Fingerprint of $T_c$ advancement in Li-doped Bi-2223 superconductors prepared by cationic molecular mixing within Pechini sol-gel synthesis

Abstract

Trilayered Bi-2223 superconductor features the highest critical temperature $T_c$ among the bismuth-based cuprate collection and symbolizes an ideal prototype for studying intrinsic superconducting properties. The previous solid-state reaction method substantiated the growth of the high-quality Bi-2223 compounds but was accompanied by excessively laborious time and effort in terms of multiple grinding, pressing, as well as calcining stages, %causing risk of constituent loss, so finding a less tedious synthesis path is imperative. Here, we present an advanced sol-gel synthesis for assembling the multicomponent complexity of Bi1.4Pb0.6Sr2Ca2(Cu1-xLix)3O10 superconductors (Li-doped Bi-2223), with $x$ = 0.0--0.20, utilizing metallic cationic molecular mixing within the chemical Pechini polyesterization route followed by single-step pyrolysis and sintering stages. Although monovalent cations such as Li$^+$ pose limitations in establishing a perplex crosslinking network or chelating mechanism in the Pechini method, they represent a unique probe to elucidate the major chemical process during polymerization. We observe that a 5 molar~\% Li-doped sample pronounces the highest $T_c$ = 111.4 K among the series of samples, as confirmed by both ac susceptibility and dc resistivity measurements, and is equivalent to the value obtained by our preceding solid state fabrication. In addition, we showcase a rare observation of layer-by-layer crystalline phase growth under microstructure probe. Through analyzing the reliable ac susceptibility data at low magnetic fields in a wide range of frequency, we provide the quantum flux formation and flux creep mechanism by Anderson-Müller's model and Cole-Cole plot.

Figures (8)

• Figure 1: Illustrating the polyesterization procedure at 85$^\circ$C of the citric acid with ethylene glycol to establish chelating agent (including dehydration process) while ethylene glycol enhances the viscosity of the precursor.
• Figure 2: Entrapping cations within polyesterisation by cross-linking and chelating mechanisms within Pechini solgel route.
• Figure 3: (a) Series of X-ray diffraction patterns of Bi$_{1.4}$Pb$_{0.6}$Sr$_2$Ca$_2$(Cu$_{1-x}$Li$_x$)$_3$O$_{10 + \delta}$ powders at room temperature with respect to Li-doping content up to 20 at. % replacement. Apparently, the samples consist of high-$T_c$ triple-cuprate phase as well as amount lower-$T_c$ double-layered Bi-2212 on surrounding boundary of grains and other impurities TAMPIERI2000119. Rietveld refinement for (b) Li0 and (c) Li5 samples based on MAUD software.
• Figure 4: Surface topography of Bi$_{1.4}$Pb$_{0.6}$Sr$_2$Ca$_2$(Cu$_{1-x}$Li$_x$)$_3$O$_{10 + \delta}$ ceramic superconductors in terms of Li-doping content with (a)--(b) for Li0 sample, (c)--(d) for Li5, (e)--(f) for Li10 and (g)--(h) for Li15 sample.
• Figure 5: Entire resistivity versus temperature $\rho(T)$ of Bi$_{1.4}$Pb$_{0.6}$Sr$_2$Ca$_2$(Cu$_{1-x}$Li$_x$)$_3$O$_{10 + \delta}$ (with $x$ = 0.0--0.20) compounds measuring in the temperature range of 50--300 K.