JPH0575712B2 - - Google Patents
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- Publication number
- JPH0575712B2 JPH0575712B2 JP62179576A JP17957687A JPH0575712B2 JP H0575712 B2 JPH0575712 B2 JP H0575712B2 JP 62179576 A JP62179576 A JP 62179576A JP 17957687 A JP17957687 A JP 17957687A JP H0575712 B2 JPH0575712 B2 JP H0575712B2
- Authority
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- Prior art keywords
- powder
- temperature
- calcination
- atmosphere
- atm
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Links
- 239000000843 powder Substances 0.000 claims description 35
- 238000001354 calcination Methods 0.000 claims description 22
- 239000011812 mixed powder Substances 0.000 claims description 14
- 238000000034 method Methods 0.000 claims description 13
- 239000002994 raw material Substances 0.000 claims description 11
- 239000000919 ceramic Substances 0.000 claims description 10
- 229910052760 oxygen Inorganic materials 0.000 claims description 10
- 238000001816 cooling Methods 0.000 claims description 9
- 239000007858 starting material Substances 0.000 claims description 8
- 238000002156 mixing Methods 0.000 claims description 3
- 239000013078 crystal Substances 0.000 description 10
- 239000002245 particle Substances 0.000 description 10
- 238000005245 sintering Methods 0.000 description 6
- 238000002441 X-ray diffraction Methods 0.000 description 4
- 238000006243 chemical reaction Methods 0.000 description 4
- 239000007789 gas Substances 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- 238000003756 stirring Methods 0.000 description 4
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 3
- 238000010438 heat treatment Methods 0.000 description 3
- 239000001301 oxygen Substances 0.000 description 3
- 230000007704 transition Effects 0.000 description 3
- AYJRCSIUFZENHW-UHFFFAOYSA-L barium carbonate Chemical compound [Ba+2].[O-]C([O-])=O AYJRCSIUFZENHW-UHFFFAOYSA-L 0.000 description 2
- 238000000354 decomposition reaction Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 1
- 206010021143 Hypoxia Diseases 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- AYJRCSIUFZENHW-DEQYMQKBSA-L barium(2+);oxomethanediolate Chemical compound [Ba+2].[O-][14C]([O-])=O AYJRCSIUFZENHW-DEQYMQKBSA-L 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- RKTYLMNFRDHKIL-UHFFFAOYSA-N copper;5,10,15,20-tetraphenylporphyrin-22,24-diide Chemical compound [Cu+2].C1=CC(C(=C2C=CC([N-]2)=C(C=2C=CC=CC=2)C=2C=CC(N=2)=C(C=2C=CC=CC=2)C2=CC=C3[N-]2)C=2C=CC=CC=2)=NC1=C3C1=CC=CC=C1 RKTYLMNFRDHKIL-UHFFFAOYSA-N 0.000 description 1
