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WO1992009090A1 - Oxydes supraconducteurs a temperature critique elevee - Google Patents

Oxydes supraconducteurs a temperature critique elevee Download PDF

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Publication number
WO1992009090A1
WO1992009090A1 PCT/US1991/008196 US9108196W WO9209090A1 WO 1992009090 A1 WO1992009090 A1 WO 1992009090A1 US 9108196 W US9108196 W US 9108196W WO 9209090 A1 WO9209090 A1 WO 9209090A1
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Prior art keywords
superconducting
oxide
oxides
group
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PCT/US1991/008196
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English (en)
Inventor
Kai Wai Wong
Xin Fei
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University of Kansas
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University of Kansas
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    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/45—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on copper oxide or solid solutions thereof with other oxides
    • C04B35/4521—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on copper oxide or solid solutions thereof with other oxides containing bismuth oxide
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N60/00—Superconducting devices
    • H10N60/80—Constructional details
    • H10N60/85—Superconducting active materials
    • H10N60/855—Ceramic superconductors
    • H10N60/857—Ceramic superconductors comprising copper oxide

Definitions

  • the present invention is broadly concerned with a method of fabricating complex superconducting oxides through appropriate selection and mixing together of a new fundamental substructure or "building block", which is 5 intrinsically superconducting, together with stoichiomet- ric proportions of the oxides making up another intrinsi ⁇ cally superconducting fundamental structure, whereby a virtual infinity of complex oxides can be formed.
  • the invention comprehends a completely rationalized method 0 of fabricating complex oxides of desirable T c values using the fundamental substructures.
  • stable, superconducting 112 and 12 ceramic oxides are described.
  • Superconductivity refers to that special state of a material where its resistance to electrical current flow suddenly and completely disappears when its tempera ⁇ ture is lowered. Below this onset or critical temperature T c , a characteristic of the material, the electrical resistance does not merely drop to a low level but it vanishes entirely. Only a very limited list of materials exhibit such a state.
  • the discovery of the first super ⁇ conductor occurred in 1911. Heike Kammerlingh Onnes discovered that Mercury lost all detectable resistance at a temperature just 4° above absolute zero.
  • a superconductor also exhibits perfect diamagne- tism below its critical temperature, i.e., it expels all magnetic field lines from its interior by producing an opposing magnetic field from a current flowing on its surface.
  • Superconductivity is the only large scale quantum phenomenon involving charges found in solid materials.
  • the current-carrying electrons in the super- conductor behave as if they were part of a dauntingly large single molecule the size of the entire specimen of the material.
  • the macroscopic quantum nature of supercon ⁇ ductors makes them useful in measuring magnetic field quantities to high precision or facilitates the measure- ment of such quantities so small as to be heretofore un easurable.
  • the present invention represents a significant departure from the prior art by providing the necessary theoretical understanding of superconductivity and a correspondingly rationalized technique for the fabrication of complex superconducting oxides.
  • the invention includes a method of fabricating superconducting ceramic oxides which comprises the steps of first providing a quantity of a fundamental oxide which is intrinsically superconducting, and preferably with the highest practical T c value, whereupon this oxide is mixed with stoichiometric propor ⁇ tions of the non-superconducting oxides making up another of the fundamental superconducting substructures, in this manner, if it is desired to produce a superconducting oxide having a T c of, e.g., 130°K, one may start with a fundamental superconducting oxide having a T c of 80°K, followed by appropriate reaction with the oxides making up another fundamental substructure whose total T c value is in excess of 50°K.
  • the specific invention hereof involves provision of a fundamental superconducting oxide of the following formula is provided:
