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Öğe Compressive behavior of large-scale square reinforced concrete columns confined with carbon fiber reinforced polymer jackets(Elsevier Sci Ltd, 2010) Turgay, Tahsin; Polat, Z.; Köksal, Hasan Orhun; Doran, Bilge; Karakoç, C.Several experimental and analytical studies on the confinement effect and failure mechanisms of fiber reinforced polymer (FRP) wrapped columns have been conducted over recent years. Although typical axial members are large-scale square/rectangular reinforced concrete (RC) columns in practice, the majority of such studies have concentrated on the behavior of small-scale circular concrete specimens. The data available for square/rectangular columns are still limited. This paper reports the results of an experimental research program on the performance of large-scale square RC columns wrapped with carbon fiber reinforced polymer (CFRP) sheets. Attention is focused on the investigation of the total effect of longitudinal and transverse reinforcement and FRP jackets on the behavior of concentrically loaded columns. A total of 20 large-scale RC columns were fabricated and tested to failure under axial loading in the structural laboratory. Three types of columns were primarily considered: unwrapped; fully wrapped; and partially wrapped. Based on the test results of RC columns, existing experimental data and procedures in the literature are also evaluated. Furthermore, stress-strain curves of the columns are successfully predicted by the analytical approach previously proposed for FRP-confined concrete. (C) 2009 Elsevier Ltd. All rights reserved.Öğe Contribution of vanadium particles to thermal movement of correlated two-dimensional pancake Abrikosov vortices in Bi-2223 superconducting system(Elsevier, 2023) Ülgen, Asaf Tolga; Erdem, Ümit; Yıldırım, Gürcan; Türköz, Mustafa Burak; Turgay, TahsinThis article breaks new ground in understanding of variation in the magnetic strength performance, flux pinning and energy dissipation mechanism of polycrystalline bulk Bi1.8Sr2.0Ca2.2Cu3.0Oy (Bi-2223) superconducting materials added with the different vanadium concentration level (0.0 <= x <= 0.30) under the magnetic field strengths applied up to 5 T for the first time. We provide the sophisticated and phenomenological discussions on the magnetoresistivity measurement results in three main sections along the paper. All the findings show that the increase of both the vanadium concentration in the crystal structure and external magnetic field strength damages significantly the magnetic strength performance, vortex dynamics, flux pinning ability and vortex lattice elasticity of bulk Bi-2223 superconducting ceramics. The vanadium addition promotes thermally the movement of correlated two-dimensional (2D) pancake Abrikosov vortices between the in-plane Cu-O-2 layers in the valance band, vortex lattice elasticity, vortex dynamics, distance for interlayer Josephson couplings and flux pinning centers and the theoretical computations confirm the remarkable degradation in the formation of super-electrons in the Bi-2223 crystal system. Thus, the vanadium addition is anticipated to be one of the best selectable materials to examine the differentiation in the thermal movement of correlated 2D Pancake Abrikosov vortices in the bulk Bi-2223 superconducting system. (c) 2022 The Author(s). Published by Elsevier Espana, S.L.U. on behalf of SECV. This is anopen access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/ by-nc-nd/4.0/).Öğe Detailed survey on minimum activation energy for penetration of Ni nanoparticles into Bi-2223 crystal structure and temperature-dependent Ni diffusivity(Springer, 2018) Zalaoğlu, Yusuf; Terzioğlu, Cabir; Turgay, Tahsin; Yıldırım, GürcanThe primary contributions of this study are not only to explore the role of diffusion annealing temperature interval 650 to 850 A degrees C on the formation of effective electron-phonon coupling or cooper-pair probabilities (percentage of clusters in the superconducting path), densities of active and dynamic electronic states at Fermi energy level, stabilization of superconductivity in the homogeneous regions, overlapping of Cu-3d and O-2p wave functions and bond strengths in the crystal matrix of Ni surface-layered Bi-2223 polycrystalline ceramics, but also to determine the temperature-dependent diffusion fast-rate and required minimum activation energy for the diffusion of Ni foreign impurities into the bulk Bi-2223 superconducting crystal structure for the first time. The dc electrical measurement results obtained show that the optimum diffusion annealing temperature is found to be 700 A degrees C for the penetration of optimum Ni concentration into the Bi-2223 crystal lattice so that the ceramic compound exposed to 700 A degrees C annealing temperature exhibits the