ნიკოლოზ მარგიანი

The paper reports preliminary results about influence of B2O3 addition on the superconducting properties of YBa2Cu3Oy system. It was shown, that the superconducting volume fraction increased due to the B2O3 addition in the range of dopant content x=0.01-0.05 compared to the undoped specimen. It will be due to the introduction of additional oxygen in the lattice of boron-doped samples.

The dependence of superconducting transition temperatures of known cuprate superconductors on the parameter, which represents the ratio of oxygen atomic index to the sum of cations, entered into the structure is investigated. Favorable conditions for high-temperature superconductivity to occur are considered.

The influence of boron oxide addition on magnetic and electrical properties of HTSC ceramics with a Bi1.7Pb0.3Sr 2Ca2Cu4Oy nominal composition was investigated. A nonmonotonous dependence of critical temperature T c(p = 0) and magnetic susceptibility on boron concentration was observed.

The effect of an admixture of boron oxide B2O3 on the superconducting properties of the bismuth-containing 2212 phase is investigated. It is found that boron doping improves the superconducting transition characteristics of Bi2Sr2Ca1Cu2Oy and Bi1.8Pb0.2Sr2Ca1Cu2Oy samples slowly cooled in a furnace. As the boron content in quenched samples of the 2212 phase increases, Tc and the relative volume of the superconducting fraction are observed to decrease monotonically. Boron doping of the 2212 phase decreases the lattice parameter c

The influence of Li and B-doping on the supercondutcing transition has been investigated in furnace-cooled and quenched into liquid nitrogen Pb-free Pb-substituted Bi-based 2212 ceramic samples. It was found that Li and B-doping enhances the critical temperature of furnace cooled Pb-substituted (Bi, Pb)- 2212 superconductor. Introduction of Li_2CO_3 in the starting composition leads to the increase of T_c in both furnace-cooled and quenched Pb-free Bi-2212 system.

The effect of B2O3 addition on the superconducting transition and grain boundary critical current density of the boron free (control) and boron doped HTS ceramics with nominal composition YBa2Cu3B x O7−y (x=0, 0.025, 0.05, 0.075, 0.1 and 0.15) has been investigated. For the lowest-level boron doping (x=0.025) an increase by nearly 1.5 times was observed in the critical current density J c compared to the control sample. The small additives of boron in YBa2Cu3B x O7−y (x=0.025 and 0.05) do not essentially affect the critical temperature T c =92.5 K of nominally pure Y123. Higher-level boron added compounds revealed a decrease in both T c and J c values. The data obtained indicate the possibility of boron dopant being inserted either into interstitial or into substitutional sites of the lattice.

Influence of boron-doping on the superconducting properties of (Bi,Pb)-2223 HTS ceramics prepared in an alumina crucibles has been investigated. X-ray diffraction, resistivity, and AC susceptibility measurements were performed on the undoped and boron-doped compounds. Obtained results have shown that B2O3 addition in the Bi1.7Pb0.3Ca2Sr2Cu3O y precursor enhances the formation of high-T c phase. The boron-doped samples with starting composition Bi1.7Pb0.3Ca2Sr2Cu3B x O y (x=0.05 and 0.5) reveal significant improvement in the zero resistivity temperature compared to the undoped sample (from 72 K up to 100 K). Boron-doping level x=1.5 results in a substantial degradation of the (Bi,Pb)-2223 phase.

Nominally pure and B2O3-added (Bi,Pb)-2223 HTS samples were synthesized in air on alumina plates. The influence of boron-doping as well as annealing conditions on the high-T c 2223 phase evolution was studied using X-ray diffraction (XRD), resistivity and AC susceptibility measurements. The B2O3-added samples with starting composition Bi1.7Pb0.3Ca2Sr2Cu3B x O y (x=0.05 and 0.5) reveal significant enhancement of 2223 phase formation compared to the undoped sample. Higher-level boron doping x=1.5 leads to the degradation of high-T c 2223 phase.

(Bi,Pb)-2223 HTSs (high temperature superconductors) were synthesized from nominally pure (reference) and BN-added Bi1.7Pb0.3Ca2Sr2Cu3O y (BN) x precursors (x=0,0.10,0.15, and 0.20) by the solid state reaction method using alumina crucibles. The influence of boron nitride addition on the phase formation kinetics and transport properties of (Bi,Pb)-2223 HTSs was studied using X-ray diffraction (XRD), resistivity and critical current density measurements. BN-added compounds reveal a significant enhancement in both the high-T c 2223 phase formation and critical current density compared to the reference specimen.

