Surface Morphology of Tl2Ba2Ca2Cu3Oy Thin Films Prepared by Thallium Diffusion Process

Adachi, Seiji; Adachi, Hideaki; Ichikawa, Yo; Setsune, Kentarou; Wasa, Kiyotaka

doi:10.1143/jjap.30.l1110

Cited by 5 publications

(4 citation statements)

References 46 publications

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“…These films have been prepared exclusively using ex situ postdeposition thallination processes, during which a precursor film is converted to the crystalline Tl 2 Ba 2 Ca 2 Cu 3 O 10 phase in the presence of a thallous oxide overpressure. 19,20,29,31,[33][34][35] A few studies have used a thallium oxide source held at a lower temperature than that of the film to maintain a thallous oxide overpressure. [34][35][36] The thallination step is most often carried out in the presence of a TlBaCaCuO powder, within a sealed gold pouch or ceramic ampoule, 21,[24][25][26][27][28] or within a closed, but unsealed, platinum or ceramic container.…”

Section: Introductionmentioning

confidence: 99%

Process optimization for the fabrication of Tl₂Ba₂Ca₂Cu₃O₁₀ thin films

Holstein

Parisi

1996

J. Mater. Res.

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A process has been developed for the fabrication of nearly single phase superconducting Tl2Ba2Ca2Cu3O10 thin films on (100) LaAlO3 substrates with a superconducting transition temperature Tc of 120 K and low microwave surface resistance at temperatures up to 110 K. Amorphous BaCaCuO precursor films were first deposited by rf magnetron sputtering and then thallinated at elevated temperatures. The double TlO layer phases (Tl2Ba2Ca2Cu3O10 + Tl2Ba2CaCu2O8) formed preferentially over the single TlO layer phases (TlBa2Ca2Cu3O9 + TlBa2CaCu2O7) at high Tl2O partial pressures. Thin films containing Tl2Ba2Ca2Cu3O10 and a small amount of CuO were prepared from Cu-rich precursor films (Cu/Ba > 1.7), while lower Cu content led to the formation of Tl2Ba2CaCu2O8 as a secondary phase. Tl2Ba2Ca2Cu3O10 film epitaxy was enhanced by carrying out the thallination in reduced oxygen partial pressures of 0.01–0.05 atm. Following the thallination step, the Tl2Ba2Ca2Cu3O10 thin films had a superconducting transition temperature Tc of only 106 ± 4 K. An additional 62 h anneal at 800 °C or an 8 h anneal at 850 °C in a Tl2O/O2 atmosphere increased the Tc to 120 K. The increase in Tc was accompanied by a decrease in the c-axis lattice constant, an enhancement in the long-range order in the c-direction, and the formation of a small amount of Tl2Ba2CaCu2O8 as a secondary phase. Minimization of surface resistance at high temperature (95–110 K) requires that the fraction of Tl2Ba2CaCu2O8 secondary phase in the films be kept low. Process routes are also described for the formation of nearly single phase TlBa2Ca2Cu3O9 and TlBa2CaCu2O7 thin films and the formation of a new ordered intergrowth phase, Tl4Ba4Ca3Cu5O18, which consists of alternating Tl2Ba2CaCu2O8 and Tl2Ba2Ca2Cu3O10 layers.

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Section: Introductionmentioning

confidence: 99%

Process optimization for the fabrication of Tl₂Ba₂Ca₂Cu₃O₁₀ thin films

Holstein

Parisi

1996

J. Mater. Res.

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“…Thallium-based thin superconducting films are considered to be very promising materials for the fabrication of various passive microelectronic devices (bandfilters, resonators, etc) due to their high critical temperature, T c , high critical current density, j c , and particularly low surface impedance at 77 K [1]. These features have been the motivation for the exploration of various methods of film fabrication such as RF sputtering [2,3], e-beam evaporation [4], thermal evaporation [5] and laser ablation [6,7]. The last method seems to be the most attractive, in that it enables one to deposit a ∼ 0.3-0.5 µm thick film in a short time (∼ 10-15 min) which is at least a factor of 10 shorter than the time needed for other methods (for example RF sputtering).…”

Section: Introductionmentioning

confidence: 99%

“…The ex situ thalliation process is thus necessary. In this process a precursor Ba 2 Ca 2 Cu 2 O x films is placed together with a Tl-rich source in an enclosure and Tl annealed at elevated temperature (700-900 • C) for a specific time, in order to increase the content of Tl in the film and to stabilize the film's properties [2,8].…”

Section: Introductionmentioning

confidence: 99%

Characterization of films prepared by laser ablation of precursor targets andex situthalliation

Chrzanowski

Meng-Burany

Xing

et al. 1996

Supercond. Sci. Technol.