- 238000006114 decarboxylation reaction Methods 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 238000007731 hot pressing Methods 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 239000002887 superconductor Substances 0.000 description 1
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/60—Superconducting electric elements or equipment; Power systems integrating superconducting elements or equipment
Landscapes
- Compositions Of Oxide Ceramics (AREA)
- Inorganic Compounds Of Heavy Metals (AREA)
- Superconductors And Manufacturing Methods Therefor (AREA)
Description
利用産業分野
この発明は、BaO−Y2O3−CuO系超電導セラ
ミツクス用原料粉末の製造方法に係り、特に
BaO源の原料粉末としてBa（NO3）2を用いて、斜
方晶の低温安定相からなり仮焼原料粉末を得る超
電導セラミツクス用原料粉末の仮焼方法に関す
る。
背景技術
従来、BaO−Y2O3−CuO系超電導セラミツク
スを製造するための出発原料の仮焼方法として
は、出発原料として、粒度3μｍ以下、純度99.9％
以上のBaCO3、Y2O3、CuO粉末を、所要の組成
比に応じて配合、混合した後、大気中で、900℃
〜1000℃の温度にて仮焼されていた。
出発原料として、Ba源にBaCO3を用いるため、
BaCO3BaO＋CO2↑の分解温度が850℃以上の
ため、仮焼温度は900℃以上にする必要があるが、
仮焼温度が950℃でも完全なる脱炭酸は行われず、
一方、焼結反応は徐々に進行し、仮焼温度と焼結
温度が重複するようになり、そのため、下記の如
き問題があつた。
すなわち、前記配合原料粉末の仮焼が不十分な
場合は、仮焼粉末に微量のBaCO3が残留し、前
記仮焼粉末を用いて焼結すると、焼結体は異常収
縮あるいはひび割れ等が生ずる恐れがあつた。
また、仮焼を十分に行うと、焼結反応が進行し
て所要の微細粉末は得られず、従つて、粉末の粒
成長が起こると、仮焼後の降温時に、斜方晶の低
温安定相への転移が前記粒子内部にまで及び難
く、粒子内に超電導相と非超電導相との混合組織
が生成される恐れがあつた。
発明の目的
この発明は、かかる現状に鑑み、従来の仮焼方
法における問題を解消し、すぐれた超電導性を有
するBaO−Y2O3−CuO系セラミツクスを製造す
るために最適な斜方晶の低温安定相組織からなる
仮焼原料粉末を得ることができる超電導セラミツ
クス用原料粉末の仮焼方法を目的としている。
発明の概要
発明者は、従来法のかかる問題を解決するた
め、BaO−Y2O3−CuO系超電導セラミツクスの
製造において、出発原料の原料粉末及び仮焼条件
について種々検討した結果、出発原料としてBa
源に、Ba（NO3）2を使用することにより、従来の
BaCO3を用いる場合の仮焼温度より200℃低い温
度での仮焼が可能となる点、また、特定のO2濃
度での仮焼条件にて仮焼を行うことにより、生成
されるBaOが大気中のCO2と可逆的に反応して
BaCO3が生成されることが防止され、かつ仮焼
後の降温時、酸素吸収により超電導相への転移を
完全に行うことができる点を知見し、この発明を
完成した。
すなわち、この発明は、
出発原料として、Ba（NO3）2、Y2O3、CuO粉
末を所要量配合混合後、
１気圧〜10気圧のO2100vol％雰囲気中で、
前記混合粉末を回動はるいは撹拌させながら
600℃〜850℃に１時間以上保持した後、
２℃／分以下の冷却速度で徐冷することを特徴
とする超電導セラミツクス用原料粉末の仮焼方法
である。
発明の好ましい実施態様
この発明において、出発原料粉は、純度99.9％
以上、粒度1μｍ以下が好ましく、かかる性状の
Ba（NO3）2、Y2O3、CuOの出発原料を、所要の
組成比に配合し混合する。
その後、１気圧〜10気圧のO2100％雰囲気中
で、600℃〜850℃に１時間以上保持する加熱条件
にて、前記混合粉末を回動あるいは撹拌する。
この発明の特徴である回動、撹拌方法は、混合
粉末がO2との接触が充分に確保されれば、公知
のいかなる方法も適用可能である。
この回動方法としては、傾斜型ロータリーキル
ンを用いて、その上方より前記混合粉末を投入す
ることにより、前記混合粉末はキルン内をO2雰
囲気と接触しながら回動、落下させて仮焼する方
法が利用できる。
また、この発明における撹拌方法としては、
O2ガス送入孔を下方に配設した粉末収容容器内
に、前記混合粉末を収容し、前記O2ガス送入孔
より、容器内の混合粉末内にO2100vol％以上の
ガスを吹込むと、前記混合粉末はO2ガスにより
撹拌され、相互接触が密になり、前記加熱条件に
て仮焼する方法を用いてもよい。
限定理由
この発明において、雰囲気をO2100％とする理
由は、Ba（NO3）2が分解してBaOになる際あるい
は降温時にBaOが残存するCO2成分と反応して、
安定な炭酸バリウムに変るのを防止し、また、
Ba（NO3）2の分解を完全に行うためである。
また、O2100％雰囲気における圧力は、１気圧
未満では、降温時に酸素欠乏になる恐れがあり、
また10気圧を超えると、圧力装置上特殊なものが
必要となり、実用的ではないため、１気圧〜10気
圧に限定する。
また、この発明において、回動あるいは撹拌す
る混合粉末の加熱条件は、600℃未満では、Ba
（NO3）2の分解並びに充分なる仮焼反応が期待で
きず、850℃を超えると、粒子同志の焼結が進行
し、粒成長が始まり好ましくないため、600℃〜
850℃とする。
また、保持時間は、Ba（NO3）2の分解並びに十
分な仮焼反応を行なわせるためには、少なくとも
１時間以上保持する必要がある。好ましくは、
