JPH03150223A - Oxide-based high-temperature superconducting substance - Google Patents

Abstract

PURPOSE:To readily synthesize a single phase and consequently enhance the Tc by stabilizing a crystal structure of a Tl-based oxide superconducting substance utilizing mutual substitution of constituent elements thereof. CONSTITUTION:The aforementioned oxide-based high-temperature superconducting substance is expressed by the composition formula Tl2+xBa2+yCu3O10+delta (¦x¦<0.6; ¦y¦<0.6, provided that x and y are not simultaneously 0; ¦delta¦<1.0). In the above-mentioned superconducting substance, e.g. <=30% Tl atomic sites are preferably substituted with Ca atoms.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to the crystal structure of a TIl-based oxide superconducting material.

The present invention relates to a substance whose single phase can be easily obtained by stabilizing the substance through mutual substitution of its constituent elements.

[Conventional technology]

Among the Tl-based oxide superconducting materials known so far, those with a superconducting critical temperature Tc of IIOK or higher are:
T Q zBazcaxcusoxo.

T I BazCazCuaOss (T Q o, a
Pbo, a) SrzCazCuaOe is known.

For the first two types, applied physics
Letters Vol. 53 (1988) pp. 432-434 (App1. Phys, Lett, 53 (1)
988) PP432-? 434). Regarding the last substance, see Science Volume 24 (19
1988) pp. 249-252 (Science, 5
3 (1988) PP 249-252).

[Problem to be solved by the invention]

T Q -B a -Ca -Cu -0 system, Ti-P
A plurality of superconducting material phases exist in the b-Sr-Ca-Cu-0 system, and it has been extremely difficult to synthesize the target material as a single phase (pure material).

For example, it is known that the substance having the highest superconducting critical temperature (Tc) in the T I -B a -Ca -Cu -0 system is T 112LBazca2Lcuaoto. However, even if an attempt was made to synthesize a single phase of this substance, substances such as T 11 zBazcuxoa et 41 zBazcuOe tend to coexist, making it extremely difficult to synthesize it as a pure substance. T sad Bat
CazCusOs, (Tffio,sPbo,s)S
Synthesizing a single phase of rzCazCuaOe was similarly difficult.

The present invention aims to easily synthesize a single phase of a Tl-based oxide superconducting material, and also aims to improve the Tc value by controlling the carrier concentration of the material.

[Means to solve the problem]

To summarize the present invention, the present invention relates to a Tffl-based oxide superconducting material, and achieves the above object by stabilizing the crystal structure of the material by mutually replacing elements constituting the material. It is in.

The present inventors have discovered that in the rl-based oxide superconducting material group,
With the aim of easily synthesizing substances having a high Tc higher than IIOK, we have mainly studied the stability of these substances by analyzing their crystal structures in detail. As a result, Tffi-based oxide superconducting materials with a high Tc of IIOK or higher have a common problem: (l) Ca atoms or Ta3
(2) Substituting a rare earth element, etc. whose ionic radius is almost the same as that of the + ion, (2) At the crystal site that should originally be completely occupied by a Ca atom, a Tll atom or a Tll atom, which is the most stable when ionized and has a trivalent ion, and Ca"÷ ion Partial substitution of atoms whose ionic radius is almost equal to that of , such as rare earth elements,
(3) Cause (1) and (2) to occur singly or simultaneously. We have discovered that this stabilizes the crystal structure and easily synthesizes a single phase of a substance with high Tc, leading to the present invention. At this time, the upper limit of the substitution rate for each crystal site is 30
It is around %. Even if the substitution rate is attempted to be higher than this, the free energy will increase and the elemental oxide or composite oxide to be substituted will appear as a different phase without IE exchange, which is not preferable.

[Effect]

By replacing the Tffi atomic site with a Ca atom or a rare earth atom, the strain in the crystal around the Tl atomic site is relaxed and the crystal is stabilized. By replacing Ca atomic sites with Tl atoms, rare earth atoms, etc., the strain in the crystal around the Ca atomic sites is relaxed, and the crystal is stabilized. Substitution of elements stabilizes the crystal structure of the substance, thereby making it possible to obtain a superconducting material that can be easily synthesized in a single phase.

In addition, when substituting elements with different stable valences, it is possible to control the carrier concentration of the material by changing the substitution rate, and as a result, superconducting materials with Tc several degrees higher than previously reported values can be created. Obtainable.

In the present invention, (1) T 11 z+xBazcaz÷ycua01+
Order δ.

(2) Ding j! t"xBazcat÷ycu30@+
δ.

