Young Ki Kim

YBCO Film With Sm Addition Using Low-Fluorine TFA-MOD Approach

Yttrium barium copper oxide (YBCO) film was synthesized by a metal-organic deposition (MOD) process with fluorine-free Y and Cu precursor. The precursor solution with Sm addition enabled further improvement of the thickness and uniformity of precursor films. The calcination and firing processes were studied, and the precursor film was successfully converted to dense and uniform YBCO film on LaAlO3 (LAO) substrate after annealing in a wet Ar and O2 atmosphere. The measured critical current density (J c) value was about 80 A/cm-w (2.66 MA/cm2). The trifluoroacetate (TFA) reduced MOD process has the advantage that it has a larger tolerance for variations in the gas flow rate and path. The results on a Sm-YBCO film deposited on LAO with a CeO2 buffer layer fabricated by MOD are also presented.

The effect of water pressure on the texture and morphology of MOD-YBCO films on buffered metal substrates

The influence of water pressure in the metal?organic deposition (MOD) method on the texture and morphology of YBa2Cu3O7?X (YBCO) films grown on buffered metal substrates was investigated. The water pressure was varied from 4.2% to 10.0%, with the other process parameters, such as annealing temperature and oxygen pressure, kept constant. In this work, a YBCO precursor solution was prepared using a fluorine-free Y and Cu precursor solution with the addition of Sm. MOD-YBCO films were fabricated by continuous slot-die coating and calcination, followed by high temperature annealing. Using x-ray diffraction analysis, unreacted phase peaks, such as BaF2 peaks, were found in the samples made at a water pressure of 4.2%; however, the BaF2 peak intensity was much reduced as the water pressure was increased. The higher water pressure of about 10.0% in this experiment led to the poor crystallinity of MOD-YBCO films, possibly due to the fast reaction with the supplied water vapor. Meanwhile, the morphologies of the YBCO films were not much different from each other in the range of water pressure of this work. The maximum critical current density of 3.8?MA?cm?2 was obtained when the sample was made at the water pressure of 6.2% and the annealing temperature of 780??C.

A Bilateral Compliance Control for Time Delayed Systems

When the bilateral control system has a time delay between the slave system and the control system, the compliance control performance is likely to be deteriorated. This paper proposed a bilateral compliance control scheme and a controller design method for the bilateral control systems with a time delay. The slave controller has a modified type of Smith predictor for the time delay in each input and output stage of an open loop unstable plant. The compliance controller is implemented by a first order low pass filter and it modifies the position of the master to the reference position. The simulation results show that the excellence of the proposed scheme