In this paper, the combined effects of B4C-doping and planetary ball milling on the phase evolution, microstructure and transport properties of Bi1.7Pb0.3Sr2Ca2Cu3Oy(B4C)x HTS with x = 0 ÷ 0.125 were studied through X-ray diffraction (XRD), scanning electron microscopy (SEM), resistivity and critical current density measurements. Obtained results have shown that B4C additive leads to the strong acceleration of high-Tc phase formation and substantial enhancement in Jc. High-energy ball milling seems to produce a more homogeneous distribution of refined doped particles in the (Bi,Pb)-2223 HTS which results in an improved intergranular flux pinning and better self-field Jc performance.

Doping of a high-temperature Bi(Pb)-2223 superconductor with various additives, which can act as pinning centers and / or accelerate the formation of a superconducting phase, is an effective tool for obtaining Bi(Pb)-2223 samples with improved characteristics. In this paper, we studied the effect of the addition of hexagonal boron nitride (h-BN) on the phase formation and critical transport current density of ceramic samples Bi(Pb)-2223. Samples with a nominal composition of Bi1.7Pb0.3Sr2Ca2Cu3Oy [BN]x, x = 0–0.25 were prepared by the solid-phase reaction method. Two different doping methods were used: the introduction of hand-ground BN powder at the initial stage of synthesis and the addition of BN powder subjected to high-energy grinding in a ball mill before pelletizing. The phase composition of the obtained samples was studied by X-ray diffraction. The microstructure and elemental composition of the samples were studied using a scanning electron microscope with an X-ray microanalyzer. The resistivity and critical current density were measured using the standard four-probe method. The results show that boron nitride is a suitable additive to increase the rate of formation and critical transport current density Bi(Pb)-2223.

The present paper reports on the impact of boron carbide (B4C) additive on phase formation and physical properties of Bi(Pb)-2223 high-temperature superconductor (HTS). Refe-rence and B4Cadded Bi(Pb)-2223 samples with nominal composition Bi1.7Pb0.3Sr2Ca2Cu3Oy(B4C)x, x=0, 0.040 and 0.075 were prepared by solid-state reaction method. Precursor powders were manually grinded in agate mortar and sintered at 8500C for 30 hours with intermediate grindings; obtained materials were pressed into pellets and annealed at 8450C for 40 hours, then cooled to room temperature in the furnace. The evolution of Bi(Pb)-2223 phase in prepared samples was investigated by X-ray diffraction (XRD) analysis and volume fraction of Bi(Pb)-2223 phase was estimated from XRD data. The lattice parameters for Bi(Pb)-2223 phase were calculated from XRD patterns. The temperature dependence of electrical resistivity ࣋)ࢀ (was measured by four-probe method. Transmission electron microscope (TEM) and scanning transmission electron Microscope (STEM) were used for microstructural and elemental analysis of synthesized samples. The ࣋)ࢀ (dependences show a twostep superconducting transition with Tc>100 K, indicating the coexistence of high-Tc 2223 and lowTc 2212 phases in prepared materials. XRD analysis confirms that B4C-doping leads to the marked enhancement of Bi(Pb)-2223 phase volume fraction from 56% for un-doped sample up to 88% at x=0.04. Gradual decrease of lattice parameters with increasing doping level can be attributed to the partial substitution of B3+ ions for Cu2+ ions. The areas with completely formed, partly formed and unformed Bi(Pb)-2223 phase have been visually revealed by the TEM/STEM imaging and elemental analysis.

The processes of heat propagation in five-layer detection pixels of the thermoelectric single-photon detector after absorption of 0.8–1000 eV energy photons are investigated by the method of computer simulation. Design of the detection pixel consisting of successive layers on a sapphire substrate of heat sink Bi2223, thermoelectric sensor CeB6, absorber Bi2223, and the antireflection layer SiO2 is proposed. The computer modelling was carried out based on the equation of heat propagation from the limited volume by the use of the three-dimensional matrix method for differential equations. Temporal dependences of the signal intensity for different thicknesses of the layers of the detection pixel are determined. It is shown that the detection pixel SiO2/Bi2223/CeB6/Bi2223/Al2O3 can register single photons in a wide spectral range from near-IR to X-ray, as well as count the number of simultaneously absorbed photons up to eight. The use of Bi2223 high-temperature superconductor in the design of the detection pixel provides a gigahertz count rate and high system detection efficiency. The simple design of the detection pixel is a prerequisite for the creation of multi-pixel sensors. A detector with such characteristics could be representative of the next generation single-photon detectors in the near future.

