V. A. Stepanov

Vapor-phase growth of Bi2Sr2Can−1CunOx (n= 1–3) single crystals

High-quality platelike Bi2Sr2Can−1CunOx (n= 1–3) single crystals with superconducting transition temperatures Tc=10, 85, and 110 K, respectively, are prepared by vapor-phase growth in closed cavities produced in a melt fluxed with KCl. The effect of synthesis and growth conditions on the Tc of the crystals is analyzed. The morphology of the crystals suggests that the most perfect, well-faceted crystals grow via vapor transport with constant feeding from the charge.

Structure and superconductivity of layered oxycarbonate Bi2Sr4Cu2CO3O8 crystals

A complex study of the elemental composition, structure, and superconducting properties of single crystals of layered oxycarbonate Bi2Sr4Cu2CO3O8 has been performed taking into consideration the growth and postgrowth annealing conditions.

Growth and properties of layered oxycarbonate Bi2Sr4Cu2CO3O8 single crystals

Layered oxycarbonate Bi2Sr4Cu2CO3O8 single crystals have been obtained for the first time by free growth in closed vapor-phase cavities. The morphology, structure, composition, and superconducting properties of these crystals have been investigated.

Dependence of superconducting properties of underdoped Bi-2201 single crystals on the charge composition and growth conditions in gas-filled cavities

High-quality Bi2 + xSr2 − yCuO6 + δ (Bi-2201) single crystals with the ratio Bi/Sr = 1.4–2.0 were grown by the free growth method in gas-filled cavities in KCl solution-melt in a range of doping levels, which provides variation in superconducting properties from insulators to optimally doped crystals. The charge composition Bi : Sr : Cu = 1.7 : 2.3 : 2.5 with excess Sr and Cu and synthesis conditions provided growth cavity formation in the KCl solution at the crystal growth stage. Lamellar single crystals and whiskers were grown under quasi-equilibrium conditions of lowered growth temperatures and partial oxygen pressure, achieved in closed gas-filled cavities.

Growth from gas cavities in a molten salt and properties of superconducting Bi2Sr2CaCu2O8+δ single crystals

Perfect single crystals of the high-temperature superconductor Bi2Sr2CaCu2O8+δ with the superconducting transition temperature TC = 72–85 K (depending on the crystallization conditions) are obtained by the method of free growth in gas cavities formed in a KCl solution-melt. The specific features of the growth process are in the formation of an enclosed growth gas cavity in a (previously synthesized) blend of a specified phase composition dissolved in KCl and the free crystal growth in this cavity. The combination of growth and high-temperature annealing in the same process made it possible to obtain uniform (ΔTC = 1.5 K) single crystals with stable superconducting properties. Annealing of the grown single crystals in oxygen or in air in the temperature range 400–850°C confirmed that the crystals with maximum values of TC are optimally doped.

Evolution of the structural and superconducting properties of Bi-HTSC monocrystals when stored in air

Complex studies of the evolution of the structural and superconducting characteristics of Bi2212 and Bi2201 monocrystals depending on their storage in air for several years have been performed. It has been found that the sample structures remain perfect, whereas the superconducting parameters change due to oxygen mobility in the crystals. The character of the changes depends on the doping degree and the composition balance with respect to cations and oxygen in the grown monocrystals.

Growth and properties of layered oxycarbonate Bi 2 Sr 4 Cu 2 CO 3 O 8 single crystals

Layered oxycarbonate Bi2Sr4Cu2CO3O8 single crystals have been obtained for the first time by free growth in closed vapor-phase cavities. The morphology, structure, composition, and superconducting properties of these crystals have been investigated.

Growth and properties of layered oxycarbonate Bi2

Layered oxycarbonate Bi2Sr4Cu2CO3O8 single crystals have been obtained for the first time by free growth in closed vapor-phase cavities. The morphology, structure, composition, and superconducting properties of these crystals have been investigated.

Structural and superconducting properties of single-crystal Bi2Sr2Can − 1CunO2n + 4 + δ (n = 1–3) whiskers grown in gas-filled cavities

Using growth inside gas-filled cavities in KCl-fluxed melts, we have obtained free-standing phasepure Bi2Sr2Can − 1CunO2n + 4 + δ (n = 1–3) whiskers possessing superconducting properties in the as-grown state. Bi-2212 whiskers have been prepared in a wide range of doping levels, from underdoped (Tc = 76.5 K) to optimally doped (Tc = 84 K). The whiskers possess high structural perfection, as shown by X-ray diffraction. Annealing under optimal conditions raises the superconducting transition temperature of the underdoped Bi-2212 whiskers to Tc max = 85.5 K (ΔTc = 1.8 K), without impairing their structural perfection.

The influence of low-temperature annealings on the structural and superconducting properties of Bi 2212 and Bi 2201 whiskers

The influence of post-growth short-term low-temperature annealings (O2, 400°C, 5–15 min) on the composition, crystal structure, and superconductivity of Bi2Sr2CaCu2O8 + δ and Bi2Sr2CuO6 + δ oxycuprate whiskers freely grown in gas cavities has been investigated. The optimal conditions for growth in closed gas cavities in a flux and post-growth annealing in oxygen were found, making it possible to obtain high-quality superconducting Bi 2212 and Bi 2201 whiskers in a wide doping range (from heavily underdoped to optimally doped) with a small rocking curve half-width (∼0.1°–0.2°) and narrow superconducting transition (ΔT = 1.5–2 K).