700℃〜750℃、10〜20時間保持するのがよい。
この発明において、出発原料をO2雰囲気中で
特定条件にて、回動あるいは撹拌させながら加熱
後、徐冷する理由は、低温安定相（超電導相）で
ある斜方晶は高温安定相の正方晶より酸素含有量
が多く、このため超電導相へ転移するには酸素を
吸収する必要があるためである。従つて、O2雰
囲気下でゆつくりと徐冷する必要がある。冷却速
度としては２℃／分以下が好ましい。
発明の効果
この発明方法により、混合原料粉末とO2雰囲
気との強制的接触が低温にて十分に行なわれ、
O2100vol％かつ高O2分圧雰囲気の使用により、
生成されるBaOが大気中のCO2と可逆的に反応し
てBaCO3が生成されることを防止され、生成仮
焼粉中には非超電導相は残存せず、すべて超電導
相からなる均一な粉体が得られる。
得られた仮焼粉を所要の粒度に微粉砕した微粉
砕仮焼粉を、Ｘ線回析法にて結晶構造を調査した
結果、斜方晶の低温安定組織からなることが分つ
た。
この発明方法により得られた微粉砕仮焼粉を、
O2100vol％以上の雰囲気中で、930℃〜950℃で
１気圧中の圧力で焼結した後、２℃／min以下の
冷却速度で冷却することにより、焼結体全体が斜
方晶の低温安定相からなるすぐれた超電導性セラ
ミツクスを得ることができる。
実施例
純度99.9％以上、粒度1.5μｍ以下のBa（NO3）2、
Y2O3、CuO粉末を、組成比２：１：３のモル比
にて配合して、アルコールを収容したボールミル
中で６時間混合した。
その後、１気圧のO2100vol％雰囲気にて充満
された径100mm×長さ４ｍの傾斜角度25°の傾斜型
加圧ロータリーキルンを用い、その上方より前記
混合粉末を投入すると、前記混合粉末は下方に回
動しながら落下する。
かかる装置にて、回動落下中に750℃で10時間
保持して加熱した後、炉冷した。
得られた仮焼粉を微粉砕した。得られた粒度
1μｍ以下の仮焼粉をＸ線回析法にて結晶構造を
測定した結果、斜方晶からなる低温安定相である
ことが分つた。
その後、前記仮焼粉を、寸法径10mm×高さ30mm
の材質SiCのダイスを用いて、O2100vol％雰囲気
で600℃、圧力500Kg／cm2にて10時間保持するホツ
トプレスを行なつた。
その後、１℃／分の冷却速度で冷却して、寸法
径10mm×高さ5.5mmの焼結体を得た。
得られた焼結体をＸ線回析法及び顕微鏡にて組
織、結晶構造を調査した結果、焼結体は斜方晶の
低温安定相を有し、Tcが90〓でマイスナー効果
を示す超電導セラミツクスが得られた。
比較例
実施例１と同一の組成比の純度99.9％以上、粒
度1.5μｍ以下のBa（NO3）2、Y2O3、CuO粉末を混
合後、実施例と同一の傾斜型加圧ロータリーキル
ンを用い、実施例と同様に上方より混合粉末を投
入し、混合粉末を下方に回動させながら落下す
る。前記装置において、回動落下中に第１表に示
す仮焼条件にて仮焼後、第１表に表す冷却条件に
冷却した。
得られた仮焼粉を微粉砕し、得られた粒度1μ
ｍ以下の仮焼粉をＸ線回析法にて結晶構造を測定
した結果を第２表に示す。
Field of Application This invention relates to a method for producing raw material powder for BaO-Y 2 O 3 -CuO-based superconducting ceramics, and in particular,
The present invention relates to a method for calcination of a raw material powder for superconducting ceramics, using Ba(NO 3 ) 2 as a raw material powder for a BaO source to obtain a calcination raw material powder consisting of an orthorhombic low-temperature stable phase. BACKGROUND ART Conventionally, as a method for calcining starting materials for producing BaO-Y 2 O 3 -CuO-based superconducting ceramics, the starting materials have a particle size of 3 μm or less and a purity of 99.9%.
The above BaCO 3 , Y 2 O 3 , and CuO powders were blended and mixed according to the required composition ratio, and then heated at 900°C in the atmosphere.
It was calcined at a temperature of ~1000℃. Since BaCO 3 is used as a Ba source as a starting material,
Since the decomposition temperature of BaCO 3 BaO + CO 2 ↑ is over 850°C, the calcination temperature needs to be over 900°C.
Even at a calcination temperature of 950℃, complete decarboxylation does not occur.
