Study of superconducting HgBa2CuO4+x from a one step low temperature reaction (original) (raw)
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Journal of Advanced Ceramics, 2016
The paper describes the sol-gel process applied to synthesize a mercury-free Ba 2 Ca 2 Cu 3 O x precursor and the physicochemical properties of an Hg 0.8 Pb 0.2 Ba 2 Ca 2 Cu 3 O 8+ high-temperature superconductor (HTS) polycrystalline sample. The Ba 2 Ca 2 Cu 3 O x precursor with desired chemical and phase compositions was obtained using EDTA gel process followed by decomposition and calcination under optimized conditions. An Hg 0.8 Pb 0.2 Ba 2 Ca 2 Cu 3 O 8+ superconductor with a fine-grained microstructure, composed predominantly of the (Hg,Pb)-1223 phase in the form of plate-like crystallites or oval grains and with advantageous magnetic properties (T c(on) = 129.2 K, T c = 6.5 K), was synthesized using the high-pressure crystallization method. At 20 K and 1 T, the critical current density of the studied sample was approximately 26 A/mm 2 , while at 4 K and 1 T it increased to 155 A/mm 2. The high volume fraction of the (Hg,Pb)-1223 phase (89.1%) in the high-T c sample was associated with the low value of the average copper valence (2.11) in the calcinated Ba 2 Ca 2 Cu 3 O x precursor. Small amounts of non-superconducting secondary phases-BaCuO 2 , CaO, CaHgO 2 , CuO, Ca 2 CuO, BaPbO 3-were also identified within the microstructure of Hg 0.8 Pb 0.2 Ba 2 Ca 2 Cu 3 O 8+ .
The synthesis and characterization of HgBa2Ca2Cu3O8+δ superconductors with substitution of Hg by Pb
Physica C: Superconductivity, 1995
The third (Hg-1223) and the fourth (Hg-1234) members of the recently-discovered homologous series Hg-Ba2Ca,_ t Cu,O2,+2+n have been synthesized by solid state reaction, carried out at 950°C under 50 kbar at different annealing times. These phases have a tetragonal cell with lattice parameters: a=3.8532(6) A, c= 15.818(2) A and a=3.8540(3) A, c = 19.006 (3) A, respectively. The c parameters are in agreement with the formula c-9.5 + 3.2 (n-l). Electron microscopy study showed similar lattice parameters as well as the occurrence of different intergrowths and stacking faults. A periodicity of 22 A has also been detected, which may be attributed to the existence of the Hg-1245 phase. EDS analysis data of several grains of Hg-1223 and Hg-1234 are in agreement with the proposed chemical formulae. AC susceptibility measurements show that an increase of the superconducting transition temperature with n in the HgBa2Ca,_ ~CunO2n+2+6 series occurs till the third member, after which a saturation seems to be achieved.
The synthesis and characterization of the HgBa2Ca2Cu3O8+δ and HgBa2Ca3Cu4O10+δ phases
Physica C: Superconductivity, 1993
The third (Hg-1223) and the fourth (Hg-1234) members of the recently-discovered homologous series Hg-Ba2Ca,_ t Cu,O2,+2+n have been synthesized by solid state reaction, carried out at 950°C under 50 kbar at different annealing times. These phases have a tetragonal cell with lattice parameters: a=3.8532(6) A, c= 15.818(2) A and a=3.8540(3) A, c = 19.006 ( 3 ) A, respectively. The c parameters are in agreement with the formula c -9.5 + 3.2 ( n -l ). Electron microscopy study showed similar lattice parameters as well as the occurrence of different intergrowths and stacking faults. A periodicity of 22 A has also been detected, which may be attributed to the existence of the Hg-1245 phase. EDS analysis data of several grains of Hg-1223 and Hg-1234 are in agreement with the proposed chemical formulae. AC susceptibility measurements show that an increase of the superconducting transition temperature with n in the HgBa2Ca,_ ~CunO2n+2+6 series occurs till the third member, after which a saturation seems to be achieved.
