Abstract:
A process for fabricating worked superconducting ceramic material of a mean grain size not more than 10 um is disclosed, which comprises the steps of: (a) preparing a metal casing containing a starting powder material having a composition for forming an oxide superconductor; (b) calcining the starting powder material contained in the casing at a temperature range of 850° to 950° C.; (c) subjecting said casing to a HIP treatment; (d) subjecting said casing containing hot deformed material to cold deformation processing; and (e) subjecting said casing to stress relief treatment by annealing in the presence of oxygen.

Description:
This is a continuation of application Ser. No. 07/234,650, filed on Aug. 28, 1988, now abandoned 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a process for fabricating superconducting ceramics materials comprising a yttrium-including rare earth element, an alkaline earth metal and copper oxide (hereinafter referred to as &#34;R-A-Cu-O based ceramics&#34;) which has a high theoretical density ratio and thus has a high critical current value. 
     Conventional processes for fabricating worked materials such as wire rods, plates, strings, coils, and ribbons made of an R-A-Cu-O based superconducting ceramics include a process in which starting powders, i.e., an R 2  O 3  powder, an alkaline earth metal carbonate powder, and a CuO powder, each having an average grain size of not greater than 10 um, are provided and compounded in a predetermined compounding ratio followed by mixing and compacting them to obtain a compacted body, which is then calcined, e.g., in an atmosphere of dry air, at a temperature of from 850° C. to 950° C. to form a superconducting ceramics having a composition of YBa 2  Cu 3  O 7 , for example, the ceramics is then ground to obtain powder of an average grain size of not greater than 10 um and filled in a pipe of silver (Ag) or copper (Cu), and the pipe filled with the ceramics powder is molded into a worked material of a predetermined shape by cold processing such as swaging, rolling with grooved rolls, and processing with a die. 
     With the above-described conventional processes, it is very difficult to fill superconducting ceramics powder in a metal pipe in a filling ratio of not lower than 50% when fabricating processed superconducting materials or members. Further, it is noted that worked materials fabricated using such compacted body of a low filling ratio when cold processed have a theoretical density ratio of at most about 90%. In addition, it is also difficult upon calcination to fabricate superconducting ceramics with an oxygen content as high as up to 100% of theoretical content, and the resulting suerconducting ceramics tends to lack oxygen. For example, when fabrication of YBa 2  Cu 3  O 7  is contemplated, product has a composition of YBa 2  Cu 3  O 7-d  where d indicates degree of deficiency of oxygen. Under the circumstances, high critical current value and high critical temperature of superconducting ceramics worked materials cannot be secured with the conventional processes. 
     Further, when the above conventional superconducting ceramics material is worked into wire rods and then into coils it tends to suffer decrease in critical current value presumably due to heterogeneity in the density of filled superconducting ceramics powder and/or poor contact or non-contact between the respective grains of superconducting ceramics powder as the result of gap formed or slipping between the grains during working into coils. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to obviate defects of the conventional processes and provide a process for fabricating processed superconducting ceramics materials having a high theoretical density ratio. 
     Another object of the present invention is to provide a process for fabricating processed superconducting ceramics materials in which deficiency of oxygen can be supplemented with ease. 
     Still another object of the present invention is to provide a process for fabricating processed superconducting ceramics materials having a high critical current value and a high critical temperature. 
     Yet another object of the present invention is to provide a process for fabricating processed superconducting ceramics materials with improved crystalline orientation. 
     Further object of this invention is to provide a process for fabricating worked superconducting ceramics material which is free of heterogeneous portion or portion in which respective grains are in poor contact or non-contact. 
     As a result of extensive investigation, it has now been found that hot isostatic press treatment when performed to apply force generated by hydrostatic press while heating to any of starting material, intermediate product or final worked R-A-Cu-O-based superconducting ceramics materials, gives rise to compressed body having a theoretical density ratio much higher than that of the processed superconducting ceramics materials fabricated in the conventional manner, and thus final worked ceramics materials fabricated exhibit high critical current value and high critical temperature. 
     Therefore, the present invention provides a process for fabricating worked superconducting ceramics material composed essentially of a yttrium-including rare earth element, an alkaline earth metal, copper and balance oxygen and unavoidable impurities, and optionally containing a metal originating from an oxygen supply agent, comprising performing hot isostatic press treatment to apply compression force to an object to be compressed at a predetermined timing during the fabrication of worked superconducting ceramics material comprising the steps of: 
     (A) providing starting powder composed of: 
     (i) a member selected from the group consisting of: 
     (1) a mixt powder composed of powders of component oxides: 
     (1-1) a yttrium-including rare earth element oxide, 
     (1-2) an alkaline earth metal oxide, and 
     (1-3) copper oxide, 
      and having a composition substantially the same as that of a contemplated superconducting ceramics, 
     (2) a mixt powder composed of powders of: 
     (2-1) a partial compound between any two of the component oxides constituting a contemplated supercoductive ceramics secelected from (1-1), (1-2) and (1-3), and 
     (2-2) the rest of the component oxides selected from (1-1), (1-2) and (1-3), 
      and having a composition substantially the same as that of a contemplated superconducting ceramics, 
     (3) powder of a superconducting ceramics composed essentially of a yttrium-including rare earth element, an alkaline earth metal, copper and balance oxygen and unavoidable impurities, 
     (4) a mixt powder composed of at least two members selected from the mixt powders (1), (2) and (3); and 
     (ii) optionally an oxygen-supply agent; 
     (B) placing the starting powder in a metal casing, and sealing the metal casing; 
     (C) optionally heat-treating the starting powder in the metal casing when the starting powder is the mixt powder (1-1), (1-2) or (1-4) at a temperature sufficient for calcining the starting powder; 
     (D) working the metal casing containing the starting powder optionally heat-treated according to the step (C) above into an article having a predetermined form; and (E) optionally heat-treating the article at a temperature of from 300° C. to 950° C.; 
     the timing of perfoming the hot isostatic press treatment being selected from (i) after the step of (B), (ii) after the step of (C), and (iii) after the step of (D). 
     In a typical aspect, the present invention provides a process for fabricating superconducting ceramics material composed essentially of a yttrium-including rare earth element, an alkaline earth metal, copper and balance oxygen and unavoidable impurities, and optionally containing a metal originating from an oxygen supply agent, comprising: 
     (a) providing starting powder composed of: 
     (i) a member selected from the group consisting of: 
     (1) a mixt powder composed of powders of component oxides: 
     (1-1) a yttrium-including rare earth element oxide, 
     (1-2) an alkaline earth metal oxide, and 
     (1-3) copper oxide, 
      and having a composition substantially the same as that of a contemplated superconducting ceramics, 
     (2) a mixt powder composed of powders of: 
     (2-1) a partial compound between any two of the component oxides constituting a contemplated supercoductive ceramics secelected from (1-1), (1-2) and (1-3), and 
     (2-2) the rest of the component oxides selected from (1-1), (1-2) and (1-3), 
      and having a composition substantially the same as that of a contemplated superconducting ceramics, 
     (3) powder of a superconducting ceramics composed essentially of a yttrium-including rare earth element, an alkaline earth metal, copper and balance oxygen and unavoidable impurities, 
     (4) a mixt powder composed of at least two members selected from the mixt powders (1), (2) and (3); and 
     (ii) optionally an oxygen-supply agent; 
     (b) placing the starting powder in a metal casing and sealing the metal casing; 
     (c) subjecting the starting powder through the metal casing to hot isostatic press treatment to render the starting powder compressed; 
     (d) optionally heat-treating the starting powder when the starting powder is the mixt powder (1-1), (1-2) or (1-4) at a temperature sufficient for calcining the starting powder prior to or after subjecting it to the hot isostatic press treatment; 
     (e) processing the compressed product to produce an article having a predetermined form; and 
     (f) optionally heat-treating the article at a temperature of from 300° C. to 950° C. 
     In another typical aspect, the present invention provides a process for fabricating worked superconducting ceramics material composed essentially of a yttrium-including rare earth element, an alkaline earth metal, copper and balance oxygen and unavoidable impurities, and optionally containing a metal originating from an oxygen supply agent, comprising: 
     1) working a wire rod composed of a metal sheath and a core into a wire rod, the core being composed of: 
     (1) powder of a superconducting ceramics composed essentially of a yttrium-including rare earth element, an alkaline earth metal, copper and balance oxygen and unavoidable impurities, and 
     (2) optionally an oxygen-supply agent, and 
     2) performing hot isostatic press treatment to apply compression force to the wire rod. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, description will at first be made on a typical embodiment of the present invention, in which HIP treatment is performed before working the superconducting ceramics material into an article and the starting material for fabricating processed superconducting ceramics material is powder of a superconducting ceramics (R-A-Cu-O) composed essentially of a yttrium-including rare earth element (R), an alkaline earth metal (A), copper (Cu), and balance oxygen (O) and unavoidable impurities. 
     Suitable examples of the yttrium-including rare earth element which can be used include yttrium (Y), erbium (Er), dysprosium (Dy), ytterbium (Yb), gadolinium (Gd), thulium (Tm), neodymium (Nd), (Lu), and samarium (Sm). Of these, yttrium is preferred. The yttrium-including rare earth elements can be used singly or in combination. 
     Suitable examples of the alkaline earth metal which can be used in the present invention include barium, strontium and calcium, with barium being preferred. The alkaline earth metal can be used singly or in combination. 
     Powder of superconducting ceramics which can be used as a starting powder in the process of the present invention can be prepared, e.g., by calcining a mixture of single component oxides with a composition substantially the same as that of a contemplated ceramics material or article in an oven at a temperature suitable for preparing ceramics, e.g., 300° to 950° C., and grinding the resulting superconducting ceramics material to have a desired mean grain size, e.g., not greater than 10 um. Generally, smaller mean grain size, e.g., not greater than 5 um, is preferred. Of course, it is possible to use superconducting ceramics material otherwise prepared as far as it has a composition of R-A-Cu-O, e.g., YBa 2  Cu 3  O 7 , to be fabricated after grinding, if desired. Examples of known ceramics include those described, e.g., in Tomoji Kawai and Masaki Kanai, Japanese Journal of Applied Physics, vol. 26, No. 5, May, 1987, pp. L736-L737; and Masanobu Kobayashi et al., ibid. pp. L754-L756. 
     The starting powder is filled and sealed in a metal casing or sheath. Preferably, the metal sheath which can permeate oxygen is used. Suitable examples of the metal which can be used include copper, aluminum, and silver. Silver based alloys which may contain one or more other elements such as platinum as far as they do not react with ceramics and they give a good influence on the strength of wire rod to be fabricated upon drawing. 
     The shape of the casing is not limited and can be of any desired form depending on the shape of articles to be contemplated as far as it is suited for holding and sealing therein starting powder. 
