Crystal structure and superconductivity in (Cu,Hg)Ba2Ca4Cu5Oy (original) (raw)
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Synthesis, structure and superconductivity of Hg0.75Mo0.25Ba2CuO4+δ
Physica C: Superconductivity, 1999
Synthesis, structure, and superconductivity of a cupric oxychloride Ca2_xNaxCu02Cl 2 have been studied. A series of polycrystalline samples with x up to about 0.20 were prepared at 6 GPa and 1173 K using a high-pressure synthesis technique. The compound contains CuO 2 planes as in La2CuO 4, but all of the oxygen atoms at the apices of the CuO 6 octahedra found in La2CuO 4 are replaced by chlorine. Hole-doped superconductivity is accomplished by partially substituting Na ~ + for Ca 2+. A systematic variation of T c, similar to that of La2_xSrxCuO 4, with a maximum value of 28 K has been found as a function of Na content. The results clearly demonstrate that the apical atoms do not play a significant role in the electron pairing mechanism leading to high-T c superconductivity.
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+ .
Structure and superconductivity ofHgBa2Ca2Cu3O8+δ
Physical Review B
We have investigated the structure, defect concentration, and superconducting properties of HgBa2Ca2Cu308+z by neutron powder diffraction, thermogravimetric analysis, and ac susceptibility. Samples with three oxygen contents and T, 's ranging from 135 to 94 K, obtained through different annealing conditions, were studied. Two defect sites were observed in all samples. The concentration of defect oxygen atoms located at a site in the center of the Hg-Oz plane, is found to vary from 0.18(2) to 0.10(2) oxygen atoms per formula unit as T, decreases from 135 to 94 K. An additional defect, which we interpret as oxygen atoms associated with the substitution of Cu on the Hg site, is found to have a Axed concentration of-0.09(2) oxygen atoms per formula unit.
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.
Structure, doping and superconductivity in HgBa2CaCu2O6+δ (Tc ⩽ 128 K)
Physica C: Superconductivity, 1993
We have studied the defect structure and superconducting properties of HgBa,CaCu 2 0 6+6 by neutron powder diffraction, AC susceptibility and DC resistivity. An as-synthesized sample has an onset T, of 128 K, the highest yet reported for this material. The critical temperature decreases slightly ( 126 K) after oxygenation, and drops to 92 K after reduction in flowing argon. Neutron diffraction data give evidence that the primary doping mechanism in this material is provided by oxygen atoms in an interstitial position, similar to the case of the one-layer compound HgBa2Cu04+d. The occupancy of this site varies from 0.08 ( 1) for the argon-reduced sample to 0.22 ( 1) for the oxygenated sample. Unlike the case of the one-layer compound, no evidence of an additional defect site was found in these samples. HgBa,CaCu 2 0 6+6 has remarkably long copper-apical oxygen distances and almost perfectly flat Cu02 planes.
X-ray single crystal structure analysis of the 1245 type superconductor Hg0.5Pb0.5Ba2Ca4Cu5O12+δ
Physica C: Superconductivity, 1995
Crystals of Hgo.sPbo.sBa2Ca4CusO12+ 8 were measured on an X-ray four-circle single-crystal diffractometer and the crystal structure was refined to R -0.033. The onset of the superconducting transition of the crystals ranges from 101 K-115 K. The space group is P4/mmm and lattice parameters of the five-layer material are a = 3.8529(3) ~,, and c = 22.172(2) ,~. Hg is partially substituted for Pb and heavy atoms are shifted away from the origin by ~ 0.38 A. Stacking faults of 1234 or 1256 material are manifest in the Fourier maps, and the amount was refined to 4.4%. These stacking faults induce an additional electron density at the ideal 0(4) site and mask a possible oxygen occupancy at (½, ½, 0). However, electron density is observed at a distance of 0.6 ,~ from (½, -~, 0), suggesting a shift of the excess oxygen atom from its ideal position. Bondlengths and distances show systematic changes with increasing number n of CuO 2 layers. Changes occur mainly in the rock-salt type layer, whereas the CaCuO 2 units remain stable over the whole Hg-12(n -1)n series.
