K. Kundzins

STM observation of dislocation chains suitable for flux pinning in YBa2Cu3O7−x films

Abstract Systematic variations of the film-growth conditions during pulsed-laser deposition (PLD) with regard to substrate temperature, oxygen partial pressure and substrate quality, allow us to establish correlations between the as-grown defect structure and the current transport properties of c -axis oriented YBa 2 Cu 3 O 7− x films. By investigating the film surface with scanning electron microscopy (SEM) and scanning tunneling microscopy (STM) the nature and the density of various defects as well as the general film-growth mode were determined. SEM pictures show the overall surface roughness and the presence of other phases (outgrowths), while higher-resolution STM pictures reveal small-scale defects down to the nm range. Transport current measurements on patterned parts of the same films show differences in the magnitude of J c as well as in its field and angle dependence. Influences of the defect structure on intrinsic pinning, weak-link properties and special features in the angular dependence of J c are discussed. Dislocation chains extending over several layers along the c -axis within the terraces of growth spirals are of special interest with regard to flux pinning. The existence of these dislocation chains can be directly implied from the present data. A higher substrate roughness and a faster growth speed of the terraces along the ab plane seem to favor the appearance of the dislocation chains.

Antiferroelectric PbZrO3 thin films: structure, properties and irradiation effects

Abstract Irradiation effects on highly oriented antiferroelectric PbZrO 3 and ferroelectric Pb 0.92 La 0.08 (Zr 0.65 Ti 0.35 )O 3 thin films are investigated being exposed to neutron irradiation up to fluence 2*10 22 m −2 . The higher resistance of antiferroelectric PbZrO 3 thin films as compared to ferroelectric heterostructures to large fluences of neutron irradiation is recognized and discussed. Influence of two factors (structural and charge) was taken into account analysing irradiation effects on materials of different polarization states: ferroelectric PLZT (ceramics and thin films) and antiferroelectric PbZrO 3 films.

Critical currents in Tl-2212 and Tl-2223 thin films

Abstract The critical currents of Tl-2212 and Tl-2223 thin films grown by sputtering and post annealing on LaAlO3 have been measured as a function of the angle between the magnetic field and the c-axis at various temperatures and magnetic fields. The results show higher critical current densities in Tl-2223 than in Tl-2212 at low temperatures. Moreover, Jc is strongly field dependent in both films, suggesting a weak pinning structure. Scaling of Jcab(θ) with the c-axis component of the applied field is observed at all temperatures in both films, which confirms the 2D-nature of the flux lines. Furthermore, the thickness dependence of Jc was investigated for Tl-2212. The effect of fast neutron and Au ion irradiation has been investigated on both films. Large enhancements of flux pinning and Jc are observed, in particular at high temperatures, without significant changes of Tc. STM studies of the surface morphology and of the growth mechanism are also presented. Steps of unexpected height are observed on the surface of both films. The surface steps are shown to develop as a consequence of different stacking sequences. A striking feature in Tl-2223 is the occurrence of blocks with non-oriented terraces. These blocks are attributed to the growth of other phases in the films.

Structure and dielectric properties of Na0.5Bi0.5TiO3-CaTiO3 solid solutions

Despite wide studies of Na0.5Bi0.5TiO3, structure of this material and its connection with the observed physical properties still raise numerous questions due to mutually contradicting results obtained. Here, structure and dielectric properties of poled and unpoled Na0.5Bi0.5TiO3-CaTiO3 solid solutions are studied, projecting the obtained concentration dependence of structure and dielectric properties on pure Na0.5Bi0.5TiO3 as the end member of this material group. X-ray diffraction patterns for Na0.5Bi0.5TiO3-CaTiO3 solid solutions reveal dominating of an orthorhombic Pnma phase, even for the compositions approaching the end composition (Na0.5Bi0.5TiO3), whereas structure of pure Na0.5Bi0.5TiO3 can be considered, assuming coexistence of rhombohedral and orthorhombic phases. This allows one to avoid appearance of a large difference of rhombohedral distortions between the unpoled and poled Na0.5Bi0.5TiO3, if the rhombohedral distortion is calculated as for single R3c phase. Features of dielectric permittiv...

Optical Gradient of the Trapezium-Shaped NaNbO3 Thin Films Studied by Spectroscopic Ellipsometry

thin films were performed in the photon energy range of 1.24–4.96 eV.Effective values of the complex refractive index and thickness nonuniformity, roughness, and depth profile of the real part of therefractive index were evaluated. An increase of the refractive index with increasing of the sample thickness was observed anddiscussed.© 2008 The Electrochemical Society. DOI: 10.1149/1.2965786 All rights reserved.Manuscript submitted May 27, 2008; revised manuscript received July 7, 2008. Published August 19, 2008.