     After filling the starting powder in the metal casing, the casing is sealed. Sealing can be performed in the air or in vacuo. The metal casing containing the starting powder is then subjected to hot isostatic press treatment (hot hydrostatic press treatment, hereinafter sometimes referred to as &#34;HIP treatment&#34;) to compress it. 
     After the compression, the resulting superconducting ceramics material is then cold- or hot-processed, e.g., by swaging, processing with grooved rolls, processing with a die, or a like, to produce articles having a desired shape, e.g., wire rods, plates, ribbons, strings, coils and the like. Also, the superconducting ceramics article surrounded by the metal casing can be processed so that at least one portion of the ceramics has an open surface; in other words, a part of or the whole metal sheath can be removed from the superconducting ceramics material as by grinding or other conventional means. During the above-described processing, annealing may be performed, if desired. 
     When superconducting ceramics wire rods and similar articles are to be fabricated, it is practically useful to process the wire rods such that the reduction of area of the wire rod is not less than 60% of the original one in order to increase critical current and critical temperature of the superconducting ceramics article. 
     Then, the processed materials can be heat-treated generally at a temperature of 300° C. to 950° C., preferably from 850° C. to 950° C., and more preferably from 900° C. to 940° C. in order to relieve or relax stress generated during processing, and/or the heat-treatment serves to increase the oxygen content of the superconducting ceramics material. 
     It is very often the case that oxygen in the resulting ceramics is deficient, with the result that characteristics such as critical current and critical temperature of the superconductive ceramics material obtained are unsatisfactory. It is advantageous to add powder of an oxygen-supply agent composed of a metal oxide to the starting powder prior to being filled in the metal casing in order to supplement oxygen, which tends to be deficient in superconducting ceramics material, during the compression and/or heat-treatment after processing. 
     Examples of the metal oxide which can be used for this purpose include Ag 2  O, MnO 2 , MoO 3 , WO 3 , V 2  O 5  and Ti 3  O 5 . The amount of the oxygen-supply agent to be added is preferably 1 to 5% by weight based on the total powder composition. When the starting powder composition containing powder of the metal oxide as an oxygen-supply agent, filled in the metal casing, is compressed or heated the metal oxide releases oxygen to compensate the ceramics composition for the deficiency of oxygen to increase the theoretical oxygen content ratio of the ceramics. 
     Alternative approach for increasing the theoretical oxygen content ratio is to provide an oxide layer on the inner surface of the metal sheath as by oxidizing the inner surface of the sheath by heating it in the air prior to introducing therein the starting powder. 
     It is sometimes useful to add the oxygen-supply agent in the starting superconducting ceramics powder and at the same time provide an oxide layer on the inner surface of the metal sheath. 
     In another typical embodiment of the present invention in which HIP treatment is performed prior to working the superconducting ceramics material into an article, processed superconducting ceramics materials or superconducting ceramics articles can generally be fabricated starting from a mixture of powder of a yttrium-including rare earth element oxide (R 2  O 3 ), powder of an alkaline earth metal oxide (AO) and powder of copper oxide (CuO). The composition of these single component oxides are blended so that the resulting mixture has a composition substantially the same as that of a final superconducting ceramics article. 
     Examples of the yttrium-including rare earth element oxide which can be used include oxides of yttrium-including rare earth element. The same yttrium-including rare earth elements described above with respect to the preceding embodiment can also be used in the instant embodiment. Of the oxides, generally yttrium oxide is preferred. The yttrium-including rare earth elements can be used singly or in combination with each other. 
     Examples of the alkaline earth metal oxide which can be used in the present invention include oxides of barium, otrontium and saleium. Darium oxide is preferred. The alkaline earth metal oxides can be used singly or in combination. 
     The single component oxides, i.e., powder of a rare earth element oxide, powder of an alkaline earth metal oxide and powder of copper oxide, each are commercially available. They can be used as they are or after being ground in order to ajust the mean grain size to a desired size. Usually, single component oxide powders to be used have a mean grain size of not greater than 10 um. Generally, smaller mean grain size, e.g., not greater than 5 um, is preferred. 
     The single component powders are well mixed with each other in a predetermined ratio appropriate for fabricating a contemplated superconducting ceramics material and the resulting mixt powder composition as a starting material is filled and sealed in a metal casing or sheath. The same metal casing described above with respect to the embodiment in which powder of superconducting ceramics powder is used as a starting powder. 
     After filling the mixt powder composition in the metal casing, the casing is sealed. Sealing can be performed in the air or in vacuo. The metal casing containing the starting powders is then subjected to calcination and compression by HIP treatment. The calcination and compression or HIP operations may be conducted in this order or in reverse order. 
     The calcination of the mixt powder composition, which may be prior to or after being subjected to HIP treatment, can be performed at a predetermined temperature, preferably ranging from 850° C. to 950° C., more preferably from 900° C. to 940° C., in the air for a period sufficient to convert the mixt powder composition into a superconductive ceramics. 
     The mixt powder composition can be compressed by HIP treatment prior to or after being subjected to calcination under the conditions described above. The hydrostatic force while heating is applied to the mixt powder composition prior to or after conversion of the composition into ceramics from outside the metal casing in the same manner as described above with respect to the embodiment starting from the superconducting ceramics powder. 
     After the calcination and HIP treatment in this order or in reverse order, the resulting superconducting ceramics is then cold- or hot-processed, which can be performed in the same manner as in the case of the HIP-treated superconducting ceramics material starting from the superconducting ceramics powder. 
     The processed materials can be heat-treated in the same manner as in the case of one fabricated starting from the superconducting ceramics powder. 
     Further, it is advantageous to add an oxygen-supply agent to the starting single component oxide powders and/or to provide an oxide layer on the inner surface of the metal casing in the same manner as the superconducting ceramics article fabricated starting from the superconducting ceramics powder. The same kind and amount of the oxygen-supply agent as described above can be used. When the mixt powder composition containing powder of the metal oxide as an oxygen-supply agent, filled in the metal casing, is calcined, the metal oxide powder releases oxygen, which compensates the ceramics composition for the deficiency of oxygen to increase the theoretical oxygen content ratio of the ceramics. Substantially no difference is observed whether the mixed powder composition containing an oxygen-supply agent is at first subjected to calcination or to HIP treatment. 
     Further, according to a variation of the above-described embodiments, powder of partial compounds between any two of the component oxides for fabricating superconducting ceramics articles, i.e., a compound between the yttrium-including rare earth element and the alkaline earth metal oxide, a compound between the alkaline earth metal and copper oxide, and a compound between copper oxide and the yttrium-including rare earth element, can be used together with powder of the remainder of the component oxides, i.e., copper oxide, the yttrium-including rare earth element, and the alkaline earth metal, respectively, instead of using a mixture of powders of single component oxides alone as a starting powder. For example, Y-Ba-CuO based superconducting ceramics articles can be fabricated using Y 2  O 3 . BaO and CuO in a composition substantially the same as that of the final ceramics. Other combinations such as CuO.BaO, and Y 2  O 3 .CuO, together with Y 2  O 3 , respectively, can also be used. Similarly, partial compounds can be used for ceramics compositions containing other yttrium-including rare earth elements. 
     The partial compounds between any two of the single component oxides for fabricating superconducting ceramics material can be commercially available or can be prepared in conventional manner, e.g., by calcining a mixture of powders of any two of the single component oxides described above in an oven at temperatures suitable for preparation of ceramics. 
     The ratio of powder of the partial compound to the remainder single component oxide which can be added is not critical as far as the resulting mixture has a composition substantially the same as that of a finally obtained superconducting ceramics article. 
     According to another variation, the mixt powder of the single component oxides, and/or the mixt powder of the partial compound and the remainder of the single component oxides, can be added to powder of the superconducting ceramics powder. In this case, the mixing ratio therebetween is not critical. 
     In the above-described variations, a processed superconducting ceramics can be obtained with substantially the same operations including calcination, HIP treatment and processing under substantially the same conditions as in the case of superconducting ceramics article obtained starting from a mixture of powders of single component oxides, and detailed explanation is omitted herein. 
     In another embodiment of this invention, HIP treatment is performed onto worked superconducting ceramics material. 
     Typical examples of the worked superconducting ceramics material which can be used include a wire rod composed of a metal sheath or tube such as Ag, Cu, stainless steel and Ni alloy, preferably Ag, and a core composed of a superconducting ceramics powder composed essentially of of a yttrium-including rare earth element, an alkaline earth metal, copper and balance oxygen and unavoidable impurities. The core may further contain an oxygen-supply agent. 
     The superconducting ceramics as a core may be the same as those used in the above-described embodiments of this invention, and it may preferably have a perovskite structure. 
     As the oxygen-supply agent can be used the same metal oxides described above with respect to the preceding typical embodiments of this invention in the same amounts as used therein. In addition, an oxide layer may be provided in the inner surface of the metal sheath similarly to the above-described embodiments, if desired. 
     The core composed of superconducting ceramics powder and optionally the oxygen-supply agent may be introduced into the metal sheath in the same manner as described hereinbefore and the thus-filled metal sheath may be worked into a wire rod having a predetermined diameter as by cold processing or working such as swaging, rolling with groved rolls, and die-processing conventionally used in the art. 
     The thus-worked material, i.e., wire rod is then further worked into a coil in a conventional manner. 
     HIP treatment of the coil thus obtained can be performed in the same manner as in the above-described embodiments. 
     If desired, the coil may be heat-treated in the same manner as in the above-described embodiments prior to or after HIP treatment. 
     According to this embodiment, not only theoretical density ratio of the superconducting ceramics powder in the article can be increased but also heterogeneity and poor contact or non-contact portion in the worked superconducting ceramics material can be avoided. 
     EXAMPLES 
     The present invention will be explained in greater detail with reference to the following examples, which should in no way be construed as limiting the present invention. 
     In tables, &#34;rem.&#34; stands for &#34;remainder&#34;. 
     EXAMPLE 1 
     Various starting powders composed of R-A-Cu-O based superconducting ceramics powders having mean grain sizes and compositions as shown in Table 1a below were filled into a cylindrical casing made of Cu having a size of 17 mm in inner diameter, 1.5 mm thick and 200 mm long at a filling ratio of 50%, and the thus-filled casing was placed in a conventional HIP apparatus. HIP treatment was performed under the following conditions: 
     