On the other hand, the sintering reaction progresses gradually, and the calcination temperature and sintering temperature come to overlap, resulting in the following problems. That is, if the blended raw material powder is insufficiently calcined, a trace amount of BaCO 3 remains in the calcined powder, and when the calcined powder is used for sintering, the sintered body may shrink abnormally or crack. I was afraid. In addition, if calcination is performed sufficiently, the sintering reaction will progress and the required fine powder will not be obtained. Therefore, if grain growth of the powder occurs, the orthorhombic crystals will become stable at low temperatures when the temperature is lowered after calcination. It was difficult for the phase transition to reach the inside of the particles, and there was a risk that a mixed structure of a superconducting phase and a non-superconducting phase would be generated within the particles. Purpose of the Invention In view of the current situation, the present invention solves the problems in the conventional calcination method and develops an orthorhombic crystal that is optimal for producing BaO-Y 2 O 3 -CuO ceramics having excellent superconductivity. The object of the present invention is to provide a method for calcination of raw material powder for superconducting ceramics, which can yield raw material powder for calcination having a low-temperature stable phase structure. Summary of the Invention In order to solve the problems of the conventional method, the inventor conducted various studies on the starting material powder and calcination conditions in the production of BaO-Y 2 O 3 -CuO-based superconducting ceramics. Ba
By using Ba(NO 3 ) 2 as a source, the conventional
It is possible to perform calcination at a temperature 200°C lower than the calcination temperature when BaCO 3 is used, and by performing calcination under the calcination conditions at a specific O 2 concentration, the BaO produced can be Reacts reversibly with CO2 in the atmosphere
This invention was completed based on the discovery that the formation of BaCO 3 is prevented and that the transition to a superconducting phase can be completely achieved through oxygen absorption when the temperature is lowered after calcination. That is, in this invention, after mixing required amounts of Ba(NO 3 ) 2 , Y 2 O 3 , and CuO powder as starting materials, the mixed powder is circulated in an atmosphere of 100 vol% O 2 at 1 atm to 10 atm. While moving or stirring
This is a method for calcination of raw material powder for superconducting ceramics, which is characterized by holding the powder at 600°C to 850°C for 1 hour or more and then slowly cooling it at a cooling rate of 2°C/min or less. Preferred embodiment of the invention In this invention, the starting raw material powder has a purity of 99.9%.
