摘要:

The structural and electronic transport properties ofABO3-type compoundsLa2/3−xRxCa1/3MnO3(R=Pr, Nd, Sm, Eu, Gd, Tb, Dy, Y, Er, and Tm) with a fixed tolerance factor oft=0.91137 is studied. Similar structure deformation, characterized by the nearly constant average Mn–O,A–O distances and Mn–O–Mn bond angles, is observed in different compounds. The metal–semiconductor transition shows a strongRdependent feature. The transition temperature decreases monotonously from 187 to 77.6 K asRvaries from Tm to Pr, with a corresponding maximum resistivity ranging from 2.34 to6.17×104 &OHgr; cm. Very different magnetoresistance effects are also observed in this series of compounds. By assuming the presence of inhomogeneous local lattice distortions due to ions with different sizes atAsites and their mismatch withBions, the lattice effects can be understood qualitatively. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118725

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report on the experimental study of electrical phenomena during explosive volcanic eruptions, which provides qualitative and quantitative insight into different fragmentation and eruption mechanisms of magmatic melt. The experiments show that air friction and surface enlargement by hydro- and/or aerodynamic magma fragmentation are only minor contributors to electrical charging of erupted particle clouds in comparison to thermo-hydraulic fracturing of magma by explosive magma/water interaction. This process has the potency to explain the frequently observed occurrence of lightning in eruption clouds of explosive volcanic events. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118726

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report on ac conductivity measurements carried out onpoly(o-methoxyaniline)films, of high molecular weight, at different doping levels. The results are typical of a disordered medium showing a constant conductivity at low frequencies and rising for higher values. In order to interpret the results, we use a model which takes into account that the sample is composed of an insulating disordered matrix sprinkled with conductive islands generated by doping, as indicated by energy dispersive x-ray microanalysis. It comes out of the fitting that the doping induces an increase in the carrier mobility, instead of increasing the density of carriers. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118688

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Ten picosecond resolution in stroboscopic scanning tunneling microscopy of repetitive phenomena has been demonstrated using tunnel junction mixing. This represents an order-of-magnitude improvement over earlier work. Through relative timing of the tunneling current signal as a function of tip position along a transmission line, additional confirmation of time-resolved signal generation at the tunnel junction has also been established. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118727

出版商:AIP    

年代:1997

数据来源: AIP