highest electrical and superconducting properties. In this respect, the material with the minimum electrical resistivity parameters of Delta rho, rho (115K) , rho (res) and rho (norm) obtains the maximum superconducting characteristics of , and RRR. Accordingly, the annealing temperature of 700 A degrees C promotes the Bi-2223 ceramics for usage in the engineering, electro-optic, industrial and large scale applications. At the same time, the diffusion coefficients [D = D(o)exp(E/k(B)T)] determined at annealing temperature ranging from 650 to 850 A degrees C are observed to be much more significant at rather higher temperatures as compared to lower temperatures. The temperature-dependent Ni diffusion coefficient is determined to be D = 3.9707 x 10(- 7)exp[- 1.132 eV/k(B)T] for the Bi-2223 particulate solid material. Namely, the diffusion coefficient is calculated to be about 3.9707 x 10(- 7)cm(2) s(- 1) when the required minimum activation energy for the introduction of heavy metal Ni ions to the bulk Bi-2223 crystal structure is computed to be about 1.132 eV, being one of the most striking points deduced form this work.Öğe Development of modulation, pairing mechanism, and slip system with optimum vanadium substitution at Bi-sites in Bi-2212 ceramic structure(Elsevier Science Sa, 2023) Ülgen, Asaf Tolga; Okur, Semih; Erdem, Ümit; Terzioğlu, Cabir; Yıldırım, Gürcan; Turgay, TahsinPresent study focuses extensively on the change in electrical, superconducting and microhardness parameters with partial substitution of trivalent V+3 impurities replacing Bi+3 ions in Bi-2212 ceramic compound with the aid of dc electrical resistivity and microhardness test measurements. Experimental findings, calculation results, and phenomenological discussions provide that the optimum vanadium substitution level is found to be x = 0.01 in the Bi2.0-xVxSr2.0Ca1.1Cu2.0Oy (Bi-2212) ceramic system for the highest conductivity, crystallinity quality, superconducting, and mechanical performance features depending on the decreased microscopic structural problems. All the findings are wholly verified by scanning electron microscopy (SEM) and X-Ray diffraction (XRD) analyses. The dc electrical measurements indicate that the optimum vanadium ions support the pairing mechanism for the formation of new polaronic states in the clusters of microdomains, and hence expand superconducting energy gap due to the enhancement of amplitude part of pair wave function in the spin-density wave systems. The excess vanadium content degrades all the basic thermodynamics and quantum mechanical quantities mentioned due to the stress-induced phase transformation. Numerically, the Bi-2212 advanced ceramic matrix prepared by the optimum vanadium impurity is noticed to present the smallest residual resistivity value of 0.08 m & omega; cm, room temperature resistivity value of 8.84 m & omega; cm, and broadening degree of 0.36 K. Similarly, the ceramic material is found to possess the highest residual resistivity ratio of 3.05, carrier concen-tration number of 0.153041, critical transition offset and onset value of 84.66 K and 85.02 K, respectively. Besides, the microhardness findings reveal that the same compound with the least sensitivity to the applied test loads exhibits the largest Hv value of 4.799 GPa, Young's moduli of 393.303 GPa, yield strength of (0.969 GPa), and elastic stiffness coefficient of 15.5574 (GPa)7/4 under the applied test load of 0.245 N. The XRD in-vestigations show that the presence of optimum vanadium impurity supports the formation of a high super-conducting phase, c-axis length, and average crystallite size. All the findings are morphologically confirmed by the SEM images. It is found that the crystallographically best crystallinity quality and view of surface morphology is observed for the optimum vanadium substitution level. All in all, new higher properties for the conductivity, crystallinity quality, surface morphology, superconducting, and microhardness parameters based on the optimum vanadium replacement encourage the Bi-2212 crystal system to use in much more application places.Öğe Effect of annealing ambient conditions on crack formation mechanisms of bulk Bi-2212 ceramic systems(Taylor & Francis Ltd, 2021) Erdem, Ümit; Akkurt, Bahadır; Ülgen, Asaf Tolga; Zalaoğlu, Yusuf; Turgay, Tahsin; Yıldırım, GürcanThis study paves way to examine the influence of different annealing conditions (temperature range of 830-850 degrees C and duration intervals 24-48 h) on the fundamental mechanical performance and characteristic quantities of polycrystalline Bi2.1Sr2.0Ca1.1Cu2.0Oy (Bi-2212) superconducting ceramics by means of Vickers microindentation hardness tests at the various indentation test loads (0.245 N <= F <= 2.940 N) and some available theoretical approaches. The annealing ambient plays an important role