Note: Descriptions are shown in the official language in which they were submitted.
Z0021~22
TITLE CR-8701
8UP~RCONDUC~ING METAL OXIDE COMPOSITIONS
AND PROCESSES rOR MANUFACTURE AND USE
BACXGROUND OF THE INVENTION
Field of the Invention
This invention relates to novel
Tl-Ba-Ca-Cu-O compositions which are
superconducting.
Reference~
Bednorz and Muller, Z. Phys. B64, lB9
(1986), disclose a superconducting phase in the
L~-Ba-Cu-O 6ystem with a superconducting
transition temperature of about 35 K. Thi~
dicclosure was sub6equently confirmed by a number
o~ investigators [see, for example, Rao ~nd
Ganguly, Current Science, 56, 47 ~lg87), Chu et
al., Science 235, 567 ~1987), Chu et al., Phys.
Rev. Lett. 58, 405 ~1987), Cava et al., Phy6.
Rev. Lett. 58, 408 ~1987), Bednorz et al.,
Europhys. Lett~ 3, 379 ~1987)]. The
cuperconducting phase has been identified a6 the
composition Lal_x~a,Sr,Ca)xCuO~_y with the
tetragonal X2NiF~-type structure and with x
typically about 0.15 and y indicating oxygen
vacancies.
Wu et al., Phys. Rev. Lett. 58, 908
(1987), disclose a superconducting phase in the
Y-Ba-Cu-O system with a superconducting
~ransi~ion temperature of about 90 K. Cava et
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zno2n22
al., Phys. Rev. Lett. 58, 1676 (1987), have
identif~ed this superconducting Y-Ba-Cu-O phabe
to be orthorhombic, distorted, oxygen-deficient
perovskite Y8a2Cu~09 ~ where ~ is about 2.1.
C. Michel et al., Z. Phys. ~ -
Condensed Matter 68, 421 (1987), disclose ~ novel
family of superconducting oxides ln the
Bi-Sr-Cu-O system. A pure phase was isolated for
the composition Bi25r2Cu20~. The material made
fsom ultrapure oxides has a superconduct~ng
transition with a midpoint of 22 R as determined
from resistivity measurements and zero resistance
below 14 K. The material made from commercial
grade oxides has a superconducting transition
w~th a midpoint of 7 K.
29 H. Maeda et al., Jpn. J. Appl. Phys.
27, L209 (1988), disclose a superconduct~ng oxide
ln the Bi-Sr-Ca-Cu-O system w~th the compo8it~0n
near BlSrCaCu20x and a superconducting trans~tion
temperature of aboYt 105 K.
The commonly assigned application,
~Superconducting Metal Oxide Compositions and
Process For Making Themn, S. N. 153,107, filed
Feb. 8, l9B8, a continuation-in-part of S. N.
152,186, filed Feb. 4, 1988, disclose
superconducting compositions having the nominal
formula si.srbcaccu30~ wherein a is from about 1
to about 3, b is from about 3/8 to about 4, c is
from about 3/16 to about 2 and x - (1.5 a + b + c
+ y) where y is from about 2 to about 5, with the
proviso that b + c is from about 3/2 to about 5,
said compositions having superconducting
.
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. ,,,: ~ ~ . ; . .
2002Q22
transition temperatures of about 70 K or higher.
It also discloses the superconducting metal oxide
phase having the formula Bi 2 S r3 - ~ Ca~Cu
wherein z is from about 0.1 to about 0.9,
preferably 0.4 to 0.8 and w i6 greater than zero
but less than about 1. M. A. Subramanian et al.,
Science 239, 1015 (1988) also disclose the
~i2Sr3 ~Ca~ CU2 t ~ ~ superconductor.
