() reaction studies of Dy and Hf

Angular distributions for the ¹⁶³Dy(t,p) and ¹⁷⁷Hf(t,p) reactions were measured using 17 MeV tritons from the McMaster University Tandem Van de Graaff accelerator. Reaction products were analyzed with a magnetic spectrograph and detected with photographic emulsions. Favored L=0 transitions confirmed assignments of the 5/2⁻[523] band in ¹⁶⁵Dy and 7/2⁻[514] band in ¹⁷⁹Hf. Additional L=0 transitions in each nuclide identified previously unknown 5/2⁻ levels in ¹⁶⁵Dy and 7/2⁻ ones in ¹⁷⁹Hf. Overall trends of L=0 strengths support the existence of subshell closures at neutron numbers 98 and 108. On the basis of a relatively strong L=2 transition, the K^π=11/2⁻ γ-vibration based on the 7/2⁻[514] state is identified at 1689 keV in ¹⁷⁹Hf, about 440 keV above its previously-assigned K^π=3/2⁻ partner.     

Texture control and its impact on the properties of SrBi2Ta2O9 thin films prepared by pulsed laser deposition

SrBi₂Ta₂O₉ (SBT) ferroelectric thin films with different preferred orientations were deposited by pulsed laser deposition (PLD). Several methods have been developed to control the preferred orientation of SBT thin films. For SBT films deposited directly on Pt/TiO₂/SiO₂/Si substrates and in situ crystallized at the deposition temperature, the substrate temperature has a significant impact on the orientation and the remnant polarization (Pr) of the films; a higher substrate temperature benefits the formation of (115) texture and larger grain size. The films deposited on Pt/TiO₂/SiO₂/Si substrates at 830 °C are (115)-oriented and exhibit 2Pr of 6 μC/cm². (115)- and (200)-predominant films can be formed by using a La_0.85Sr_0.15CoO₃ (LSCO) buffer layer or by annealing amorphous SBT films deposited on Pt/TiO₂/SiO₂/Si substrates at 450 °C using rapid thermal annealing (RTA). These films exhibit good electric properties; 2Pr of the films are up to 12 μC/cm² and 17 μC/cm², respectively. The much larger 2Pr of the films deposited on the LSCO buffer layer and of the films obtained by RTA than 2Pr of the films deposited on Pt/TiO₂/SiO₂/Si substrates at 830 °C is attributed to a stronger (200) texture. Received: 30 January 2001 / Accepted: 30 May 2001 / Published online: 25 July 2001     

Effects of electron-hole excitations in ion-surface collisions

We investigate effects related to electron-hole pair production and atomic level shift in atom scattering at surfaces by using a recently proposed exactly soluble model. We show that electron-hole pair production weakens Stückelberg oscillations and enhances loss of memory of the initial atomic charge state for narrow bands because of the diffusion of an electron or hole captured by the band. Wide band materials tend to display memory loss at lower velocities than do narrow band materials. Allowing the atomic energy level to shift above the Fermi energy tends to reduce memory loss.     

Geodesics of Spherical Dilaton Spacetimes

The properties of spherical dilaton black hole spacetimes are investigated through a study of their geodesics. The closed and non-closed orbits of test particles are analysed using the effective potential and phase-plane method. The stability and types of orbits are determined in terms of the energy and angular momentum of the test particles. The conditions of the existence of circular orbits for a spherical dilaton spacetime with an arbitrary dilaton coupling constant α are obtained. The properties of the orbits and in particular the position of the innermost stable circular orbit are compared to those of the Reissner-Nordstrom spacetime. The circumferential radius of innermost stable circular orbit and the corresponding angular momentum of the test particles increase for α≠ 0.     