on the operable slip systems and crystal quality. The bulk Bi-2212 superconducting compound prepared at 840 degrees C and 24 h is found to be the least sensitive to the applied test load due to less structural problems, voids, cracks and stress raisers in the crystal system. Conversely, the excess annealing ambient complicates remarkably the control of crack growth size and velocity. Thus, relatively lower load can lead to the formation of crack and acceleration of crack rate up to the critical size and terminal velocity. The samples exhibit the typical indentation size effect (ISE) behavior as a result of predominant character of elastic recovery mechanism. As for the theoretical examination in the saturation limit regions, the indentation-induced cracking (IIC) model wins the comparison as it provides the most accurate results to the experimental findings.Öğe Effect of diffusion annealing temperature on crack-initiating omnipresent flaws, void/crack propagation and dislocation movements along ni surface-layered bi-2223 crystal structure(2018) Yıldırım, Gürcan; Turgay, TahsinThis study aims to find out the crucial variations in the mechanical performance and characterization of Bi-2223 superconducting compounds with the diffusion annealing temperatures interval 650 °C-850 °C by means of Vickers hardness measurements exerted at the different applied indentation test loads (0.245 N-2.940 N) and derived theoretical findings. All the experimental results and theoretical evidences showed that the mechanical characterization and performances improve with the increment in the diffusion annealing temperature up to 700 °C due to the development in structural properties. Namely, the optimum annealing temperature of 700 °C resulting in the optimum penetration of Ni impurities into both the superconducting grains and over the grain boundaries develops the crystallinity of Bi-2223 crystal structure. In other words, the surface energy related to the crack-initiating omnipresent flaws, void/crack propagation and dislocation movement reduces due to the augmented critical stress value. In this respect, the diffusion annealing temperature of 700 °C develops the mechanical durability, stiffness, ideal fracture and flexural strength. However, after the certain diffusion annealing temperature value of 700 °C, the crystallinity tends to degrade considerably and in fact dwelling in the worst crystal structure for 850 °C annealing temperature. Accordingly, the initial crack growths, sizes of crack-producing flaws, void/crack propagation and dislocation movement in the copper-oxide consecutively stacked layers reach much more rapidly to the critical speeds due to the increased stress amplification so that the Bi-2223 compound with the augmented brittle behavior breaks at even lower test load. Moreover, it is observed that the presence of optimum nickel impurities in the crystal structure strengthens the standard indentation size effect behavior.Öğe Evaluation of load-independent microhardness values in Plateau regions of Vanadium substituted Bi-2212 ceramics(IOP Publishing Ltd, 2022) Ülgen, Asaf Tolga; Okur, Semih; Erdem, Ümit; Pakdil, Murat; Turgay, Tahsin; Yıldırım, GürcanThis study reveals extensively effect of homovalent V/Bi partial replacement in Bi2.0-xVxSr2.0Ca1.1Cu2.0Oy ceramic matrix (0.00 <= x <= 0.30) on the key mechanical design performance parameters and load-independent Vickers microhardness parameters in plateau limit region by means of experimental microhardness tests and semi-empiric approaching models. It is found that the vanadium substitution level of x = 0.01 is observed to be optimum amount in the Bi-2212 crystal lattice for refinement of fundamental mechanical properties due to the enhancement in stabilization of durable tetragonal phase, surface residual compressive stress and elastic recovery mechanism. Conversely, from the replacement level of x = 0.01 onwards, the lattice strain field and stress concentration sites enhance significantly depending on the increase of microscopic structural problems, interaction problems between adjacent layers and crack-initiating flaws in Bi-2212 ceramic system. Correspondingly, stress-induced phase transformation begins to play predominant role, and excess vanadium substituted ceramic materials are easily broken at relatively smaller test load. Moreover, the models indicate that every ceramic compound shows standard indentation size effect (ISE) feature due to predominant behavior of elastic recovery in crystal structure. Hence, presence of optimum vanadium ions strengthens typical ISE characteristic behavior. Furthermore, among semi-empirical models the indentation-induced cracking (IIC) model exhibits the highest performance to inspect real microhardness values of Bi2.0-xVxSr2.0Ca1.1Cu2.0Oy ceramic compounds in the plateau limit region.