The systems Y3-xCexA15012, Ys-~CexA15-zGazO12, and Y3-x-zGdzCexA15012 were studied. It was found that the solid solubility of Ce 3 § in Y3A15012 varies with the atmosphere during firing. Only 2 mole per cent (m/o) of Ce ~ § can be dissolved in the yttrium aluminum garnet in air while almost 6% Ce 3 § enters the garnet lattice when fired at 1450~ under a hydrogen atmosphere. Complete solid solutions were observed in the systems Y3A15Ol~-Gd~A15012 and Y3A15012-Y3GasO12. The cathodoluminescence emission-peak position of the Ce 3 § ion in Y~A15012 host shifted to a longer wavelength while the latttice parameter of the solid solution expanded when Gd 3. ions were substituted for y3 § On the other hand, the emission-peak position shifted to a shorter wavelength when the garnet host contained Ga s § ions in the A13 § position. The lattice parameter of the solid solution increased with Ga concentration. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 169.230.243.252 Downloaded on 2015-03-24 to IP Vol. 120, No. 2 Ce s § ACTIVATED Y3A15Ol~ 281
The nucleation and movement of 180° domain walls in BaTiO3 crystals with salt-water electrodes has been observed directly by partial switching and repeated differential etching at applied fields from 2 to 450 kV/cm. Most of the polarization was found to be reversed by sidewise growth of new domains at these fields, as it is at lower fields, but the sidewise wall velocities are higher, as high as 105 cm/sec. The nuclei are originally circular cylinders, becoming squared up by sidewise growth whose lowest velocity is along the 100 crystal axis. The sidewise wall velocity and the nucleation rate each vary as E1.4, thereby causing the known E−1.4 variation of ts. The nucleation rate dependence is not understood, but the wall-velocity dependence agrees strikingly with a previously uncalculated prediction of the Miller-Weinreich theory. This indicates that, at both high and low applied fields, the apparent sidewise motion of 180° domain walls is due to the nucleation and forward growth of knife-shaped steps on the previously existing wall.
Phys. Rev. LettersThis Letter describes a new method of studying the properties of metals and other conductors by inducing large electric charges on them. The method involves depositing a thin film of the substance to be studied onto a ferroelectric crystal and measuring the film properties while the polarization of the substrate is directed toward and away from the film. The difference in film properties between the two substrate polarization states is the quantity of interest. This technique has produced changes of 2% in the resistance of 100A-thick gold films on BaTi0 3 , of 0.0013°K in the superconducting transition temperature of 160A-thick tin films on triglycine sulfate (TGS), and of as much as 0.7% in the reflectivity of 200A-thick silver and 150A-thick gold films.The ferroelectric polarization effect, like the similar field effect, 1 " 4 is described by the relation a = AD =A(E+4nP)(1) n n for the density a of charge on a capacitor plate as a function of the discontinuity AD n in the normal component of the electric displacement. E is the electric field and P is the polarization. Previous charge changing has been effected by varying the term E in (1) (field effect); the present method varies the term P (at negligible values of E) by reversing a ferroelectric capacitor. The first advantage of the ferroelectric method is that the charge densities are much higher since 47rP for common ferroelectrics (e.g., BaTiO s ) is 3xl0 8 V/cm compared to the breakdown strength of usual dielectrics (~10 6 V/cm). The reversal of polarization of BaTi0 3 changes the charge induced on its electrodes by 3xl0 14 electrons/cm 2 , or by 3xl0 20 electrons/cc if the electrode is 100 A thick. The second advantage of the ferroelectric method is that the effects are measured, after the polarization is reversed, with no electric field JL2, 69 (1964); A. L. Fetter, Phys. Rev. 138, A429 (1965). Reference 4, Sec. 29.applied to the dielectric. Since the quantities measured are ordinarily very small electric voltages or currents, this can be a great advantage.In order to test the hypothesis that the changes of film properties are due to charging, several experiments using the electrical resistivity as the property of interest were performed. Films were evaporated onto both sides of etched ferroelectric single crystals in a conventional high-vacuum plater at about 10~6 Torr. The conductivity of the film was measured by a fourelectrode method at constant current with the polarization of the ferroelectric directed toward or away from the film, using a potentiometer principle to detect the small voltage changes precisely. The amount of charge needed to reverse the polarization was always measured during reversal and was always found to equal the product of the electrode area on the crystal times twice the published polarization of the crystal (26 /iC/cm 2 for BaTi0 3 and 2.8 /iC/cm 2 for TGS). The resistance changes were believed to occur in the films rather than in the substrates because the ferroelectric crystals used have resistivities of ...
Scanning tunneling microscopy (STM) on a sputtered and annealed Pt25Ni7s(l 11) single crystal reveals a network of subsurface lattice mismatch dislocations caused by platinum enrichment due to preferential sputtering and recoil mixing. Atomically resolved STM topographs are compared with simulations of these dislocations using embedded atom potentials. This allows one to estimate the depth of the dislocations, and thus the thickness of Pt enrichment, which is three monolayers on the 500 eV Xe + sputtered and five monolayers on the Ar + sputtered surface, compatible with the depth of radiation damage. PACS numbers: 61.70.Jc, 61.80.Jh, 68.35.Dv, 68.35.Fx Lattice mismatch is a frequent phenomenon in the growth of thin films, where dislocations caused by the different lattice constants of substrate and film have been observed by transmission electron microscopy [1,2] and scanning tunneling microscopy (STM) [3,4]. In the present Letter we show for the first time a case of lattice mismatch dislocations which is due to enrichment of one alloy component by sputtering, and we are able to employ atomically resolved STM topographs for a full characterization of this dislocation system. Determination of dislocation density and comparison with simulations of individual dislocations yield both the composition and the thickness of the enriched layer. This offers a totally new method of surface analysis for such systems, based entirely on geometrical information.The STM analysis has been performed with a customized commercial instrument (Omicron micro-STM). Preparation and STM work were done in the same ultrahigh vacuum chamber with a base pressure below 1 x 10"" ,0 mbar. For sputtering a 500 eV Ar or Xe beam inclined 70° to the surface normal was used, yielding a current density of 0.7 juA/cm 2 . The sample was cleaned by repeated cycles of sputtering and annealing until no contaminations were detectable by low-energy ionscattering spectrometry (LEIS) below 770 K, and approximately 1% of a monolayer of sulfur at 1000 K. After annealing above 970 K the crystal showed large terraces separated by nearly straight and parallel monatomic steps and no dislocations.If the crystal is sputtered with a dose of some 10 16 ions cm" 2 and annealed thereafter at temperatures between 600 and 870 K, shallow ditches 0.2-0.5 A deep and 20-50 A wide appear on the surface. Some ditches run along or across monatomic steps without being influenced by the steps, which makes a pure surface phenomenon (restricted to the first layer) implausible. With higher ion dose, the number of these ditches grows, and they form a network of hexagons with triangles at their edges, as shown in Fig. 1. The contrast is mainly topographical, since /(z) measurements and variation of the tunneling voltage between ±0.5 mV and 10 V did not show any evidence of electronic (density of state) effects. STM images after oxygen adsorption did not show any differences between ditches and the flat regions, which would indicate different chemical composition [6].Atomic resolution top...
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