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Synthesis and Superconductivity of the HgBa2Ca2Cu3Ox superconductors
Physiea C 235-240 (1994) 895-896
PHY$1CA
North-Holland
Synthesis and Superconductivity of the HgBa2Ca2Cu30 x Superconductors Sung-lk L¢¢a,b, Sergey Leea,c, Mi-Ock Muna, and Myoung-Kwang Baea aDepartment of Physics, Pohang University of Science and Technology, Pohang, 790-784, Korea bphysics Division, Research Institute of Industrial Science and Technology, Pohang, 790-600, Korea eDepartment of Chemistry, Moscow State University, Moscow 119899,Russia We produced the HgBa2Ca2Cu308+ x (Hg-1223) superconductors by changing the composition, mercury vapor pressure and reaction temperature. We found that the high mercury pressure is essential for the formation cf the Hg-1223 phase by preventing the decomposition of HgO at low temperature. This sample was characterized by the X-ray diffraction, Auger electron microprobe, AC susceptibility and resistivity measurement.
1. INTRODUCTION Recently, superconductivity above 130 K was discovered for the Hg-containing cuprate. [1,2]. However, it was found that this superconductor is a composite multi-phase of HgBa2Can+lCUn" O2n.2+x (n=i to 5). it " known that the phase for n=3 (Hg-1223) is responsible for the 130 K superconductivity, but the single phase of Hg-1223 phase has not yet been produced. lk,-. In this paper, we report a method to prc~.ace ~ sample which contains the Hg-1223 as the main phase. From the x-ray diffraction, we could not find any other phase except for n=3. We found that high mercury pressure inside the quartz tube and heating temperature higher than 850 °C is essential for the formation of Hg-1223. This high mercury pressure inhibits the formation of CaHgO2 by preventing the decomposition of HgO below the reaction temperature.
nominal compositions of Ba2Ca 1Cu2Oy, Ba2Ca 1 5Cu2 5Or and Ba2Ca2Cu30 v. These reagents were" hefited several times between 650°C and 700° C for 20 h with intermediate grindings. Then we made a sample in the form of a pellet and heat treated it at 920°C inside the oxygen atmosphere for ,,~,"" h -~ith two intermediate grindings Then a HgO powder form (yellow) was added in a nitrogen mmos~hcre. We kep~ tbc pclie~ in an ahm~ina tube m prevent direct contact with the quartz. We placed this alumina tube inside a quartz tube. We tried every meth~ to reduce the -,.,,.,pry ~ ' space inside the quartz ampoule. The pressure of Hg vapor once HgO is decomposed in the quartz tube was between 80 and 300 arm. The samples were heated to a temperature between 800 and 950°C, kept at this temperature for 5 h and then slowly cooled (80 K/h) to room temperature. Finally we oxidized the samples in flomng ox3'gen at 300°C for 20 h.
2. E X P E ~ M E N T A L
3. RESULTS AND r~l~tu~S~ON
The s)~athesis of the samples is consisted of two steps. First is the production of a precursor pellet for Ba2Ca2Cu30 7 and second is a formation of the
For the synthesis of the Hg-1223 phase. ~ve used the pellets ~!th varic.us nominal compositions of HgBa2Ca 1Cu2Ov, HgBa2C~2Cu3Ov, and HgBa2Cal 5Cu25Oy • We found thaf if vapor pressure of Hg is low, only Hg-1201 together ,~ith larger amounts of impurity ( CaHgO2, BaCuO2 and Ba2Cu30 5 ) are formed. The reason for the Rack of the Hg-1223 is the decomposition of HgO at about
and HgO inside evacuated quartz tubes. The precursor pellets Ba2Ca2Cu30 7 were prepared by mixing appropriale amounts of nitrate form from Ba, Ca, and Cu. We made three reagents with
0921-4534/94/S07,00 & 1994 - Elsevier Scie~3ce B.V. All rights rcserx'cd. SS!)I {D21-4Sq4(04)0! (11 ] -()
S.-L Lee et al./Physica C 235-240 (1994) 895-896
896
Tablel. Volume fraction of the phase from XRD analysis
Sample Number
Nominal Composition
0.10
Estinated t Volume fraction (°C) by XRD (%) Hg1223 Hg1212
#1
HgBa2CaI Cu2Oy
#2 #3
#4 #5 #6 #7 #8 #9
800
-
100
800 HgBa2Ca].sCu2.50y 800 830
45 40 63
55 60
850
75
900 880 900 930
100 100 75
25 25
HgBa2Ca2Cu30v
--
0.0~
37
