Paraconductivity and excess Hall effect of YBa sub 2 Cu sub 3 O sub x thin films

+ =96.6 K. These values are in good agreement with those from other published work. There was considerable scatter in the coherence length and phase relaxation time for films with different critical temperatures and oxygen contents. These results were process dependent but appear to be related to the 60 K phase transition in the T sub c -x phase diagram. This is reported for the first time. The excess Hall effect of a number of c-axis oriented YBa sub 2 Cu sub 3 O sub x thin films, with a range of T sub c values, was determined as a function of temperature and analysed in terms of excess Hall effect theories for the direct and indirect fluctuations of the order parameter. Results are presented for the electron-hole asymmetry parameter obtained from the fit to the excess Hall effect data. For all samples studied, beta is negative and has a small magnitude, as a result, the fluctuation Hall conductivity are dominated by the Maki-Thompson (MT) process rather than the Aslamazov-Lark in (Al) process. We generally observe that the Aslamazov-Larkin (AL) contribution to the excess Hall effect is negative close to T sub c and the Maki-Thompson (MT) contribution is positive and dominates at higher temperatures. The electron-hole asymmetry parameter for optimum doped films was small with typical value: beta=-0.067. This low value suggests that there might be a certain degree of symmetry between electrons and holes in YBa sub 2 Cu sub 3 O sub x. The impedance of the films was measured YBCO and a transition width DELTA T sub c =2-5 K. But some other films exhibited lower critical temperatures T sub c (onset)= 62-70 K and broader transitions DELTA T sub c = 10.4-13.6 K. These reductions in T sub c and the broadening of the transition are due to oxygen deficiency. This is shown by the c-axis lattice parameter calculations. All films grown using T2 and T3 exhibited lower critical temperatures and broader transitions for the same reason. A novel heater element was manufactured and a previous heater design was modified for adaptation of the new element and a new substrate heater which can operate reliably in air, vacuum and highly oxidizing atmospheres was built. It has been used routinely and successfully to provide substrate temperature of up to 750 deg C with 200 W power input. The paraconductivity of a number of c-axis-oriented YBa sub 2 Cu sub 3 O sub x thin films, with a range of c-axis lattice parameters and T sub c -values, was determined as a function of temperature and analyzed in terms of the paraconductivity due to direct and indirect fluctuations contributions. Results are presented for the c-axis coherence length and the phase-relaxation time at 100 K obtained from the fit to the paraconductivity data. The paraconductivity results for optimum doped films were: c-axis coherence length: xi sub c (0)=1.25 A; pair breaking parameter: delta=0.05; phase-relaxation time at 100 K: tau subphi=0.066 ps; and two-three dimensional crossover temperature: T sup and the results obtained compared with two-fluid theory. The films were purely inductive for temperatures below T sub c as expected. The measured variation of inductance near T sub c was in qualitative agreement with two-fluid theory applied to a thin film. The inductance results showed the occurrence of a peak at T sub c which is inversely proportional to the frequency of the applied AC signal as expected from the theory. For temperatures between 300 K to near T sub c the film reactance varied linearly with temperature. For temperatures near T sub c the film reactance varied non-linearly just prior to the superconducting transition. This non-linearity probably arises from fluctuations due to excess diamagnetism. Superconducting YBa sub 2 Cu sub 3 O sub x thin films were produced by in situ off-axis RF magnetron sputter deposition using a stoichiometric single target (T1). The effects of individual deposition parameters on the film properties are discussed. The transition temperatures for films deposited on MgO (100) are slightly lower than that for the SrTiO sub 3 and LaAlO sub 3 (100)-oriented substrates. The lower transition temperatures in the MgO substrates are most likely the result of the larger lattice mismatch with YBa sub 2 Cu sub 3 O sub x. All films grown on (100) substrates are c-axis oriented. The orientation of the sputtered YBCO films appears to depend only on the substrate orientation and not on the substrate material choice. Typical results for the c-axis lattice parameter c for various YBCO thin films sputtered onto SrTiO sub 3 , LaAIO sub 3 and MgO all (100)-oriented substrates with a range of T sub c values are presented. Three different targets were used in the course of this work: the first one (T1) was a 60 mm diameter, 3 mm thickness high density commercial YBCO disc; the second one (T2) was a 35 mm diameter, 4 mm thickness high density YBCO disc; and the third one (T3) was a 60 mm diameter, 3 mm thickness YBCO powder pressed then sintered on a copper plate substrate. The latter two were manufactured in house and are reported here for the first time. The best results were obtained using T1. The best films had T sub c (onset)= 89-93 K close to that of bul