Determination of solid solubility level of Ho nanoparticles in Y-123 superconducting matrix and strong Cu1 site preference of nanoparticles

• Published in: Journal of alloys and compounds 2014-10, Vol.610, p.361-371
• Main Authors: Sarıtekin, N.K., Zalaoglu, Y., Yildirim, G., Doğruer, M., Terzioglu, C., Varilci, A., Gorur, O.
• Format: Article
• Language: English
• Subjects: Ceramics; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cuprates superconductors (high tc and insulating parent compounds); Electron microscopy; Exact sciences and technology; Grain boundaries; Hardness measurement; Mechanical characterization; Physics; Superconductivity; X-ray diffraction; Y-based cuprates
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2014.04.037

The excess Ho particles inserted in the Y-123 superconducting matrix not only damage the crystal plane alignments and crystallinity of poly-crystallized Y-123 bulk samples but also lead to the phase transition from optimally doped state to the underdoped position in the crystal structure. [Display omitted] •Identification of Y-123 ceramics by ρ–T, Jc, XRD, SEM, EDX, HV and density measurements.•Optimum dopant level of x=0.100 for Ho concentration in the Y-123 crystal structure.•Phase transition from optimally doped to the underdoped position with excess Ho impurities (x>0.100).•Improvement of mechanical behavior with increase in strength of interaction between grains.•Superiority of IIC model to HK approach for the description of the real microhardness values. This comprehensive study reports the effect of the Ho inclusions on the microstructural, electrical, mechanical and superconducting characteristics of YBa2Cu3O7−δ ceramic superconductors with the aid of standard characterization methods including the bulk density, dc resistivity (ρ–T), transport critical current density (Jc), X-ray diffraction (XRD), electron dispersive X-ray (EDX), scanning electron microscopy (SEM) and Vickers microhardness (HV) investigations. The experimental results such as the degree of granularity, hole (filling) localization effect, room temperature resistivity, onset–offset critical transition temperature, degree of the broadening, thermodynamic fluctuations (spin-gap opening temperature), crystallinity, crystal plane alignments (texturing), crystal structure, grain size, phase purity and lattice parameters, appearance of flux pinning centers, grain boundary weak-links (interaction between the superconducting grains), surface morphologies (grain size distribution), real (load independent) microhardness values, elemental compositions and distributions belonging to the pure and Y-site Ho substituted Y-123 superconducting samples are discussed in detail for the first time. Moreover, mechanical characterization enables us to theoretically determine the elastic (Young’s) modulus and yield strength being in charge of the potential mechanical applications. Additionally, the load dependent microhardness values of the Y-site Ho substituted Y-123 materials have not been modeled by the available theoretical methods (Hays–Kendall and indentation-induced cracking approach) up to the present. All the experimental findings show that the microstructural, electrical, mechanical and supercond