Öğe Evolution of residual compressive stress regions in Co-diffused Bi-2212 engineering ceramics with annealing temperature(Springer, 2024) Mercan, Ali; Erdem, Umit; Ulgen, Asaf Tolga; Gulen, Mahir; Turkoz, Mustafa Burak; Turgay, Tahsin; Yildirim, GurcanThe role of diffusion annealing temperatures intervals 600-850 degrees C on durable tetragonal phase, surface morphology, and main mechanical performance parameters of Co surface-layered Bi2.1Sr2.0Ca1.1Cu2.0Oy (Bi-2212) samples has extensively been examined by scanning electron microscopy (SEM), Electron Dispersive X-ray (EDX) technique and microindentation Vickers hardness (Hv) tests. The experimental findings have shown that every material prepared has presented different composition distributions on the specimen surface as a consequence of the successful production of materials. Besides, the mechanical characteristics and durable tetragonal phase have been noted to enhance significantly with the enhancement of annealing temperature up to 650 degrees C due to the formation of new slip systems, surface residual compressive stress regions, connections between grains, and chemical bonding between the foreign and host atoms. Further, the optimum temperature has led to the reduction in stored internal strain energy and degree of granularity in the Co-diffused Bi-2212 crystal system. In this respect, the sample with the least sensitive to the external forces has exhibited the highest elastic modulus of 0.5445 GPa, shear modulus of 17.8515 GPa, yield strength of 181.5 MPa, and resilience of 369.1 MPa under 0.295 N. Accordingly, the cracks and dislocations have preferred to propagate throughout the transcrystalline regions, and crack growth size was easily controlled. Similarly, the saturation limit region has begun at relatively higher applied test load magnitudes. Conversely, the excess annealing temperature has caused the increase in the agglomeration of cobalt ions throughout the intergranular regions. Correspondingly, the activation of stress-induced phase transformation has been triggered seriously. Bi-2212 ceramic compound exposed to the optimum diffusion annealing temperature exhibits the most uniform surface view and crystalline quality with the densest surface morphology and the largest particle distributions and orientations. Moreover, every material studied has perfectly presented the characteristic indentation size effect behavior. The examination of granularity degree depending on elasticity moduli has verified all the Hv test results and discussions. All in all, this study guides the use of engineering ceramics in more application areas due to the increase in their service life.Öğe Key mechanical design performance features and mechanical characterization of poly-crystallized Bi2.1Sr2.0-xTixCa1.1Cu2.0Oy superconducting ceramic cuprates(2019) Turgay, Tahsin; Zalaoğlu, Yusuf; Yıldırım, GürcanThe primary scope of this study is to examine the variations of key mechanical design performance features and mechanical characterization of Bi2.1Sr2.0-xTixCa1.1Cu2.0Oy superconductors via Vickers hardness tests performed at different test loads between 0.245 N and 2.940 N. The materials are prepared within the molar ratios of 0≤x≤0.10 by using the ceramic method in the atmospheric air. The measurement findings obtained indicate that the increment of Sr/Ti partial substitution level regresses remarkably the key design mechanical performances namely mechanical strength, stability, stiffness, critical stress, toughness, flexural strengths and mechanical durability. This means that the existence of Ti impurity matrix leads to the enhancement in the problematic defects, crack initiation sites and stress raisers based on the crack-producing omnipresent flaws. Accordingly, the propagation of the problematic defects accelerates considerably at lower indentation test loads applied, and the problematic defects locate easily in their critical propagation speed. All in all, the crystal defects are out of control, and the Sr/Ti partial substituted Bi2.1Sr2.0-xTixCa1.1Cu2.0Oy superconductiors are much easier broken. Additionally, it is noted that every material produced show the typical indentation size effect but in diminish trend with enhancing Sr/Ti partial replacement level. The load-dependent mechanical parameters such as Young’s modulus, yield strength, fracture toughness, brittleness index and elastic stiffness coefficients are also discussed in the text.Öğe Modeling aspects concerning the axial behavior of RC columns(2011) Köksal, Hasan Orhun; Turgay, Tahsin; Karakoç, Cengiz; Ayçenk, S.This paper is concerned with the axial behavior of the RC columns. Stress-strain relationships of experimentally tested RC columns under concentric loading are compared with the predictions of the Koksal model. Moment-curvature analyses of RC sections are also performed employing the same model in a self-developed moment-curvature program for confined concrete. Results are compared with the output of EXTRACT which uses the Mander concrete model. © 2011 WIT Press.