Z. z. Sheng et al., Nature 332, 55
(1988) disclose superconductivity in the
Tl-sa-Cu-o system in samples which have nominal
compositions Tl2Ba2Cu3O~ and TlBaCu3O5 5
sOth samples are reported to have onset
temperatures above 90 K and zero resigtance at
81 R. The ~amples were prepared by mixing and
ao grinding appropriate amount~ of ~aCo3 ~nd CuO
with an agate mortar and pe~tle. ~h~ mixture
wa~ heated in air at 925C for more than 24 hour~
with ~everal intermediate grindings to obtain a
uniform black oxide 8a-Cu oxide powder which was
mixed with an appropriate amount of Tl2O3,
completely ground and pressed into a pellet with
a diameter of 7 mm and a thickness of 1-2 mm.
The pellet was then put into a tube furnace which
had been heated to 880-910C and was heated for
2-5 minutes in flowing oxygen. As soon as it had
slightly melted, the sample was taken from the
furnace and quenched in air to room temperature.
It was noted by visual inspection that Tl2O3 had
partially volatilized as black smoke, part had
become a light yellow liquid, and part had
reacted with Ba-Cu oxide forming a black,
.
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-: : : .: .
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partially melted, porous material.
Z. Z. Sheng et al., Nature 332, 138
(1988) disclose ~uperconductivity ~n the
~l-Ca-Ba-Cu-O ~ystem in samples which have
nominal compositions Tl2CalBaCu3Og~ with onset
of superconductivity at 120 K.
R. M. Hazen et al., Phys. Rev. Lett.
60, 1657 (1988), disclose two superconducting
phases in the Tl-Ba-Ca-Cu-O system,
~l2Ba2ca2cu~olo ~nd Tl2~a2CaCU2O~, both wit
onset of 6uperconductivity near 120 K. C. C.
Torardi et al., Science 240, 631 (1988) disclose
the prepar~tion of Tl2Ba2C~2 Cu3 l o with ~n o
of superconductivity of 125 K.
S. S. P. Parkin et al., Phys. Rev.
Lett. 61, 750 (1988), disclose the structure
TlBa2 Ca2 CU3 09 ~y with transition temperatures up
to 110 K.
M. Hervieu et ~l., J. Solid State Chem.
75, 212 tl988), disclose the oxide
2~ TlBa2Cacu2o~-y-
C. C. ~orardi et al., Phys. ~ev. B 38,
225 (1988), disclose the oxide Tl2Ba2CuO6 with an
onset of ~uperconductivity at about 90 K.
The commonly assigned application,
"Superconducting Metal Oxide Compositions and
Processes For Manufacture and Use~, S. N.
236,088, filed Aug. 24, 1988, a
continuation-in-part of S. N. 230,636, filed Aug.
10, 1988, disclose superconducting compositions
having the nominal formula Tl.Pb.CabSr~CudOx
wherein a is from about 1/10 to about 3/2, b is
. . ~ : , , :
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from about 1 to about 4, c is from about 1 to
about 3, d is from about 1 to about 5, e is from
about 3/10 to about 1 and x - (a ~ b ~ c ~ d + e
+y) where y i8 from about 1/2 to about 3. These
compositions have an onset of superconductivity
of at least 70 K.
Numerous papers have appeared
relating to the above compositions. The highest
transition temperature reported for any of the
above compositions at this time i8 125 K for
Tl2Ba2Ca2 CU3 X as disclosed by S. S. P. Parkin et
al., Phys. Rev. Lett. 60, 2539 ~198B)
J. M. ~iang et al., Appl. Phys. ~ett.
53, 15 (1988) disclose a composition
TlBa2Ca3Cu~Ox with an onset of superconductivity
at lSS K and a zero resistance at 123 ~ CaCO3,
BaCO3 and CuO powders were ground together and
calcined for 15 hour~ with lntermediate
grindings. The sa-Ca-Cu-o powders were mixed
with Tl2O3 to yleld a ~ixture with nominal
compo~ition TlBaCa3Cu3Ox. This mixture was
ground, pressed and sintered for lS minute~ in
flowing 2- Composition ratios of the
T}:Ca:sa:Cu in the ~uperconductor vary from
1:2:2:3 to 1:2:3:4.
SUMMARY OF T~E INVENTION
This invention provides novel
superconducting compositions having the nominal
formula Tlsa.cabcu~ox wherein a is from about
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.
,
.
