo
standard superconductors like Pb establishes bulk nature of superconductivity.The plot of M versus H(e Fig. 1,int)at1.7K is typical of that of type-II supercon-ductors with a value of lower criticalfield of about400 Oe.In order to render further support to the bulk nature of superconductivity,C was also measured down to2.5 K and the upturn obrved in the data obtained
below 3K(e Fig.1,bottom int)is sufficient to establish bulk superconductivity;the broadened signal around the transition could possibly due to inhomogeneities.The values of the Debye temperature and the electronic term (γ)inferred from the data in the range5-15K turn to be about130K and2.5mJ/mol K2respectively.If one employs this value ofγ,the value of∆C/γT c turns to be clo to3,which is far away from the weak coupling value of1.35.
To conclude,we report the formation of a new com-pound,Y2PdGe3,in the hexagonal AlB2-structure and studied its physical characteristics.This compound has been identified to be the lone superconductor till date in this family of ternary rare-earth compounds.We hope that the obrvation of superconductivity in a AlB2-type compound,not containing B,may be helpful for overall theoretical understanding of high T c in MgB2.Finally we would like to state that a weak superconducting signal around7K has been obtained even in the composition Y2PdSi3[21].
†E-mail address:s.in
Y 2PdGe 3
T (K)托腹带
χ (e m u / m o l )-8-40
25 Oe H ( kOe)048
M (e m u / g )-0.4
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0.4T = 1.7 K ZFC FC T (K)024
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4
C (m J /m o l K )2040
6080