(3) τj! We propose a superconducting material consisting of zBazcazcuxOto÷δ.

The substance (1) has the crystal structure shown in Figure 1, the substance (2) has the crystal structure shown in Figure 2, and the substance (3) has the crystal structure shown in Figure 3. desirable.

Table 1 shows T11zBaxcazcusO*o+δ.

7 IIBazCazCuxOs+δ, T I Sr
zCazCusO@+δ.

7 Q zBah, asro, acazcusOxo÷
δS Tl Bat, aSro, aCazCuaOs+
δ.

τ11 o, sPbo, asrzcazcusoe÷δ
The value of the thermal vibrational parameter of the Tl atom located at the Tl atom site is shown.

In all substances, the value is extremely large, over 2.0 (person 2), indicating that the crystal is unstable in this region.

Note that the value of X represents the substitution rate when this Tl atom site is replaced by a Ca atom.

Table 1 ITfl z(rJBa2caz(t+x)CuaOt
o+δ l 2. Medium, a l 1.
71 1.41 1.31IT n x-xBa2ca
z÷, ICU70g÷δ 12. inside, ti, inside,
Shin, 31st Precinct T Q x-xsr2Caz+*cuslJ
a+ δ 12.912.2 l
1.8 Giant, Monkey, 41ITn z(z-x)Bat, a
Sro, aCaz(t+x) CuaOxo÷δ, width,
811, middle, middle, lIIT Q x-xF3ax, as
ro, scaz(x+x)Cs3o-δ 12. Middle, 8
11, middle, middle, 11 Table 1 shows the Tlm of the Tl atom site.
The values of thermal vibration parameters when some atoms are replaced with Ca atoms are also shown. It can be seen that as the H conversion rate X increases, the value of the thermal vibration parameter decreases. This shows that by replacing some of the TJI atomic sites with Ca atoms, this crystal site is stabilized, and by extension, the entire crystal is stabilized.

An attempt was made to prepare a sample with a substitution rate of 0.4 or more and to determine the thermal vibration parameters at that time, but the -Ca element was not sufficiently dissolved and precipitated as CaO, resulting in a sample with a substitution rate of 0.4. could not be created. The crystals shown in Table 1 were obtained by Rietveld analysis of the X-ray diffraction measurement results of the sample powder. Also. Each sample was prepared by a solid phase reaction method using oxides of each component element as starting materials.

In Table 2, τ11 zBazcazcuaoto÷δ.

7 jl BatCazCusOsorderδ , T l
SrzCazCusOkai + δ.

111 zBax, iSro, tsCazCusOlo
÷δ.

771 Bam, aSro, sCazCuaO@+ δ
.

7 ao, sPbo, ssrzcazcuxoo÷δ
These superconducting materials show the bond angle of Cu -0-Cu in the crystal.

There are two types of crystal sites for Cu atoms, but the bond angle of Cu -0-Cu with respect to Cu atoms in the Cu -0 plane portion sandwiched by Ca atoms on both sides is always 180 degrees, so here What is shown is Cu -0-C with respect to the Cu atom located at the other crystal site.
is the bond angle of u. In any substance, this bond angle is 174 degrees to 176 degrees. Originally, Cu
The bond angle of -0-Cu should be 180 degrees, and the fact that this angle is not 180 degrees indicates that some strain exists in this part of the crystal.

This large internal strain is thought to reduce the stability of the crystal. Table 2 also shows the Cu-0-Cu bond angles when some of the Ca atoms at the Ca atom sites of these substances are replaced with Tlm atoms. Substitution rate y
as it grows larger.

As the Cu -0-Cu bond angle approaches 180 degrees,
It can be seen that the strain is relaxed and the entire crystal is stabilized. Although an attempt was made to produce a sample in which If steering y was 0.4 or more, a different phase was generated and it was not possible to obtain a sample in which y was 0.4 or more.

Note that in Table 2, the value of y is Tl for the CaJif child site.
Represents the substitution rate when atoms are substituted.

Table 2 IT n z(m+y)Ba2cIz(t-y)Cu3
0to+δ I 1741175 117611
7611771IT Q t+zyBafaz(z-y
)Cu70s÷δ l 1741174117411
75117511T2】Reizysr2Caz(ny)
Cu30s÷δ 11741174
11751 1751 17611Tffiz(t÷y
) Baz, aSro, eCaz(ty) CuaOto
+δ117 out of 76 1176117611771jTl
1 z+zyBau, asro, acaz(z-y)C
uaOs÷δI 174117511761176 +
17711rQo, a+mPbo, asr 龜(z-y
)Cu30s+δl 175117511751176
11761 As shown above, a part of the Tl child site is C
By substituting a part of the Ca atom site with a Ti atom, the crystal structure of the superconducting material is stabilized, and therefore it becomes possible to obtain a material that is easier to synthesize in a single phase.