Öğe Nonlinear finite element modeling of rectangular/square concrete columns confined with FRP(Elsevier Sci Ltd, 2009) Doran, Bilge; Köksal, Hasan Orhun; Turgay, TahsinNumerous confinement models which can be categorized as design or analysis oriented have been proposed for predicting the behavior of fiber-reinforced polymer (FRP)-confined concrete columns. Analysis-oriented models generally use an incremental procedure for plotting the entire stress-strain response while design-oriented models predict the load-carrying and deformation capacities of the column with closed form expressions. As a comprehensive approach, this paper primarily deals with the nonlinear finite element modeling of rectangular/square concrete columns wrapped with FRP in order to simulate the compressive behavior under concentric loading. Adopting cohesion and internal friction values of Drucker-Prager criterion from a previous study of the authors, emphasis is placed on both the determination of confining stress and the lateral-to-axial strain relation. Thirty three small and large scale specimens. including slender columns, tested by four different researchers are numerically analyzed for this crucial relation between the behavior of concrete and composite jacket. The distribution of confining stresses at the mid-height plane of the columns is evaluated on the basis of analysis. Confining stresses obtained from nonlinear finite element analyses (NLFEA) are also compared with both uniform confining pressure for cylindrical specimens and effective stresses calculated by using a shape factor recommended by ACI 440.2R-02. Comparisons show that the confining pressure values obtained from the assumption of uniform stress distribution over the surface of concrete core are consistent with the maximum lateral pressure at the corners while effective lateral pressure can be considered as minimum confining stresses on flat sides. (C) 2008 Elsevier Ltd. All rights reserved.Öğe Reveal of relationship between microscopy architecture and mechanical performance of Y/Bi substituted Bi-2212 engineering ceramics(Wiley, 2024) Yilmaz, Tolgahan; Kurtul, Gulnur; Ulgen, Asaf Tolga; Erdem, Umit; Mercan, Ali; Turgay, Tahsin; Yildirim, GurcanThis study aims to find out how the crystallinity quality, surface morphology, and mechanical performances change with the substitution of yttrium (Y) for bismuth (Bi) impurity within molar ratios of 0.00 <= x <= 0.12 in the Bi2.0-xYxSr2.0Ca1.1Cu2.0Oy (Bi-2212) cuprates to reveal the dependence of micro surface topology on the substitution mechanism and achieve a strong relation between the impurity ions and crystallization mechanism. The materials are prepared by ceramic method. It is found that all the experimental findings improve remarkably with increasing yttrium impurity molar ratio of x = 0.01. Scanning electron microscopy (SEM) images indicate that the optimum Y ions strengthen the formation of flaky adjacent stacked layers due to the changes of thermal expansion, vibration amplitude of atoms, heat capacitance, reaction kinetics, activation energy, nucleation temperature, thermodynamic stability, and intermolecular forces. Besides, new engineering novel compound produced by optimum Y ions presents the best crystallinity quality, uniform surface view, greatest coupling interaction between grains, largest particle size distributions/orientations, and densest/smoothest surface morphology. Hardness measurement results totally support the surface morphology view. Moreover, mechanical design properties and durability of the tetragonal phase improve significantly with increasing replacement level of x = 0.01 due to the induction of new surface residual compressive stress areas, slip systems, and chemical bonding between the foreign and host atoms. Besides, the same sample exhibits the maximum strength and minimum sensitivity to loads depending on reduction of stored internal strain energy and degree of granularity. Consequently, cracks tend to propagate predominantly within the transcrystalline regions. Furthermore, each material investigated exhibits the characteristic behavior of the indentation size effect. In summary, the optimum Y-doped Bi-2212 sample paves the way for the expanded use of engineering ceramics across various applications based on the enhanced service life.Research Highlights The presence of the optimum yttrium impurity significantly decreases the Ea value. As the Y/Bi replacement increases up to the molar substitution level of x = 0.01, the mechanical design properties and durability of the tetragonal phase enhance significantly. Mystery of the change in the