Structure, doping and superconductivity in HgBa2CaCu2O6+delta (Tc <= 128 K)
Physica C, 1993
We have studied the defect structure and superconducting propertiess of HgBa 2CaCu 2O 6+δ by neutron powder diffraction, AC susceptibility and DC resistivity. An as-synthesized sample has an onset Tc of 128 K, the highest yet reported for this material. The critical temperature decreases slightly (126 K) after oxygenation, and drops to 92 K after reduction in flowing argon. Neutron diffraction data give evidence that the primary doping mechanism in this material is provided by oxygen atoms in an interstitial position, similar to the case of the one-layer compound HgBa 2CuO 4+δ. The occupancy of this site varies from 0.08 (1) for the argon-reduced sample to 0.22 (1) for the oxygenated sample. Unlike the case of the one-layer compound, no evidence of an additional defect site was found in these samples. HgBa 2CaCu 2O 6+δ has remarkably long copper-apical oxygen distances and almost perfectly flat CuO 2 planes.
Structure, doping and superconductivity in HgBa2CaCu2O6+d (Tc ? 128 K)
Physica C, 1993
We have studied the defect structure and superconducting properties of HgBa,CaCu 2 0 6+6 by neutron powder diffraction, AC susceptibility and DC resistivity. An as-synthesized sample has an onset T, of 128 K, the highest yet reported for this material. The critical temperature decreases slightly ( 126 K) after oxygenation, and drops to 92 K after reduction in flowing argon. Neutron diffraction data give evidence that the primary doping mechanism in this material is provided by oxygen atoms in an interstitial position, similar to the case of the one-layer compound HgBa2Cu04+d. The occupancy of this site varies from 0.08 ( 1) for the argon-reduced sample to 0.22 ( 1) for the oxygenated sample. Unlike the case of the one-layer compound, no evidence of an additional defect site was found in these samples. HgBa,CaCu 2 0 6+6 has remarkably long copper-apical oxygen distances and almost perfectly flat Cu02 planes.
Synthesis, Structure and Superconductivity of ( H g 0.65 V 0.35 ) S r 2 ( C a 1- x N d x ) C u 2 O z
Japanese Journal of Applied Physics, 1997
Synthesis, structure, and superconductivity of a cupric oxychloride Ca2_xNaxCu02Cl 2 have been studied. A series of polycrystalline samples with x up to about 0.20 were prepared at 6 GPa and 1173 K using a high-pressure synthesis technique. The compound contains CuO 2 planes as in La2CuO 4, but all of the oxygen atoms at the apices of the CuO 6 octahedra found in La2CuO 4 are replaced by chlorine. Hole-doped superconductivity is accomplished by partially substituting Na ~ + for Ca 2+. A systematic variation of T c, similar to that of La2_xSrxCuO 4, with a maximum value of 28 K has been found as a function of Na content. The results clearly demonstrate that the apical atoms do not play a significant role in the electron pairing mechanism leading to high-T c superconductivity.
Bulletin of Materials Science, 2001
In this paper we have reported investigations on the effect of simultaneous substitution of Bi and Tl at the Hg site in the oxygen deficient HgO δ δ layer of HgBa 2 Ca 2 Cu 3 O 8+δ δ cuprate superconductor. Bulk polycrystalline samples have been prepared by the two-step solid state reaction process (precursor route). It has been observed that the as grown HgBi 0⋅ ⋅2-x Tl x Ba 2 Ca 2 Cu 3 O 8+δ δ (with x = 0⋅ ⋅00, 0⋅ ⋅05, 0⋅ ⋅10, 0⋅ ⋅15, 0⋅ ⋅20) corresponds to the 1223 phase. It has been found that the T c varies with the average cationic size of the dopant cations. The optimum T c of ~ 131 K has been found for the composition HgBi 0⋅ ⋅15 Tl 0⋅ ⋅05 Ba 2 Ca 2 Cu 3 O 8+δ δ . This composition leads to the average dopant cation size of ~ 1⋅ ⋅108 Å which is very close to the size of Hg 2+ (~ 1⋅ ⋅11 Å). The microstructure for HgBi 0⋅ ⋅15 Tl 0⋅ ⋅05 Ba 2 Ca 2 Cu 3 O 8+δ δ has been found to be most dense and this phase exhibits the highest stability. The J c of the optimum material HgBi 0⋅ ⋅15 Tl 0⋅ ⋅05 Ba 2 Ca 2 Cu 3 O 8+δ δ is found to be ~ 1⋅ ⋅29 × × 10 3 A/cm 2 at 77 K.