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Thin films of Tl 2 Ba 2 CaCu 2 O 8 (Tl-2212) were grown on LaAlO 3 (001) single crystals by excimer laser ablation using Tl-free Ba 2 CaCu 2 O x targets and subsequent ex situ thalliation. The thalliation process of the film precursor (Ba 2 CaCu 2 O x ) took place in an Al 2 O 3 crucible containing the precursor and Tl-2212 powder. The procedure was carried out at a temperature T a = 820-870 • C and under a reduced oxygen pressure p(O 2 ) = 20-400 Torr. The resulting Tl-2212 films were characterized by XRD, AES, EDAX, ECP, Raman spectroscopy and a.c. susceptibility measurements. The films exhibited epitaxial, c-axis-oriented growth with critical temperatures T c = 98-106.5 K, transition widths T c = 0.5-1 K, and critical current densities at 77 K of j c = (1.2-3.5) × 10 6 A cm −2 . EDAX measurements showed that the films were as a rule somewhat Tl and Ba deficient but Ca rich (Tl 1.7 Ba 1.9 Ca 1.1 Cu 2 O 8 ). AES depth profiling revealed a noticeable depth dependence of the Ca and Ba distribution, though the combined concentration of these elements (Ba + Ca) was fairly constant throughout the whole film thickness. It is postulated that cation disorder (Ba Ca substitution) is responsible, at least in part, for the high critical current density observed in the Tl films. These point defects would contribute to the strong pinning of the flux lines in the films by creating a dense network of pinning centres.

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“…Consequently, it has been suggested [20] that high-quality Tl-2223 films could be formed through an entirely solid-state route. Although most investigators empirically found that the processing of Tl-2212-free ceramics [10,12,[21][22][23][24][25][26][27] and films [28][29][30][31][32][33][34][35][36][37] required sintering or annealing temperatures above 850 • C, it has been shown by Lee and coworkers [38,39] that these temperatures could be lowered below 830 • C by operating in reduced oxygen partial pressures (0.03-0.15 atm). This result suggests that the amount of intermediate liquid phase might be considerably reduced by optimizing the processing parameters.…”

Section: Introductionmentioning

confidence: 99%

Pathway for the formation of the Tl-2223 phase: anin situneutron powder diffraction study

Galez

Soubeyroux

Hopfinger

et al. 2001

Supercond. Sci. Technol.

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The reaction pathway for the formation of Tl 2 Ba 2 Ca 2 Cu 3 O z (Tl-2223) has been investigated by in situ neutron powder diffraction. The experiments were carried out in an initially evacuated closed system on two samples with nominal compositions Tl 1.7 Ba 2 Ca 2 Cu 3 O z and Tl 2.3 Ba 2 Ca 2 Cu 3 O z . We find that, under these conditions, the formation path implies Tl 2 BaO 4 , Tl 6 Ba 4 O 13 and Tl 2 Ba 2 CaCu 2 O 8 (Tl-2212) according to the sequence: precursors/oxides → Tl 2 BaO 4 → Tl 6 Ba 4 O 13 → Tl-2212 → Tl-2223.The difference with respect to the sequence observed in an open system (precursors/oxides→Tl-2201→Tl-2212→Tl-2223) is explained by the low temperature reaction (780 K) between the TlO x vapour and the free BaO resulting from the decomposition of BaCuO 2 used as a precursor. The conversion from Tl-2212 to Tl-2223 occurs at 1075 K and does not involve the formation of a liquid phase but the solid-state diffusion of the Ca and Cu species and the restructuring of the Tl-2212 lattice. However, this conversion does not occur when the Tl content is 2.3, in agreement with previous works on phase equilibria. The reacted samples were characterized by high-resolution neutron powder diffraction, ac susceptibility measurements and SEM/EDX. Some original results on crystal structures and, to a lesser extent, on phase equilibria are also given.

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Surface Morphology of Tl₂Ba₂Ca₂Cu₃O_y Thin Films Prepared by Thallium Diffusion Process

Cited by 5 publications

References 46 publications

Process optimization for the fabrication of Tl₂Ba₂Ca₂Cu₃O₁₀ thin films

Process optimization for the fabrication of Tl₂Ba₂Ca₂Cu₃O₁₀ thin films

Characterization of films prepared by laser ablation of precursor targets andex situthalliation

Pathway for the formation of the Tl-2223 phase: anin situneutron powder diffraction study

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Surface Morphology of Tl2Ba2Ca2Cu3Oy Thin Films Prepared by Thallium Diffusion Process

Cited by 5 publications

References 46 publications

Process optimization for the fabrication of Tl2Ba2Ca2Cu3O10 thin films

Process optimization for the fabrication of Tl2Ba2Ca2Cu3O10 thin films

Characterization of films prepared by laser ablation of precursor targets andex situthalliation

Pathway for the formation of the Tl-2223 phase: anin situneutron powder diffraction study

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Product

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Surface Morphology of Tl₂Ba₂Ca₂Cu₃O_y Thin Films Prepared by Thallium Diffusion Process

Process optimization for the fabrication of Tl₂Ba₂Ca₂Cu₃O₁₀ thin films

Process optimization for the fabrication of Tl₂Ba₂Ca₂Cu₃O₁₀ thin films