Furthermore, by substituting atoms with different stable valences in the crystal, in addition to stabilizing the crystal as described above, it is possible to change the carrier concentration of the substance. We are in the process of researching this invention.

It has been found that even in Tl-based oxide superconductors, Tc changes with changes in carrier concentration.

In Figure 4, T m zBazcazcuaoto÷δ.

A sample was prepared in which the Tl atom site and the Ca atom site of T 11 BazCazCuaO@+δ were replaced with a Ca atom or a Tl atom, and the relationship between the Tc and the carrier concentration was shown. The carrier concentration is determined by measuring the Hall coefficient.

The horizontal axis represents the number of carriers per Cu atom in the crystal. As is clear from Figure 4, the carrier concentration is 0.
．． It can be seen that the highest Tc is obtained near 23.

Therefore, by substituting a part of a conventionally known superconductor with another atom with a different valence, it becomes possible to improve the Tc value.

〔Example〕

Examples of the present invention will be described below.

Example 1 As raw materials, T fl toa, B a O, Ca
O and Cu O were used, and the composition ratio of each metal element was Tl:Ba:Ca:Cu=2.2:2.0:1 in atomic ratio.
Weigh so that 8=3.0. First of all, BaO
.

The three components CaO and CuO are mixed and fired in the air at a temperature of 860° C. for 10 hours. The obtained product was thoroughly ground in an agate mortar and fired again in the air at a temperature of 860° C. for 10 hours. What was obtained in this way is the Tlz from earlier.
Os was added, thoroughly mixed and pulverized in a mortar, and then compacted into a disk shape with a diameter of 30 m and a thickness of 21111 mm, sealed in a sealable crucible, and fired at 850° C. for 1 hour.

At this time, since the composition of the sample may deviate from the target composition due to evaporation of the Tl element, an appropriate amount of powder having the same composition as the sample is placed inside the crucible to prevent composition deviation.

The powder X-ray diffraction pattern of the sample thus prepared is shown in Figure 5. When this powder Xa diffraction data was analyzed by the Rietveld method, 7 jl z, zBazc
It was confirmed that it was a single phase of at, acuaOxo÷δ. Also T Q zBazcazcuaOxo÷δ
It was confirmed that 10% of the Ca atoms in the crystal sites originally occupied by Ca atoms were replaced by TJI atoms. Further, the Cu-0-Cu bond angle at this time was 176 degrees.

The temperature dependence of the electrical resistance of this sample is shown in Figure 6.
This indicates that a superconducting transition has occurred near .

A rapid decrease in electrical resistance was observed, and it was confirmed that the specific resistance of the sample was 10 −Ω·1 or less at 115K. When the volume fraction of the superconducting portion in the sample was evaluated by the alternating current magnetic susceptibility method, a portion that transitioned to superconductor appeared near 120, and approximately 100% of the portion transitioned to superconductor at IIOK. The Hall coefficient of this sample was measured and the number of carriers per # atom in the crystal was counted and found to be 0.22.

Comparative Example 1 T QzOs, B a O, Ca O, C as raw materials
Using uO, the composition ratio of each metal element is T in atomic ratio.
a:Ba:Ca:Cu=2.0:2.0:2.0:3.
The sample was prepared under the same conditions as in Example 1. FIG. 7 shows the powder xm diffraction pattern of the sample obtained.

It can be seen that a considerable proportion of crystal phases other than 711 zBazcazcuso÷6 coexist. The temperature dependence of the electrical resistance of this sample is shown in Figure 8. A part of the sample near 120 has undergone superconducting transition, but
Even at 100K, the specific resistance of the sample was approximately 0.1 mΩ·, indicating that the sample had poor characteristics as a superconductor. When the volume fraction of the superelectric part in the IIOK sample was evaluated using the AC magnetic susceptibility method, it was found to be approximately 30
It was about %.

From Example 1 and Comparative Example 1, it can be seen that partial substitution of Ca atom sites by Tl atoms facilitates single-phase synthesis of superconducting materials.

Example 2゜ Table 3 shows TnzBazcazcuaOto÷δ.

7 Q BazCazCuaO*+δ, T 11 S
rzCazCuaOs+δ.

7 El zBax, asro, scazcuaoxo
÷δ.

T 11 Bam, aSro, @CazCuaOeshaδ
.