         ______________________________________Pressure:           1700 atmTemperature:        750° C., and______________________________________ 
    
     Retention Time: 1 hour thus forming a compressed body having a theoretical density ratio shown in Table 1b below. The compressed body was cold processed by subjecting it to swaging and grooved roll-processing, each in a plurality of times, followed by drawing the product into wire rod at an area reduction shown in Table 1b below to obtain wire rods. The wire rods were annealed for stress-relief at a predetermined temperature in the range of from 300° C. to 500° C. to fabricate superconducting ceramics wire rods. 
     For comparison, the same procedures as above were repeated except HIP treatment was omitted to obtain comparative wire rods. 
     The theoretical density ratio and critical current (Jc) of the superconducting ceramics wire rods thus obtained were determined and the results obtained are shown in Table 1b. 
     From the results shown in Table 1a and 1b below, it can be seen that the superconducting ceramics wire rods fabricated according to the process of the present invention had a theoretical density ratio much higher than that of the comparative wire rods. These results correspond to high critical current. 
     
                       TABLE 1a______________________________________ Starting Powder         MeanRun   Composition (wt. %)     GrainNo.   R         A         Cu     O    Size (um)______________________________________1-1   Y: 13.3   Ba: 41.2  28.6   rem. 0.91-2   Er: 22.5  Ba: 36.9  25.6   rem. 3.51-3   Dy: 22.0  Ba: 37.1  25.8   rem. 3.21-4   Yb: 23.1  Ba: 36.6  25.4   rem. 4.21-5   Cd: 21.4  Ba: 37.4  26.0   rem. 3.11-6   Tm: 22.6  Ba: 36.8  25.5   rem. 3.81-7   Nd: 20.0  Ba: 38.1  26.5   rem. 4.11-8   Lu: 23.3  Ba: 36.5  25.3   rem. 3.61-9   Sm: 20.7  ba: 37.7  26.2   rem. 3.51-10  Y: 13.5   Ba: 37.7  29.0   rem. 4.1           Sr:  2.71-11  Lu: 23.5  Ba: 35.1  25.7   rem. 3.2           Ca:  0.51-12  Same as 1-1 above1-13  Same as 1-2 above1-14  Same as 1-3 above1-15  Same as 1-4 above1-16  Same as 1-5 above1-17  Same as 1-6 above1-18  Same as 1-7 above1-19  Same as 1-8 above1-20  Same as 1-9 above1-21   Same as 1-10 above1-22   Same as 1-11 above______________________________________ 
    
     
                       TABLE 1b______________________________________         Characteristics of Wire Rod Theoretical               Theoretical Density   Area    Diameter                           Density Ratio     Reduc-  of      Ratio of                                   Critical After     tion    Wire Rod                           Wire Rod                                   CurrentRun   HIP (%)   (%)     (mm)    (%)     (A/cm.sup.2)______________________________________1-1   99.9      99      1.4     99.9    64001-2   99.6      99      1.4     99.5    32001-3   99.7      95      3.1     99.7    39001-4   99.8      95      3.1     99.8    53001-5   99.6      95      3.1     99.7    57001-6   99.7      95      3.1     99.6    42001-7   99.8      99      1.4     99.9    36001-8   99.5      99      1.4     99.6    41001-9   99.8      99      1.4     99.7    37001-10  99.7      99      1.4     99.8    48001-11  99.4      99      1.4     99.6    49001-12  --        Same as 1-1 above                         86.5     1501-13  --        Same as 1-2 above                         84.0     301-14  --        Same as 1-3 above                         81.7     201-15  --        Same as 1-4 above                         83.5     301-16  --        Same as 1-5 above                         86.5     301-17  --        Same as 1-6 above                         85.5     201-18  --        Same as 1-7 above                         84.4     301-19  --        Same as 1-8 above                         84.0     601-20  --        Same as 1-9 above                         85.5     201-21  --         Same as 1-10 above                         87.1     1501-22  --         Same as 1-12 above                         83.5     70______________________________________ 
    
     EXAMPLE 2 
     R-A-Cu-O based superconducting ceramics powder having mean grain sizes and compositions as shown in Table 2a below and a metal oxide powder as an oxygen-supply agent as shown in Table 2a below were blended at a blend ratio shown in Table 2a. After mixing, the resulting starting powder compositions were each filled into a cylindrical casing made of Cu having a size of 17 mm in inner diameter, 1.5 mm thick and 200 mm long at a filling ratio of 50%. After sealing it in vacuo, the thus-filled casing was placed in a conventional HIP apparatus. HIP treatment was performed under the following conditions: 
     
         ______________________________________Pressure:           1700 atmTemperature:        750° C., and______________________________________ 
    
     Retention Time: 1 hour thus forming a compressed body having a theoretical density ratio shown in Table 2b below. The compressed body was cold processed by subjecting it to swaging and grooved roll-processing, each in a plurality of times, followed by drawing the product into wire rod at an area reduction shown in Table 2b below to obtain wire rods. The wire rods were annealed for stress-relief at a predetermined temperature in the range of from 300° C. to 500° C. to fabricate R-A-Cu-O type superconducting ceramics wire rods. 
     For comparison, R-A-Cu-O based superconducting ceramics powder having a mean grain size and composition shown in Table 2a was filled in the same cylindrical Cu casing as described above at a filling ratio of 50%. After sealing it in vacuo, the casing was immediately cold processed under the same conditions as above to obtain wire rod, which was then heat-treated at a predetermined temperature in the range of from 300° to 500° C. for 10 to 20 minutes to anneal it for stress relief, thus producing comparative wire rods. 
     The theoretical density ratio, theoretical oxygen content ratio, critical temperature (Tc) and critical current (Jc) of the superconducting ceramics wire rods thus obtained were determined and the results obtained are shown in Table 2c. 
     From the results shown in Table 2c below, it can be seen that the superconducting ceramics wire rods fabricated according to the process of the present invention had a theoretical density ratio and a theoretical oxygen content ratio much higher than those of the comparative wire rods. These results correspond to high critical current and high critica temperature. 
     