The present paper reports on the impact of graphene (Gr) addition on the microstructure and thermoelectric properties of Bi2Sr2Co1.8Oy ceramics. Reference and graphene added to

Bi2Sr2Co1.8Oy+x wt. % Gr thermoelectric (TE) materials (x=0, 0.15, 0.35, 0.70, and 1.15) were prepared by using the solid-state reaction method. The phase purity and microstructure of the

samples were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. XRD analysis revealed that the addition of graphene did not alter the structure of

Bi2Sr2Co1.8Oy and this compound remained as a single-phase. SEM analysis showed slight increase of the amount of grains with smaller sizes for 0.35-0.70 wt. % Gr and deterioration of texturing degree for 1.15 wt. % graphene additive. Electrical transport characteristics of prepared materials were studied and values of their power factor (PF) were calculated. It was found that the incorporation of graphene into the Bi2Sr2Co1.8Oy ceramics resulted in a monotonic decrease of electrical resistivity for 0.15-0.70 wt. % Gr while the Seebeck coefficient of all synthesized samples remained practically unaffected. Graphene addition leads to 1.4-fold enhancement of the power factor from 37.0 µW/(m⋅K2) at 973 K for the reference sample to 50.7 µW/(m⋅K2 ) for the sample with 0.70 wt. % Gr additive.

The nominally pure and boron-doped YBa2Cu3B x O7−y samples with B-doping level x varying between 0 and 0.15 were prepared by the solid state reaction. X-ray diffraction analysis shows that all the obtained compounds are single YBa2Cu3O7−y phase. The small additives of boron in YBa2Cu3B x O7−y (x=0.025 and 0.05) do not essentially affect the critical temperature T c and it remains near 90 K. The higher-level boron doping causes degradation of T c and tail remains on the ρ(T) curve for x=0.15 at 65 K. Lowest-level boron doping applied leads to a significant improvement in J c compared to the undoped sample (from 100 A cm−2 for a control sample to 147 A cm−2 for a B-doped sample with x=0.025). Grain boundary critical current density and superconducting volume fraction decrease with increasing amount of added B2O3. The obtained results indicate possibility of boron dopant being entered into the lattice-sites.

PbMo6S8 polycrystalline superconductors have been studied in a weak linearly polarized oscillating field orientated at various angles to a constant field and also in a weak circularly polarized oscillating field superimposed on it a constant field. Measurements have been carried out in various temperature intervals and for various values of variable and constant fields. Numerical results of our experiments have shown that the isotropic theoretical model is preferable for investigating the sample.

Two series of the nominally pure (control) and boron-doped (Bi,Pb)-2223 HTSs with composition Bi1.7Pb0.3Ca2Sr2Cu3BxOy (x=0, 0.05, 0.5, 1.5) were prepared under the different conditions: in an alumina crucibles and on an alumina plates. The influence of boron-doping as well as annealing conditions on the high-Tc 2223 phase evolution was studied using X-ray diffraction (XRD), resistivity and AC susceptibility measurements. Obtained results indicate that boron dopant drastically accelerates the formation of (Bi,Pb)-2223 HTS synthesized in an alumina crucibles. The boron-doped sample with x=0.5 revealed significant improvement in the Tc compared to the control sample (from 72K up to 100K). On the other hand, the additives of boron (x=0.05 and 0.5) have shown to have a beneficial effect on the formation of (Bi,Pb)-2223 HTSs prepared by the heat treatment of precursors on alumina plates, although do not essentially affect the critical temperature Tc=102 K of nominally pure compound. 

The influence of addition of lead borate Pb(BO2)2 and boron oxide B2O3 on the phase evolution and superconducting properties of (Bi, Pb)-2223 HTSs synthesized by the solid-state reaction method in alumina crucibles has been studied. X-ray diffraction, resistivity, critical current density, and AC susceptibility measurements were performed on the prepared compounds. Obtained results have shown that boron-containing dopants lead to the drastic enhancement of the (Bi, Pb)-2223 phase formation. Boron-doped samples reveal a significant increase in both the zero resistivity temperature and transport critical current density compared to the undoped specimen. On the other hand, a high content of boron-containing dopants causes the appearance of a very low-T c 2201 phase and leads to a deterioration of coupling between superconducting grain boundaries. Obtained results could enable us to develop a cheap and energy efficient fabrication technology for nearly single (Bi, Pb)-2223 phase superconducting materials via heat treatment of boron-incorporated precursors in an alumina crucibles.