2()02n~2
2 to about 4, b is from about 7/2 to about 5, c
is from about 9/2 to about 7 and x - (a + b + c +
y) where y is from about 1/2 to about 3.
Preferably, a is from about 2 to about 3, b is
about 4, c is about 5, and y i 6 from about 1/2 to
about 2. The onset of superconductivity for
these compositions is at a temperature of at
least 130 K.
These superconducting compositions can
be prepared by heating a m~xture of the oxides of
Tl, Ca and Cu and the peroxide of Ba or a
precursor oxide mixture prepared from these
oxides, the relative amounts of the oxides chosen
so that the atom~c ratio Tl:Ba:Ca:Cu is l:a:b:c,
to a temperature of about 940C to about 980C,
maintain~ng that temperature for about 5 m~nutes
or more, said heatlng beinq carried out ln a
controlled atmosphere, e. g., ln ~ sealed tube
made of ~ non-reacting metal such a6 gold, which
prevents ~ny of the reactants including the
metals and oxygen from escaping.
8RIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a plot of the flux
excluded by a composition of this invention as a
function of temperature.
DETAILED DESCRIPTION OF T~E INVENTION
-
The superconducting compositions of
this invention can be prepared by the following
process. The oxide mixture used in this process
is prepared so that the atomic ratio Tl:Ba:Ca:Cu
.:
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5 i8 l:a:b:c wherein a is from about 2 to about 4,
b is from about 7/2 to about 5, c is from about
9/2 to about 7 and x - (a + b + c + y) where y is
from about 1/2 to about 3. Preferably, a is
about 2, b is about 4, c is about 5, and y is
from about 1/2 to about 2.
The oxide mixture can be prepared
directly by choosing quantities of the oxide
reactants Tl2O3, CaO and CuO ~nd the peroxide
BaO2 such that the atomic ratio Tl:~a:Ca:Cu is
l:a:b:c and mixing them, for ex~mple, by grinding
them together in a mortar.
Alternatively, a precursor oxide
mixture can be prepared by choo~ing quantities of
the oxide reactants Tl2O3, CaO and CuO and the
peroxide BaO2 such that the àtomic r~tlo
a:Ca:Cu $~ l:a:b:c. The barium peroxide,
calcium oxide and copper oxide are ground
together and this grey mixture i~ then heated in
an alumina crucible in a muffle furnace in
air, the temperature being increased from ambient
temperature, about 20C, to about 800C ~n a
period of about 2 hours. The temperature is held
at about 800C for 1 hour. The ~ample is then
cooled and the black powder i8 recovered. This
powder is re-ground and ground together with the
thallium oxide to give the precursor oxide
mixture.
The oxide mixture is then heated in a
controlled atmosphere. One convenient way to
accomplish a controlled atmosphere is to place
the oxide mixture in a tube made of a
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2~0Z~?22
non-reacting metal such as gold and then sealing
the tube by crimping or, preferably, by welding
or fusing. The precursor oxide mixture is less
destructive of the gold tubes and i8 preferred
for this reason. The sealed tube is placed in a
furnace and heated to a temperature of about
940C to about 9B0C and maintained at a
temperature in this range, i. e., about 940C to
about 980C, for about 5 minutes or more.
Maintaining the sample at such a temperature for
5 minutes is sufficient to form the
superconductor of the invention when the sample
is heated from 700C to a temperature in the
prescribed range at a rate o 50C/min and
subsequently cooled at a rate of 10C/min to
600C. Faster heating and cooling rates may
require 60mewhat longer m~lntenance tlme~.
Maintenance ti~es o up to an hour or more can be
used but csrrosion of the gold tube becomes
evident ~t about that time and ma~ntenance times
of about 5 to about 60 minute~ are typical. The
~mple is then cooled to ambient temperature and
the ~hiny grey-black metallic-appearing ingot
recoYered. During the thermal cycle the gold
tube typically bloats; however, at the end of the
procedure there is not excess pressure in the
tube when it is cut open. The recovered material
is a shiny qrey/black
metallic ingot with a surface bejeweled with
black shiny platelets. The black shiny platelets
have proven to be single crystals of known
materials, e. g., Tl-sa-Ca-Cu compositions with
:
-,
. :
- . --- : ~ -
2()02 )22
Tl:Ba:Ca:Cu atomic ratios of 1:2:1:2 and 1:2:2:3
with lesser Tc's.