                       TABLE 2a______________________________________ Starting Powder      MeanRun   Composition (wt. %)  GrainNo.   R        A        Cu    O    Size (um)                                     Content______________________________________2-1   Y: 13.3  Ba: 41.2 28.6  rem. 0.5    98.02-2   Er: 22.5 Ba: 36.9 25.6  rem. 0.7    97.02-3   Dy: 22.0 Ba: 37.1 25.8  rem. 1.0    98.82-4   Yb: 23.1 Ba: 36.6 25.4  rem. 1.2    97.52-5   Gd: 21.4 Ba: 37.4 26.0  rem. 2.0    99.02-6   Tm: 22.6 Ba: 36.8 25.5  rem. 0.6    98.82-7   Nd: 20.0 Ba: 38.1 26.5  rem. 2.5    97.02-8   Lu: 23.3 Ba: 36.5 25.3  rem. 3.0    98.82-9   Sm: 20.7 Ba: 37.7 26.2  rem. 3.1    99.02-10  Y: 13.5  Ba: 37.7 29.0  rem. 0.8    98.5          Sr:  2.72-11  Lu: 23.5 Ba: 35.1 25.7  rem. 2.0    99.0          Ca:  0.52-12  Same as 2-1 above             1002-13  Same as 2-2 above             1002-14  Same as 2-3 above             1002-15  Same as 2-4 above             1002-16  Same as 2-5 above             1002-17  Same as 2-6 above             1002-18  Same as 2-7 above             1002-19  Same as 2-8 above             1002-20  Same as 2-9 above             1002-21   Same as 2-10 above           1002-22   Same as 2-11 above           100______________________________________ 
    
     
                       TABLE 2b______________________________________  Oxygen Supply Agent                Mean Grain ContentRun      Composition Size (um)  (wt. %)______________________________________2-1      Ag.sub.2 O  5          2.02-2      MnO.sub.2   6          3.02-3      MoO.sub.3   4          1.22-4      Ag.sub.2 O  5          2.0    V.sub.2 O.sub.3                8          0.52-5      WO.sub.3    6          1.02-6      V.sub.2 O.sub.3                8          1.22-7      Ag.sub.2 O  5          3.02-8      V.sub.2 O.sub.3                8          0.7    Ti.sub.3 O.sub.5                4          0.52-9      Ti.sub.3 O.sub.5                4          1.02-10     MnO.sub.2   6          0.5    WO.sub.3    7          1.02-11     Ti.sub.3 O.sub.5                4          1.02-12     --          --         --2-13     --          --         --2-14     --          --         --2-15     --          --         --2-16     --          --         --2-17     --          --         --2-18     --          --         --2-19     --          --         --2-20     --          --         --2-21     --          --         --2-22     --          --         --______________________________________ 
    
     
                                           TABLE 2c__________________________________________________________________________              Heat Treatment   Theoretical    Area        Diameter              Theoretical                    Theoretical   Density    Reduc-        of    Density                    Oxygen   Ratio Aft.    tion        Wire Rod              Ratio Content                          Jc   TcRun   HIP (%)    (%) (mm)  (%)   Ratio (%)                          (A/cm.sup.2)                               (°K.)__________________________________________________________________________2-1   99.0  98  2.0   99.9  99.9  5000 992-2   99.0  98  2.0   99.8  99.9  2900 952-3   98.8  90  3.8   99.5  99.8  3600 932-4   99.2  95  3.1   99.8  99.9  4900 962-5   99.3  95  3.1   99.6  99.8  5400 942-6   98.7  98  2.0   99.2  99.7  3100 932-7   99.2  98  2.0   99.8  99.8  3300 942-8   99.3  90  3.8   99.8  99.6  3200 932-9   99.5  90  3.8   99.7  99.8  3300 952-10   99.2  95  3.1   98.7  99.5  4200 982-11   99.6  95  3.1   99.9  99.6  4100 902-12   --    Same as 2-1 above              89.4  99.2   210 902-13   --    Same as 2-2 above              88.3  99.1   55  882-14   --    Same as 2-3 above              87.2  99.0   62  872-15   --    Same as 2-4 above              83.8  99.0   83  872-16   --    Same as 2-5 above              85.0  99.0   115 862-17   --    Same as 2-6 above              82.6  99.0   20  872-18   --    Same as 2-7 above              83.4  98.9   30  852-19   --    Same as 2-8 above              88.5  99.0   65  872-20   --    Same as 2-9 above              89.0  99.1   190 862-21   --     Same as 2-10 above              83.6  99.0   85  862-22   --     Same as 2-11 above              85.6  98.9   120 85__________________________________________________________________________ 
    
     EXAMPLE 3 
     Various starting powders composed of R-A-Cu-O based superconducting ceramics powders having mean grain sizes and compositions as shown in Table 3a below were filled at a filling ratio of 50% into a cylindrical casing made of Cu having a size of 17 mm in inner diameter, 1.5 mm thick and 200 mm long and having formed on its inner surface an oxide layer of a thickness of 30 um by holding it in the air at a temperature of 450° C. for 10 hours, and the thus-filled casing was placed in a conventional HIP apparatus. HIP treatment was performed under the following conditions: 
     
         ______________________________________Pressure:           1700 atmTemperature:        850° C., andRetention Time:     1 hour______________________________________ 
    
     thus forming a compressed body having a theoretical density ratio shown in Table 3b below. The compressed body was cold processed by subjecting it to swaging and grooved roll-processing, each in a plurality of times, followed by drawing the product into wire rod at an area reduction shown in Table 3b below to obtain wire rods. The wire rods were annealed for stress-relief at a predetermined temperature in the range of from 300° C. to 500° C. for a predetermined period of time in the range of 20 to 60 minutes in an oxygen-containing atmosphere with a partial pressure of oxygen of 2 atm, thus fabricating R-A-Cu-O type superconducting ceramics wire rods. 
     For comparison, the same procedures as above were repeated except that Cu casing without having formed an oxide layer on its inner surface was used and that HIP treatment was omitted to obtain comparative wire rods. 
     The theoretical density ratio, theoretical oxygen content ratio, critical temperature (Tc) and critical current (Jc) of the superconducting ceramics wire rods thus obtained were determined and the results obtained are shown in Table 3c. 
     From the results shown in Table 3c below, it can be seen that the superconducting ceramics wire rods fabricated according to the process of the present invention had a theoretical density ratio much higher than that of the comparative wire rods. These results correspond to high critical current. 
     
