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Jturopili 
luropear 
Offlca eu 



chee Patantamt 
an Patent Office 
uropa+n daa brevets 



0 Publication numbor: 



0 275 343 

A1 



© EUROPEAN PATENT APPLICATION 

0 AppKcatton numoor: 87100^61. g @ , n( C) < H01L 39/12 

© Dale of filing 2101.87 



0 Oat© of publication of application: 
27.07.88 Bulletin 84/30 

0 Designated Contracting States: 

AT B6 CH Of ES FR OB OR IT LI LU NL SB 



0 Applicant: International Business Machinal 
Corporation 
Old Orohard Road 
Armonk. N.Y. 10804(U8) 

© invantor: Bednorz, Johannes Oaorg, Dr. 
5onnenbargstraat© 47 
CH-8134 Adllawll(CH) 
Inventor: MUllar, Carl Alexander, Prof.Dr.. 
Haldanatraaaa 84 
CM-8908 Hedlngen(CH) 
Invantor: Takaahlge, Maaaakl, Dr. 
flotfarbweg 1 
CH-8803 RUachllkon(CH) 

© Repreaentatlve: Rudaok. QUntar O.. DlpUng. 
IBM Corporation SMumerttraaae 4 
CH-8803 RUachllkon(CH) 



© Naw superconductive compounda of the K2NIP4 atructural type having a high tranaltlon 
temperature, and method (or fabricating same. 

© The superconductive compounda are oxides of 

the general formula RE,„Ae.TM.C>4_ v . wherein BE is 

a rare earth. AE is a member of the group of alkaline 

earths or a combination of at least two member of 

that group, and TM is a transition metal, and wherein 

x < 0.3 and 0.1 £ y i0,5. The method for making 

these compounds involves the steps of coprecipitat- 

»ng aqueous solutions of the respective nitrates of 

the constituents and adding the copreopitate to ox- 
alic acid, decomposing the precipitate and causing a 
^solid-state reaction at a temperature between 500 

and 1200 # C for between one and eight hours, for- 
COrning pellets of the powdered product at high pres- 
sure, sintering the pellets at a temperature between 

500 and 1000'C for between one half and three 
hours, and subjecting the pellets to an additional 
^annealing treatment at a temperature between 500 
and 1200*C for between one half and five hours in a 
^protected atmosphere permitting the adjustment of 
Q^the oxygen content of the final product 
LU 



x«fox Copy C*ntr* 



0 27fl 343 



2 



NfW aUPIRCONOUCnVt COMPOUNOS OF THI KM\f> STnUCTVWAL TYPf HAVINO A HIOH TRANSITION 
TIMPIRATURI, AND MCTHOO fOf\ PAORICATINQ 8AMI 



Field of the Invention 

The mvontion relates 10 * new class of supor- 
conductors. m particular to components of the 
KjNip! type of structure hiving superconductor 
properties below a relatively high transition tem- 
perature, and to a method for manufacturing those 
compounds. 



Ba^ ground of the Invention 

Superconductivity is usually defined as the 
complete loss of electrical resistance of a material 
at a wen-defined temperature. It Is known to occur 
m many materials: About a quarter of the elements 
and over 1000 alloys and components have been 
found to be superconductors. Superconductivity it 
considered a property of the metallic stale of the 
material, in that all known superconductors are 
metallic under the conditions that cause them to 
*uperconduct. A few normally non-metallic materi- 
als, for example, become superconductive under 
very high pressure, the pressure converting them 
to metals before they become superconductors 

Superconductors are very attractive for the 
generation and energy-saving transport of electrical 
power over long distances, as materials for forming 
the coils of strong magnets for use In plasma and 
nuclear physics, in nuclear resonance medical di- 
agnosis, and m connection with the magnetic lovita- 
non of fast trains. Power generation by thermonu- 
clear fusion, for *xample. will require very large 
magnetic fields which can only be provided by 
superconducting magnets. Certainly, superconduc- 
tors will also find application in computers and 
high-speed slgnaJ processing and data communica- 
tion. 

While the advantages of superconductors are 
quite obvious, the common disadvantage of all 
superconductive materials so far known lies in their 
very low transition temperature (usually called the 
critical temperature T c ) which is typically on the 
order of a few degrees Kelvin. The element with 
the highest T c is niobium (9.2 K). and the highest 
known T c is about 23 K (or NB 3 Qe at ambient 
pressure. 