Irradiation effects in lead zirconate thin films

Lead zirconate PbZrO3 (PZ) and PbZr0.53Ti0.47O3 (PZT) sol-gel films with a thickness of up to 1.5 μm were deposited on TiO2/Pt/TiO2/SiO2/Si substrates by spin coating technique and heterostructures of the same composition as well as on Pb0.92La0.08 (Zr0.65Ti0.35)O3 (PLZT-8) (with a thickness of 0.4 μm) were pulse laser deposited (PLD) on Pt/Ti/SiO2/Si. Observation of a typical antiferroelectric (AFE) double hysteresis loop in obtained PZ heterostructures at room temperature was attributed to the superior dielectric strength in case of thin film materials. The thermal behavior of dielectric permittivity ε of PZ film reveals a maximum near 225°C on heating and 219°C on cooling. The higher resistance of antiferroelectric PZ thin films as compared to ferroelectric (e.g., PZT, PLZT-8) heterostructures to neutron irradiation (up to fluence 2x1022m-2)* is recognized and discussed.

Thermo-optical studies of NaNbO3 thin films

Thermo-optical studies of sodium niobate NaNbO3 (NN) thin films, deposited by the pulsed laser ablation technique on Si/SrRuO3 substrates, were performed by spectroscopic ellipsometry in the temperature range 300-550°C. Optical constants at the room temperature were measured in the spectral range 250-1000 nm. Substantial changes in the refractive index temperature behaviour (taken at λ = 300 nm) were found at temperatures 370, 445, 503, 520, and 532°C, where the first and the last temperatures are the phase transitions P → R and S → T1, respectively. Other temperatures (445, 503, and 520°C) are suggested as the points of some local structural changes in the NN film.

Structure and Properties of Pb(LuNb)O3-PbTiO3 Ceramics and Thin Films

The crystallographic features of binary system Pb(LuNb)O3-PbTiO3 (PLuNT) including the morphotropic phase boundary (MPB) region between tetragonal P4mm and pseudo-monoclinic M phases are reported and discussed with respect to dielectric, polarization and electromechanical characteristics. Non-isovalent doping of PLuNT in the Pb sublattice according to 2Pb2+ → 2La3+ + □A either in both components or maintaining the PbTiO3 unmodified: (i) shifts the MPB to the pseudo-monoclinic side of the phase diagram; (ii) diminishes the distortion of the unit cell (c/a −1 = 0.009 at 2 mol.% of La); (iii) reduces the coercive field to 15.8 kV/cm in the first case and below 10 kV/cm in the latter case. Simultaneously high values of maximum polarization Pm = 50.3 μC/cm2 and remnant polarization Pr ≅ 40.3 μC/cm2 maintain. The films of PLuNT with composition near the MPB formed by in situ pulsed laser deposition (PLD) onto LSCO/(100)MgO exhibited ferroelectric (FE) behaviour with Pm ≅ 29 μC/cm2, Pr ≅ 14 μC/cm2, Ec ≅ 70 kV/cm. The zero-field dielectric permittivity ϵ = 300–450 at room temperature, and demonstrates a relaxor type broad peak around 350°C. Au/PLuN/LSCO thin film heterostructures exhibit FE behaviour as well in contrast to typical AFE features of PLuN ceramic; a diffuse peak of ϵ was observed around 100°C. The lower degree of structural ordering is considered to be the main factor in the different behaviour of thin films and bulk ceramic material.

Neutron irradiation effects on sol-gel PZT thin films

Abstract Preferentially (100) oriented PbZr0.53Ti0.47O3 (PZT) sol-gel films spin cited on Si/TiO2/Pt substrates are studied. Si/TiO2/Pt/PZT/Au heterostructures exposed to high fluence neutron irradiation (2 × 1018 n/cm2, average energy >0.1 MeV; accompanied by gamma rays dose 7.1 × 109 rad, energy ∼ 1 MeV; Tirrad.<60°C) are examined. Recovering of properties is observed at post-irradiation isochronal annealing to elevated temperatures. Dielectric permittivity as well as tg6 decrease after neutron irradiation. The most pronounced radiation-induced polarization change exhibited by the shape of hysteresis loops is caused by an internal bias field.

The Effects of 3d Admixtures on Properties of Relaxor PLZT8/65/35 Ceramics

A study of the effects of the 3d dopants Mn, Fe, Co, Ni, and Cu on relaxor behavior and other properties of the ferroelectric PLZT8/65/35(La8) ceramic compound by X-ray diffraction, electron microscopy and other techniques is reported. The complex dielectric permittivity ϵ* = ϵ′-iϵ′′ is measured in the 20–400°C range of temperature at frequencies within the range of 102 – 106 Hz. Essential changes caused by the admixtures in the behavior of dielectric permittivity with frequency and temperature are observed along with changes in the XRD SEM patterns are observed. The mechanisms of the phenomena are discussed.