500°C which is 300 to 400 degrees below the reaction temperature. In this case, CaHgO 2 forms first and inhibits the formation of Hg-1223 [3,4]. To cure this problem, we increased Hg vapor pressure inside the quartz tube to enhance the decomposition temperature. We tried every method to reduce the empty space inside the tube. We easily obtained the nominal Hg vapor pressure over 200 arm. and confirmed the reduction of the CaHgO2 For the study of temperature effect, we used the pellet of HgBa 2 Ca 1 5 Cu2 5 0 y . Since the sample does not touched the quar~ tubb, we could increase ,h,, temperature hig,~ than 800°C without quartz contamination. Several different temperatures between 800 and 900°C were chosen. From the x-ray diffraction pattern, we d_eterm_ined the content of the Hg-1212 and 1223 phases. We used the ratio from the intensities of the strongest line (103) for Hg-1212 and (103) for Hg-1223. The amount of the Hg-!223 phase was increased at m~;ue~ iemperaiures. We also used the nominal composition of H g.~ . . . . , gBa2,-a2CuaOy as a sto~chmmetnc m~xture of the components. "l~heresult of XRD analysis is shown in table 1. We found that there are no traces of superconducting phases a~ 880°C in this composition. However, a drastic change of superconductivity appears at 900°C. We found that the sample contains Hg-1223 as the main superconducting phase. The amount of BaCuO 2 still remains. With further increase of the tempe1.,." ~ L
rv
0.00 100
150
2oo
2rio
300
T (K) Fig. 1 The resistance curve for the single phase Hg1223 sample (circle) with that for the mixture of Hg- 1223 and Hg- ! 212 phase (triangle)
rature i.e. at 930°C, Hg-1212 forms again. At a temperature of 950°C, quartz ampole breaks down. We found that optimum temperature for Hg-1223 formation is about 900°C for our ease. 4. CONCLUSION We studied the formation of the Hg-!223 phast and found that high mercury vapor pressure above 200 atm and a narrow heating temperature range around 900 ° C were essential. And We observed that the high mercury vapor pressure that is related to the imhibition of HgO decomposition at low temperature is crucial for the formation of the Hg-1223 phase. REFERENCES [I] A.Schilling, M.Cantoni, J.D.Guo and H.R.Ott Nature (London) 363 (1993) 56. [2] M.Cantoni, A.Schilling, H.U.Nissen and H.R.Ott, Physica C 2i5 (!993) ! !. [3] E.VAntipov, S.M.Locreiro, C.Chaillout, J.J.Capponi, J.L.Tholence, S.N.Putilin and M.Marezio, Physica C 215 (1993) 1. [4] R.L.Meng, L.Beauvais, X.N.Zang, Z.J.Huang, Y.Y.Sun, Y.Y.Xue and C.W.Chu, Phvsica C 2t6 (1993) 21.
PHY$1CA
North-Holland
Synthesis and Superconductivity of the HgBa2Ca2Cu30 x Superconductors Sung-lk L¢¢a,b, Sergey Leea,c, Mi-Ock Muna, and Myoung-Kwang Baea aDepartment of Physics, Pohang University of Science and Technology, Pohang, 790-784, Korea bphysics Division, Research Institute of Industrial Science and Technology, Pohang, 790-600, Korea eDepartment of Chemistry, Moscow State University, Moscow 119899,Russia We produced the HgBa2Ca2Cu308+ x (Hg-1223) superconductors by changing the composition, mercury vapor pressure and reaction temperature. We found that the high mercury pressure is essential for the formation cf the Hg-1223 phase by preventing the decomposition of HgO at low temperature. This sample was characterized by the X-ray diffraction, Auger electron microprobe, AC susceptibility and resistivity measurement.
1. INTRODUCTION Recently, superconductivity above 130 K was discovered for the Hg-containing cuprate. [1,2]. However, it was found that this superconductor is a composite multi-phase of HgBa2Can+lCUn" O2n.2+x (n=i to 5). it " known that the phase for n=3 (Hg-1223) is responsible for the 130 K superconductivity, but the single phase of Hg-1223 phase has not yet been produced. lk,-. In this paper, we report a method to prc~.ace ~ sample which contains the Hg-1223 as the main phase. From the x-ray diffraction, we could not find any other phase except for n=3. We found that high mercury pressure inside the quartz tube and heating temperature higher than 850 °C is essential for the formation of Hg-1223. This high mercury pressure inhibits the formation of CaHgO2 by preventing the decomposition of HgO below the reaction temperature.
nominal compositions of Ba2Ca 1Cu2Oy, Ba2Ca 1 5Cu2 5Or and Ba2Ca2Cu30 v. These reagents were" hefited several times between 650°C and 700° C for 20 h with intermediate grindings. Then we made a sample in the form of a pellet and heat treated it at 920°C inside the oxygen atmosphere for ,,~,"" h -~ith two intermediate grindings Then a HgO powder form (yellow) was added in a nitrogen mmos~hcre. We kep~ tbc pclie~ in an ahm~ina tube m prevent direct contact with the quartz. We placed this alumina tube inside a quartz tube. We tried every meth~ to reduce the -,.,,.,pry ~ ' space inside the quartz ampoule. The pressure of Hg vapor once HgO is decomposed in the quartz tube was between 80 and 300 arm. The samples were heated to a temperature between 800 and 950°C, kept at this temperature for 5 h and then slowly cooled (80 K/h) to room temperature. Finally we oxidized the samples in flomng ox3'gen at 300°C for 20 h.