Accordingly, most known superconductors re* 
quire liquid helium for cooling and this, in turn, 
requires an elaborate technology and as a matter 
of principle involves a considerable investment in 
cost and energy. 

It is. therefore, an obiect of the present inven- 



tion to propose compositions for high*T € suporcon. 
ductors and a manufacturing method for producing 
compounds which exhibit such a high critical tem- 
perature that cooling with liquid helium is obviated 

3 so as to considerably reduce the cost involved and 
to save energy, 

The present invention proposes to use com- 
pounds having a layer-type structure of the kind 
known from potassium nickel fluoride KjNirV This 

to structure is in particular present in oxides of the 
general composition REiTM.Oi. wherein RE stands 
for the rare earths (lanthanides) and TM stand* for 
the so-called transition metals. It is a characteristic 
of tho present Invention that in the compounds in 

'? question the RE portion is partially substituted by 
one member of tho alkaline earth group of metals, 
or by a combination of the members of this alkaline 
earth group, and that the oxygen content is at a 
deficit. 

20 For example, one such compound that meets 

the description given above is lanthanum copper 
oxide LajCuO* in which the lanthanum -which be- 
longs to the 1118 group of elements-is in part substi- 
tuted by one member of the neighboring HA group 
25 of elements, viz. by one of the alkaline earth metals 
(or by a combination of the members of the MA 
group), e.g.. by barium. Also, the oxygen content of 
the compound is incomplete such that the com- 
pound will have the general composition La,. 
20 ,BaXu04. v . wherein x i 0.3 and y < 0.5. 

Another example for a compound meeting the 
general formula given above is lanthanum nickel 
oxide wherein the lanthanum is partially substituted 
by strontium, yielding the general formula La,. 
js iSr.NlO^ . Still another example is cerium nickel 
oxide wherein the cerium is partially substituted by 
calcium, resulting in Cej„Ca,NI04. y . 

The following description will mainly refer to 
barium as a partial replacement for the lanthanum 
*Q m a LajCuO* compound because it is the 8a-La- 
Cu-0 system which is. at least at present, the best 
understood system of all possible. Some com- 
pounds of the Ba-La*Cu-0 system have been de- 
scribed by C. Michel and B. Raveau in Rev. Chim 
45 Min. 21 (1984) 407. and by C. Michel. L. Er-Rakho 
and B. Raveau in Mat. Res. Bull.. Vol. 20. 0985) 
667*671. They did. however, not find nor try to find, 
superconductivity. 

Experiments conducted m connection with the 
so present invention have revealed that h»gh-T c super- 
conductivity »s present in compounds where the 
rare earth is partially replaced by any one or more 
of the other members of the same MA group ol 
elements, i.e. the other alkaline earth metals. Ac- 



2 



0 278 340 



4 



tuilly. the T« ol LajCuO*. t wiih $r* it higher and n 
super conductivity -induced diamaQnetitm 'arge» 
than that found with Ba J and Ca J 

At a mailer of fact, only a small number of 
oxidea it known (o exhibit superconductivity, 
among thorn the Li-Ti-0 syttem with ontett of 
superconductivity as high at i3.7 K. at reported by 
OC. Johnston. H. Prakash, W.H. Zachanaten and 
R. Vitvanalhan m Mat. Res. Bull 8 (1973) 777 
Other known superconductive oxides include Nb- 
doped SrTiOj and BaPbt.,Bl.Oi . reported respec- 
tively by A. Baratotf and 0 Blnnig in Physics I08B 
(1981) 1335. and by A.W. Sleight. J.L GlHson and 
F E. Bierstedt m Solid State Commun. 17 (1975) 
27. 

The X-ray analysis conducted cy Johnston et 
al. revealed the pretence in their Ll-TI-u ;ystem of 
three different crystallography phases, on* ol 
them, with a spinel structure, showing the high 
critical temperature. The Ba-La-Cu-0 system, too. 
exhibits a number of crystallographic phases, 
namely with mlxed-vaient copper constituents 
which have itinerant electronic states between non- 
Jahn-Teller Cu 3 and Jahn-Toller Cu a ions. 

This applies likewise to systems where nickel 
is used in place of copper, with NP being me 
Jahn-Teller constituent, and Ni 1 being the non- 
Jahn-Teller constituent. 