  • t R is a metal selected from the group consisting of the rare earth metals and metals having a 3 + valency;
  • Q is a dopent different from R and selected from the group consisting of the rare earth metals, Ca, Sr, Ba, 10 Tl, Bi, Pb, Sb, Te, W and V; x is above zero and less than 1, and preferably less than about 0.3; d is an oxygen deficiency factor for insuring a substantial ionic valency balance which is less than zero 15 but sufficient to establish the stability of the oxide; and z is greater than zero but less than 1, and preferably less than about 0.6.
  • This quantity of superconducting oxide is then 20 mixed with stoichiometric quantities of non-superconduct ⁇ ing oxides required for the fabrication of a fundamental superconducting oxide different from the foregoing and having one of the formulae II.
  • M, R, Q, x and d are as previously defined;
  • A is a metal selected from the group consisting of Ca, Sr, Ba, Na, and K;
  • Q * is a dopent different from A and selected from 30 the group consisting of the rare earth metals, Ca, Sr, Ba, Tl, Bi, Pb, Sb, Te, W and V.
  • cate the oxides represented by formulae II and III is used to fabricate a complex superconductor, typically by grinding and sintering.
  • the aforementioned starting 112 superconductor of formula I is itself novel, i.e., the invention further includes a new class of 12 oxides represented by formula I.
  • the invention also comprehends new stable 112 superconductors having the formula IV.
  • R is a metal selected from the group consisting of the rare earth metals, Ca, Sr, Ba, Ag, Tl, K or Na, x is above zero and less than 1 (and preferably from about 0.05 to 0.3), and Q ** is a dopent different from R and selected from the group consisting of Ca, Sr, Ba, Tl, Bi, Pb, Sb, Te, W and V, and said dopent is present at a level such that the sum of the valences of R and at least 3;
  • A is a metal selected from the group consisting of Ca, Sr, Ba, Na and K, and the sum of the valences of A and Cu is less than 6, and d is an oxygen deficiency factor for ensuring a substantial ionic valency balance which is less than zero but sufficient to establish the stability of the oxide; and i and j are both equal to 1.
  • Exemplary 112 oxides in accordance with the invention include whereas the new 12 oxides are exemplified by the represen ⁇ tative superconductor
  • Figure 1 is a schematic representation of the crystalline structure of the three fundamental supercon ⁇ ducting "building blocks" useful in the fabrication of complex superconductors (structures (a)-(c)), and the shifted, stacked crystalline structure of two (c) cubic structures (structure (d) ) , with representative atoms for each structure being illustrated;
  • Fig. 2 is the resistivity curve for the funda ⁇ mental superconducting oxide Ca 08 Bi 02 SrCu 2 0 5 , after the alpha-stage heat treatment;
  • Fig. 3 is another resistivity curve for the oxide of Fig. 2, but after the sample was placed within a helium gas refrigerator for 24 hours;
  • Fig. 4 is another resistivity curve for the oxide of Fig. 2, after the Fig. 3 data was obtained, and upon reheating of the sample from 15°K to room temper ⁇ ature;
  • Fig. 5 is the resistivity curve of the Fig. 4 sample after the sample was placed in air for more than one day and the temperature decreased from about room temperature;
  • Fig. 6 is the resistivity curve of the Fig. 5 sample upon elevation of temperature from about 15°K;
  • Fig. 7 is a graph of a Meissner effect deter- mination made using 0.22 grams of the Fig. 2 supercon ⁇ ducting oxide;
  • Fig. 8 is the resistivity curve developed using the 123 superconducting oxide YBa 2 Cu 3 0 7 . d ;
  • Fig. 9 is a graph of a Meissner effect deter- mination made using 0.23 grams of the Fig. 8 oxide;
  • Fig. 10 is the resistivity curve developed using the oxide Pr ⁇ Ba ⁇ Cu ⁇ O,. ⁇ ) ⁇ ;
  • Fig. 11 is the resistivity curve developed using the oxide Y 0 .8 Ba o.2 Cu 2 ( ° ⁇ -z F z ) -d'
  • Fig. 12 is the resistivity curve developed using the oxi d e Yo.7 Ba o.3 C 0 ⁇ - 2 F z -d'
  • Fig. 13 is a graph of a Meissner effect determi ⁇ nation made using the oxide of Fig. 12;
  • Fig. 14 is an X-ray crystallography graph developed using the oxide YCu 2 0 4 _ d , showing the structure to be non-superconducting;
  • Fig. 15 is an X-ray crystallography graph devel- oped using the doped oxide Y 1 . ⁇ Ba ⁇ Cu 2 (0 1 . 2 F z ) 4 . d , showing the same to be superconducting;
  • Fig. 16 is an X-ray crystallography graph similar to that of Fig. 14, but depicting the results derived from the use of oxide ⁇ 0 . 9 Ba o. ⁇ Cu 2 (° ⁇ - z F zU- d '