T Q o, hPbo, ssrzcazcusOn+δ
of the sample in which the Tl atom site of was replaced with Ca atom,
The value of X, which indicates the volume fraction of the superconducting portion at 100 K, represents the substitution rate when Tl atomic sites are replaced by Ca atoms.

Table 3 1 1G 10.0510. l
lO,210,33μa x(z-JBa!caz(z
+x) Cua 擢) 10+ δ 5-11 +
l I-11141-, 8a Cu+, CusOs+J
13017019511001901 DoQr
-Srxcaz+xcn30tr"8 l s
l 651751701651ITU z(t-JBa
t, aSro, eCaz(t+JcusOzo÷δl−
1-111118flTat-xBau, asr◎, 龜(l◆8)ωA1δ lωshi5 oyster 10011 one book-X=
In the case of O, this corresponds to a composition that is conventionally known. The specific preparation method for each sample was as follows: All raw materials used were oxides of each component element, and the only difference was the blended composition of the raw materials depending on the sample.Other than that, all conditions were unified as described in Example 1. .

This result shows that by replacing the TIII atomic site with Ca JJ, it is possible to easily synthesize a single phase of a superconducting material having a high Tc of 100 K or more.

Table 4 shows the temperatures at which the electrical resistance of these samples became 10-aΩ·1 or less, indicating that the samples according to the present invention are of better quality than the conventional ones.

The value of X represents the substitution rate when this Tl atom site is replaced by a Ca atom.

Table 4 1 piece 41 x (x-x) Ba 1x (x + w) Cu, I
Oxo÷δ lsol 18 out of 110111
1 Ill lITl1 t-xBaKamagamiaOe+δ
1750051107110 China 11τl x-
Sr Mug-1 6 1 River-10 Nakagawa River lr11z (t
-x) Bat, aSro, aCaz(z+x)CuaO
07 and 8-ITl x-xB in zo+δl-1-11O
at, asro, 8c1z(z+x)CuaO-δ 1
92110 Monkey 0 Shinkawa River Example 3゜Table 5,
.

111 BazCazCuaOe+δ, T II S
rzCazCusOta÷δ.

7 II zBat, asro, acazcuaozo
÷δ.

Baz, aSro, aCazCuaO@+δ.

7 m o, sPbo, asrzcazcusOs+δ
The value of y indicates the volume fraction of the superelectric part at 100K of the sample in which the Ca atomic sites of are replaced with TlJl atoms.The value of y is the substitution rate when the Ca atomic sites are replaced with Tn atoms represent

Table 5 1w conversion rate (y) lITf
A z(i+y)Ba龜(z-y)CuaOto÷6
1501851-001-” “11Tlt◆2JRa
Cua (i-y) CuaO*+δ 13015 ”I
"l"11Tffitsumst-2Caz(t-y)
CuaO*+δ l sl
60 I 701 75+ 6011Tffizb
÷y) Ban, aSro, eCaz(z-y)Cu30
to+6165+ 85 1 1001 1001
751ITl1 t+zyBaz, 4Sro, scaz
(z−y)CuaOe+δ −90ltooltool
701ITl1o-b+wPbo,I,Srselfcx-
y) r,uylJta+δ lsol as 1100
The case of 1951801y=Q corresponds to a conventionally known composition. The specific preparation method for each sample was as follows: All raw materials used were oxides of each component element, and the only difference was that the blending composition of the E (material) differed depending on the sample. unified.

This result shows that by replacing Tffi atomic sites with Ca Jii atoms, it is possible to easily synthesize a single phase of superconducting material having a high Tc of 100 K or more.

Table 6 shows the temperature at which the electrical resistance of these samples became 10-60.1 or less, indicating that the samples according to the present invention are of better quality than the conventional ones.

A value of 1 represents the substitution rate when Ca atom sites are replaced by Tn atoms.

Table 6 IM conversion rate (y) 1jTll
z(t+y)Ba2Caz(z-y)CuaOxo+
6 1801 1091125+1221 99
11 Ti t+bBamuz(t-y)CuJe+5
175110311231123111011Tl
x+zysr龜(t-y)CuaOe+5 123
1871109110019511 TIIz(l+y
) Baz, 4Sro, eCaz(z-y)CuaOio
+δ 1901 uoluoln month 891jTm
z+mBat, 4Sro, ecaz(z-y)Cu30
e+δ 1921109110811051851jT
41 o, s+mPbo, asr2Caz(i-y)
CuaOe+6 18111051109110119
31 Example 4゜The samples prepared in Examples 1.2 and 3 were left at a temperature of 850°C in the atmosphere for 10 minutes to 1 hour to remove T in the substance.
Some of the element evaporated. As a result, if the number of atomic defects generated at the T Q ff child site is -15% or less,
No decomposition of the superconducting material phase with Tc higher than 100 once formed was observed. However, the missing amount is 20%
It was found that when the amount exceeds Ml, it decomposes and the characteristics of the sample deteriorate significantly.