Above, the particle size is preferably 1 μm or less, and with such properties
Starting materials Ba(NO 3 ) 2 , Y 2 O 3 , and CuO are mixed in a desired composition ratio. Thereafter, the mixed powder is rotated or stirred in a 100% O 2 atmosphere of 1 atm to 10 atm under heating conditions of maintaining the temperature at 600° C. to 850° C. for 1 hour or more. As the rotating and stirring method which is a feature of this invention, any known method can be applied as long as sufficient contact of the mixed powder with O 2 is ensured. This rotating method involves using a tilted rotary kiln, charging the mixed powder from above, and causing the mixed powder to rotate and fall in the kiln while coming into contact with an O 2 atmosphere, thereby calcining the kiln. is available. In addition, the stirring method in this invention is as follows:
The mixed powder is stored in a powder storage container with an O 2 gas inlet hole provided below, and a gas containing 100 vol% or more of O 2 is blown into the mixed powder in the container through the O 2 gas inlet hole. When the powder is mixed, the mixed powder is stirred by O 2 gas and comes into close contact with each other, and then calcined under the heating conditions described above. Reason for limitation In this invention, the reason why the atmosphere is 100% O 2 is that when Ba(NO 3 ) 2 decomposes to become BaO or when the temperature is lowered, BaO reacts with remaining CO 2 components.
It prevents barium carbonate from turning into stable barium carbonate, and
This is to completely decompose Ba(NO 3 ) 2 . In addition, if the pressure in a 100% O 2 atmosphere is less than 1 atm, there is a risk of oxygen deficiency when the temperature drops.
Moreover, if the pressure exceeds 10 atm, a special pressure device will be required and it is not practical, so the pressure is limited to 1 atm to 10 atm. In addition, in this invention, the heating conditions for the mixed powder that is rotated or stirred are below 600°C.
Decomposition of (NO 3 ) 2 and sufficient calcination reaction cannot be expected, and if the temperature exceeds 850°C, sintering of particles will proceed and grain growth will begin, which is undesirable.
The temperature shall be 850℃. In addition, the holding time must be at least 1 hour in order to decompose Ba(NO 3 ) 2 and cause a sufficient calcining reaction. Preferably,
It is best to hold the temperature at 700°C to 750°C for 10 to 20 hours. In this invention, the reason why the starting materials are heated under specific conditions in an O 2 atmosphere while rotating or stirring, and then slowly cooled is because the orthorhombic crystal, which is a low-temperature stable phase (superconducting phase), is a tetragonal crystal, which is a high-temperature stable phase. This is because it has a higher oxygen content than crystals, and therefore needs to absorb oxygen in order to transition to a superconducting phase. Therefore, it is necessary to cool slowly and slowly under an O 2 atmosphere. The cooling rate is preferably 2° C./min or less. Effects of the Invention According to the method of this invention, forced contact between the mixed raw material powder and the O 2 atmosphere is sufficiently carried out at a low temperature.