F1UX exclusion measurements on the
compositions of this invention, prepared as
described above, show an onset of
6uperconductivity at about 130-132 N.
Resi~tivity measurements on the as prepared ingot
shows onset at about 135 K and zero resistance at
about 116 K. The superconductivity arises from
the bulk of the composition. Based on flux
i5 exclusion measurements at least 30% of each of
the samples is superconducting~ X-ray powder
diffraction typically g$ves very weak lines.
Longer maintenance times at the maximum heating
temperature have produced samples which show
di~crete x-ray llnes. The 22 A ~2.2 nm~ c axis
which i~ observed in the powder d~ffraction
pattern is what is calculated for a 1245
~Tl:Ba:Ca:Cu atomic ratio) phase using a formula
of Ihara et al., Nature 334, 510 (1988).
Electron microscopy results have shown
intergrowth of layered pha~es ~ncluding a 1245
phase.
Superconductivity can be confirmed by
observing magnetic flux exclusion, i.e., the
Meissner effect. This effect can be measured by
the method described in an article by E. Polturak
and B. Fi~her in Physical Review B, 36,
5586(1987).
The superconducting compositions of
this invention can be used to conduct current
extremely efficiently or to provide a magnetic
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field for magnetic imaging for medical purposes.
Thus, by cooling the composition in the form of a
wice or bar to a temperature below the
superconducting transition temperature, ~TC ), in
a manner well known to those in thi~ field, and
initiating a flow o~ electrical current, one can
obtain such flow without any electrical resistive
losses. To provide exceptionally high magnetic
fields with minimal power losses, the wire
mentioned previously could be wound to form a
coil which would be cooled to a temperature below
the superconducting transition temperature before
inducing any current into the coil. Such fields
can be used to levitate ob~ects as large as rail-
road car~. ~hese superconducting compositions
29 are ~16O u8eful in Josephson devices such as
SQUIDS ~superconducting quantum interference
devices) and in instruments that are based on the
Josephson effect ~uch as high ~peed eampling
circuits and voltage standards.
EX~MPLES OF THE INVENTION
EXAMPLE 1
0.456 g of Tl2O3, 1.020 g of BaO2,
0.448 g of CaO and 0.960 g of CuO, corresponding
to a Tl.Ba:Ca:Cu atomic ratio of 1:3:4:6, were
ground together in an agate mortar for about 3
minutes to form a fine grey powder. This powder
was loaded into a gold tube, about 3 inches long
and 1/4 inch in diameter (7.6 cm long and 0.64 cm
., . ;
.- . :. .
2~02n22
in diameter) and the gold tube was crimped shut.
The tube was placed in a quartz tube furnace and
heated in a slow oxygen flow in the following
manner. The tube was heated from ambient
temperature, about 20C, to 700C at a rate of
about 3C/min and then from 700C to 977C in ten
minutes. Over the next five minutes the
temperature decreased to 950C. Power to the
furnace was then shut off and the tube was
allowed to cool to room temperature in the
furnace. The tube was then removed from the
furnace and cut open. The grey-black ingot
product was recovered.
Flux exclusion measurements showed the
onset of superconductlvity at about 130 R.
EXAMPLES 2-4
In Example 2, 0.456 g of Tl2O3, 1.020 g
of ~aO2, 0.448 g of CaO and 0.960 9 of CuO,
corresponding to a Tl:Ba:Ca:Cu atom~c ratio of
1:3:4:~, were ground together in an agate mortar
for about 3 minutes to form a fine grey powder.
This powder was loaded into a gold tube, about 3
inches long and 1/4 inch in diameter (7.6 cm long
and 0.64 cm in diameter) and the gold tube was ~.
crimped shut. The tube was placed in a quartz
tube furnace and heated in a slow oxygen flow in
the following manner. The tube was heated fr~m
ambient temperature, about 20C, to 700C at a
rate of about 3C/min and then from 700C to
950C at a rate of about 25C/min. The
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2~ 21~2
12
temperature was maintained at 950C for S min and
then cooled to 600C at a rate of about 10C/m~n.