〔Effect of the invention〕

According to the present invention, a single phase of Tl-based oxide superconducting material having a high Tc can be easily produced, so that a superconductor with good characteristics can be efficiently produced.

In addition, by setting the direct conversion factor of the elements to an appropriate value, it is possible to obtain a superconducting material with a higher 'rc by several degrees than those conventionally known, which is advantageous in terms of application.

[Brief explanation of the drawing]

Figures 1 to 3 are schematic diagrams showing the crystal structure of superconducting materials;
FIG. 4 is a characteristic diagram showing the relationship between carrier concentration and Tc of a superconducting material, FIG. 5 is a graph showing a powder X-ray diffraction pattern of a sample prepared in Example 1 of the present invention, and FIG. A characteristic diagram showing the temperature dependence of electrical resistance of the sample prepared in Example 1, Figure 7 is a graph showing the powder X-ray diffraction pattern of the sample prepared in Comparative Example 1, and Figure 8 is a graph showing the sample prepared in Comparative Example 1. FIG. 3 is a characteristic diagram showing the temperature dependence of the electrical resistance of FIG. (a)...-Crystal sites that should originally be completely occupied by Ti atoms, (b)...-Crystal sites that should originally be completely occupied by Cam atoms; Daily Sheet 3 Diagram 1, Umbrella Yer 1 I' (good]

Claims (13)

[Claims] 1. Tl_2+_xBa_2Ca_2+_yCu_3
O_1_0+δ (where |x|<0.6, |y|<0.
6, but x+y are not 0 at the same time. |δ|<1.0)
An oxide-based high-temperature superconducting material characterized by the following: 2. 2. The oxide-based high-temperature superconducting material according to claim 1, wherein 30% or less of Tl atomic sites are substituted with Ca atoms. 3. An oxide-based high-temperature superconducting material having a compositional formula of Tl_2Ba_2Ca_2Cu_3O_1_0+δ (where -1.0<δ<1.0). 4. The superconducting material according to claim 3, characterized in that the substitution rate of Tl atomic sites by Ca atoms is 0.1% or more and 30% or less, and the substitution rate of Ca atomic sites by Tl atoms is 30% or less. superconducting material. 5. The superconducting material according to any one of claims 1 to 4, wherein the total occupancy of crystal sites that should originally be completely occupied by Tl atoms is 85% or more and 100% or less. material. 6. The superconducting material according to any one of claims 1 to 5, wherein the carrier concentration per Cu atom in the material is 0.
．． A superconducting material characterized in that it is 1 or more and 0.4 or less. 7. The composition formula is Tl_1+_xBa_2Ca_2+_yCu_3O_9
A superconducting material characterized by being represented by +δ (|x|<0.3, |y|<0.6, however, x and y are never 0 at the same time. |δ|<1.0) . 8. In the superconducting material according to claim 7, originally Tl
A superconducting material characterized in that Ca atoms substitute part of crystal sites that should be completely occupied by atoms. 9. In the superconducting material according to claim 7, originally Ca
A superconducting material characterized in that Tl atoms replace a portion of crystalline sites that should be completely occupied by atoms. 10. In the superconducting material according to claim 7, originally T
A superconducting material characterized in that Ca atoms replace some of the crystal sites that should be completely occupied by L atoms, and Tl atoms replace some of the crystal sites that should originally be completely occupied by Ca atoms. 11. 9. The superconducting material according to claim 8, wherein the substitution rate of Tl atom sites by Ca atoms is 30% or less. 12. The composition formula is Tl_1Ba_2Ca_2Cu_3O
_9+δ (-1.0<δ<1.0), and a crystal site in which Ca atoms replace a part of the crystal site that should originally be completely occupied by Tl atoms, and which should originally be completely occupied by Ca atoms. A superconducting material characterized in that some of the sites are replaced by Tl atoms. 13. The composition formula is Tl_1+__xSr_2Ca_2+_yCu_3O_
9+δ (|x|<0.3, |y|<0.6, x and y are not 0 at the same time. |δ|<1.0).