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Possible RT superconductivity from Pb3CO5-Ag2O (PACO) system
Physica
ELSEVIER
C 341-348
(2000)
723-725 www.elszvier.nl/locate/physc
Possible RT superconductivity
from Pb,CO,-Ag,O (PACO) system
D. Djureka, Z. Medunic”, A. Tonejcb and M. PaljeviCC aA. Volta Applied Ceramics (AVAC), Kesten brijeg 5, HR-10000 Zagreb, Croatia bFaculty of Sciences, Physics Dept., BijeniEka 32, HR-10000 Zagreb, Croatia ‘Ruder BoSkoviC Institute, BijeniEka 54, HR-10000 Zagreb, Croatia Some interesting results that could be eventually explained as coming from superconductivity Pb,CO,-AgrO (PACO) system are reported. Samples prepared at 340-350 OC in combined CO,-0,
(SC) in
atmosphere
exhibit low resistance states at room temperature (RT) with resistivity three orders of magnitude lower than that of silver. In addition, characteristic threshold current density dependence of electric resistance together with the DC susceptibility data obtained on balance support the idea of superconductivity
1. COMPONENTS
More efficient preparation is achieved by the use of PbC0,.2PbO
The most common superconductors
property
of high Tc
plane.
Pb,OCO,
PbCO,.PbO
(Pb,CO,
which exhibits
modification
important for reproducible
structure and electric conductivity in some preferred shannonite
(PC2P, CO,/PbO=1/3)
only one crystallographic
synthesized so far is their layered
crystallographic
in PACO system.
the fact
preparation. PC2P may
be prepared [3] by carbonization of tetragonal PbO ,
in l-3 bar flowing CO, at 3OO’C for 24 hours and
or PCP) with CO,/PbO=O.5
exhibits
X-ray diffractions
at d=3.01 A (I=lOO),
consists of PbCO, - PbO... layers [I,21 and doping
d=2.96 A (1=24), d=2.94 8, (1=31), d=2.88 li (1=49),
with Ag,O (Ag,CO,) may result in a number of novel
d=2.87 8, (Ial),
d=2.78 A (1=26).
metals. One modification of PbCO ,.PbO (a-PCP) may be obtained by carbonization of tetragonal PbO (lith-
2. PREFTRJNG AND ANNEALING
arge) at 3OOOCin 3-5 bar of flowing CO, with characteristic (1=32),
X-ray diffractions d=4.05
8, (1=54),
(CuK, ) at d=4.17 8, d=3.24
The powders of PC2P and Ag,O (PACO) are
8, (I=lOO),
mixed in corresponding
d=3.21 8, (I=lOO), d=2.87 8, (1=58), d=2.58 8, (1=34). Carbonization of tetragonal PbO at 300°C by 8-30 bar flowing
and prefired for 24 hours in 4-5 bar of flowing CO,
in j3-PCP with
at 33OOC. The mixture was then cooled to RT and
characteristic X-ray diffractions at d=3.29 8, (I=lOO),
reground to powder subsequently pressed in pellets
d=2.68 8, (1=41), d=2.37 A(I=10.6), d=2.32 8, (1=20).
by the use of 2 tons press between adequate hardened
For CO, pressures
CO, results
atomic Ag/Pb proportions
in a magnetic stirrer with ethanol as mixing agent
higher than 50 bars cerussite
steel dies. The usual dimensions of pellets are 5x5x0.3
PbCO, is obtained at 3OOOC.The mixing of p-PCP
mm’. For better estimation
as well as of a-PCP with Ag,O or Ag,CO, resulted
temperature in CO,-0,
in no metallic phases so far.
situ electrical
092
I -4534/00/$ - see front I -4534(00)00662-6
PI1 SO92
matter
0 2000
Elsevier
Science
B.V.
All rights reserved.
of optimal annealing
atmosphere
resistance
we measure in
of the pellets
during
D. Lljurek et al./Pl~_vstca C 341-348 (2000)723-725
124
annealing by the use of two probe 50 microns gold wires glued on the pellet with silver paint. During the heating stage in CO,-0,
atmosphere
at a rate
‘,‘t
PACO 512
megaohms
8
followed by an abrupt decrease to ten .
ohms at 340-345OC
which is actual annealing
1.0
;
&)=60 bar pfZO,)=45 bar
.“‘.
I”“‘.
0
00
”
0
OS
Pb,CO,+Ag,O
0
“--
B
1=1mA
oI=lA
temperature.
...
l
SK/mm the resistance of pellet usually exhibits 20
* ’ D e 0
l
0
20
40
60
80
100
t("C)
Figure 2.TGA decomposition
0”‘.
.I’..
0
.‘.
