Diamagnetism and Strutural Transition
in the Ba
2 Cu 3 O 4 Cl 2 Compound
M. S.da Luz, C. A. M. dos Santos, A. J. S.Mahado, and B. Ferreira
GrupodeSuperondutividade, Departamento deEngenhariadeMateriais -FAENQUIL
PoloUrbo-IndustrialGlebaAI-6,CEP12600-000,Lorena, SP,Brazil
Reeivedon28February,2002
Thisworkpresents astudyof strutural and magnetiproperties ofthe Ba
2 Cu 3 O 4 Cl 2 (Ba2342)
ompound. Doped samples with K or Sr in the Ba site and Zn or Mg in the Cu site of the
Ba2342 were prepared using a solid state diusion method. They were haraterized by X-ray
powderdiratometry,sanningeletronmirosopyandd-magnetization. SampleswithBa2342
ompositionpresentedtetragonalstrutureoftheI4/mmmspaegroupwhenheat-treatedat750 O
C.
AstruturaltransitionwasobservedwhenthesamplesweredopedwithZnorMgorheat-treatedat
700 O
C.d-MagnetizationmeasurementsperformedinSQUIDshowedtheexisteneofdiamagneti
signal. Adiereneofthemagnetimomentsmeasuredatzeroeldooled (ZFC)andeld-ooled
(FC)proedureswasobservedsuggestingtheexisteneof loalizedsuperondutivityinthis
oxy-hloridesystem.
I Introdution
Inthelast years greatattentionhasbeengiventothe
study of themagneti properties in the Ba
2 Cu 3 O 4 Cl 2
(Ba2342) ompound, speially due to the presene of
opper-oxygen planes with Cu
3 O
4
stoihiometry and
distane between Cu-O atoms similar to the
high-ritialtemperatureeramisuperondutors(1.95
A)
[1-5℄. TheBa2342ompoundisreportedtohave
tetrag-onalstrutureoftheI4/mmmspaegroupandtwokind
of Cu atoms in the rystalline struture. Due to this
struture severalauthors havereporteddierent
mag-netieets[2-7℄. Toobtaininformationaboutthe
in-ueneof theLa intheBa site,reently,JinhuaYeet
al. [8℄ presented results showing a diamagneti
tran-sition lose to 20K and a metal like behavior to the
eletrial resistanein the normalstate. Theyargued
thatthisbehaviorwasausedbythesubstitutionwith
La 3+
.
Thus, in order to obtain more information about
magnetiandstruturalpropertiesofBa2342,wehave
doped this ompound withKorSr inthe Basite and
Zn orMg in theCusiteandperformedmeasurements
of X-ray powderdiratometry, sanningeletron
mi-rosopy,d-magnetizationandeletrialresistane.
II Experimental proedure
Samples with Ba
2 x K x Cu 3 O 4 Cl 2
(0 x
0.1), Ba 1:8 Sr 0:2 Cu 3 O 4 Cl 2 , Ba 2 Cu 2 ZnO 4 Cl 2 and
Ba Cu MgO Cl nominal omposition were prepared
by solid state diusion method using SrCO
3 , BaCO 3 , SrCl 2 .6H 2 0, BaCl 2 .2H 2
0, CuO, K
2
O, ZnO and MgO
powderof high purity. These powderswere grounded
in the appropriated amounts and alined at
650-700 O
C. After this proedure, the alined powders
were ompated into pellets at 500MPaand sintered
between 700 and 750 O
C depending on starting
om-position. All preparedsamples were haraterized by
X-ray powder diratometry, eletrial resistaneand
d-magnetizationmeasurementsperformedinaSQUID
(Quantum Design)in the zeroeld ooled (ZFC)and
eld ooled(FC)proedures. Some sampleswerealso
haraterized by sanningeletronmirosopy
aom-plishedwithenergydispersivespetrosopy(EDS).
III Results and disussion
Fig. 1 presents X-ray diratograms for the
Ba 2 x K x Cu 3 O 4 Cl 2
system. The(hkl)presentedin the
top of the Fig. 1 is in agreement to the Kipka and
Bushbaum referene's [1℄. Wean see that the
sam-plesaresinglephaseinthexrangeofKdoping. Atthe
sameheat treatment, wealsoobservethat aninrease
ofKompositiontox=0.15produesimpurityphases
in this system. Using these x-rays diratograms we
an alulate the lattie parameters. Fig. 2shows a
slowinreasing oftheaand b parameters,therefore,
axisdereasesasafuntion oftheKontent,
suggest-inganapproximationoftheCu-Oplanes. Samplewith
Ba Sr Cu O Cl heattreatedat700 O
presentsa similar x-ray powder diratogramsuh as
non-dopedsample. When,samplesweredopedwithZn
or Mg and heat treated at730 O
C, onean see an
en-largement of somepeaks. Fig. 3showsresults to the
doping with ZnO for a sample with Ba
2 Cu
2 ZnO
4 Cl
2
nominal omposition. Weobservethatthere is inthis
sample minor ZnO impurities(see symbol).
There-fore, we an relate the others peaks with the Ba2342
struture. Resultsofsanningeletronmirosopyand
EDSprovidethattheZniseetivelyinorporatedinto
thegrains. Essentially,thesameresultswereobtained
to theMg doping.
