ANISOTROPY AND CRYSTALLITE MISALIGN MENT IN TEXTURED SUPERCONDUCTOR S D. M. Gokhfeld12 S. V. Semenov12 M. I. Petrov1 I. V. Nemtsev123 and D. A. Balaev12

2025-04-30 0 0 877.5KB 11 页 10玖币

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ANISOTROPY AND CRYSTALLITE MISALIGNMENT IN TEXTURED

SUPERCONDUCTORS

D. M. Gokhfeld1,2, S. V. Semenov1,2, M. I. Petrov1, I. V. Nemtsev1,2,3, and D. A. Balaev1,2

1 Kirensky Institute of Physics, Federal Research Center KSC SB RAS, Krasnoyarsk, 660036 Russia

2 Siberian Federal University, Krasnoyarsk, 660041 Russia

3 Federal Research Center ―Krasnoyarsk Science Center of the Siberian Branch of the Russian Academy of

Sciences‖, Krasnoyarsk, 660036, Russia

A misalignment of anisotropic crystallites causes small values of anisotropy and decreases

the critical current density of textured polycrystalline superconductors. To relate the crystallite

misalignment and out-plane anisotropy, the magnetic properties of the textured Bi2223

polycrystalline superconductor were investigated. A distribution of orientation angles of

crystallites was determined using different data: scanning electron microscopy images and

hysteresis magnetization loops when an external magnetic field was applied at different angles

with respect to the texturing plane of the sample. It was demonstrated that the standard deviation

of the distribution and the magnetic disorder angle of crystallites in textured samples can be

determined from the magnetization data in perpendicular directions. These data may be either the

irreversible magnetization measured for two different orientations of the sample or the

simultaneously measured magnetization projections parallel and perpendicular to the magnetic

field.

1. Introduction

The outstanding values of the critical current density in the ab plane jc,ab and the high

critical temperatures could bring Bi2Sr2CaCu2O8+x (Bi2212) and Bi2Sr2Ca2Cu3O10+x (Bi2223) at

the top of superconductor applications. However, the strong anisotropy coefficient γ ⪞ 100 of

these materials [1] hinders their rise. The overall critical current density jc of polycrystalline

superconductors is very sensitive to arrangement of crystallites [2]. An alignment is crucially

important for textured superconductors and tapes [3–8]. The crystallite misalignment strongly

decreases jc as well as γ. Bi2212 and Bi2223 textured ceramics usually have low γ and low jc

values (e.g., γ ≈ 1.7-2.5 and jc ≈ 0.1~1 kA/cm2 at T = 77.4 K [9–13]) as compared with single

crystals and wires. Optimization of the current carrying capacity in textured superconductors

requires information about a distribution of crystallite orientation angles and reasons of the

misalignment.

In anisotropic type-II superconductors, the vortex lattice and magnetization depend on an

angle between the external magnetic field and the crystal principal axes [14–17]. The

magnetization of textured polycrystalline sample is resulted from collective response of the

crowd of crystallites. So the degree of texture in these samples is essential. The degree of texture

is estimated from X-ray diffraction data (θ-2θ and ω-scans) [7, 18, 19]. In recent work [13], the

integral magnetic method was suggested. The magnetic misalignment angle θ* was introduced to

characterize texture in the Bi2223 superconductor. This angle θ* equals an averaged value of the

modulus of crystallite deviation from the texturing plane. In presented work, new ways are paved

to determine the distribution of the crystallite orientation angles and the corresponding magnetic

misalignment angle θ* in the textured superconductors.

2. Experimental methods

The textured Bi2223+Ag ceramics was produced by two step route [9]. At the first stage

the polycrystalline ceramics were synthesized from Bi2O3, SrCO3, PbO, CuO, CaCO, and Ag

powder by the solid-state synthesis. Porosity of the synthesized material is about 60% [20]. At

the second stage the texture was created: the porous material was impregnated by ethanol,

pressed up to 500 MPa, and annealed at 830 °C for 50 hours.

Scanning electron microscopy (SEM) was carried out using a Hitachi TM4000Plus

microscope. Magnetization was measured using a Lakeshore VSM 8604 vibrating sample

magnetometer. Measurements were carried out at 77.4 K for different orientations of the rotated

sample relative to the external magnetic field H. The sample had a parallelepiped form and sizes

of 10×1×1 mm3. The wider sides of the sample corresponded to the texturing plane. A schematic

for magnetization measurements is shown on figure 1. Two magnetization projections were

measured: Mx along the H direction (it is a general magnetization) and My perpendicular to H.

Fig. 1. Schematic for magnetization measurements. The numbers mark the magnet coils (1),

the measuring coils (2), and the sample (3).

3. Experimental results

SEM images of the sample side, which is perpendicular to the texturing plane, are shown

on figures 2a,b. As seen, light particles of Ag are surrounded by darker crystallites of Bi2223.

The diameter of the silver particles is about 20 μm. The Bi2223 crystallites have a flake-like

form with the sizes about 10 μm × 10 μm × 1 μm. The most of crystallites are oriented along the

texturing plane. However some of the crystallites are tilted because they go around the silver

particles. We measured the values of the tilt θ of each crystallites on four different SEM images.

The obtained distribution of crystallite orientation angles is presented on figure 2c. The

distribution has a characteristic bell-like form.

The angle dependencies of the magnetization projections at H = 5 kOe, which is much

higher than the irreversibility field, are shown on figure 3a (α changes from –180° to +180° at

this figure). The period of these dependencies is equal to 180°. It can be seen, the positions of Mx

= 0 do not correspond to the extremum positions of My.

Fig. 2. Crystallites in the textured sample. a), b) SEM images of the sample side perpendicular

to the texturing plane. c) Distribution of crystallite orientation angles. The bar chart is data

obtained from SEM images. The normal distribution curve is computed (3) for σ = 28°.

Vertical dash lines separate the quartiles.

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摘要：

ANISOTROPYANDCRYSTALLITEMISALIGNMENTINTEXTUREDSUPERCONDUCTORSD.M.Gokhfeld1,2,S.V.Semenov1,2,M.I.Petrov1,I.V.Nemtsev1,2,3,andD.A.Balaev1,21KirenskyInstituteofPhysics,FederalResearchCenterKSCSBRAS,Krasnoyarsk,660036Russia2SiberianFederalUniversity,Krasnoyarsk,660041Russia3FederalResearchCenter―Krasnoy...

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ANISOTROPY AND CRYSTALLITE MISALIGN MENT IN TEXTURED SUPERCONDUCTOR S D. M. Gokhfeld12 S. V. Semenov12 M. I. Petrov1 I. V. Nemtsev123 and D. A. Balaev12

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