SYNTHESIS AND CHARACTERIZATION OF BZO DOPED YBCO SUPERCONDUCTING FILMS WITH DIFFERENT TYPES OF PRECURSORS Murat BEKTAŞ Dr. Işıl BİRLİK Dr. Osman ÇULHA Doç. Dr. Mustafa TOPARLI Supervisor: Prof. Dr. Erdal ÇELİK DOKUZ EYLUL UNIVERSITY DEPARTMANT OF METALLURGICAL & MATERIALS ENGINEERING

Content AIM Of THE STUDY INTRODUCTION Superconductivity TFA-MOD Technique EXPERIMENTAL STUDIES Characterization of; YBCO Thin Film Production from Oxide Powder YBCO Thin Film Production from Acetate-based Presursor CONCLUSION

AIM OF THE STUDY TFA-MOD process using highly purified metal acetates as starting materials are rather expensive and thus it is desirable to find more economic route. Recently, several attempts to use oxide powders such as commercially available REBCO powder as starting materials have been reported which showed comparable J c (critical current density) for the YBCO films. In this study, two different types of BaZrO 3 doped YBa 2 Cu 3 O 7-δ (YBCO) superconducting thin films were prepared using commercially available YBCO powder and yttrium, barium and copper acetate on SrTiO 3 (STO) substrates by TFA-MOD method. The effect of precursor type on the film structure and superconducting properties were studied.

SUPERCONDUCTIVITY

Superconductivity was first discovered in 1911 by the Dutch physicist, Heike Kammerlingh Onnes. He discovered that the electical resistance goes to zero when mercury is cooled at about 4.2K.

T c against time illustrating the remarkable development following the discovery in 1986 of the high temperature superconductors.

During current flow, Lorentz force acts on vortices. Vortices move and generate electrical resistance Problem Pinning of vortices by non superconducting areas. Solution Power applications and high field applications Nuclear magnetic resonance (NMR) Superconducting magnetic energy storage (SMES) HTS conductors need to possess a high critical current density under high magnetic fields. Improving the in-field J c has been a topic of enormous technological importance!!! Importance of Flux Pinning for HTS Crystal defects act as natural pinning centers Fine precipitates of non-superconducting phases Dislocations Oxygen vacancies Small-angle grain boundaries Twin boundaries Dislocation Oxygen vacancies Vortex and Flux Pinning

Artificial Pinning Centers Types of defects such as Y 2 BaCuO 5 inclusions or the introduction of random BaMeO 3 (Me: Mn, Zr, Ir, Hf,...) nanoparticles. By building up a layered distribution of a second phase such as Y 2 BaCuO 5 or Y 2 O 3 using a multilayer deposition. Process induced modifications with excess yttrium, and decoration of substrate surfaces by nanoscaled particles. Types of Defects Point Defects Columnar Defects Planar Defects Defects need to be of similar size as the coherence length Coherence length in HTS are on the order of nanometers. So, nanoparticles are necessary. Compatibility of the nano-structure with superconductor is required.

YBCO (YBa 2 Cu x ) The compound YBa 2 Cu x, sometimes called YBCO or Y-123 compound, in its orthorhombic form is a superconductor below the transition temperature T c =92 K. YBCO has perovskite structure. The structure of YBa 2 Cu 3 O 7-x. YBa 2 Cu 3 O 6 Tetragonal YBa 2 Cu 3 O 7 Orthorhombic Copper chains Copper planes

TFA-MOD Schematic illustration of metal organic deposition using trifluoroacetates (TFA-MOD) for fabricating YBCO superconductors.

EXPERIMENTAL STUDIES

YBCO Thin Film Preparation Preparation of transparent solutionCoating (Spin Coating)Heat treatmentCharacterization

Schematic illustration of coating solution preparation by ytrium, barium and copper acetates. Y(OCOCH 3 ) 3 Ba(OCOCH 3 ) 2 Cu(OCOCH 3 ) 2 Dissolve in De-ionized water Add TFA (CH 3 COOH) Refining with evaporator Blue gel with impurities (H 2 O, CH 3 COOH) Coating solution with impurities (H 2 O, CH 3 COOH) Refining with evaporator Blue gel with solvent (CH 3 OH) 0.25 M coating solution Solvent (CH 3 OH) Solvent (CH 3 OH) Schematic illustration of coating solution preparation by YBCO powder. YBCO powder (Alfa Aesar %99,9) Dissolve in a mixture of propionic acid and TFA (8:1) Magnetic stirrer at 120°C Refine with evaporator Sticky, dark blue gel Adjust the final concentration to 0.25M with a mixture of propionic acid:acetone =1:3. Repeat Solution Preparation YBCO oxide powder + propionic acid Sol A Y, Ba and Cu acetates + methanol Sol B