                       TABLE 3a______________________________________ Starting Powder         MeanRun   Composition (wt. %)     GrainNo.   R         A         Cu     O    Size (um)______________________________________3-1   Y: 13.3   Ba: 41.2  28.6   rem. 0.73-2   Er: 22.5  Ba: 36.9  25.6   rem. 2.43-3   Dy: 22.0  Ba: 37.1  25.8   rem. 3.13-4   Yb: 23.1  Ba: 36.6  25.4   rem. 2.63-5   Cd: 21.4  Ba: 37.4  26.0   rem. 3.73-6   Tm: 22.6  Ba: 36.8  25.5   rem. 3.43-7   Nd: 20.0  Ba: 38.1  26.5   rem. 4.23-8   Lu: 23.3  Ba: 36.5  25.3   rem. 3.73-9   Sm: 20.7  Ba: 37.7  26.2   rem. 3.53-10  Y: 13.5   Ba: 37.7  29.0   rem. 4.1           Sr:  2.73-11  Lu: 23.5  Ba: 35.1  25.7   rem. 3.0           Ca:  0.53-12  Same as 3-1 above3-13  Same as 3-2 above3-14  Same as 3-3 above3-15  Same as 3-4 above3-16  Same as 3-5 above3-17  Same as 3-6 above3-18  Same as 3-7 above3-19  Same as 3-8 above3-20  Same as 3-9 above3-21   Same as 3-10 above3-22   Same as 3-11 above______________________________________ 
    
     
                                           TABLE 3b__________________________________________________________________________              Heat Treatment   Theoretical    Area        Diameter              Theoretical                    Theoretical   Density    Reduc-        of    Density                    Oxygen   Ratio Aft.    tion        Wire Rod              Ratio Content                          Jc   TcRun   HIP (%)    (%) (mm)  (%)   Ratio (%)                          (A/cm.sup.2)                               (°K.)__________________________________________________________________________3-1   99.9  99  1.4   99.9  99.8  6900 933-2   98.8  99  1.4   99.8  99.7  3400 903-3   99.7  98  2.0   99.8  99.6  4100 873-4   99.9  95  3.1   99.9  99.8  5200 893-5   99.7  98  2.0   98.7  99.5  5500 893-6   99.6  98  2.0   99.7  99.9  4300 883-7   99.7  95  3.1   99.7  99.4  3700 873-8   99.7  95  3.1   99.8  99.7  4300 913-9   99.8  95  3.1   99.9  99.8  3500 853-10   99.6  98  2.0   99.8  99.8  4900 933-11   99.7  98  2.0   99.9  99.6  5200 923-12   --    Same as 3-1 above              87.1  98.7   190 913-13   --    Same as 3-2 above              84.3  98.7   40  883-14   --    Same as 3-3 above              82.1  98.8   20  853-15   --    Same as 3-4 above              83.5  98.8   30  883-16   --    Same as 3-5 above              84.0  98.8   30  873-17   --    Same as 3-6 above              84.9  98.8   40  853-18   --    Same as 3-7 above              84.2  98.7   30  853-19   --    Same as 3-8 above              84.0  98.9   60  903-20   --    Same as 3-9 above              83.9  98.7   20  843-21   --     Same as 3-10 above              85.4  98.7   140 913-22   --     Same as 3-11 above              84.9  98.8   40  90__________________________________________________________________________ 
    
     EXAMPLE 4 
     As starting powder, R 2  O 3  powder, AO powder and CyO powder each having a predetermined mean grain size of from 0.5 to 10 um were blended at a blend ratio shown in Table 4a. After mixing, the resulting mixture was filled into a cylindrical casing made of Ag having a size of 17 mm in inner diameter, 1.5 mm thick and 200 mm long at a filling ratio of 50% and the casing was sealed in vacuo. Then, the thus-filled casing was was calcined by holding it in the air at a predetermined temperature of 850° to 950° C. to convert the powders in the metal casing into supercoducting ceramics, which was then placed in a conventional HIP apparatus. HIP treatment was performed under the conditions: 
     
         ______________________________________Pressure:             1700 atmTemperature:          850° C.Retention Time:       1 hour______________________________________ 
    
     thus formiong compressed body having a theoretical density ratio as shown in Table 4b below. The compressed body was cold processed by subjecting it to swinging and grooved roll-processing, each in a plurality of times, followed by drawing the product into wire rod at an area reduction shown in Table 3b below. Then, the wire rod was annealed for stress-relief at a predetermined temperature in the range of from 300° to 500° C. for 20 to 60 minutes, thus producing R-A-Cu-O based superconducting ceramics wire rods. 
     For comparison, R-A-Cu-O based superconducting ceramics powder having a mean grain size and composition shown in Table 4a was filled in the same cylindrical Ag casing as described above at a filling ratio of 50%. After sealing it in vacuo, the casing was immediately cold-processed under the same conditions as above to obtain wire rod, which was then heat-treated in the same manner as above to effect annealing for stress relief, thus producing comparative wire rods. 
     The theoretical density ratio, critical temperature (Tc) and critical current (Jc) of the superconducting ceramics wire rods thus obtained were determined and the results obtained are shown in Table 4c. 
     From the results shown in Table 4c below, it can be seen that the superconducting ceramics wire rods fabricated according to the process of the present invention had a theoretical density ratio much higher than that of the comparative wire rods. These results correspond to high critical current and high critical temperature. 
     
                       TABLE 4a______________________________________    Starting PowderRun      Composition (wt. %)No.      R2O3               AO      CuO______________________________________4-1      Y.sub.2 O.sub.3 :             17.15     BaO: 46.59                                 rem.4-2      Er.sub.2 O.sub.3 :             25.97     BaO: 41.63                                 rem.4-3      Dy.sub.2 O.sub.3 :             25.50     BaO: 41.89                                 rem.4-4      Yb.sub.2 O.sub.3 :             26.54     BaO: 41.32                                 rem.4-5      Cd.sub.2 O.sub.3 :             24.95     BaO: 42.21                                 rem.4-6      Tm.sub.2 O.sub.3 :             26.13     BaO: 41.55                                 rem.4-7      Nd.sub.2 O.sub.3 :             25.12     BaO: 42.98                                 rem.4-8      Lu.sub.2 O.sub.3 :             26.73     BaO: 41.21                                 rem.4-9      Sm.sub.2 O.sub.3 :             24.23     BaO: 42.61                                 rem. 4-10    Y.sub.2 O.sub.3 :             17.41     BaO: 42.58                                 rem.                       SrO:  3.20 4-11    Lu.sub.2 O.sub.3 :             27.09     BaO: 39.66                                 rem.                       CaO:  0.76______________________________________ 
    
     
                       TABLE 4a&#39;______________________________________                          Mean  Starting Powder         GrainRun    Composition (wt. %)     SizeNo.    R         A         Cu     O    (um)______________________________________4-12   Y:     13.3   Ba:  41.2 28.6   rem. 0.94-13   Er:    22.5   Ba:  36.9 25.6   rem. 3.44-14   Dy:    22.0   Ba:  37.1 25.8   rem. 3.34-15   Yb:    23.1   Ba:  36.6 25.4   rem. 4.14-16   Cd:    21.4   Ba:  37.4 26.0   rem. 3.24-17   Tm:    22.6   Ba:  36.8 25.5   rem. 3.54-18   Nd:    20.0   Ba:  38.1 26.5   rem. 4.44-19   Lu:    23.3   Ba:  36.5 25.3   rem. 3.74-20   Sm:    20.7   Ba:  37.7 26.2   rem. 3.54-21   Y:     13.5   Ba:  37.7 29.0   rem. 4.2                Sr:   2.74-22   Lu:    23.5   Ba:  35.1 25.7   rem. 3.2                Ca:   0.5______________________________________ 
    
     
                       TABLE 4b______________________________________TheoreticalDensity   Area    Diameter TheoreticalRatio     Reduc-  of       DensityAft. HIP  tion    Wire Rod Ratio   JcRun  (%)       (%)     (mm)     (%)     (A/cm.sup.2)______________________________________4-1  99.9      98      2.0      99.9    61004-2  99.7      98      2.0      99.7    29004-3  99.7      90      3.8      99.8    37004-4  99.8      95      3.1      99.8    49004-5  99.7      95      3.1      99.8    55004-6  99.6      98      2.0      99.7    42004-7  99.8      98      2.0      99.9    32004-8  99.6      90      3.8      99.8    31004-9  99.8      90      3.8      99.8    32004-10 99.7      95      3.1      99.7    42004-11 99.6      95      3.1      99.7    45004-12 --        Same as 4-1 above                         87.0     1104-13 --        Same as 4-2 above                         87.2     604-14 --        Same as 4-3 above                         84.9     704-15 --        Same as 4-4 above                         85.0     704-16 --        Same as 4-5 above                         82.1     504-17 --        Same as 4-6 above                         86.0     704-18 --        Same as 4-7 above                         85.1     704-19 --        Same as 4-8 above                         85.0     304-20 --        Same as 4-9 above                         86.5     404-21 --         Same as 4-10 above                         85.2     1004-22 --         Same as 4-11 above                         84.1     40______________________________________ 
    
     EXAMPLE 5 
     As starting powder, R 2  O 3  powder, AO powder and CuO powder each having a predetermined mean grain size of from 0.5 to 10 um were blended at a blend ratio shown in Table 5a below. After mixing, the resulting mixture was filled into a cylindrical casing made of Ag having a size of 17 mm in inner diameter, 1.5 mm thick and 200 mm long at a filling ratio of 50% and the casing was sealed in vacuo. Then, the thus-filled casing was placed in a conventional HIP apparatus. HIP treatment was performed under the conditions: 
     
