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Rietveld refinement of YBa{sub 2}Cu{sub 3-x}Ni{sub x}O{sub y} prepared by quenching and oxygen gettering

Description: We have refined the structures for YBa{sub 2}Cu{sub 2.94}Ni{sub 0.06}O{sub y} (2% Ni) and YBa{sub 2}Cu{sub 2.80}Ni{sub 0.20}O{sub y} (6.67% Ni) at y {approximately} 6.95 and y {approximately} 6.5 contents. Oxygen was reduced by two independent methods: quenching from 690{degrees}C and oxygen gettering at 450{degrees}C. Cu-0 bond lengths were calculated based on Rietveld structure refinements for the various samples; they indicate the likely occupancy of Ni in the plane (Cu2) site of the 123 superconductor.
Date: October 1, 1995
Creator: Rodriguez, M.; Eatough, M. & Licci, F.
Partner: UNT Libraries Government Documents Department

Oriented lead zirconate titanate thin films: Characterization of film crystallization

Description: Film processing temperature and time was varied to characterize the pyrochlore-to-perovskite crystallization of solution-derived PZT 20/80 thin films. 3000 {Angstrom} thick films were prepared by spin deposition using <100> single crystal MgO as substrate. By controlled rapid thermal processing, films at different stages in the perovskite crystallization process were prepared with the tetragonal PZT 20/80 phase being <100>/<001> oriented relative to the MgO surface. An activation energy for the conversion process of 326 kJ/mole was determined by use of an Arrhenius expression using rate constants found by application of the method of Avrami. Activation energy for formation of the PZT 20/80 perovskite phase of the solution-derived films compared favorably with that calculated from data by Kwok and Desu for sputter-deposited 3500 {Angstrom} thick PZT 55/45 films. Similarity in activation energies indicates that the energetics of the conversion process are not strongly dependent on the method used for film deposition.
Date: November 1, 1993
Creator: Voigt, J. A.; Tuttle, B. A.; Headley, T. J.; Eatough, M. O.; Lamppa, D. L. & Goodnow, D.
Partner: UNT Libraries Government Documents Department

Relationships between ferroelectric 90{degree} domain formation and electrical properties of chemically prepared Pb(Zr,Ti)O{sub 3} thin films

Description: For PZT films deposited on Pt coated substrates, remanent polarization is a monotonic function of thermal expansion of the substrate, a result of 90{degree} domain formation occurring as the film is cooled through the transformation temperature. PZT film stress in the vicinity of the Curie point controls 90{degree} domain assemblages within the film. PZT films under tension at the transformation temperature area-domain oriented; whereas, films under compression at the transformation temperature are c-domain oriented. From XRD electrical switching of 90{degree} domains is severely limited. Thus, formation of these 90{degree} domains in vicinity of the Curie point is dominant in determination of PZT film dielectric properties. Chemically prepared PZT thin films with random crystallite orientation, but preferential a-domain orientation, have low remanent polarization (24 {mu}C/cm{sup 2}) and high dielectric constant (1000). Conversely, PZT films of similar crystalline orientation, but of preferential c-domain orientation, have large remanent polarizations (37 {mu}C/cm{sup 2}) and low dielectric constants (700). This is consistent with single-crystal properties of tetragonally distorted, simple perovksite ferroelectrics. Further, for our films that grain size - 90{degree} domain relationships appear similar to those in the bulk. The effect of grain size on 90{degree} domain formation and electrical properties are discussed.
Date: July 1, 1994
Creator: Tuttle, B. A.; Garino, T. J. Voigt, J. A.; Headley, T. J.; Dimos, D. & Eatough, M. O.
Partner: UNT Libraries Government Documents Department