Solution Preparation Precursors Name of Solution Doped-BZO concentration (mol%)Name of Films YBCO powder SolA00 F-A0 SolA16 F-A1 SolA212 F-A2 SolA318 F-A3 Yttrium, Barium and Copper acetates SolB00 F-B0 SolB16 F-B1 SolB212 F-B2 SolB318 F-B3 Adding Zr-penthanedionate results in: YBa 2-x Cu 3 O 7-δ + x(BaZrO 3 ) X= 0.006, 0.012, (corresponds 6, 12 and 18 mol% BaZrO 3 )

substrate Application of precursor solution on STO Rotating 6000rpm, 6000 rpm s -1 Evaporation of solvent with spin speed All process takes place in a dry nitrogen atmosphere at -25 ˚C dew point. Pyrolysis Crystallization Oxygenation Dry O 2 Wet O 2 Wet N ppm O 2 Dry O 2

Characterization of Solutions & YBCO Films Solution characterization; Viscosity and contact angle, DTA-TG ( Differential Thermal Analysis-Thermal Gravimetric Analysis), YBCO film characterization; XRD (X-Ray Diffractometer), SEM (Scanning Electron Microscopy) Physical properties ; Inductive T c measurement Inductive J c measurement

Solution Characterization Solution Name Viscosity m(Pa.s) Contact Angle ( o ) Sol A Sol A16.99 Sol A Sol A Sol B Sol B14.76 Sol B24.64 Sol B34.30 Viscosity and Contact Angle

DTA-TG Solution Characterization Sol A Sol B Below 200 o C: Evaporation and release of acetic acid and gel network water. 233 o C: Large loss in mass, combustion reaction due to the presence of acetate groups and loss of TFA, initial formation of BaF 2 and CuO phases. 275 °C: Formation of a yttrium intermediate as Y 2 O 3. Final combustion: Release of relatively large quantity of CO and CO 2.

Characterization of YBCO Films 2-Theta (Co K α radiation) Intensity (a.u.) F-A0 F-A1 F-A2 F-A3 (002) YBCO (004) YBCO (007) YBCO (003) YBCO (100) STO XRD F-A seriesF-B series (00l) reflections of the YBCO phase and (100) STO substrate indicate that the YBCO film has a strong c-axis texture. (004) and (007) orientations of YBCO are lower than expected for a textured structure. Major peaks (00l) YBCO and (h00) substrate. BZO (200) peak intensities increases slightly with increasing BZO concentration. (103) orientation of YBCO is observable, peak intensity decreases as the BZO concentration increases. F-B3 F-B2 F-B1 F-B0

Characterization of YBCO Films (a) (d) (c) (b) Surface morphologies of (a) F-A0, (b) F-A1, (c) F-A2 and (d) F-A3 films. (a) (b) (d) (c) Surface morphologies of (a) F-B0, (b) F-B1, (c) F-B2 and (d) F-B3 films. SEM F-A series F-B series

Characterization of YBCO Films Resistivity vs. temperature and Dependence of critical temperature T c and transition width ΔTc on the amount of BZO concentration graphs doped and undoped YBCO films prepared from Sol A and Sol B. Tc (Critical Temperature) F- A series F- B series

Characterization of YBCO Films Jc (Critical Current Density) Dependence of inductively measured critical current density J c on the amount of BZO concentration graph for YBCO films prepared from Sol A & Sol B

Conclusion YBCO superconducting thin films were successfully prepared from YBCO powder and yttrium, barium, copper acetate precursors via TFA-MOD method on STO single crystal substrates and BZO was incorporated into the structures of them as artificial pinning centers. According to SEM images, YBCO films prepared from SolA exhibit better surface morphology and all of them are generally formed by c-axis oriented grains. BZO doped YBCO films present a denser surface structure with decreasing porosity compared with the undoped YBCO films. On the other hand, 18 mol% BZO doped sample surface possesses bigger sized grains in comparison to the fine grains of 6 and 12 mol% BZO doped sample surfaces. As a result of J c measurements, 6 mol% BZO doped YBCO sample prepared from SolA (YBCO powder) has the highest J c value.

Thanks for your attention… ACKNOWLEDGEMENT TO; TUBITAK-109M054 Leibniz Enstitute For Solid State and Materials Research Dresden