The effect of lead borate Pb(BO2)2 doping on the phase formation and superconducting properties of (Bi,Pb)-2223 high-temperature superconductivity (HTS) has been studied. Samples with nominal composition Bi1.7Pb0.3−xSr2Ca2Cu3O y [Pb(BO2)2] x , x = 0–0.3, were prepared by the standard solid-state processing. The appropriate mixtures were calcined at 850 °C for 30 h. The resulting materials were pressed into pellets and annealed at 840 °C for 30 h in air. X-ray diffraction, resistivity, and critical current density measurements were performed on the undoped (reference) and Pb(BO2)2-doped (Bi,Pb)-2223 compounds. The dominance of the low-T c 2212 phase over the high-Tc 2223 phase was observed in the reference sample. With the increasing of doping level, the 2223 phase is significantly enhanced and its increase is associated with the decrease of the 2212 phase. Our results show that the sample with x = 0.075 is the best in the present study. The calculated volume fraction of (Bi,Pb)-2223 phase increases from ∼25 % for reference specimen to ∼85 % for x = 0.075 in a short sintering time (60 h). The (Bi,Pb)-2223 sample with x = 0.075 (0.15 wt% boron) reveals significant enhancement of critical current density (from 25 up to 360 A/cm2) compared to the reference sample. Obtained results could enable us to develop an accelerated and simple method for producing a high purity (Bi,Pb)-2223 superconducting materials by a proper amount of Pb(BO2)2 doping.

Doping of thermoelectric materials with various additives is a promising approach for increasing the functional efficiency of thermoelectric materials of different classes. This paper presents preliminary results of studying the impact of the strontium borate dopant Sr(BO2)2 on the power factor (PF) of the oxide thermoelectric Bi2Sr2Co1.8Oy. Samples with the nominal composition Bi2Sr2–x[Sr(BO2)2]xCo1.8Oy, x = 0–0.15, were prepared by the solid-phase reaction method. The temperature dependences of the resistivity and Seebeck coefficient were measured, and the power factor of the synthesized materials was calculated. The results obtained show that doping with strontium borate enhances the power factor of Bi2Sr2Co1.8Oy thermoelectric.

In this work, Pb(BO2)2-doped Bi2Sr2Co1.8Oy thermoelectric materials with composition Bi2−x[Pb(BO2)2]xSr2Co1.8Oy (x = 0, 0.075, 0.15, 0.25) were prepared through the solid-state

reaction method. Electron transport and microstructural characteristics of prepared materials were studied, and values of their power factor were calculated. It was found that the slight doping of Bi2Sr2Co1.8Oy with lead borate leads to the decrease in electrical resistivity at 923 K from 126 to 76.5 mΩ cm for x = 0.15. The resistivity increases upon further Pb(BO2)2 doping for x = 0.25. The increase in the Seebeck coefficient was observed with an increase in dopant content from x = 0.15 up to 0.25. The Pb(BO2)2 doping resulted in a 1.8-fold enhancement of the power factor from 21.7 µW/(m K2) at 923 K in the reference sample to 38.2 µW/(m K2 ) in the doped sample with

x = 0.15. Partial substitution of Bi2O3 by Pb(BO2)2 also promotes both grain growth and densification of Bi2Sr2Co1.8Oy thermoelectric ceramics.

Proper Doping of a high-temperature superconductor (HTS) Bi(Pb)-2223 is an effective route to prepare Bi(Pb)-2223 HTS with enhanced transport characteristics. In this paper, we studied the impact of Ca(BO 2 ) 2 doping on high-T c phase formation kinetics and transport critical current density of Bi(Pb)-2223. Samples with a nominal composition of Bi 1.7 Pb 0.3 Sr 2 Ca 2-x Cu 3 O y [Ca(BO 2 ) 2 ] x , x = 0 −0.15 were prepared by the solid-state reaction method. The phase evolution of the prepared materials was studied by X-ray diffraction analysis (XRD). The resistivity and critical current density were measured by the standard four-probe method. Scanning electron microscopy (SEM) combined with Energy Dispersive X-ray (EDX) microanalysis (SEM-EDX) was used to examine the microstructure and elemental composition of samples. The obtained results show that Ca(BO 2 ) 2 doping leads to the promotion of the high-T c phase formation and enhancement of the transport critical current density ( Jc) in Bi(Pb)-2223 HTS.