Power to the furnace was then shut off and the
tube wa5 allowed to cool to room temperature ln
the furnace. The tube was then removed from the
furnace and cut open. The grey-black ingot
product was recovered.
Flux exclusion measurements showed the
onset of superconductivity at about 130 K.
Examples 3 and 4 were carried out
essentially as described for Example 2 except
that in Example 3, 0.456 g of Tl2O~, 0.680 g of
BaO2, 0.44B g of CaO and 0.960 g of CuO,
corresponding to a Tl:Ba:Ca:Cu atomic ratio of
1:2:4:6, were ground to form a fine grey powder
and ln Example 4, 0.456 g of Tl2O~, 1.020 g of
B~O2, 0.448 g of CaO and 0.B00 g of CuO,
corresponding to a Tl:Ba:Ca:Cu atomic ratio of
1:3:4:5, were ground together to form a fine grey
powder.
~lux exclusion measurementc ~howed the
onset of superconductivity at about 130 g for
Examplç 3 and at about 132 K for Example 4.
EXAMPLE 5
A precursor oxide mixture was prepared
by grinding together 5.10 g of BaO2, 2.25 g of
CaO and 4.00 g of CuO. ~his grey mixture was
then heated in an alumina crucible in a muffle
furnace in air from ambient temperature, about
20C, to aoooc in a period of 2 hours. ~he
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. . :',; " ', ' , " ' : ' ' '
" .. ' . '. ' . ' ~ '
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S temperature was held at 800C for 1 hour and then
reduced to ambient. The black powder product wa6
recoveced and re-ground. The powder contained
the elements Ba:Ca:Cu in the atomic ratio 3:4:5.
2.30 g of this black powder was ground
10together with 0.456 9 of Tl2 03 to give a material
with the atomic ratio of Tl:Ba:Ca:Cu of 1:3:4:5.
This powder was loaded into gold tube, about 3
inches long and 1/4 inch in diameter (7.6 cm long
and 0.64 cm in diameter). The tube was sealed at
both ends by fus~ng and placed on an alumina boat
which was placed in a horizontal quartz tube
furnace.
Heating was carried in the following
manner. The temperature was increased from room
temperature to 700C at a rate of about 3C/min.
The temperature was then ~ncrea~ed from 700C to
977C at a rate of about 18.5C/mln. The sample
cooled to 950C over the next 5 minute~ and wa~
maintained at 950C for 10 min. The sample was
then cooled in the furnace to 600C at a rate of
about 10C/min. The sample was then removed from
the furnace and cooled to room temperature.
The recovered material is a shiny
grey-black metallic ingot with a surface
bejeweled with black shiny platelets.
Flux exclusion measurements showed the
onset of superconductivity at about 132 X.
EXAMPLE 6
A precursor oxide mixture was prepared
,
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. . . . .
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S by grinding together 1.020 g of BaO2, 0.448 9 of
CaO and 0.800 g of CuO. This grey mixture wa8
then heated in an alumina crucible in a muffle
furnace in air from ambient temperature, about
20C, to 800C in a period of 2 hours. The
temperature was held at B00C for l hour and then
reduced to ambient. The black powder product was
recovered and re-ground. The powder contained
the elements Ba:Ca:Cu in the atomic ratio 3:4:5.
2.300 g of this black powder was ground
lS together with 0.342 g of Tl2O3 to give a material
with the atomic ratio of Tl:Ba:Ca:Cu of
0.75:3:4:5 which, rounded off to integers, is
approximately 1:4:5:7. This powder was loaded
into gold tube, about 3 lnches long and 1/4 inch
in diameter (7.6 cm long ~nd 0.64 cm ~n
diameter). The tube was sealed at both ends by
fusing and placed on ~n alumina boat which was
placed in a horizontal quartz tube furnace.
