Oxide electronics

Abstract:

We present the submicron visualization of surface acoustic wave (SAW) fields within interdigital transducers (IDTs) obtained by a scanning acoustic force microscope. Utilizing the nonlinear force curve of the tip-to-surface interaction, a periodic deflection of the cantilever appears when the SAWs are excited intermittently. This deflection depends on the amplitude of the surface oscillation and was measured by lock-in technique. SAWs with operating frequencies above 600 MHz were detected. The influence of the mass loading on the local oscillation amplitude was studied for various layer thicknesses of the IDT electrodes. © 1997 American Institute of Physics.

Abstract:

The n = 3 and n = 5 members of the homologous series Srn-1,Cun+1O2n have been synthesised by a high-pressure, high-temperature technique and characterized by X-ray powder diffraction and electron microscopy as well as EDS microanalysis. The solubility range of Sr4-xNdxCu6O10 solid solution was found to be <0.1. The crystal structure of Sr4Cu6O10 was refined from neutron powder diffraction data.

Abstract:

The structural changes of stoichiometric LiNbO3 at temperatures up to 1470 K have been investigated by neutron powder diffraction. At Tc ≈ 1460 K, LiNbOi transforms from a paraelectric high-temperature (R3c) to a ferroelectric low temperature structure (R3c). The phase transition is of coupled order-disorder and displacive type. In the high-temperature phase, Li is highly disordered over two off-centre positions, whereas Nb takes a centrosymmetric position within O6 octahedra. An analysis of anisotropic displacement parameters shows that the probability density function of Li is extended along c, that of the oxygens is more or less perpendicular to the Nb-O bonds, and that of Nb is slightly extended in the a - b plane at high temperatures. An increase of the tilt angle of the NbO6 octahedra away from an h.c.p. arrangement towards a perovskite structure was observed. The octahedra become almost regular at high temperatures. Comparison with an earlier investigation of congruent lithium niobate shows a quite similar behaviour, however, all parameters of the latter are closer to those of the perovskite structure at same temperatures. Anomalies in the behaviour of the order parameters, a more complicated disorder and a high mobility of Li at high temperatures are explained by the competition of the order-disorder and displacive character of the phase transition. © 1997, Walter de Gruyter. All rights reserved.

Abstract:

Mn K-edge X-ray absorption near edge structure (XANES) measurements have been made to study the temperature-dependent lattice effects in the La0.75Ca0.25MnO3 system. The high-resolution XANES spectra recorded with high signal-to-noise ratio have allowed us to study the temperature dependence of the Jahn-Teller splitting indicated directly by the dipole forbidden pre-peaks corresponding to transition in Mn 3d states. The results show splitting of the eg state in its two orbitals (dx2-y2 and d3z2-r2). The energy splitting shows anomalous temperature dependence across the giant magnetoresistance transition temperature. © 1997 Plenum Publishing Corporation.

Abstract:

Neutron and synchrotron X-ray powder diffraction techniques have been used to refine the crystal and magnetic structures of the n = 2 Ruddlesden-Popper (RP) system Sr2LaMn2O7. The sample is shown to be biphasic, although both phases are of the RP type and have similar structural parameters. The majority phase (81%) adopts a collinear antiferromagnetic structure below ∼210 K whereas the minority phase is ferromagnetically ordered below ∼125 K. The ordered magnetic moments lie in the xy plane in both phases. The behavior observed is discussed in terms of the interplay between structural and electronic factors. Comparison with data obtained previously by other workers leads to the conclusion that our results have some general significance in the study of n = 2 RP systems.