  • Fig. 17 is an X-ray crystallography graph developed using the doped oxide Pr o ⁇ Ba o 2 Cu 2 ⁇ °i- z F z ⁇ 4 - d ' aru
  • Fig. 18 is a schematic representation depicting the crystalline structure of the oxide Ca 08 Bi 02 SrCu 2 0 5 , which is a combination of the substructures (a) and (c) depicted in Fig. 1.
  • T c Culprate superconductors can be viewed as the stacking of substructures which themselves are also super ⁇ conducting and whose electronic band structures can be first simulated.
  • the existence of the superconductor depends on the existence of an intrinsic valence hole band separated by a relatively narrow band-gap to an empty conduction band.
  • the stability of the entire complex high T c structure depends on the stability of each substructure or "building block.” From this viewpoint, the existence of at least three cubic substructures can be postulated, as shown in Fig. 1.
  • the structure 1(a) has been realized in the non-copper cubic BiBa.,_.
  • the structure 1(b) is not symmetric and must exist by shifted stacking.
  • the sim ⁇ plest is represented by the La 2 _ ⁇ Ba ⁇ Cu0 4 .
  • the structure 1(c) a substructure in many Culprate superconductors, has never heretofore been fabricated per se. Similar to the structure 1(b), 1(c) also forms the shifted stacking of two cubics as shown in Fig. 1(d). Thus, this 1(d) struc ⁇ ture has two Cu0 2 planes.
  • the method for fabricating the structure 1(d) is very different from those reported for the fabrication of the now well known Culprate oxide superconductors.
  • the basic structure _ must be provided by YCu 2 0 4 . d and not by BaCu 2 0 3 .
  • a two- step process is usually best for the fabrication as described below.
  • the vertical scale is the voltage of the standard 4-probe technique, and is a measure of the resistance in arbitrary units.
  • An AC of 1mA at 27Hz was used as the current source.
  • the sample was then left inside the He gas of a commercial APD refrigerator for over 24 hours.
  • the resistivity was then found to drop by one order of magni ⁇ tude (Fig. 3) .
  • the temperature of the refrigerator was increased and the R-T relation has the shape of the curve C shown in Fig. 4.
  • the sample holder was tapped occasionally to avoid anomalies due to poor contacts. No fluctuations in the voltage output were recorded.
  • Japanese Patent Document No. 130,420 purportedly describes a 112 superconducting oxide of the formula YBaCu 2 0 5 . It has been determined, however, that undoped 112 rare earth oxides do not exist. In the case in question, mixture, grinding and sintering of molar propor ⁇ tions of 2 0 3 , CuO and BaO will yield a crystalline structure actually made up of separate phases of a 123 superconducting oxide, YBa 2 Cu 3 0 7 . d and the non-superconduct- ing oxide Y 2 BaCu ⁇ ⁇ , along with residual quantities of the starting oxide CuO. Indeed, in Fig. 1 of the publication, the authors depict the well-known 123 structure. The 123 superconducting oxide is known, and the resistivity and Meissner effect data respecting this oxide is set forth in Figs. 8 and 9.
  • the present invention comprehends a new family of 12 Culprate oxide superconductors as defined in formula I above.
  • the critical temperatures of this family are on the order of 90°K. They have an orthorhombic unit cell which consists of the half unit shifted stacking of a cubic structure upon another.
  • the following examples describe the fabrication of representative 12 oxides of this family.
  • the 12 superconducting oxide Y._ x Ba x Cu 2 (° ⁇ - z F z - d was fabricated using a two-step procedure.
  • the non-superconducting oxide YCu 2 0 4 . d was fabricated, and in the second step this oxide was ground together with BaF 2 to form the final superconducting oxide defined above.
  • molar ratios of Y 2 0 3 and CuO were employed to achieve the nominal structure YCu 2 0 35 . These starting oxides were ground together to achieve an average particle size of about 10 "4 mm, and were pressed into pellets using a hydraulic press (8 tons pressure) .
  • the YCu 2 0 4 . d oxide was reground and mixed with a molar amount of BaF 2 (SrF 2 could be used as an alternative to BaF 2 ) to form the nominal composition YBa ⁇ Cu 2 0 4 F 2 ⁇ , with x ranging from about 0.2 to 1.0.
  • These materials were again ground to the same particle size described above, and pressed into pellets using the 8 ton press.
  • the pellets were placed inside an aluminum oxide ceramic tube having one open end and one closed end. The open end of this tube was substantially but not completely blocked by the closed end of another identical ceramic tube, and both tubes were placed inside a Lindberg 5423.3 tube furnace.
