RU2241676C1 - Perovskite-like terbium-based ruteno-cuprate as magneto-ordered superconducting material - Google Patents

Abstract

FIELD: superconductors.

SUBSTANCE: invention relates to preparation of novel complex perovskite-like terbium-based ruteno-cuprate, consisting in that high-purity powders of ruthenium, terbium, cerium, and copper oxides plus strontium carbonate in required stoichiometric amounts are homogenized in acetone, resulting mixture is calcined at 960^оС for 8 h in air and then pressed. Synthesis is carried out in air/nitrogen mixture at 1010^оС for 8 h followed by double annealing at 1050^оС in air for 10 h. Product has following empirical formula: (Ru_0.5Cu_0.5)Sr₂(Tb_0.7Ce_0.3)Cu₂O₁₀.

EFFECT: achieved superconducting and magnetic properties.

Description

The invention relates to the production of a new complex perovskite-like ruthenium cuprate based on terbium, which is a promising material in many fields of technology. In particular, this complex terbium-based perovskite-like cuprate after processing in oxygen under pressure can be used in electronics and computer engineering (superconducting quantum interferometers, superconducting memory elements), energy (power storage devices), medicine (superconducting tomographs), etc.

Similar perovskite-like cuprates of the general composition RuSr ₂ (Ln, Ce) ₂ Cu ₂ O _10-δ (Ln = Dy, Ho, Y) are low-temperature magnetic ordering superconductors that are obtained from the starting components using high pressure and temperature techniques (pressure 6 GPa, temperature 1200 ° C). [VPS Awana and E. Takayama-Muromachi, Physica C, 2003. V.390. P.101]

Of all perovskite-like cuprates, perovskite-like cuprates based on copper — CuYBa ₂ Cu ₂ O _7-δ — are most widely used in energy storage devices, in electromagnets, current leads, and current limiters. This is due to the high temperature superconductivity of this phase.

However, copper-based perovskite-like cuprates have a number of serious drawbacks. So, resistance to moisture is not high enough, there is a high sensitivity of superconducting properties to the oxygen content, incongruent melting.

The objective of this invention was to obtain a new complex perovskite-like ruthenium cuprate based on terbium composition (Ru _0.5 Cu _0.5 ) Sr ₂ (Tb _0.7 Ce _0.3 ) ₂ Cu ₂ O ₁₀ , which was obtained by solid-phase sintering of the starting components. The presence of ruthenium ions in the compound determines the possibility of manifesting not only superconducting, but also magnetic properties that are absent in CuYBa ₂ Cu ₂ O _7-δ . [I. Felner, U. Asaf, Y. Levi, and O. Millo, Phys. Rev B.55. R3374 (1997)].

Samples weighing 2 g were obtained in a muffle furnace in alundum crucibles. A stoichiometric mixture of the starting components corresponding to the composition of (Ru _0.5 Cu _0.5 ) Sr ₂ (Tb _0.7 Ce _0.3 ) ₂ Cu ₂ O _10-δ is calcined in powder at 960 ° C for 8 hours in air Then, the obtained sample ground and pressed into a tablet with a diameter of 10 mm was synthesized at 1010 ° С in a mixture of air and nitrogen for 8 hours. Then the sample was ground, pressed into a tablet and annealed for 2 times at 1050 ° С in air for 8 hours After the first stage of annealing, the sample was ground and pressed again. The sample was cooled with the furnace. The resulting sample of the charge composition (Ru _0.5 Cu _0.5 ) Sr ₂ (Tb _0.7 Ce _0.3 ) ₂ Cu ₂ O ₁₀ (sample I) was then annealed in oxygen at 1050 ° C for 8 h (sample II).

High-purity powders of ruthenium, terbium, cerium, copper, and strontium carbonate oxides were used as starting materials for the preparation of the charge. The substances were weighed in the following weight ratio: ruthenium oxide - 8.00 wt.%, Terbium oxide - 30.78 wt.%, Cerium oxide - 12.41 wt.%, Copper oxide - 23.90 wt.%, Strontium carbonate - 35.49 wt.% (When heated, decomposition occurs according to the reaction SrCO ₃ → SrO + CO _2. Strontium oxide - 24.91 wt.%). The starting materials were thoroughly mixed in acetone for homogenization.

The composition and structure of the phase with a charge composition (Ru _0.5 Cu _0.5 ) Sr ₂ (Tb _0.7 Ce _0.3 ) ₂ Cu ₂ O ₁₀ , which is part of sample I, are determined by the full-profile X-ray method:

Tetragonal syngony.

Space group: 14 / mmm.

Cell parameters: a = 3.802 (2), c = 28.470 (20) A.

Cell Volume: 411.54A ³ .

Molecular mass: 806.190.

Number of formula units in a cell: 2.

Density: 6.505 g / cm ³ .

In the structure of the phases of the general composition (Ru, Cu) Sr ₂ (Tb, Ce ⁴⁺ ) ₂ Cu ₂ O _{10 the} “atoms” (Tb, Ce ⁴⁺ ) are not located in the center of the tetragonal prisms, the “atoms” (Ru, Cu) are in a distorted octahedron, the Sr and Cu atoms are located in defective cuboctahedra and in tetragonal pyramids, respectively.

The polycrystalline sample was taken on a DRON-3M automatic X-ray diffractometer (CuKα ₁ ) during scanning with a step of 0.02 ° in 2θ and an exposure of 15 s. Cell parameters of a new complex perovskite-like ruthenium cuprate based on terbium were determined and refined by the least squares method using the PoowTool program (the external standard is α-Al ₂ O ₃ powder: a = 4.7588 (1), c = 12.993 (2) A from the American Bureau standards). The composition and structure were refined by the Rietveld method using the DBWS-9411 program [Young RA, Sakthivel A., Moss TS, Paiva-Santos CO "Rietveld analysis of X-Ray and neutron powder diffraction patterns". User's guide to program DBWS-9411. March 30, 1995]. The experimental data array was processed using the PROFILE FITTING V 4.0 program. To describe the shape of the peak, the pseudo-Voigt or Pearson function was selected at 8.0 FWHM, where FWHM is the average peak width at half height. After the coefficient of reduction to the absolute scale, counter zero, background, unit cell parameters and sample displacement was specified, the step of refining the structural and profile parameters by gradually adding profile parameters with a specified background was followed. The structural parameters were refined in several stages: first, only the coordinates of the atoms, then the thermal parameters in the isotropic approximation for fixed positional, then the population of positions for fixed positional and thermal. At the final stage, both the thermal parameters and the population of the positions were refined simultaneously with the remaining parameters fixed for each atom.

The microstructure of the obtained compound was determined using a QUANTA-400 scanning electron microscope.

Electrical measurements were performed by the standard four-contact method in the temperature range 4.2–300 K. A sample of the charge composition (Ru _0.5 Cu _0.5 ) Sr ₂ (Tb _0.7 Ce _0.3 ) ₂ Cu ₂ O ₁₀ (sample I) showed semiconductor properties, and sample II turned out to be a low-temperature superconductor with a transition temperature to the superconducting state at T _c ~ 5 K.

Magnetic measurements were performed using a capacitive touch magnetometer placed in a superconducting solenoid. The magnetization of the samples was measured in magnetic fields at 140 KE at a temperature of 4.2 K. Sample II had magnetic ordering at T _m ~ 95 K.

Claims (1)

Perovskite-like ruthenium cuprate based on terbium (Ru _0.7 Cu _0.5 ) Sr ₂ (Tb _0.7 Ce _0.3 ) ₂ Cu ₂ O ₁₀ as a magnetically ordered superconducting material.