         ______________________________________Pressure:            1600 atmTemperature:          850° C.Retention Time:        1 hour______________________________________ 
    
     thus forming a compressed body. The compressed body together with the metal casing was calcined by holding it in the air at a predetermined temperature in the range of 850° to 950° C. to convert the powders in the metal casing into superconducting ceramics. The superconducting ceramics compressed body (HIP-compressed calcined body) had a high theoretical density ratio shown in Table 5b. The compressed body was cold processed by subjecting it to swaging and grooved roll-processing, each in a plurality of times, followed by drawing the product into wire rod at an area reduction shown in Table 5a below. Then, the wire rod at an area reduction shown in Table 5a below. Then, the wire rod was annealed for stress-relief at a predetermined temperature in the range of from about 300° to 500° C. for 20 to 60 minutes, thus producing R-A-Cu-O based superconducting ceramics wire rods. 
     For comparison, R-A-Cu-O based superconducting ceramics powder having a mean grain size and composition shown in Table 5a&#39; was filled in the same cylindrical Ag casing as described above at a filling ratio of 50%. After sealing it in vacuo, the casing was immediately cold processed under the same conditions as above to obtain wire rod, which was then heat-treated in the same manner as above to effect annealing for stress-relief, thus producing comparative wire rods. 
     The theoretical density ratio and critical current (Jc) of the superconducting ceramics wire rods thus obtained were determined and the results obtained are shown in Tables 5b. 
     From the results shown in Table 5b below, it can be seen that the superconducting ceramics wire rods fabricated according to the process of the present invention had a theoretical density ratio much higher than that of the comparative wire rods. These results correspond to high critical current. 
     
                       TABLE 5a______________________________________    Starting PowderRun      Composition (wt. %)No.      R.sub.2 O.sub.3    AO      CuO______________________________________5-1      Y.sub.2 O.sub.3 :             17.15     BaO: 46.59                                 rem.5-2      Er.sub.2 O.sub.3 :             25.97     BaO: 41.63                                 rem.5-3      Dy.sub.2 O.sub.3 :             25.50     BaO: 41.89                                 rem.5-4      Yb.sub.2 O.sub.3 :             26.54     BaO: 41.32                                 rem.5-5      Gd.sub.2 O.sub.3 :             24.95     BaO: 42.21                                 rem.5-6      Tm.sub.2 O.sub.3 :             26.13     BaO: 41.55                                 rem.5-7      Nd.sub.2 O.sub.3 :             23.58     BaO: 42.98                                 rem.5-8      Lu.sub.2 O.sub.3 :             26.73     BaO: 41.21                                 rem.5-9      Sm.sub.2 O.sub.3 :             24.23     BaO: 42.61                                 rem. 5-10    Y.sub.2 O.sub.3 :             17.41     BaO: 42.58                                 rem.                       SrO:  3.20 5-11    Lu.sub.2 O.sub.3 :             27.09     BaO: 39.66                                 rem.                       CaO:  0.76______________________________________ 
    
     
                       TABLE 5a&#39;______________________________________                          Mean  Starting Powder         GrainRun    Composition (wt. %)     SizeNo.    R         A         Cu     O    (um)______________________________________5-12   Y:     13.3   Ba:  41.2 28.6   rem. 0.95-13   Er:    22.5   Ba:  36.9 25.6   rem. 3.15-14   Dy:    22.0   Ba:  37.1 25.8   rem. 3.05-15   Yb:    23.1   Ba:  36.6 25.4   rem. 3.85-16   Cd:    21.4   Ba:  37.4 26.0   rem. 3.05-17   Tm:    22.6   Ba:  36.8 25.5   rem. 3.55-18   Nd:    20.0   Ba:  38.1 26.5   rem. 3.25-19   Lu:    23.3   Ba:  36.5 25.3   rem. 3.45-20   Sm:    20.7   Ba:  37.7 26.2   rem. 3.75-21   Y:     13.5   Ba:  37.7 29.0   rem. 4.1                Sr:   2.75-22   Lu:    23.5   Ba:  35.1 25.7   rem. 3.7                Ca:   0.5______________________________________ 
    
     
                       TABLE 5b______________________________________TheoreticalDensity   Area    Diameter TheoreticalRatio     Reduc-  of       DensityAft. HIP  tion    Wire Rod Ratio   JcRun  (%)       (%)     (mm)     (%)     (A/cm.sup.2)______________________________________5-1  99.8      98      2.0      98.8    51005-2  99.8      98      2.0      98.4    31005-3  99.7      98      2.0      99.1    32005-4  99.9      98      2.0      99.8    30005-5  99.6      95      3.1      97.9    31005-6  99.8      90      3.8      98.3    29005-7  99.6      90      3.8      99.0    36005-8  99.6      90      3.8      98.4    29005-9  99.7      90      3.8      98.8    31005-10 99.8      95      3.1      99.1    43005-11 99.7      95      3.1      98.9    39005-12 --        95      2.7      86.7     1905-13 --        95      2.7      85.9     405-14 --        95      2.7      86.0     705-15 --        98      1.7      87.7     1105-16 --        98      1.7      88.8     805-17 --        90      3.8      82.1     705-18 --        95      2.7      85.5     605-19 --        95      2.7      84.9     505-20 --        95      2.7      86.1     305-21 --        90      3.8      82.9     1105-22 --        90      3.8      83.0     30______________________________________ 
    
     EXAMPLE 6 
     As starting powder, R 2  O 3  powder, AO powder and CuO powder having a predetermined mean grain size of from 0.5 to 10 um and various metal oxide powders were blended at a blend ratio shown in Table 6a. After mixing, the resulting mixture was filled into a cylindrical casing made of Cu having a size of 17 mm in inner diameter, 1.5 mm thick and 200 mm long at a filling ratio of 50% and the casing was sealed in vacuo. The metal casing was calcined by holding it in the air at a predetermined temperature in the range of 850° to 950° C. to convert the powders in the metal casing into superconducting ceramics. Then, the thus-synthesized ceramics was then placed in a conventional HIP apparatus. HIP treatment was performed under the conditions: 
     
         ______________________________________Pressure:            1700 atmTemperature:          750° C.Retention Time:        4 hour______________________________________ 
    
     thus forming a compressed body having a theoretical density rato shown in Table 6b. The superconducting ceramics compressed body (HIP-compressed calcined body) had a high theoretical density ratio shown in Table 6b. Then the compressed body was cold processed by subjecting it to swaging and grooved roll-process-ing, each in a plurality of times, followed by drawing the product into wire rod at an area reduction shown in Table 6b below. Then, the wire rod was heat-treated at a predetermined temperature in the range of from 300° to 500° C. for 10 to 20 minutes to effect annealing for stress-relief, thus producing R-A-Cu-O based superconducting ceramics wire rods. 
     For comparison, R-A-Cu-O based superconducting ceramics powder having a mean grain size and composition shown in Table 6a&#39; was filled in the same cylindrical Cu casing as described above at a filling ratio of 50%. After sealing it in vacuo, the casing was immediately cold processed under the same conditions as above to obtain wire rod, which was then heat-treated in the same manner as above to effect annealing for stress-relief, thus producing comparative wire rods. 
     The theoretical density ratio, theoretical oxygen content ratio, critical temperature (Tc) and critical current (Jc) of the superconducting ceramics wire rods thus obtained were determined and the results obtained are shown in Tables 6b. 
     From the results shown in Tables 6a and 6b below, it can be seen that the superconducting ceramics wire rods fabricated according to the process of the present invention had a theoretical density ratio and theorethical oxygen content ratio much higher than those of the comparative wire rods. These results correspond to high critical current and high critical temperature. 
     