The existence of Jahn-Teller poiarons is con- 
ducting crystals was postulated theoretically by 
K.H. Hoeck. H. Nlckisch and H. Thomas m Helv. 
Phys. Acta 58 (1983) 237. Poiarons have large 
electron-phonon interactions and. therefore, are fa- 
vorable to the occurrance of superconductivity at 
h»gh critical temperatures. 

Generally, the Ba-La-Cu-0 system, when sub- 
jected to X-ray analysis reveales three individual 
crystallographic phases, viz. 

* a first layer-type perovskite-Hke phase, related to 
the KjNiF 4 structure, with the general composition 
La,. B Ba»Cu04-y. with X««ci and yiO; 

- a second, non-conducting CuO phase; and 

- a third, nearly cubic perovskite phase ot the 
general composition Lai.,8d,Cu03. v which appears 
to be independent of the exact starting composi- 
tion. 

as has been reported in the paper by J.G. Bednorz 
and K.A. Muller in Z. Phys. B - Condensed Matter 
64 (1986) 189-193. Of tnese three phases the first 
one appears to be responsible for the high-T c 
superconductivity, the critical temperature showing 
a dependence on the barium concentration in that 
phase. Obviously, the Ba 2 substitution causes a 
mixed-valent state ot Cu 2 and Cu J to preserve 
charge neutrality. It is assumed that the oxygen 
deficiency, y. is the same in the doped and un* 
doped crystallites. 

Both LazCuO* and LaCuOi are metallic conduc- 



tors at high tomperaluret in tho absence ol barium. 
Ac'uaiiy. both aro motait like LaNlOv Oetptte their 
metallic character, the Ba-La-Cu-0 type matenalt 
are ceramics, at are tho other compound! Of the 

5 REjTM Oi type, and their manufacture more or lest 
foitowt the known principles of coramic fabrication. 
The preparation of a Ba-La-Cu-0 compound, for 
example, m accordance with the preoent invention 
typically mvoivos the following manufacturing 

to slept: 

• Preparing aqueout solutlont of the respective 
nitrates of banum, lanthanum and copper and 
coprecipitatton therof in their appropriate ratios. 

• Adding the copreclpitate to oxalic 5Cid and for- 
rs ming an intimate mixture of the retpect.ve oxalates. 

• Oecompotmg the precipitate and causing a solid* 
state reaction by heating the precipitate to a tem- 
perature between 500 and 1200*C for one to eight 
hours. 

20 - Pressing the resulting product at a pressure of 
about 4 kbax to form pellets. 
- Re-heattng the pellets to a temperature between 
500 and 900* C for one half to three hours for 
sintering. 

75 It wilt be evident to those skilled In the art that 

if the partial substitution of the lanthanum by stron- 
tium or calcium is desired, the particular nitrate 
thereof will have to be used In place of the barium 
nitrate of the example described above. Also. If the 

jo copper of this example Is to be replaced by an- 
other transition metal, the nitrate thereof will obvi- 
ously have to be employed. 

Experiments have shown that the partial con- 
tents of tho individual compounds In the starling 

33 composition play an important rote in the formation 
of the phases present m the final product. While, as 
mentioned above, the final Ba-La-Cu-0 system ob- 
tained generally contains the said three phases, 
with the second phase being present only to a very 

40 small amount, the partial substitution of lanthanum 
by strontium or calcium (and perhaps beryllium) 
will result tn only one phase existing in the final 
Laj .Sr.CuO^t or La 2 .„Ca B Cu04. v . respectively, pro- 
vided x < 0.3. 

45 With a ratio of 1:1 lor the respective (Ba. La) 

and Cu contents, one may expect the said three 
phases to occur in the final product. Setting aside 
the said second phase, i.e. the CuO phase, whose 
amount is negligible, the relative volume amounts 

so ol the other two phases are depender * on (he 
barium contents in the La ? „Ba,Cu0 4 y complex. At 
the 1:1 ratio and with an x » 0 02. the onset ol a 
localization transition is observed, i.e.. the resistiv- 
ity increases with decreasing temperature, and 

55 there is no superconductivity. 