mechanical performance features of the Y-doped Bi-2212 advanced ceramic compound against the applied test loads is related to the microscopy architecture.imageÖğe Stress-strain model for concrete confined with CFRP jackets(Elsevier Sci Ltd, 2009) Turgay, Tahsin; Köksal, Hasan Orhun; Polat, Z.; Karakoç, C.Enhancement of strength and ductility is the main reason for the extensive use of FRP jackets to provide external confinement to reinforced concrete columns especially in seismic areas. Therefore, numerous researches have been carried out in order to provide a better description of the behavior of FRP-confined concrete for practical design purposes. Most of the existing models are based on the improved or modified forms of the well known empirical formula of Richart et al. derived from the tests on concrete cylinders. Compressive strength of concrete is predicted without a failure criterion for this modeling approach. There exist only a few models that employ the simplified or modified forms of five-parameter failure criterion proposed by William-Warnke. This paper primarily concentrates on the modeling of FRP-confined concrete using a practical failure surface based on only unconfined compressive strength of concrete. A large comparative analysis is accomplished for the existing test data of 127 cylindrical concrete specimens confined with CFRP jackets. The performance of five existing analytical models for the prediction of the compressive strength of FRP-confined concrete is evaluated leading to the detection of the proposed approach as the most accurate one through this comparative study. Moreover, the complete stress-strain curves of eight concrete cylinders obtained from four different experimental studies are plotted adopting both the stress-strain relation of Saenz and the predictions for compressive strength of the approach. Comparisons between the experimental and analytical results point out that the proposed approach provides satisfactory predictions for both the compressive strength and the stress-strain plots of CFRP-confined concrete. (C) 2008 Elsevier Ltd. All rights reserved.Öğe Support of polaronic states and charge carrier concentrations of YBa2Cu3O7-y ceramics by oxygen and Mn2O3 impurity(Wiley, 2024) Kurtul, Gulnur; Yildirim, Gurcan; Turgay, Tahsin; Terzioglu, C.The influence of oxygen and Mn2O3 impurity addition intervals 0.01 <= x <= 0.30 on the basic electrical conductivity, stabilization, crystallinity quality, grain boundary couplings, structural, orbital hybridization mechanisms, and superconducting properties of YBa2Cu3O7-yMnx ceramics has extensively been analyzed by electrical resistivity, X-ray diffraction investigations, and related theoretical results. It has been found that there is a strong link between the production conditions and fundamental characteristic features. All the results deduced have enabled us to discuss the variation of electron-electron and electron-phonon interactions, order parameter for super-electrons and cooper-pairs, organization of Cu-O coordination, homogeneities of oxidation states, microscopic structural problems, electronic density states, and grain boundary couplings between the adjacent layers in the YBa2Cu3O7-y ceramics. Similarly, we have discussed the change in the formation of pairing mechanisms and bipolarons in the polarizable lattices in the microdomain clusters. The results have shown that both the presence of oxygen and optimum manganese impurity of x = 0.07 led to the enhancement in the fundamental characteristic features related to the basic physical, quantum mechanical, and thermodynamics features. Thus, the material produced at the most ideal conditions has exhibited the best orthorhombic crystal structure with the distortion degree of 6.419 x 10(-3), paring mechanism, and crystallinity quality due to the development of orthorhombicity and oxygen ordering degree. Namely, the addition of optimum manganese impurity has organized the Cu-O coordination and stabilized the crystal structure as much as possible. Numerically, the sample prepared with x = 0.07 Mn ions has displayed the largest crystallite size, c-axis length, residual resistivity ratio, onset, and offset critical temperatures of 10.977, 11.723 & Aring;, 73 nm, 98.320 K, and 100.504 K, respectively. Conversely, the same material has demonstrated the smallest oxygen ordering degree of 6.714, strain of 44.015 x 10(-3), and a- and b-axis lengths of 3.792 and 3.841 & Aring;. On the other hand, the oxygen-free annealing condition and excess manganese impurity have completely damaged the whole mechanism because of the phase transition from orthorhombic to tetragonal (structural O-T transition) crystal structure. To sum up, the oxygen and optimum manganese impurity have encouraged the YBa2Cu3O7-y superconductors to use in much more application fields.