By using 100vol% O2 and high O2 partial pressure atmosphere,
The produced BaO is prevented from reversibly reacting with CO 2 in the atmosphere to produce BaCO 3 , and no non-superconducting phase remains in the produced calcined powder, which is a uniform mixture consisting entirely of superconducting phases. A powder is obtained. The resulting calcined powder was finely pulverized to a desired particle size, and the crystal structure of the finely pulverized calcined powder was investigated by X-ray diffraction, and it was found that it consisted of an orthorhombic low-temperature stable structure. The finely pulverized calcined powder obtained by the method of this invention is
After sintering at 930°C to 950°C at a pressure of 1 atm in an atmosphere containing O 2 100vol% or more, the entire sintered body becomes orthorhombic by cooling at a cooling rate of 2°C/min or less. Excellent superconducting ceramics consisting of a low-temperature stable phase can be obtained. Example Ba(NO 3 ) 2 with a purity of 99.9% or more and a particle size of 1.5 μm or less,
Y 2 O 3 and CuO powder were blended at a molar ratio of 2:1:3 and mixed for 6 hours in a ball mill containing alcohol. Thereafter, when the mixed powder is introduced from above into a pressurized rotary kiln with a diameter of 100 mm and a length of 4 m and an inclination angle of 25°, which is filled with an atmosphere of 100 vol% O 2 at 1 atm, the mixed powder flows downward. It falls while rotating. In this device, the material was heated by holding it at 750° C. for 10 hours while rotating and falling, and then cooled in a furnace. The obtained calcined powder was finely pulverized. Obtained particle size
The crystal structure of the calcined powder of 1 μm or less was measured by X-ray diffraction, and it was found to be a low-temperature stable phase consisting of orthorhombic crystals. Then, the calcined powder was
Using a die made of SiC material, hot pressing was carried out at 600° C. and a pressure of 500 Kg/cm 2 for 10 hours in an atmosphere of 100 vol% O 2 . Thereafter, it was cooled at a cooling rate of 1° C./min to obtain a sintered body with dimensions of 10 mm in diameter and 5.5 mm in height. The microstructure and crystal structure of the obtained sintered body were investigated using X-ray diffraction and a microscope, and it was found that the sintered body has an orthorhombic low-temperature stable phase and is a superconductor exhibiting the Meissner effect with a Tc of 90〓. Ceramics were obtained. Comparative Example After mixing Ba(NO 3 ) 2 , Y 2 O 3 , and CuO powder with the same composition ratio as in Example 1 with a purity of 99.9% or more and a particle size of 1.5 μm or less, the same inclined pressure rotary kiln as in Example was used. As in the example, the mixed powder is introduced from above, and the mixed powder is rotated downward as it falls. In the above device, the samples were calcined under the conditions shown in Table 1 during rotating and falling, and then cooled to the cooling conditions shown in Table 1. The obtained calcined powder is finely pulverized to obtain a particle size of 1μ.
Table 2 shows the results of measuring the crystal structure of the calcined powder with a diameter of m or less using an X-ray diffraction method.
【表】【table】
Claims (1)
粉末を所要量配合混合後、 １気圧〜10気圧のO2100％雰囲気中で、 前記混合粉末を回動あるいは撹拌させながら
600℃〜850℃に１時間以上保持した後、 ２℃／分以下の冷却速度で徐冷することを特徴
とする超電導セラミツクス用原料粉末の仮焼方
法。[Claims] 1. Ba(NO 3 ) 2 , Y 2 O 3 , CuO as starting materials
After mixing the required amount of powder, the mixed powder is rotated or stirred in a 100% O 2 atmosphere of 1 atm to 10 atm.
A method for calcination of raw material powder for superconducting ceramics, which comprises holding the powder at 600°C to 850°C for 1 hour or more and then slowly cooling it at a cooling rate of 2°C/min or less.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP62179576A JPS6424065A (en) | 1987-07-17 | 1987-07-17 | Calcination of raw material powder for superconducting ceramic |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP62179576A JPS6424065A (en) | 1987-07-17 | 1987-07-17 | Calcination of raw material powder for superconducting ceramic |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS6424065A JPS6424065A (en) | 1989-01-26 |
| JPH0575712B2 true JPH0575712B2 (en) | 1993-10-21 |
Family
ID=16068145
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP62179576A Granted JPS6424065A (en) | 1987-07-17 | 1987-07-17 | Calcination of raw material powder for superconducting ceramic |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS6424065A (en) |
-
1987
- 1987-07-17 JP JP62179576A patent/JPS6424065A/en active Granted
Non-Patent Citations (1)
| Title |
|---|
| JAPANESE JOURNAL OF APPLIED PHYSICS * |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS6424065A (en) | 1989-01-26 |
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