With x ' 0.1 at the same 1:1 ratio, there 'S a 
resistivity drop at the very high critical temperature 
of 35 K 



3 



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With a .(Ba.la) versus Cu ratio of 2:1 m tho 
starting composition, trv; composition of the 
LajCuC^.Ba phase, which was assumed to bo re- 
sponsible for the serconductivity. is imitated, with 
tho result that now only two phasos are present, ? 
the CuO phase not existing. With a barium content 
of x -0.15. the resistivity drop occurs at T r • 26 
K. 

The method for preparing the Ba-La-Cu-0 
complex involves two heat treatments for the »o 
precipitate at an elevatod temperature for several 
hours. In the experiments carried out In connection 
with the present invention it was found that Dost 
rosults were obtained at 900 *C for a decomposition 
and reaction period of 5 hours, and again at 900 # C '3 
for a sintering period of one hour. These values 
apply to a ratio 1:1 composition as well as to a 2:1 
compoution. 

For the ratio 2:1 composition, a somewhat 
hiQher temperature is permissible owing to the jo 
melting point of the composition being higher in the 
absence of excess copper oxide. Yet it is not 
possible by high-temperature treatment to obtain a 
one-phase compound. 

Measurements of the dc conductivity were con- « 
ducted between 300 and 4 2 K. For barium-doped 
samples, for example, with x < 0.3. at current 
densities of 0.5 A/cm 2 , a high-tomperature metallic 
behavior with an increase m resistivity at low tem- 
peratures was found. At still lower temperatures, a jo 
sharp drop in resistivity (>90%) occurred which for 
higher current densities became partially sup- 
pressed. This characteristic drop was studied as a 
function of the annealing conditions. I.e. tempera- 
ture and oxygen partial pressure. For samples an- js 
nealed m air. the transition from itinerant to lo- 
calised behavior was not found to be very pro- 
nounced, annealing in a slightly reducing atmo- 
sphere, however, lea* to an increase in resistivity 
and a more pronounced localization effect At the *o 
same time, the onset of the resistivity drop was 
shifted towards higher values of the critical tem- 
perature. Longer annealing times, however, com- 
pletely destroy the superconductivity. 

Cooling the samples from room temperature. 45 
the resistivity data first show a metaMike decrease. 
At low temperatures, a change to an increase oc- 
curs m the case of Ca compounds and for the 8a- 
substituted samples. This increase is followed by a 
resistivity drop, showing the onset of Superconduc- so 
tivity at 22 12 K and 33 1 2 K for the Ca and Ba 
compounds, respectively. In the Sr compound, the 
resistivity remains metallic down to the resistivity 
drop at 40tl K. The presence of localization ef- 
fects, however, depends strongly on alkaline-earth 55 
•on concontration and sample preparation, that is to 
say, annealing conditions and also on the density 
which have to be optimized. All samples with low 



concontiations of Ca. Sr, and 6a show a strong 
tendency : j localisation before the resistivity drop 
occur. 

Apparently, the onset of the luperconductivily. 
10 the vaiuo of the critical tomporaturo T«, it de- 
pendent, among other parameters, on the oxygon 
content of the final compound. It seemi that a 
certain oxygen deficiency is necessary for the ma- 
terial to have a high-T 0 behavior. In accordance 
with the present invention, the mothod described 
above for making the lajOuOi:Ba complex is com- 
plemented by an annealing step during which the 
oxygen content of the final product can bo ad- 
justed. Of course, what was said in connection with 
the formation of the LajCuCVBa compound, like- 
wise applies to other compounds of the general 
formula REjTM.O^AE, such as. e.g. NdjNIO^Sr. 

In the cases where a heat treatment for de- 
composition and reaction and/or for sintering was 
performed at a relatively low temperature, i.e. at no 
more than 950 *C, the final product Is subjected to 
an annealing step at about 900*C for about one 
hour m a reducing atmosphere. It Is assumed that 
the net effect of this annealing step Is a removal of 
oxygen atoms from certain locations In the matrix 
of the RE/TM.Oi complex, thus creating a distortion 
in its crystalline structure. The Oj partial pressure 
for annealing in this case may be between 10* 
and 10* bar. 

In those cases where a relatively high tempera- 
ture (i.e. above 950 # C) was employed lor the heat 
treatment, it might be advantageous to perform the 
annealing step in a slightly oxidizing atmosphere. 
This would make up for an assumed exaggerated 
romoval of oxygen atoms from the system owing to 
the high temperature and resulting in a too severe 
distortion of the system's crystalline structure. 