Synthesis and magnetic characterization of the high-Tc superconducting compound HgBa2CuO4+δ
Physica C: Superconductivity, 1993
Bulk superconducting samples of HgBa2CuO4+ 6 (hereafter denoted as Hg-1201) were prepared by solid state reaction of stoichiometric quantities of HgO and Ba2CuO3 precursors. The "as-synthesized" Hg-1201 samples had a Tc of 95 K, as defined by the onset of diamagnetism. The crystal symmetry was found to be tetragonal with lattice parameters, a=3.876(2) A, and c= 9.515 (3) A, similar to the literature values. Finely ground X-ray specimens were stable upon exposure to ambient air for a period of ~ 24 h. Magnetic characterizations were conducted using a SQUID based DC magnetometer. Studies of the transition region in low applied fields showed complete screening and evidence for weak intergrain coupling of the randomly oriented crystallites. High field magnetic hysteresis studies showed rapid decay of hysteresis of the magnetization (proportional to the current density), both with applied field and temperature. These findings are attributed to the presence of substantial thermally activated flux motion.
Physica C: Superconductivity, 1998
Ž . Thanks to a novel technique thermobaric analyser or TBA for measuring the in-situ pressure in quartz tubes, we have investigated the formation and stability of HgCaO and its competition with the Hg,Re-1223 in the superconductor 2 synthesis. The pressure determination has enabled us to obtain thermodynamic values such as D H , D S , from which f f formation temperatures and stability of the binary oxide were determined. This fact has made possible to minimise the presence of this impurity applying suitable heating and cooling ramps in the thermal treatment leading to the formation of Hg,Re-1223. It has been observed that the faster the heating ramp, the less HgCaO phase was formed. However, the 2 cooling ramp only influenced the Hg,Re-1223 stability, being more advantageous to perform slow cooling rates. In summary, the in-situ pressure measurement has permitted to ascertain the way to minimise the HgCaO impurity content and 2 hence to improve the quality of the ceramic Hg,Re-1223 superconductor. q
Single crystal study of the “1201” superconductor Hg0.8Bi0.2Ba2CuO4+δ
Physica C: Superconductivity, 1996
Single crystals of the "1201" mercury based cuprate have been grown for the first time. Their structure determination allows the classical Jahn-Teller distortion of the octahedral copper layer to be confirmed and gives evidence for the presence of oxygen at the level of the Hg/Bi layer leading to the formula Hgo.sBio.2Ba2CuO4. 3. The [Hgo.sBio.20~L layers can then be described as built up from HgO 2 sticks that coexist with BiO 6 octahedra, bismuth being nearly pentavalent. The magnetic study of these crystals shows that they exhibit superconductivity up to 75 K (Te(midpoint -62 K)), with 100% superconducting volume fraction at low temperature. Moreover the M(B) loops exhibit fishtail shapes which were not present for measurements on ceramics. The fishtail and irreversibility lines of (Hg, Bi)-1201 are studied for the HIIc geometry. These data are compared with those of Tl-single crystals; it appears that (Hg, Bi)-1201 is quite similar to T1 monolayers and differs greatly from TI bilayers. This underlines the influence of structural anisotropy in both Hg-and Tl-cuprates on their superconducting properties.
Synthesis of Superconducting Ceramics Hg 0.82 Re 0.18 Ba 2 Ca 2 Cu 3 O 8+δ with Different Values of
Materials Science Forum, 2008
Samples of the superconducting ceramics Hg 0.82 Re 0.18 Ba 2 Ca 2 Cu 3 O 8+ were prepared by solid-vapor reaction technique. The preparation of the ceramic precursor started with a mixture of Ba 2 Ca 2 Cu 3 O x and ReO 2 powders with molar ratio 1:0.18. The precursor material was submitted to annealing under three different partial pressures of oxygen using a mixture of oxygen/argon at ratios: 5/95 (sample A), 10/90 (sample B) and 15/85 (sample C). X-ray powder diffraction analysis of the precursors identified the phases BaCuO 2+x , Ba 2 Cu 3 O 5+x , Ba 4 CaCu 3 O 8+x , Ca 2 CuO 3 and Ca 5 Re 2 O 12 at different ratios in the samples, indicating an increment in the oxygen content from sample A to sample C. Finally, the precursors with different oxygen contents were blended with HgO at molar ratio 1:0.82 and treated in a sealed high pressure furnace to produce the high Tc superconducting ceramics. Rietveld refinement of XRD data showed differences in the crystal structures of the samples. The measurement of thermopower at room temperature resulted in distinct values, confirming the different oxygen sample doping.