SO ~(0,)
‘.
100
.’
of PACO 5 12.
In addition, the undissolved Ag,O is visible in X-
1%I
(bar)
ray diffraction pattern and this sounds for provided
Figure 1. Phase diagram of PC2P-Ag,O system.
doping concentration of Ag in PCP to be less than Ag/Pb=1/5. TGA decomposition performed
in vacuu
(fig.2.) on PACO 5 12 sample (annealed under 60 bar 0, and 35 bar CO,) stresses CO ,/Pb0=0.58 which is
3. PHASES
somewhat higher than ideal PCP value 0.5 as a reThe study of PC2P-Ag,O system with atomic
sult of decomposed PbCO, and Bystrom phases.
Ag/Pb=0.20 (PACO 512) annealed for 24 hours at 345OC for various
pressures
CO,-0,
results
in
diagram shown in fig. 1. and sketched on the basis of resistive
properties.
Open
circles
represent
insulating state resulting from higher oxycarbonates with CO,/PbO > 0.5, while metallic samples which result from Ag doped intermediate Bystrom phases [4,5] are denoted correspond
by full circles.
Full squares
to samples which show SC properties
stable for several weeks or months. Empty squares belong to samples with SC properties disappearing after several days. X-ray diffraction pattern recorded on samples denoted by full squares reveals the presence of a-PCP, intermediate Bystrom phases as well as PbCO! as underlying compound.
4. RESISTIVE AND MAGNETIC PROPERTIES The samples for the measurement of electric resistance were prepared in two ways. Firstly, for higher measuring
currents ranging up to several
amperes we use four probe method with 100 microns gold wires pressed together
before
with prefired
annealing
powders.
procedure
The contact
resistance is several milliohms. Secondly, for lower measuring currents four probe measurements
are
provided by the use of 30 microns gold wires and silver paint with contact resistance
ranging from
3-50 ohms. The ultimate accuracy of in-phase signal
D. Djurek
et al./Physica
C 341-348
(2000)
125
723-725
resistance measurement for measuring current of one ampere in 1lo-235
Hz frequency range by the use of
52 IO lock-in amplifier is 1O-8ohms. The out-of-phase component of ac voltage signal never exceeded 10 percents of in-phase signal in normal resistance state and is usually half an order of magnitude higher low
resistance
resistance
state giving
measurements
rise to uncertainty
up
in
of
/
0
ZFC
-5
_lo _-_____L>
PACO512
t
to 5.10 -8ohms.
I
I
100
200
300
400
Figure 4. DC susceptibility of PACO 512. As it is shown on curve (a) of fig.4. The sample was p(O,)=60
bar
cooled in zero field down to 100 K and reheated in
p(CO,)=35 bar
magnetic field which is
followed by suppression
of the weight up to 290 K and an increase by further heating up to 70°C. The
-8
average magnetic field
gradient was - 120 gausscm -I and sample dimensions 5x5 mmr. The magnetic field estimated in the center of sample was -20-35 gauss. The accurate measure0
100
200
300
400
500
600
ments of dc susceptibility are limited by ferromagnetic
700
contribution of Fe
t(%
impurities extended in some
samples up to 300 ppm. In addition, in several samples tested SC properties are confined to thin layer Figure 3. Temperature dependence of electric
(2-5 microns) which was estimated by fine grinding.
resistance of PACO 5 12 sample.
Interior of samples is found to be semiconducting.
The measurement of electric resistance for sample
REFERENCES
PACO 512 annealed at 345OC for 24 hours under p(O,)=60
bar and p(CO,)=45
bar reveals
the
transition to SC state (fig.3.) with onset at nearly 70°C for measuring current 1 mA. An enhancement
of
electric resistance by application of 1A measuring current is evident. At 20°C for measuring current of 0.5 A the resistivity is about 10-l pohmcm which is three orders of magnitude less than that of silver. The only materials known so far to exhibit resistivities less than that of silver are superconductors. DC magnetic susceptibility measurements were performed on balance with sensitivity of 0.1 mg on sample of mass 113 mg.
1. D. A. Grisafe and W. B. White, Am. Mineral. 49 (1964) 1184. 2. A. C. Roberts, J. A. R. Stirling, G. J. C. Carpenter, A. J. Criddle, G. C. Jones, T. C. Birkett and W. D. Birch, Mineral. Mag. 59 (1995) 305. 3. G. Pannetier, S. Fenistein and G. DjegaMariadassou, Bull. Sot. Chim. Fr. (1964) 701. 4. A. Bystrom, Arkiv. Kemi Min. Geol. 20Al No 11 (1945). 5. J. S. Anderson and M. Stems, J. Inorg. Nucl. Chem. 11 (1959) 272.
