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this temperature. Thus, deposition temperatures around 840 ℃ are kept during further op- timization of the deposition conditions. Consequently, the T$_{c}$ values resistively determined from samples fabricated under optimized deposition conditions ( T = 830 ℃ , f = 5 Hz) of up to 15.8 K are considerably closer to the optimum and typically sharp ΔT$_{c}$ < 0.3 K are 

