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

N. K. Man, Huu T. Do+2 more|arXiv (Cornell University)|Mar 3, 2026

Physics of Superconductivity and Magnetism被引用 0

一句话总结

论文报道通过 Pechini 溶胶-凝胶路线以单步烧结合成 Li 掺杂的 Bi-2223 超导体，发现 Li5（5 at.％）使 Tc 达到最高值 111.4 K，并分析了交流磁化率与磁通蠕变行为。

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.

研究动机与目标

• 研究 Li+ 代替对 Bi-2223 相形成与超导特性的影响，所用材料为 Pechini 溶胶-凝胶法制备的 Bi-Pb-2223。
• 理解 Li 掺杂 Bi(Pb)-2223 的合成-结构-性能关系，重点关注相纯度、晶格参数与晶粒连通性。
• 在不同 Li 掺杂水平下，利用直流电阻率和低场交流磁化率表征超导转变与磁通钉扎/蠕变行为。

提出的方法

• 通过 Pechini 聚酯化溶胶-凝胶路线（来自硝酸盐和螯合剂（柠檬酸、乙二醇））合成 Li 掺杂 Bi(Pb)-2223（x = 0.0–0.20，步长为 0.05）。
• 在 650 C 进行热解后，在 850 C 烧结七天以形成 Bi-2223 相；与固相法进行比对。
• 用 XRD 及 Rietveld 精修表征 Bi-2223/2212 相及晶格参数；观察 Li 相关的相行为。
• 用 SEM 观察表面形貌以评估晶粒尺寸与界面。
• 在低磁场下测量直流电阻率 ρ(T) 与交流磁化率 χ′、χ″，以确定 Tc 和晶间/晶内转变。
• 应用 Anderson-Müller 磁通蠕变模型与 Cole-Cole 图分析来自频率依赖的交流磁化率的磁通动力学。

Fig. 1: Illustrating the polyesterization procedure at 85 ∘ C of the citric acid with ethylene glycol to establish chelating agent (including dehydration process) while ethylene glycol enhances the viscosity of the precursor.

实验结果

研究问题

• RQ1 Li+ 掺杂水平对 Li 掺 Bi(Pb)-2223 在 Pechini 溶胶-凝胶法中形成 Bi-2223 相及晶格参数的影响是什么？
• RQ2 哪些 Li 掺杂水平能在该溶胶-凝胶路线中优化转变温度 Tc 和晶粒连通性？
• RQ3 低场交流磁化率测量如何揭示 Li 掺杂 Bi-2223 的晶内与晶间转变及磁通蠕变行为？
• RQ4 与其他溶胶-凝胶法相比，Pechini 溶胶-凝胶法在实现 Bi-2223 的高 Tc 与相纯度方面有何优势？

主要发现

x	a (Å)	c (Å)	Tc (K)	Hac (A/m)	freq (Hz)	Precursors	sintering (C)	Refs
Li0	3.825(6)	37.147(2)	107.4	12	10	nitrates, CA	850	Ours
Li5	3.826(3)	37.048(6)	111.4	12	10	nitrates, CA	850	Ours
Li10	3.831(1)	37.113(2)	107.6	12	10	nitrates, CA	850	Ours
Li15	3.810	37.139(0)	83.5	12	10	nitrates, CA	850	Ours
Li20	3.835(5)	37.099(5)	N/A	–	–	nitrates, CA	850	Ours
Bi-2223	3.835	37.074(4)	110.9	64	333	nitrates, EDTA	air, 850, 100	[8]
Bi-2223+TiO2 (0.2%)	3.833	37.069(1)	106.4	64	333	nitrates, EDTA	air, 850, 100	[8]
Bi-2223+TiO2 (0.4%)	3.832	37.064(2)	103.8	64	333	nitrates, EDTA	air, 850, 100	[8]

• Li 掺杂在 5 at.% 时形成 Tc 峰值 Tc = 111.4 K（±0.2 K），在交流磁化率与直流电阻率中均可观测到。
• Li0 样品显示 Bi-2223 相的贡献为 62.9%，Li5 样品对 Bi-2223 的存在感更强（62.9% 对 58.5% Bi-2212）；较高的 Li 含量降低了 Bi-2223 的可见度。
• Li5 提供最优的电阻转变，在大约 100 K 处实现零阻，通过该掺杂水平观测到晶粒连通性增强。
• 交流磁化率揭示两步式的晶内与晶间转变；频率相关的位移表明晶界处存在磁通蠕变与涡旋动力学。
• Cole-Cole 图显示与晶内/晶间过程对应的两个峰；在 12 A/m 时磁通蠕变的活化能 εa ≈ 0.56 eV（±0.06 eV）。
• XRD 指出 Bi-2223 为主要相，检测到 Bi-2212 不纯物并且未见 Li2O 峰；Li 掺杂略微减小晶格参数（a ≈ 3.825–3.835 Å，c ≈ 37.048–37.147 Å）。

Fig. 2: Entrapping cations within polyesterisation by cross-linking and chelating mechanisms within Pechini solgel route.