High Temperature Superconductors in the La1+xBa2-xCu3Oy System (original) (raw)
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A comparative study of superconducting LaBa2Cu3O7−δ and La3−xBa3+xCu6O14+δ
Journal of Solid State Chemistry, 1988
Based on X-ray diffraction and electron microscopy it is shown that oxides of the general formula La Ba2Cus0,-~ become tetragonal when 6 deviates slightly from 0. This tetragonal structure is similar to that of La3-xBa3+xCt+,014+8, with a cubic perovskite subcell and triple periodicity. Electron micrographs of these tetragonal oxides show 90" microdomains. Orthorhombic LaBa2Cu,0,-8 with high T, (-77 K) is found only when 6 = 0; this sample is subject to formation of twins. Fluorine substitution seems to favor superconductivity. 0 19% Academic Press. Inc.
On the evolution of superconductivity in La1.5−xBa1.5−xCa2xCu3O7−δ(0.0⩽x⩽1.0)
Physica C: Superconductivity, 1993
Simultaneous replacement of La and Eta by Ca in Lat.~Bal.sCu3OT+~ (336 phase) was attempted to explore the possible transformation of non-superconducting 336-phase into the superconducting 1113-phase (CaBaLaCu3OT_s) and thereby investigating the evolution of superconductivity as a function of"x" in LaLs_~Bat.s_xCaz~Cu307_a (0.0 ~<x~< 1,0). In this system, single phase compounds result only for x ~< 0.3 and nearly phase pure compounds result for x values in the range 0.3 ~< x ~< 0.6, whereas samples with x>0.6 contain a substantial amount of impurity phases. All samples with 0.2~<x~< 1.0 were found to be superconducting with Tc values in the range 57-72 IC On the other hand, partial replacement of either La or Ba by an equivalent amount of Ca in La~.sBal.sCu307 +6 resulted in a different T©-behaviour, viz. the sample with nominal composition LaLs (Bat.oCao.s)Cu3OT+j exhibiting a T¢(R=0) value of 45 K, whereas the one with composition (Lat.oCae.s)Bat.sCu3OT_a exhibiting a higher Tc value of 72 IC The present studies sulgest that the actual cationic composition for the high-To superconducting phase in the Ca-Ba-La-Cu--O system need not be in the 1 : 1 : 1 : 3 ratio.
ON THE MECHANISM OF HIGH-TEMPERATURE SUPERCONDUCTIVITY IN Ba–La(Y)—Cu–O TYPE SYSTEMS
International Journal of Modern Physics B, 1987
An extended molecular crystal model is put forward for the mechanism of high-temperature superconductivity in the typical perovskite-like structures Ba~La 2 rfuO 4 and Ba2YCu306~+ts~, 0 < x ~< 0.4. It is shown that the Jalan-Teller effect of the Cu :÷ cation brings about an attractive pairing interaction between the hybridized 3d 9 electron states. The critical temperature is estimated and compared with the available experimental data.
Journal of Superconductivity, 2000
It has been reported that, by adding equal amounts of CaO and CuO to non superconducting La3Ba3Cu6Oz (La-336), a series of superconductors with nominal compositions La3Cay Ba3Cu6+y Oz were prepared with maximum Tonc ∼ 80K. Similar studies on addition of CaO and CuO in nonsuperconducting LaBaCu2Oz (La-112) resulted into superconducting LaCaBaCu3Oz (La-1113). To date no attempt has been made to synthesize La2CaBa2Cu5Oz (La-2125) superconducting phase by addition of CaO and CuO to non superconducting La2Ba2Cu4Oz (La-224) system. Also no reports are published to study the effect of replacing larger La3+-ions (1.01Å) by smaller rare earth ions viz Y3+(0.89Å), Er3+(0.91Å), Gd3+(0.91Å) on the structural and superconducting properties of (La2−x Rx )Ba2(Cay Cu4+y )Oz (LRBCaC); 0.0 ≤ x ≤ 0.5; y=2x system. In this paper, we report the method of synthesis, structural and superconducting property characterization using X-ray diffraction, oxygen content measurements using iodometry, resistivity measurements using d.c. four probe technique and a.c. susceptibility measurements in the temperature range RT to 15K. Also a comparative study, on the evolution of superconducting phase with Ca-concentration for different rare earth substitutions for LRBCaC system in the context of hole doping mechanism, is carried out.
Studies on La2−xPrxCayBa2Cu4+yOz (x=0.1–0.5, y=2x) type mixed oxide superconductors
Solid State Communications, 2003
The La 2-x Pr x Ca y Ba 2 Cu 4+y O z (LaPrCaBCO) mixed oxides have been studied for their structural and superconducting properties using X-ray diffraction (XRD), d. c. resistivity, d. c. susceptibility and iodometric double titration. All the LaPrCaBCO samples for x = 0.1 -0.5, exhibit tetragonal crystalline structure with P 4/mmm space group as determined by Rietveld analysis of the X-ray diffraction data.
Effect of Ca Substitution on the Superconductivity of La 2.5 Y 0.5 CaBa 3 (Cu 0.88 Fe 0.12 ) 7 O z
Journal of Superconductivity, 1998
The structural and superconducting properties of single-phase La2.5−y Y0.5Ca1+y Ba3 (Cu0.88Fe0.12)7Oz (LYCaBCuFe) (y= 0.0−1.0) compounds with triple perovskite structure are investigated using X-ray diffraction, resistivity, a.c. susceptibility, and oxygen content measurements. Increasing Ca substitution for La resulted in a decrease in unit cell axes and volume. T cR=0 shows a marginal increase from 31 K to 37 K for y = 0.0−0.21 and thereafter it decreases with increasing y leading to zero T cR=0 at y ≥ 0.84. This shows that the suppression of T c from 80 K to 31 K by Fe doping at x = 0.12 La2.5Y0.5CaBa3(Cu1−x Fex )7Oz cannot be compensated by appropriate hole doping with Ca in LaYCaBCuFe.
Electronic structure of high-temperature superconductors II. La-Ba-Cu-O systems
Czechoslovak Journal of Physics, 1996
Electronic structure of La2_xBa~CuO4 superconductors has been studied. Model systems Lal0CuO~-~ ~, Laa0cuO+~ and LagBaCuOl+43 with various Ba positions have been investigated using the quasirelativistic INDO molecular orbital method. The oxidation state of copper atoms corresponds to Cu(II). The influence of Ba/La substitution on copper atoms is much lower than on their oxygen ligands sphere.
Effect of calcium substitution on superconductivity and hole concentration in La1·5Ba1·5Cu3O z
Bulletin of Materials Science, 1998
The superconducting properties of single phase La1·5−x Cax+y Ba1·5−y Cu3Oz , 0·0≤x≤0·60 (LC) and 0·0≤y≤0·70 (CB), compounds with tetragonal triple-perovskite structure are studied, using X-ray diffraction for their resistivity, a.c. susceptibility, and oxygen-content. La1·5−x Cax Ba1·5Cu3Oz (LC) samples, 0·15≤x≤0·60, are superconducting withT cR=0 between 40 and 74 K. With the increase inx, the oxygen content, hole concentration in the CuO2 layers as well as theT c increase. It is interesting to find that although the hole concentration and oxygen stoichiometry of the LaCa0·5+y Ba1·5−y Cu3Oz (CB) compounds increase with the increase iny, theT cR=0 remains nearly constant around 74 K fory=0·0−0·70. A correlation exists between theT c and the hole concentration for LC and CB compounds.