2. E X P E ~ M E N T A L
3. RESULTS AND r~l~tu~S~ON
The s)~athesis of the samples is consisted of two steps. First is the production of a precursor pellet for Ba2Ca2Cu30 7 and second is a formation of the
For the synthesis of the Hg-1223 phase. ~ve used the pellets ~!th varic.us nominal compositions of HgBa2Ca 1Cu2Ov, HgBa2C~2Cu3Ov, and HgBa2Cal 5Cu25Oy • We found thaf if vapor pressure of Hg is low, only Hg-1201 together ,~ith larger amounts of impurity ( CaHgO2, BaCuO2 and Ba2Cu30 5 ) are formed. The reason for the Rack of the Hg-1223 is the decomposition of HgO at about
and HgO inside evacuated quartz tubes. The precursor pellets Ba2Ca2Cu30 7 were prepared by mixing appropriale amounts of nitrate form from Ba, Ca, and Cu. We made three reagents with
0921-4534/94/S07,00 & 1994 - Elsevier Scie~3ce B.V. All rights rcserx'cd. SS!)I {D21-4Sq4(04)0! (11 ] -()
S.-L Lee et al./Physica C 235-240 (1994) 895-896
896
Tablel. Volume fraction of the phase from XRD analysis
Sample Number
Nominal Composition
0.10
Estinated t Volume fraction (°C) by XRD (%) Hg1223 Hg1212
#1
HgBa2CaI Cu2Oy
#2 #3
#4 #5 #6 #7 #8 #9
800
-
100
800 HgBa2Ca].sCu2.50y 800 830
45 40 63
55 60
850
75
900 880 900 930
100 100 75
25 25
HgBa2Ca2Cu30v
--
0.0~
37
500°C which is 300 to 400 degrees below the reaction temperature. In this case, CaHgO 2 forms first and inhibits the formation of Hg-1223 [3,4]. To cure this problem, we increased Hg vapor pressure inside the quartz tube to enhance the decomposition temperature. We tried every method to reduce the empty space inside the tube. We easily obtained the nominal Hg vapor pressure over 200 arm. and confirmed the reduction of the CaHgO2 For the study of temperature effect, we used the pellet of HgBa 2 Ca 1 5 Cu2 5 0 y . Since the sample does not touched the quar~ tubb, we could increase ,h,, temperature hig,~ than 800°C without quartz contamination. Several different temperatures between 800 and 900°C were chosen. From the x-ray diffraction pattern, we d_eterm_ined the content of the Hg-1212 and 1223 phases. We used the ratio from the intensities of the strongest line (103) for Hg-1212 and (103) for Hg-1223. The amount of the Hg-!223 phase was increased at m~;ue~ iemperaiures. We also used the nominal composition of H g.~ . . . . , gBa2,-a2CuaOy as a sto~chmmetnc m~xture of the components. "l~heresult of XRD analysis is shown in table 1. We found that there are no traces of superconducting phases a~ 880°C in this composition. However, a drastic change of superconductivity appears at 900°C. We found that the sample contains Hg-1223 as the main superconducting phase. The amount of BaCuO 2 still remains. With further increase of the tempe1.,." ~ L
rv
0.00 100
150
2oo
2rio
300
T (K) Fig. 1 The resistance curve for the single phase Hg1223 sample (circle) with that for the mixture of Hg- 1223 and Hg- ! 212 phase (triangle)
rature i.e. at 930°C, Hg-1212 forms again. At a temperature of 950°C, quartz ampole breaks down. We found that optimum temperature for Hg-1223 formation is about 900°C for our ease. 4. CONCLUSION We studied the formation of the Hg-!223 phast and found that high mercury vapor pressure above 200 atm and a narrow heating temperature range around 900 ° C were essential. And We observed that the high mercury vapor pressure that is related to the imhibition of HgO decomposition at low temperature is crucial for the formation of the Hg-1223 phase. REFERENCES [I] A.Schilling, M.Cantoni, J.D.Guo and H.R.Ott Nature (London) 363 (1993) 56. [2] M.Cantoni, A.Schilling, H.U.Nissen and H.R.Ott, Physica C 2i5 (!993) ! !. [3] E.VAntipov, S.M.Locreiro, C.Chaillout, J.J.Capponi, J.L.Tholence, S.N.Putilin and M.Marezio, Physica C 215 (1993) 1. [4] R.L.Meng, L.Beauvais, X.N.Zang, Z.J.Huang, Y.Y.Sun, Y.Y.Xue and C.W.Chu, Phvsica C 2t6 (1993) 21.