Srinivas Sathiraju

Studies on Ba/sub 2/YNbO/sub 6/ buffer layers for subsequent YBa/sub 2/Cu/sub 3/O/sub 7-x/ film growth

In this paper, we are reporting a dielectric oxide buffer Ba/sub 2/YNbO/sub 6/ (BYNO) and its performance on various substrates for a potential buffer layer for the growth of YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) coated conductors. Ba/sub 2/YNbO/sub 6/ is a moderate dielectric. Using pulsed laser deposition, epitaxial BYNO films were grown at 850/spl deg/C with an oxygen pressure of 200 mTorr on single crystal MgO (100) substrate and ion beam assisted sputter deposited MgO buffered hastelloy metal substrates. The surface morphology of the BYNO films reveals out growths even though the average surface roughness is only 2-8 nm. The texture of BYNO films is /spl sim/8/spl deg/ and thickness of these layers /spl sim/100 nm on metal substrates. Highly c-axis oriented YBCO films were deposited on BYNO buffered substrates. Critical transition temperatures (T/sub c0/) determined from electrical transport measurements vary between 88-89 K and corresponding critical current densities (J/sub c/) ranging from 0.5-1 MA/cm/sup 2/ at 77 K.

Nd-doped YBa/sub 2/Cu/sub 3/O/sub 7-x/ films deposited by pulsed laser ablation

Nd doped YBa/sub 2/Cu/sub 3/O/sub 7-x/ targets (Nd/sub x/Y/sub 1-x/Ba/sub 2/Cu/sub 3/O/sub 7-x/; x=0, 0.2, 0.4, 1) were prepared in-house and were used to deposit films by pulsed laser ablation in 300 mTorr of oxygen to study the Nd substitution effects on the film properties. Film composition was found to match very closely to the composition of the targets as determined from X-ray photoelectron spectroscopy. The critical transition temperature (T/sub c/) was found to be reduced as the Nd substitutions were increased in the films. Raman spectra taken from the films indicate that c-axis misalignment and some cation disorder may be present in the films with poor T/sub c/. Transport critical current density (J/sub c/) of 3/spl times/10/sup 6/ A/cm/sup 2/ was measured in Nd/sub 0.4/Y/sub 0.6/Ba/sub 2/Cu/sub 3/O/sub 7-x/ films.

Formation of the YBa2Cu2NbOy phase in thin films

Abstract : We report the systematic substitution of Nb at the Cu1 site of YBa2Cu2NbOy in thin films to form a new phase of YBa2Cu2NbO8. These films were deposited on SrTiO3(100) crystals using pulsed laser deposition and deposited at an optimal temperature of 850 degrees C. Films were characterized using x-ray diffraction (XRD), atomic force microscopy, x-ray photoelectron spectroscopy (XPS), micro-Raman spectroscopy, and transmission electron microscopy. XRD of these films indicate c-axis oriented YBa2Cu2NbOy formation. XPS and micro-Raman spectroscopy analysis suggests Cu exists in the +2 state.