Resistivity and susceptibility measurements, as 
a function of temperature, of Sr 2 and Ca 2 -doped 
LajCuO^ ceramics show the same general ten- 
dency as the 8a 2 -doped samples: A drop m re- 
sistivity p(T). and a crossover to diamagnetism at a 
slightly lower temperature. The samples containing 
Sr 2 actually yielded a higher onset than those 
containing 8a 2 and Ca 2 . Furthermore, the dia- 
magnetic susceptibility is about three times as 
large as for the Ba samples. As the ionic radius of 
Sr 2 nearly matches the one of La J . it seems that 
the size effect does not cause the occurrence of 
superconductivity. On the contrary, it is rather ad- 
verse, as the data on Ba 2 and Ca 2 indicate. 

The highest T c 's for each of the dopant ions 
investigated occur for those concentrations where, 
at room temperature, the Re 2 .«TM„04. v structure is 
close to the orthorhombic-tstragonal structural 
phase transition which may be related to the sub- 
stantial eleciron-phonon interaction enhanced by 
the substitution. The alkaline-earth substitut-cn of 



4 



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0 275 343 



8 



the rare earth metal is dearly important, and quite 
likely create! TM ions with no e 0 Jahn-Teiler or- 
bitals. Therefore, the absence of these J.-T. or- 
bital*, that ii. J.-T. hofei near the Fermi energy 
probably playi an important role for the T c en- 
hancement. 



Clalma 

1 ) Superconductive compound of the REiTM.O* 
type having a transition temperature above 26 K. 
wherein the rare earth (RE) is partially substituted 
by one or more members of the alkaline earth 
groups of elements (A£). and wherein the oxygen 
content is adjusted such that the resulting crystal 
structure is distorted and comprises a phase of tho 
general composition RE,.»AE«TM.04-y . wherein TM 
represents a transition metal, and x < 0.3 and y < 
0.5. 

2) Compound in accordance with claim 1. 
wherein the rare earth (RE) is lanthanum and the 
transition metal (TM) is copper. 

3) Compound in accordance with claim 1. 
wherein the rare earth is cerium and the transition 
metaJ is nickel. 

4) Compound in accordance with claim 1. 
wherein the rare earth is lanthanum and the transi- 
tion metal is nickel. 

5) Compound In accordance with claim 1. 
wherein barium is used as a partial substitute for 
the rare earth, with x < 0.3 and 0.1 1 y i 0.5. 

6) Compound in accordance with claim 1. 
wherein calcium is used as a partial substitute for 
the rare earth, with x < 0 3 and 0.1 S y S 0.5. 

7) Compound in accordance with claim 1. 
wherein strontium is used as a partial substitute for 
the ra/e earth, with x < 0.3 and 0.1 S y i 0.5. 

8) Compound in accordance with claim 1. 
wherein the rare earth is lanthanum and the transi- 
tion metaJ is chromium. 

9) Compound is accordance with claim 1. 
wherein the rare earth is neodymium and the tran- 
sition metaJ is copper. 

10) Method for making superconductive com- 
pounds of the REiTM.Oj type, with RE being a rare 
earth, TM being a transition metal, the compounds 
having a transition temperature above 26 K, com- 
prising the steps of: 

- preparing aqueous solutions of the nitrates of the 
rare earth and transition metal constituents and of 
one or more of the alkaline earth metals and 
coprecipitation thereof in their appropriate ratios; 

- adding the coprecipitate to oxalic acid and for- 
ming an intimate mixture of the respective oxalates; 

- decomposing the precipitate and causing a solid- 
state reaction by heating the precipitate to a tem- 
perature between 500 and 1200'C for a period of 



time between one and eight hours; 

• allowing the resultant powder product to cool; 

• preiung the powder at a presiure of between 2 
and 10 kbar to form pellets: 

9 • re-adfuiting the temperature of the pellet! to a 
value between 500 and 1000*C for a period of time 
between one half and three houri for sintering; 

• subjecting the pellets to an additional annealing 
treatment at a temperature between 500 and 

»o 1200»C for a period of time between one half and 
5 hours in a protected atmosphere permitting the 
adjustment of the oxyrjen content of the final prod- 
uct which hat a final composition of the form Re t . 
«TM.O*^. wherein * < 0.3 and 0.1 < y < 0.5. 

1 5 ii) Method In accordance with claim 10. 

wherein the protected atmosphere Is pure oxygon. 