  • Figs. 12 and 13 are respectively the resistivity and Meissner effect graphs of the most optimum oxide prepared in accordance with this method, namely
  • Fig. 11 is a resistivity effect graph respecting the oxide Yo. 8 Ba o. 2 u 2 (° ⁇ - z F z ) 4 - d *
  • a comparison of Figs. 11 and 12 will demonstrate that the Fig. 11 oxide has a lower T c and a transition which is not as sharp as that found in Fig. 12. This results from the fact that in the Fig. 11 compound, there is insufficient fluorine present in the structure, as compared with Fig. 12.
  • the greater amount of BaF 2 used in the fabrication of the Fig. 12 compound thus greatly influences the T c value and transition characteristics.
  • the starting oxide Pr 2 0 3 may be used in a manner otherwise identical to that described above, where the BaF 2 or SrF 2 should be employed to give an x value of from about 0.2 to 1 in the nominal formula Pr,,. ⁇ Ba ⁇ Cu 2 (0 1 . z F z ) 4 . d .
  • the rare earth Culprate superconductors in accordance with the invention are made using BaF 2 or SrF 2 rather than normal oxides for two reasons.
  • YCu 2 0 4 is itself oxygen deficient simply from electro-valency considerations.
  • any further substitution of Y by Ba will further increase the oxygen deficiency to an extent that the structure would become unstable unless placed in a pure oxygen environment.
  • replacement of some oxygen with twice the amount of fluorine eliminates the presence of excessive vacant cation sites in the struc ⁇ ture.
  • the Y 1 . ⁇ Ba ⁇ Cu 2 (0 1 . z F 2 ) 4 . d phase is formed at 1250°C.
  • the Cu0 2 plane carries the charged carriers.
  • One of the features of the present invention is the fact that the T c value of a complex superconductor can be related to the geometrical structure, and subunit makeup, of the superconductor.
  • the invention provides a practical, systematic means of increasing the T c values of new superconductors.
  • the total excitation gap of the charged excitonic pair is directly proportional to the intrinsic hole density of the system.
  • Each substructure like the 112 substructures described above
  • the total intrinsic hole density is the linear sum of these substructures intrinsic hole density and the final T c of the sample is therefore obtainable using the following two criteria: (i) T c is the linear sum of that provided by the substructures; (ii) If the T c sum rule fails in a particular sample, it may be a multi-phase one and the sudden drops of the R-T curve may be used to guess the various substructures that might compose the sample.
  • the Cu-112 substructure has a T c of 80-90°K
  • the known 111 substructure (corresponding to Fig. 1(b)) has a T c of 35-45°K.
  • T c value of 40°K we come up with T c value of the 2223 structure to lie between 110 to 130°K, and that of the 2122 structure to be between 70-90°K.
  • the 123 structure is nothing more than the extended 112 structure as discussed above. Therefore, we expect its T c to be also of 80-90°K; so far, the known superconductors follow the sum rule.
  • the 1234 structure should have a T c of 120-130°K.
  • a T c prediction for the 1324 structure is difficult, because the Fig. 1(c) substructure is difficult to fabricate.
  • the 1324 composition can easily form the single-phase 123 substructure unless the complete structure is carefully fabricated in successive ⁇ sive steps.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Structural Engineering (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Compounds Of Heavy Metals (AREA)
  • Compositions Of Oxide Ceramics (AREA)

Abstract

On a fabriqué des oxydes supraconducteurs complexes par une sélection et un emploi appropriés de 'blocs de construction' fondamentaux supraconducteurs. Ainsi, l'invention fournit un procédé rationalisé de fabrication d'oxydes complexes ayant des valeurs de Tc avantageusement élevées. Un autre aspect de l'invention a trait à de nouveaux oxydes supraconducteurs 112 et 12.
PCT/US1991/008196 1990-11-13 1991-11-04 Oxydes supraconducteurs a temperature critique elevee Ceased WO1992009090A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US61220190A 1990-11-13 1990-11-13
US612,201 1990-11-13
US783,356 1991-10-28

Publications (1)

Publication Number Publication Date
WO1992009090A1 true WO1992009090A1 (fr) 1992-05-29

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Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
CHEMICAL ABSTRACTS, Vol. 115, No. 26, Abstract No. 292378K; & SOLID STATE COMMUNICATIONS, Vol. 79, No. 11, September 1991, X. FEI et al., "The Superconducting 112 Oxides". *

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