LOW-RESISTANCE Bi/Pb CERAMICS CONTAINING Ts = 295К-315K PHASES SYNTHESIZED IN A SOLAR FURNACE (PARKENT)

The aim of this work is to obtain bulk textured superconducting ceramics based on glass-crystalline precursors of the Bi1.7Pb0.3Sr2Ca(n-1)CunOy (n=5-9) series. Technologies for obtaining superconducting materials are presented. The advantages of melt methods and “Super Fast Aloys Quenching–T” technology is shown. Compositions, methods of synthesis and study of properties of precursors and ceramics obtained by solar energy are presented. The interrelation of the morphology of glass-crystalline precursors and superconducting ceramics based on them is revealed. It is shown that nano-sized nuclei are the basis on which superconducting phases with Ts = 295-315K are formed as a result of the peritectic reaction. The mechanism of conduction in nanostructured layered ceramics containing higher superconducting phases is proposed. The contribution to the conductivity of low-resistance ceramics is assumed due to the mutual influence of Bi / Pb homologous phases, which represent a “quasi” heterogeneous system by analogy with the mechanism proposed by Rashba for heterophase semiconductors.

Study of the fracture features of layered ceramics in its microvolumes by indentation methods

Technology and modes of ZrB2―SiC layered ceramic composites manufacturing have been developed. The structures, elastic characteristics and strength properties of the materials under investigation have been studied. Effect of internal stress fields on fracture processes in the indentation area and mechanical properties of the ceramics in its microvolumes has been investigated both in layers and at their interfaces. Using values of contact tensile strength along different directions in layers of the composites, effective residual thermal stresses have been calculated (≈180 MPa). The obtained data on contact tensile strength and effective crack resistance, taking into consideration the contributions of residual stresses to their values, have been used for estimations of contact strength and crack resistance of the layer materials themselves. The fracture toughness measured by the three-point bending method is 3,3—3,7 MPa · m1/2. Analysis of the data obtained indicates that the spark notch provides a greater sharpness of the crack tip and better conditions for measuring K1c, while processing with a blade picks up a sharp thermal crack in the notch tip. The elastic properties of the multilayer system (SiC—15% ZrB2) + (SiC—30% ZrB2) were studied using ultrasonic research methods. The values of the velocities of sound and elastic characteristics are sufficiently large and close to those expected from the models of the composite, which does not contain noticeable porosity and microcracks in the layers themselves and in the region of their boundaries. For directions along and across the plane of the layers, the values of Young's moduli differ by about 6%. For the directions of propagation of an ultrasonic wave along and across the layers, anisotropy of ultrasonic velocities of ~5% and elastic moduli of ~10—12% is observed, which may be due to the texture that develops in the structure of the layers during hot pressing. Keywords: layered ceramics, indentation, strength properties, thermal stresses.