~eating was carried in the following
manner. The temperature was increased from room
temperature to 700C at a rate of about 3C/min.
The temperature was then increased from 700C to
968C at a rate of about 25C/min. The sample
was maintained at 968C for 15 min. The sample
was then cooled in the furnace to 600C at a rate
of about 10C/min. The sample was then removed
from the furnace and cooled to room temperature.
The recovered material is a shiny
grey-black metallic ingot with a surface
3S bejeweled with black shiny platelets.
F1UX exclusion measurements showed the
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onset of superconductivity at about 130 K.
EXAMPLE 7
An oxide mixture containing the
elements 8a:Ca:Cu in the atomic ratio of 3:4:5
was prepared essentially as described in Example
6.
2.300 g of this black powder was ground
together with 0.456 g of Tl2O3 to give a material
with the atomic ratio of Tl:Ba:Ca:Cu of 1:3:4:5.
Thls powder was loaded into gold tube, about 3
inches long and 1/4 inch in diameter (7.6 cm long
and 0.64 cm in diameter). The tube was sealed at
both ends by fusing and placed on an alumina boat
which wa~ placed ~n a horizontal quartz tube
furnace.
Heating was carried in the following
manner. The temperature was lncreased from room
temperature to 700C at a r~te of about 3C/min.
The temperature was then increased from 700C to
977C at a rate of about 25C/min. The sample
was maintained at 977C for 15 min. The ~ample
was then cooled in the furnace to 600C at a rate
of about 10C/min. The sample was then removed
from the furnace and cooled to room temperature. ~.
The recovered material is a shiny
grey-black metallic ingot with a surface
bejeweled with black shiny platelets.
This Example was essentially repeated
several times and the products were essentially
identical.
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Flux exclusion measurements were
carried out on one of these products and the
results are shown in Fig. 1 where the flux
excluslon is plotted as a function of
temperature. The plot shows the onset of
superconductivity at about 132 K.
X-ray diffraction was carried out on a
powder obtained by grinding one of the~e
products. The d-spacings, the relative
$ntens$t$es and the indices of a set of observed
reflections of the x-ray powder diffraction
pattern which are always present when onset of
superconductivity is observed at a temperature of
130 K or above is shown in Table I.
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TABLE I
d-spacinq, nm Intensity hkl
2.20000 m 001
0.37924 m 101
0.36339 w 102
100.34088 m 103
0.31540 s 104
0.28974 w 105
0.27224 ms 110
0.26552 w 106
150.25522 s 113
0.24444 w 009
0.24398 w 114
0.24346 w 107
0.20636 m 109
200 ~ 20577 m 117
0.19250 ms 200
0.17011 ms 212
w - weak
m - medlum
s - 6trong
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18
S EXAMPLE 8-13
In each of these Examples a precursor
oxide mixture containing the elements Tl:Ba:Ca:Cu
in the atomic ratio of 1:3:4:5 wa~ prepared,
placed in a gold tube and then placed in a
furnace essentially as described in Example 5.
Heating was carried in the following
manner. The temperature was increased from room
temperature to 700C at a rate of about 3C/min.
The temperature was then increased from 700C to
a maximum temperature, T~x, at a specified rate.
The sample was maintained at T..x for a specified
time and was then cooled ln the furnace to 600C
at a rate of 10C/~in except for E~ample 12 for
20 which the rate wa~ 50C/min. The ~ample was then i.
~emoved from the furnace and cooled to room
temperature.
The recovered material is a shiny
grey-black metallic ingot with a surface
25 be~eweled with black shiny platelets.
~lux exclusion measurements were
carried out on each product.
The specified rate of heatinq from
700C to T~,x~ the temperature T~.x, the time for
30 which the temperature was maintained at T~.x and ~.
the temperature of the onset of superconductivity
are shown in Table II.
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5 TAE~LE I I
Heating Main.
Rate Time Temp.
Example 700C-T~.X T~x at T~,x Onset
No.C/min C min K
~ 25 940 15 130
9 6 977 15 130
977 60 130
11 S0 g77 5 132
12 25 977 15 130
13 25 977 5 131
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