Figure1. X-raydiratograms fortheBa2 xKxCu3O4Cl2
system.
Ontheotherhand,inordertoverifyifthereisthe
samesplitofpeakstonon-dopedsamples,wehave
per-formed heat treatments at 700 O
C. Fig. 4 presents a
resumetothe(103)and(114)peaksforseveral
ompo-sitionsheat treatedat dierenttemperatures. Wean
observethepresene ofenlargedpeaksforthesamples
heattreatedatlowesttemperatures. InZn-doped
sam-pletreatedat730 O
C(Fig. 4),weanunambiguously
observe two peaks for eah (hkl). These results
sug-gestthatthereisaphasetransitioninthisoxy-hloride
system. Preliminaryresultsofpowderdiration
simu-lation,suggestthatthisbehaviorisrelatedtoa
tetrag-onal to orthorrhombi phase transition with
dereas-ingtemperature,whihissimilartotheYBa
2 Cu
3 O
7 Æ
Figure2. LattiesparametersfortheBa2 xKxCu3O4Cl2
system.
Figure 3. X-ray powder diratograms for Ba2Cu3O4Cl2
Figure 4. Zooming of the (103) and (114) peaks for the
following nominal ompositions and heat treatments: a)
Ba2Cu3O4Cl2 at 750 O
C, b) Ba2Cu3O4Cl2 at 700 O
C, )
Ba
2 Cu
2 ZnO
4 Cl
2 at 730
O
C, d) Ba
2 Cu
2 ZnO
4 Cl
2 at 750
O
C
ande)Ba2Cu2MgO4Cl2 at730 O
C.
Finally, in order to verify the magneti
behav-ior of this system, we have performed several
d-magnetization measurements in SQUID. In Fig. 5 is
presented some ZFC and FC magnetization urves as
a funtion of temperature measured at 20 Oe.
De-pending onthe sampleomposition,wean observea
diamagneti signal aomplishedwith two transitions
lose to 30 Kand 100K. The mostimportant fat of
thesemagnetizationmeasurementsisrelatedtothe
ex-isteneofdierenebetweenZFCandFCurves. This
an indiate the presene of superondutivityin this
system. To verify this possibility, transport
proper-tieswereperformedusingstandardfour-probemethod,
whihdemonstratedthatallsamplesareinsulators
be-low room temperature. These results suggest that if
thereissuperondutivityinthesamplesitmust
loal-izedintherystallinestruture[10℄.
IV Conlusion
ThisworkpresentsthedopingeetsofK,Sr,Zn and
MgatomsontheBa2342ompound. Thedoping
stud-iesprovideasplit ofthepeaks, whih was interpreted
asanexperimentalevideneofaphasetransitioninthis
oxy-hloride system. d-Magnetization measuredas a
funtion oftemperaturepresenteddiamagneti signals
Figure 5. Magneti moment as afuntionof temperature
measured at 20 Oe for several starting nominal
omposi-tions. ThediereneofZFCandFCmagnetizationsuggests
theexisteneofsuperondutivityintheBa2342system.
ZFC and FC proedures were interpreted as a
evi-deneofloalizedsuperondutivityintheBa2342
om-pound.
Aknowlegments
The authors are grateful to R. R. da Silva, Y.
KopelevihandC.A. Rodriguesforexperimental
sup-port. This work has been supported by the FAPESP
(GrantsNo. 00/08972-1and00/03610-4).
Referenes
[2℄ H.C.Shmelz,M. S.Golden,S.Haner,M. Knupfer,
Krabbes,J.Fink,H.Rosner,R.Hayan,H.Eshrig,A.
Muller,Ch.JungandG.Reihardt;Phys.Rev.B57,
10936 (1998).
[3℄ Y. Yamada, N. Suzuki, and J. Akimitsu, Physia B
213-214,191(1995).
[4℄ F. C. Chou, Amnon Aharony, R. J. Birgeneau, O.
Entin-Wohlman,M.Greven,A.B.Harris,M.A.
Kast-nerY.J.Kim,D.S.Kleinberg,Y.S.Lee,andQ.Zhu,
Phys.Rev.Letters 78,535(1996).
[5℄ B.Ferreira, A.J. S.Mahadoand C.A. M.dos
San-tos; 38Congresso Brasileiro deCer^amia, June,
18-21, 1994.
[6℄ K.Ruk, D. Ekert, G. Krabbs, M. Wolf, and K. H.
Muller, Journal of Solid State Chemistry 141, 378
(1998)
[7℄ J.Rihter,A.Voigt,J.Shulenburg,N.B.Ivanovand
R.Hyan,J.Magn.Magn.Mater.177-181,737(1998).
[8℄ Jinhua Ye, Zhigang Zou, and Akiyuki Matsushita,
Phys.C341-348,489(2000).
[9℄ J.D.Jorgensen,B.W.Veal,W.K.Kwok,G.W.
Crab-tree, A Umezawa, L. J. Nowiki and A. P. Paulikas,
Phys.Rev.B36,5731(1987).
[10℄ R.R.daSilva,J.H.S.TorresandY.Kopelevih,Phys.