ELSEVIER
C 341-348
(2000)
723-725 www.elszvier.nl/locate/physc
Possible RT superconductivity
from Pb,CO,-Ag,O (PACO) system
D. Djureka, Z. Medunic”, A. Tonejcb and M. PaljeviCC aA. Volta Applied Ceramics (AVAC), Kesten brijeg 5, HR-10000 Zagreb, Croatia bFaculty of Sciences, Physics Dept., BijeniEka 32, HR-10000 Zagreb, Croatia ‘Ruder BoSkoviC Institute, BijeniEka 54, HR-10000 Zagreb, Croatia Some interesting results that could be eventually explained as coming from superconductivity Pb,CO,-AgrO (PACO) system are reported. Samples prepared at 340-350 OC in combined CO,-0,
(SC) in
atmosphere
exhibit low resistance states at room temperature (RT) with resistivity three orders of magnitude lower than that of silver. In addition, characteristic threshold current density dependence of electric resistance together with the DC susceptibility data obtained on balance support the idea of superconductivity
1. COMPONENTS
More efficient preparation is achieved by the use of PbC0,.2PbO
The most common superconductors
property
of high Tc
plane.
Pb,OCO,
PbCO,.PbO
(Pb,CO,
which exhibits
modification
important for reproducible
structure and electric conductivity in some preferred shannonite
(PC2P, CO,/PbO=1/3)
only one crystallographic
synthesized so far is their layered
crystallographic
in PACO system.
the fact
preparation. PC2P may
be prepared [3] by carbonization of tetragonal PbO ,
in l-3 bar flowing CO, at 3OO’C for 24 hours and
or PCP) with CO,/PbO=O.5
exhibits
X-ray diffractions
at d=3.01 A (I=lOO),
consists of PbCO, - PbO... layers [I,21 and doping
d=2.96 A (1=24), d=2.94 8, (1=31), d=2.88 li (1=49),
with Ag,O (Ag,CO,) may result in a number of novel
d=2.87 8, (Ial),
d=2.78 A (1=26).
metals. One modification of PbCO ,.PbO (a-PCP) may be obtained by carbonization of tetragonal PbO (lith-
2. PREFTRJNG AND ANNEALING
arge) at 3OOOCin 3-5 bar of flowing CO, with characteristic (1=32),
X-ray diffractions d=4.05
8, (1=54),
(CuK, ) at d=4.17 8, d=3.24
The powders of PC2P and Ag,O (PACO) are
8, (I=lOO),
mixed in corresponding
d=3.21 8, (I=lOO), d=2.87 8, (1=58), d=2.58 8, (1=34). Carbonization of tetragonal PbO at 300°C by 8-30 bar flowing
and prefired for 24 hours in 4-5 bar of flowing CO,
in j3-PCP with
at 33OOC. The mixture was then cooled to RT and
characteristic X-ray diffractions at d=3.29 8, (I=lOO),
reground to powder subsequently pressed in pellets
d=2.68 8, (1=41), d=2.37 A(I=10.6), d=2.32 8, (1=20).
by the use of 2 tons press between adequate hardened
For CO, pressures
CO, results
atomic Ag/Pb proportions
in a magnetic stirrer with ethanol as mixing agent
higher than 50 bars cerussite
steel dies. The usual dimensions of pellets are 5x5x0.3
PbCO, is obtained at 3OOOC.The mixing of p-PCP
mm’. For better estimation
as well as of a-PCP with Ag,O or Ag,CO, resulted
temperature in CO,-0,
in no metallic phases so far.
situ electrical
092
I -4534/00/$ - see front I -4534(00)00662-6
PI1 SO92
matter
0 2000
Elsevier
Science
B.V.
All rights reserved.
of optimal annealing
atmosphere
resistance
we measure in
of the pellets
during
D. Lljurek et al./Pl~_vstca C 341-348 (2000)723-725
124
annealing by the use of two probe 50 microns gold wires glued on the pellet with silver paint. During the heating stage in CO,-0,
atmosphere
at a rate
‘,‘t
PACO 512
megaohms
8
followed by an abrupt decrease to ten .
ohms at 340-345OC
which is actual annealing
1.0
;
&)=60 bar pfZO,)=45 bar
.“‘.
I”“‘.
0
00
”
0
OS
Pb,CO,+Ag,O
0
“--
B
1=1mA
oI=lA
temperature.
...
l
SK/mm the resistance of pellet usually exhibits 20
* ’ D e 0
l
0
20
40
60
80
100
t("C)
Figure 2.TGA decomposition
0”‘.
.I’..
0
.‘.
SO ~(0,)
‘.
