Chemical Approach to the Deposition of Textured CeO₂ Buffer Layers Based on Sol Gel Dip Coating

Abstract

Abstract. The widespread use of vacuum techniques for the development of coated conductors, in which buffer and superconducting (REBa 2 Cu 3 O 7- ) layers are deposited epitaxially on a substrate, is well established in the research environment. However, obtaining uninterrupted deposition at high speed, increasing flexibility in composition and in film thickness and attaining independence of geometric constraints are areas in which many vacuum techniques will need sustained development in order to answer industrial demands. This work describes the deposition of textured CeO 2 buffer layers based on sol gel dip coating under atmospheric environment and from aqueous precursor materials. Research has been performed towards the deposition of CeO 2 -buffer layers using the amorphous citrate method on sapphire substrates and Ni-W foils. Coating is performed using the dip-coating technique, which allows extension to a continuous system. The withdrawal speed and the thermal treatment have been optimised in order to obtain highly oriented (00l) layers exhibiting a smooth and crack-free morphology both on ceramic and metallic substrates. From the results it was concluded that sintering atmosphere and sintering temperature play a crucial role in the growth mechanism. This study describes the structural and morphological analysis of the thin layer with special attention to the difference between ceramic and metallic substrates. IntroductionThe development of high temperature superconductors, such as YBa 2 Cu 3 O x (YBCO), has resulted in many applications in the fields of electronics, microwave and conductor technologies. For this reason, ceramic superconductors have been deposited as thin films by various methods (e.g. pulsed laser deposition, sputtering, electron beam co-evaporation…) on many substrates, including SrTiO 3 , LaAlO 3 , MgO, Al 2 O 3 and flexible metallic substrates such as Ni and Ni alloys. These coated conductors are promising in the applications of transmission cables, motors, energy storage, magnets, fault current limiters, etc…. Excellent epitaxial relationships exist between YBCO and SrTiO 3 and LaAlO 3 1-3. These substrates however are expensive and are often only available in small sizes. For technical and industrially sized applications, the use of inexpensive and flexible metallic substrates becomes necessary. However, it has been shown that YBCO films deposited directly onto the latter substrates exhibit poor superconducting properties, because of chemical interactions and/or large structural mismatches 4. In order to grow a good quality YBCO thin film, it is necessary to use buffer layers such as CeO 2 5, Yttria-Stabilized Zirconia (YSZ) 6, MgO 7, SrTiO 3 8, BaZrO 3 9 etc. Amongst these, CeO 2 is usually considered as a high quality material, because of the good lattice match of the (100) plane with the YBCO (00l) plane, the comparable thermal expansion coefficient (11.6x10 -6 K -1 for CeO 2 , 12-13 x 10 -6 K -1 for YBCO), the oxidation

Influence of Morphology and Texture of CeO2 on YBa2Cu3O7 (YBCO) Growth and BaCeO3 Formation in Solution‐Derived Synthesis

“…[14,16,31] Ce(NO 3 ) 3 (Sigma-Aldrich, Ce III nitrate hexahydrate) was used in a 0.45 m concentration in a 1:3 ratio with citric acid (Carl Roth, citric acid monohydrate, Ͼ99.5 %). The pH was set at 6.1 using ammonia (Carl Roth, ammonia, 25 %).…”

CeO2 Buffer Layers for HTSC by an Aqueous Sol‐Gel Method – Chemistry and Microstructure

“…[19][20][21] Starting from the thermal process in Figure 4, we mainly focused on the sintering step (at approximately 1050°C) and its according ambient Ar-(5 %)H 2 atmosphere.…”

Chemical Solution Deposition—Basic Principles

“…In surface preparation, frequently, the hydrophilic/hydrophobic character of the surface is controlled to match the coating solution properties. For example, Van Driessche et al 19 reported on improving the wettability of Ni -4at%W tapes SUBSTRATE SURFACE PREPARATION by chemically cleaning them in a hot mixture of hydrogen peroxide and formic acid followed by ultrasonic cleaning in methanol. These tapes were degreased in trichloroethylene, acetone, and methanol prior to the chemical cleaning process for deposition of CeO 2 and La 2 Zr 2 O 7 buffer layers.…”