12) Method in accordance with claim 10. 
wherein the protected atmosphere is a reducing 
atmosphere with an oxygen partial pressure be- 

70 tween 10 * and 10 5 bar. 

13) Method In accordance with claim 10. 
wherein the decomposition step Is pedormed at a 
temperature of 900*C for 5 hours, and wherein the 
annealing stop Is performed at a temperature of 

75 900 # C for one hour in a reducing atmosphere with 
an oxygen partial pressure between 10 1 and 10* 
oar. 

14) Method In accordance with claim 10, 
wherein lanthanum Is used as the rare earth and 

30 copper Is used as the transition metal, and wherein 
barium Is used to partially substitute for the lan- 
thanum, with x < 0.2. wherein the decomposition 
step is performed at a temperature of 900*C for 5 
hours, and wherein the annealing step is performed 

35 in a reducing atmosphere with an oxygen partial 
pressure on the order of 10 3 bar and at a tem- 
perature of 900 *C for one hour. 

15) Method in accordance with claim 10. 
wherein lanthanum Is used as the rare earth and 

40 nickel is used as the transition metal, and wherein 
barium is used to partially substitute for the lan- 
thanum, with x < 0.2. wherein the decomposition 
step is performed at a temperature of 900 *C for 5 
hours, and wherein the annealing step is performed 

45 in a reducing atmosphere with an oxygen partial 
pressure on the order of 10 3 bar and at a tem- 
perature of 900*C for one hour. 

16) Method in accordance with claim 10. 
wherein lanthanum is used as the rare earth and 

so copper is used as the transition metal, and wherein 
caicium is used to partially substitute for the lan- 
thanum, with x < 0.2, wherein the decomposition 
step is performed at a temperature of 900 # C for 5 
hours, and wherem the annealing step is performed 

55 in a reducing atmosphere with an oxygen partial 
pressure on the order of 10 3 bar and at a tem- 
perature of 900 *C for one hour. 



5 



0 275 343 



17) Method in accordance with claim 10. 
wherein lanthsnum is used as the rare earth and 
copper it used as the transition metal, and wherein 
strontium li used to partially lubstitute lor the 
lanthanum, with x < 0.2. wherein the decomposition 5 
step <s performed at a temperature of 900 # C for 3 
hows, and wherein the annealing step ie performed 

in a reducing atmosphere with an oxygen partial 
pressure on the order of 10 5 bar and at a tem- 
perature of 900 *C for one hour. 'o 

18) Method in accordance with claim 10. 
wherein cerium Is used as the rare earth and nickel 
is used as the transition metal, and wherein barium 
is used to partially substitute for the cerium, with x 

< 0.2, wherein the decomposition step is per- ts 
formed at a temperature of 900 # C for 3 hours, and 
wherein the annealing step Is performed In a re- 
ducing atmosphere with an oxygen partial pressure 
on the order of 10 3 bar and at a temperature of 
900 # C for one hour. 70 



6 



European PttmnX 

Office 



EUROPEAN 8EARCH REPORT 



ApfMicetton numtxr 



EP 87 10 0961 



DOCUMENTS CONSIDERED TO Be RELEVANT 



C***»on of document wtm indication. wnen> approo* tete, 
off 



Ae*ev*nt 

to cUim 



ClASa4F»CAT»ON 0* TM| 



D , A 



REVUE DE CHIMIE MINERALE, vol. 
21, 1984, pages 407-425, Paris, 
FR; C. MICHEL at al.i "Oxygen 
intercalation in mixed valence 
copper oxides related to the 
perovskites" 

page 417, paragraph 2 - page 
425 * 



H 01 L 39/12 



Tf CHNtCAL "HOI 
fttAftCHIOflnt a*) 



H 01 L 39/00 



Tr># cx*Mm M*rcft report hM b**n drawn up to* mi\ ci*+m« 



BERLIN 



17-07-1987 



ROUSSEL A T 



CATEGORY OF CITED DOCUMENTS 

particularly relevant if taken eione 
particularly relevant tf combined witn inomtf 
document of th* *ame category 
technological background 
non-wntt»f) disclosure 
intermediate dOCum«nt 



T : theory or principle underlying the invention 
E : earlier patent document, but published on. or 

aftef tt>e filing date 
D : document cited in the application 
L : document cited for otr>er reasons 

& : member of the same patent family, corresponding 
document