100
.’
of PACO 5 12.
In addition, the undissolved Ag,O is visible in X-
1%I
(bar)
ray diffraction pattern and this sounds for provided
Figure 1. Phase diagram of PC2P-Ag,O system.
doping concentration of Ag in PCP to be less than Ag/Pb=1/5. TGA decomposition performed
in vacuu
(fig.2.) on PACO 5 12 sample (annealed under 60 bar 0, and 35 bar CO,) stresses CO ,/Pb0=0.58 which is
3. PHASES
somewhat higher than ideal PCP value 0.5 as a reThe study of PC2P-Ag,O system with atomic
sult of decomposed PbCO, and Bystrom phases.
Ag/Pb=0.20 (PACO 512) annealed for 24 hours at 345OC for various
pressures
CO,-0,
results
in
diagram shown in fig. 1. and sketched on the basis of resistive
properties.
Open
circles
represent
insulating state resulting from higher oxycarbonates with CO,/PbO > 0.5, while metallic samples which result from Ag doped intermediate Bystrom phases [4,5] are denoted correspond
by full circles.
Full squares
to samples which show SC properties
stable for several weeks or months. Empty squares belong to samples with SC properties disappearing after several days. X-ray diffraction pattern recorded on samples denoted by full squares reveals the presence of a-PCP, intermediate Bystrom phases as well as PbCO! as underlying compound.
4. RESISTIVE AND MAGNETIC PROPERTIES The samples for the measurement of electric resistance were prepared in two ways. Firstly, for higher measuring
currents ranging up to several
amperes we use four probe method with 100 microns gold wires pressed together
before
with prefired
annealing
powders.
procedure
The contact
resistance is several milliohms. Secondly, for lower measuring currents four probe measurements
are
provided by the use of 30 microns gold wires and silver paint with contact resistance
ranging from
3-50 ohms. The ultimate accuracy of in-phase signal
D. Djurek
et al./Physica
C 341-348
(2000)
125
723-725
resistance measurement for measuring current of one ampere in 1lo-235
Hz frequency range by the use of
52 IO lock-in amplifier is 1O-8ohms. The out-of-phase component of ac voltage signal never exceeded 10 percents of in-phase signal in normal resistance state and is usually half an order of magnitude higher low
resistance
resistance
state giving
measurements
rise to uncertainty
up
in
of
/
0
ZFC
-5
_lo _-_____L>
PACO512
t
to 5.10 -8ohms.
I
I
100
200
300
400
Figure 4. DC susceptibility of PACO 512. As it is shown on curve (a) of fig.4. The sample was p(O,)=60
bar
cooled in zero field down to 100 K and reheated in
p(CO,)=35 bar
magnetic field which is
followed by suppression
of the weight up to 290 K and an increase by further heating up to 70°C. The
-8
average magnetic field
gradient was - 120 gausscm -I and sample dimensions 5x5 mmr. The magnetic field estimated in the center of sample was -20-35 gauss. The accurate measure0
100
200
300
400
500
600
ments of dc susceptibility are limited by ferromagnetic
700
contribution of Fe
t(%
impurities extended in some
samples up to 300 ppm. In addition, in several samples tested SC properties are confined to thin layer Figure 3. Temperature dependence of electric
(2-5 microns) which was estimated by fine grinding.
resistance of PACO 5 12 sample.
Interior of samples is found to be semiconducting.
The measurement of electric resistance for sample
REFERENCES
PACO 512 annealed at 345OC for 24 hours under p(O,)=60
bar and p(CO,)=45
bar reveals
the
transition to SC state (fig.3.) with onset at nearly 70°C for measuring current 1 mA. An enhancement
of
electric resistance by application of 1A measuring current is evident. At 20°C for measuring current of 0.5 A the resistivity is about 10-l pohmcm which is three orders of magnitude less than that of silver. The only materials known so far to exhibit resistivities less than that of silver are superconductors. DC magnetic susceptibility measurements were performed on balance with sensitivity of 0.1 mg on sample of mass 113 mg.
1. D. A. Grisafe and W. B. White, Am. Mineral. 49 (1964) 1184. 2. A. C. Roberts, J. A. R. Stirling, G. J. C. Carpenter, A. J. Criddle, G. C. Jones, T. C. Birkett and W. D. Birch, Mineral. Mag. 59 (1995) 305. 3. G. Pannetier, S. Fenistein and G. DjegaMariadassou, Bull. Sot. Chim. Fr. (1964) 701. 4. A. Bystrom, Arkiv. Kemi Min. Geol. 20Al No 11 (1945). 5. J. S. Anderson and M. Stems, J. Inorg. Nucl. Chem. 11 (1959) 272.