                       TABLE 6a______________________________________                        Oxygen Starting Powder        SupplyRun   Composition (wt. %)    AgentNo.   R.sub.2 O.sub.3  AO         CuO  (wt. %)______________________________________6-1   Y.sub.2 O.sub.3 :          16.81   BaO: 45.66 rem. Ag.sub.2 O                                         26-2   Er.sub.2 O.sub.3 :          25.71   BaO: 41.21 rem. WO.sub.3                                         16-3   Dy.sub.2 O.sub.3 :          25.19   BaO: 41.39 rem. V.sub.2 O.sub.3                                         1.26-4   Yb.sub.2 O.sub.3 :          26.14   BaO: 40.70 rem. Ti.sub.3 O.sub.5                                         1.56-5   Cd.sub.2 O.sub.3 :          24.33   BaO: 41.15 rem. Ag.sub.2 O                                         2                                  MnO.sub.2                                         0.56-6   Tm.sub.2 O.sub.3 :          25.82   BaO: 41.05 rem. MoO.sub.3                                         1.26-7   Nd.sub.2 O.sub.3 :          23.34   BaO: 42.55 rem. Ti.sub.3 O.sub.5                                         16-8   Lu.sub.2 O.sub.3 :          26.20   BaO: 40.39 rem. Ag.sub.2 O                                         1                                  V.sub.2 O.sub.3                                         0.5                                  MoO.sub.3                                         0.56-9   Sm.sub.2 O.sub.3 :          23.50   BaO: 41.33 rem. MnO.sub.2                                         3  6-10 Y.sub.2 O.sub.3 :          16.54   BaO: 40.45 rem. Ag.sub.2 O                                         5                  SrO:  3.04 6-11 Lu.sub.2 O.sub.3 :          26.01   BaO: 38.07 rem. WO.sub.3                                         2                  CaO:  0.73      Ti.sub.3 O.sub.5                                         2______________________________________ 
    
     
                       TABLE 6a&#39;______________________________________                          Mean  Starting Powder         GrainRun    Composition (wt. %)     SizeNo.    R         A         Cu     O    (um)______________________________________6-12   Y:     13.3   Ba:  41.2 28.6   rem. 1.06-13   Er:    22.5   Ba:  36.9 25.6   rem. 3.36-14   Dy:    22.0   Ba:  37.1 25.8   rem. 3.16-15   Yb:    23.1   Ba:  36.6 25.4   rem. 3.86-16   Cd:    21.4   Ba:  37.4 26.0   rem. 3.06-17   Tm:    22.6   Ba:  36.8 25.5   rem. 3.56-18   Nd:    20.0   Ba:  38.1 26.5   rem. 3.36-19   Lu:    23.3   Ba:  36.5 25.3   rem. 3.26-20   Sm:    20.7   Ba:  37.7 26.2   rem. 3.66-21   Y:     13.5   Ba:  37.7 29.0   rem. 4.2                Sr:   2.76-22   Lu:    23.5   Ba:  35.1 25.7   rem. 3.4                Ca:   0.5______________________________________ 
    
     
                                           TABLE 6b__________________________________________________________________________                Oxidative Heat Treatment   Theoretical             Theoretical   Density     Diameter                Theoretical                      Oxygen   Ratio Area  of    Density                      Content   Aft. HIP    Reduction          Wire Rod                Ratio Ratio Jc   TcRun   (%)   (%)   (mm)  (%)   (%)   (A/cm.sup.2)                                 (°K.)__________________________________________________________________________6-1   99.0  98    2.0   99.8  99.9  6100 996-2   99.2  98    2.0   99.7  99.9  2900 996-3   99.1  90    3.8   99.8  99.8  3650 976-4   99.3  95    3.1   99.9  99.9  4700 996-5   99.0  95    3.1   99.1  99.9  5000 996-6   99.6  98    2.0   99.9  99.8  4000 976-7   99.3  98    2.0   99.8  99.8  3200 966-8   99.5  90    3.8   99.9  99.8  3100 966-9   99.2  90    3.8   99.7  99.9  3100 996-10   99.4  95    3.1   99.7  99.9  4500 1006-11   99.1  95    3.1   99.8  99.8  4100 906-12   --    Same as 6-1 above                89.5  99.2   200 906-13   --    Same as 6-2 above                88.3  99.1   50  886-14   --    Same as 6-3 above                87.2  99.0   60  876-15   --    Same as 6-4 above                84.5  99.0   100 886-16   --    Same as 6-5 above                85.6  99.1   110 896-17   --    Same as 6-6 above                83.3  99.1   20  896-18   --    Same as 6-7 above                83.6  98.8   30  826-19   --    Same as 6-8 above                89.0  99.0   190 856-20   --    Same as 6-9 above                90.0  98.9   210 806-21   --     Same as 6-10 above                82.1  99.2   15  926-22   --     Same as 6-11 above                84.8  98.9   95  82__________________________________________________________________________ 
    
     EXAMPLE 7 
     As starting powder, R 2  O 3  powder, AO powder and CuO powder having a predetermined mean grain size of from 0.3 to 10 um and various metal oxide powders were blended at a blend ratio shown in Table 7a. After mixing, the resulting mixture was filled into a cylindrical casing made of Cu having a size of 17 mm in inner diameter, 1.5 mm thick and 200 mm long at a filling ratio of 50% and the casing was sealed in vacuo. Then, the thus-filled casing was placed in a conventional HIP apparatus. HIP treatment was performed under the conditions: 
     
         ______________________________________Pressure:            1700 atmTemperature:          750° C.Retention Time:        1 hour______________________________________ 
    
     thus forming a compressed body having a theoretical density rato shown in Table 7b. The compressed body together with the metal casing was calcined by holding it in the air at a predetermined temperature in the range of 850° to 950° C. to convert the compressed powders in the metal casing into superconducting ceramics. The superconducting ceramics compressed body (HIP-compressed calcined body) had a high theoretical density ratio shown in Table 7b. The compressed body was cold processed by subjecting it to swaging and grooved roll-processing, each in a plurality of times, followed by drawing the product into wire rod at an area reduction shown in Table 7a below. Then, the wire rod was annealed for stress-relief at a predetermined temperature in the range of from 300° to 500° C. for 10 to 20 minutes, thus producing R-A-Cu-O based superconducting ceramics wire rods. 
     The comparison, R-A-Cu-O based superconducting ceramics powder having a mean grain size and composition shown in Table 7a&#39; was filled in the same cylindrical Cu casing as described above at a filling ratio of 50%. After sealing it in vacuo, the casing was immediately cold processed under the same conditions as above to obtain wire rod, which was then heat-treated in the same manner as above to effect annealing for stress-relief, thus producing comparative wire rods. 
     The theoretical density ratio, theoretical oxygen content ratio, critical current (Jc) and critical temperature (Tc) of the superconducting ceramics wire rods thus obtained were determined and the results obtained are shown in Tables 7b. 
     From the results shown in Tables 7b below, it can be seen that the superconducting ceramics wire rods fabricated according to the process of the present invention had a theoretical density ratio much higher than that of the comparative wire rods. These results correspond to high critical current. 
     
                       TABLE 7a______________________________________                         Oxygen  Starting Powder        SupplyRun    Composition (wt. %)    AgentNo.    R.sub.2 O.sub.3               AO        CuO   (wt. %)______________________________________7-1    Y.sub.2 O.sub.3 :            16.81  BaO: 45.66                             rem.  Ag.sub.2 O                                         27-2    Er.sub.2 O.sub.3 :            25.71  BaO: 41.21                             rem.  WO.sub.3                                         17-3    Dy.sub.2 O.sub.3 :            25.19  BaO: 41.39                             rem.  V.sub.2 O.sub.3                                         1.27-4    Yb.sub.2 O.sub.3 :            26.14  BaO: 40.70                             rem.  Ti.sub.3 O.sub.5                                         1.57-5    Gd.sub.2 O.sub.3 :            24.33  BaO: 41.15                             rem.  Ag.sub.2 O                                         2                                   MnO.sub.2                                         0.57-6    Tm.sub.2 O.sub.3 :            25.82  BaO: 41.05                             rem.  MoO.sub.3                                         1.27-7    Nd.sub.2 O.sub.3 :            23.34  BaO: 42.55                             rem.  Ti.sub.3 O.sub.5                                         17-8    Lu.sub.2 O.sub.3 :            26.20  BaO: 40.39                             rem.  Ag.sub.2 O                                         1                                   V.sub.2 O.sub.3                                         0.5                                   MoO.sub.3                                         0.57-9    Sm.sub.2 O.sub.3 :            23.50  BaO: 41.33                             rem.  MnO.sub.2                                         3  7-10 Y.sub.2 O.sub.3 :            16.54  BaO: 40.45                             rem.  Ag.sub.2 O                                         5                   SrO:  3.04 7-11  Lu.sub.2 O.sub.3 :            26.01  BaO: 38.07                             rem.  WO.sub.3                                         2                   CaO: 0.73       Ti.sub.3 O.sub.5                                         2______________________________________ 
    
     
                       TABLE 7a&#39;______________________________________                          Mean  Starting Powder         GrainRun    Composition (wt. %)     SizeNo.    R         A         Cu     O    (um)______________________________________7-12   Y:     13.3   Ba:  41.2 28.6   rem. 1.07-13   Er:    22.5   Ba:  36.9 25.6   rem. 3.37-14   Dy:    22.0   Ba:  37.1 25.8   rem. 3.17-15   Yb:    23.1   Ba:  36.6 25.4   rem. 3.87-16   Gd:    21.4   Ba:  37.4 26.0   rem. 3.07-17   Tm:    22.6   Ba:  36.8 25.5   rem. 3.57-18   Nd:    20.0   Ba:  38.1 26.5   rem. 3.37-19   Lu:    23.3   Ba:  36.5 25.3   rem. 3.27-20   Sm:    20.7   Ba:  37.7 26.2   rem. 3.67-21   Y:     13.5   Ba:  37.7 29.0   rem. 4.2                Sr:   2.77-22   Lu:    23.5   Ba:  35.1 25.7   rem. 3.4                Ca:   0.5______________________________________ 
    
