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W e have produced epitaxial thin films of superconducting Y-Ba-CU-0 grown onto ( 110) and (100) oriented SrTiO, and MgO substrates by in situ RF sputter deposition. The impedance of the films has been measured and the results compared with two-fluid theory. The impedance of t h e films depended strongly on crystallographic orientalion. Between room temperature and the critical temperature T, the film reactance was inductive for well orientated (100) films and capacitive for (013) orientated films. The films were purely inductive for temperatures below T , , with a constant value equal to the film inductance aner flux exc!usi=n due to the Meissner e!lect.

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The c-axis lattice parameter of YBa2CusOx thin films deposited on SrmO3(iOO) and MgO(100) has been carefully measured and compared with the critical temperature and normalized resistance of a number of films. The films were prepared in situ using RF magnetron off-axis sputter deposition in the high-pressure regime. The Tc dependence on the c-axis expansion has previously been reported to be much weaker in thin films than in bulk material and considered not to be entirely due to 0 deficiency in the chain sites. However, the change in c i s less than 1% and conflicting results have previously been obtained. By comparing x-ray diffraction peak shifts relative to substrate peaks and also detailed analysis of (001) data we have obtained unambiguous evidence for the c-axis expansion. We find that the Tc versus c-axis expansion tends to follow bulk values for films on MgO(100) but for films sputtered onto Sr~O,(lOO) the Tc is fairly constant with c-axis expansion. In the latter films we also find a-axis-orientated grains, which account for higher resistance values and the shape of the RfT curves. The stability of Tc with c-axis expansion is considered to be partly due to the presence of the a-axis-orientated grains.

The sign of the Hall effect provides critical transport information both for the normal state and superconducting state of High Temperature Superconductors. For Hall effect measurements in thin films, a contact misalignment of only a few micrometers produces a significant longitudinal voltage in addition to the transverse Hall voltage. This misalignment voltage is usually cancelled by reversing the current and magnetic field. However problems may arise for normal state transport in anisotropic materials and vortex flow in the mixed state. In this paper the effect of misalignment of the Hall sidearm electrodes is considered in detail for the case of c‐axis oriented YBa2Cu3Ox thin films. The longitudinal voltage produced by the sidearm displacement is used with the Hall voltage to determine a localized Hall tangent. For the normal state this value is found to be in good agreement with the average Hall tangent for the whole film. Differences found between the localized and average Hall tangents for the transition region suggests a method for detecting the motion of single vortices.

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