Relaxor Behaviour and Ferroelectric Properties of （Li0.12Na0.88） （Nb0.9-xWa0.10Sbx）O3 Lead-Free Ceramics

New lead-free ceramics （Lio.12Na0.88） （Nbo.9-x Ta0.10 Sbx） 03 （0.01 × 0.06） are synthesized by solid-state reaction method. The dielectric, piezoelectric and ferroelectric properties of the ceramics are studied. The dielectric constant dependence with temperature and frequency of the ceramic specimen with x = 0.04 shows typical characteristics of relaxor ferroelectrics, and the Vogel-Fulcher relationship is fulfilled. The dielectric behaviour and its relation to the phase transition phenomena are discussed. The polarization hysteresis loops at room temperature are also measured.     

Impedance of an electric dipole located in a cylindrical cavity in a dissipative medium

The electromagnetic fields of an electric dipole located inside a cylindrical cavity or empty tunnel are formulated. The results are used to deduce an expression for the change of self-impedance due to the presence of the cavity or tunnel walls. A numerical evaluation of the resultant convergent integral and a summation of the angular harmonic series were performed. An important finding is that the input resistance of the dipole is approximately a constant for frequencies less than about 25 MHz for a typical tunnel radius of 2 m. Such results are shown to be in qualitative agreement with an earlier analysis of an electric dipole over a dissipative half-space.     

Restructuring of the surface region in SrTiO3

 The combination of x-ray diffraction analysis with surface sensitive techniques reveals a chemical inhomogeneity in the surface region of monocrystals of SrTiO₃ prepared under low and high partial pressure of oxygen at elevated temperatures. A solid state reaction leads to the formation of a multilayer-type structure. For oxidized crystals we observe AO-rich Ruddlesden-Popper phases at the surface and Magnelli phases of Ti in deeper layers of the surface region. The order of the layered structure is reversed for the reduced crystals with Ti-oxides of different oxidation levels at the surface and Ruddlesden-Popper phases in lower parts of the surface region. It is argued that this restructuring influences the electrical properties of SrTiO₃. Received: 12 July 1996/Accepted: 24 July 1996     

Electromagnetic wave propagation in a rectangular waveguide partially loaded with magnetized planar ferrite

The propagation of electromagnetic waves in a rectangular waveguide containing a slab of transversely magnetized planar ferrite is investigated. Numerical results indicate a large differential phase shift on application of small magnetic fields when the easy plane is oriented normal to the waveguide axis. This suggests the possibility of application in ‘Remanence Operation’ at high frequencies. Work partially supported by CSIR (India).     

Studies on the applicability of slit metal vessels in fast theta-pinch discharges

The applicability of slit metal vessels for fast magnetic plasma compression was experimentally investigated. The results were encouraging for small diameter vessels when the time needed for plasma compression was not significantly longer than the time for the development of the limiting shortcircuiting arcs across the slit gaps. Applicability of large diameter slit metal vessels was only achieved after superposition of magnetic bias fields. The limiting effects were identified and the condition for the necessary bias field is presented. It is shown further that satisfactory efficiencies of shockwave heating in slit metal vessels can be achieved only if apart from superposition of bias fields the width of the metal strips is reduced to the order of centimeter.     

Pyroelectric effects in magnetoelectric multilayer composites

Magnetoelectric and pyroelectric properties have been investigated in heterostructures of nickel zinc ferrite (NZFO)-lead zirconate titanate (PZT) and lanthanum calcium manganite (LCMO)-PZT. The magnetoelectric (ME) coupling, mediated by mechanical strain, is found to be two orders of magnitude stronger in NZFO-PZT than in LCMO-PZT. The pyroelectric effect is investigated by measuring the current through the sample as the temperature is varied at 0.1 K/s. For NZFO-PZT the pyroelectric coefficient is in the range 0.2-15 nC/cm² K, depending on the temperature. A much weaker current is observed in LCMO-PZT. A reversal in the current direction is detected when the thermal cycle is switched from heating to cooling. The pyroelectric coefficient is found to scale with the strength of ME interactions. A clear correlation between pyroelectric current and ME interactions is evident from the results.