     
                                           TABLE 7b__________________________________________________________________________                Oxidative Heat Treatment   Theoretical             Theoretical   Density     Diameter                Theoretical                      Oxygen   Ratio Area  of    Density                      Content   Aft. HIP    Reduction          Wire Rod                Ratio Ratio Jc   TcRun   (%)   (%)   (mm)  (%)   (%)   (A/cm.sup.2)                                 (°K.)__________________________________________________________________________7-1   99.8  98    2.0   99.9  99.9  6000 997-2   99.6  98    2.0   99.8  99.9  2850 957-3   99.7  90    3.8   99.7  99.8  3600 937-4   99.4  95    3.1   99.7  99.9  4700 997-5   99.3  95    3.1   99.8  99.9  5300 1007-6   99.4  98    2.0   99.9  99.8  4000 957-7   99.5  98    2.0   99.5  99.8  3100 927-8   99.8  90    3.8   99.8  99.8  3000 907-9   99.5  90    3.8   99.7  99.8  3000 937-10   99.2  95    3.1   99.6  99.9  4000 997-11   99.3  95    3.1   99.7  99.8  4000 907-12   --    Same as 7-1 above                89.5  99.2   200 907-13   --    Same as 7-2 above                88.3  99.1   50  887-14   --    Same as 7-3 above                87.1  99.0   60  877-15   --    Same as 7-4 above                83.7  99.0   80  887-16   --    Same as 7-5 above                84.5  99.0   100 887-17   --    Same as 7-6 above                82.7  99.0   20  867-18   --    Same as 7-7 above                83.6  98.9   40  827-19   --    Same as 7-8 above                88.5  99.0   200 857-20   --    Same as 7-9 above                89.0  99.1   190 877-21   --     Same as 7-10 above                83.4  99.0   100 867-22   --     Same as 7-11 above                85.6  98.9   160 82__________________________________________________________________________ 
    
     PREPARATION EXAMPLE 1 
     As starting powders are provided yttrium oxide (Y 2  O 3 ) powder having a mean grain size of 6 um, barium carbonate (BaCO 3 ) powder having a mean grain size of 6 um, and copper oxide (CuO) powder having a mean grain size of 6 um. These powders were blended at a blend ratio as follows: 
     
         Y.sub.2 O.sub.3 :BaCO.sub.3 :CuO=1/2:2:3 
    
     and well mixed. The resulting mixt powder was calcined in the air at a temperature of 900° C. for 12 hours to produce a compound having a composition of YBa 2  Cu 3  O 7  and a perovskite structure. The compound was then pulverized to obtain superconducting ceramics powder having a mean grain size of 1.3 um. 
     PREPARATION EXAMPLE 2 
     As starting powders are provided yttrium oxide (Y 2  O 3 ) powder having a mean grain size of 6 um, barium carbonate (BaCO 3 ) powder having a mean grain size of 6 um, and copper oxide (CuO) powder having a mean grain size of 6 um. These powders were blended at a blend ratio by weight of: 
     
         Y.sub.2 O.sub.3 :BaCO.sub.3 :CuO=15.13:52.89:31.98 
    
     and well mixed. The resulting mixt powder was calcined in the air at a temperature of 900° C. for 20 hours to produce a compound having a composition of YBa 2  Cu 3  O 7  and a perovskite structure. The compound was then pulverized to obtain superconducting ceramics powder having a mean grain size of 5 um. 
     EXAMPLE 8 
     The superconducting ceramics powder obtained in Preparation Example 1 above was filled in a Cu tube having a size of 23 mm in outer diameter, 20 mm in inner diameter, and 200 mm in height. The tube was processed by swaging and further processed using a die to fabricate a superconducting ceramics wire rod having a diameter of 1 mm. The wire rod was cut into three equal parts. Two of them were worked into coils each having a diameter of 30 mm. One of the thus-obtained superconducting ceramics coils was further subjected to HIP treatment under the conditions: 
     
         ______________________________________Pressure:            2000 atmTemperature:          800° C.Retention Time:        1 hour______________________________________ 
    
     The superconducting ceramics wire rod, superconducting ceramics coil and HIP-treated superconducting ceramics coil were each measured for their critical temperature Tc (° C.) and critical current density (A/cm 2 ) at 77° K. The results obtained are shown in Table 8 below. 
     
                       TABLE 8______________________________________Article        Tc (°K.)                   Jc (A/Cm.sup.2)______________________________________Wire Rod       94       320Coil           92        70HIP-treated    94       2600Coil______________________________________ 
    
     EXAMPLE 9 
     The superconducting ceramics powder obtained in Preparation Example 1 above was filled in an Ag tube having a size of 23 mm in outer diameter, 20 mm in inner diameter, and 200 mm in height. The tube was processed with grooved rolls and further processed using a die to fabricate a superconducting ceramics wire rod having a diameter of 2 mm. The wire rod was cut into three equal parts. Two of them were worked into coils each having a diameter of 50 mm. One of the thus-obtained superconducting ceramics coils was further subjected to HIP treatment under the conditions: 
     
         ______________________________________Pressure:            2000 atmTemperature:          800° C.Retention Time:        1 hour______________________________________ 
    
     The superconducting ceramics wire rod, superconducting ceramics coil and HIP-treated superconducting ceramics coil were each subjected to oxidative heat-treatment under the conditions: 
     
         ______________________________________Partial Pressure of Oxygen:                   2 atmTemperature:           850° C.Retention Time:        100 minutes______________________________________ 
    
     The thus-treated article were measured for their respective critical temperature Tc (° K) and critical current Jc (A/cm 2 ). The results obtained are shown in Table 9 below. 
     
                       TABLE 9______________________________________Article        Tc (°K.)                   Jc (A/Cm.sup.2)______________________________________Wire Rod       95       430Coil           94        60HIP-treated    95       3400Coil______________________________________ 
    
     EXAMPLE 10 
     The superconducting ceramics powder obtained in Preparation Example 2 and AgO powder having a mean grain size of 6 μm which was provided as a starting powder were blended at a blend ratio shown in Table 10 below and well mixed. The resulting mixt powder was filled in an Ag tube having a size of 20 mm in inner diameter, and 1.5 mm thick, and the tube was processed by rotary swaging to reduce size to 3 mm in diameter and then processed using a die to fabricate a wire rod having a diameter of 1 mm. The wire was worked into a coil of 30 mm in diameter. The coil thus-obtained was subjected to HIP treatment under the conditions: 
     
         ______________________________________Pressure             2000 atmTemperature           800° C.Retention Time         1.0 hour______________________________________ 
    
     The HIP-treated superconducting ceramics coil was measured for its critical temperature Tc (°C.) and critical current density (A/cm 2 ) at 77° K. 
     For comparison, the same procedures as above were repeated except that mixt powder containing AgO in amounts outside the preferred range was used. 
     The results obtained are shown in Table 10 below in which Runs 1 to 5 are according to this invention and Runs 6 to 9 are comparative ones. 
     
                       TABLE 10______________________________________Composition of Mixt Powder Characteristics of CoilRun       AgO    YBa.sub.2 Cu.sub.3 O.sub.7                          Tc  Jc______________________________________1         1.0    remainder     96  49002         2.0    remainder     98  52003         3.0    remainder     98  57004         4.0    remainder     97  56005         5.0    remainder     97  49006         --*    remainder     87  14107          0.5*  remainder     90  26508          6.0*  remainder     89  25309          7.0*  remainder     79  1200______________________________________ Note: The symbol &#34;*&#34; indicates that the conditions used were outside the scope of this invention. 
    
     EXAMPLE 11 
     The HIP-treated superconducting ceramics Ag wire rod coil obtained in Run No. 6 in Example 10 above was subjected to oxidative heat-treatment under the conditions: 
     
         ______________________________________Partial Pressure of Oxygen:                   2 atmTemperature:           850° C.Retention Time:         10 minutes______________________________________ 
    
     The critical temperature Tc (°K.) and critical current Jc (A/cm 2 ) of the thus-treated coil which were measure are as follows: 
     
         ______________________________________Critical Temperature Tc:                   97° K.Critical Current Jc:   4300 A/cm.sup.2______________________________________ 
    
     These values are comparable to those of Run Nos. 1 to 5 in Example 10. 
     Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore, to be understood that within the scope of the appended claims the invention may be practicesd otherwise than as specidically described.