H. Barfuß

Temperature dependence of the electric field gradient in CdSe and HfO2

The time differential perturbed angular correlation technique was applied to study the electric field gradient in the semiconductor CdSe and the insulator HfO2 at different temperatures. Whereas the semiconductor CdSe shows an increasing quadrupole coupling constant with increasing temperature, the insulator HfO2 exhibits no temperature dependence of the electric field gradient over the whole temperature range investigated.

Charge carrier governed temperature dependence of the electric field gradient for111Cd in tellurium

Using the TDPAC-method with the proble nucleus111Cd the electric quadrupole interaction (QI) in the trigonal semiconductor Te has been investigated in the temperature range 77 K≦T≦655 K. In contrast to most metals the quadrupole frequencyvQ increases with increasing temperature. This is a consequence of the fact that in metals the charge carrier density is temperature independent, whereas in semiconductors it strongly increases with temperature. A comparison between the temperature variation of the quadrupole coupling constantvQ and that of the charge carrier density leads to the conclusion that the QI in Te is governed by changes in the free electron density.

Electric quadrupole interaction of111Cd in the system Sb1−xMx (M=Ag,Cd,In,Sn), Sb2Te3, Bi2Te3 and In2Te3

We have performed TDPAC-measurements to investigate the static quadrupole interaction of111Cd in the classic semimetal Sb. The coupling constant depends on the concentration of small amounts of metal admixtures. The only exception is the system Sb1−xAgx. The temperature dependence of the efg in the narrow gap semiconductors Sb2Te3 and Bi2Te3 is similar to that one in Te. In contrast to these results the efg in the III–VI-semiconductor In2Te3 is temperature independent.

THE ELECTRIC QUADRUPOLE INTERACTION IN THE DI- AND TRIFLUORIDES OF THE TRANSITION METALS AND IN THE TRIFLUORIDES OF THE RARE EARTH ELEMENTS

Using the time differential perturbed angular distribution (TDPAD) the electric quadrupole interaction at the 19F site for the di- and trifluorides of the transition metals and the trifluorides of the rare earths was investigated. The measurements show a dependence of ~Q on the 3d-electrons in the first mentioned targets, whereas there is no dependence of ~Q on the 4f-electrons in the rare earth trifluerides.

The electric hyperfine interaction in some covalent bonded fluorine molecules

Abstract With the time differential perturbed angular distribution method (TDPAD) we have investigated the electric hyperfine interaction in the fluorine molecule, group IV tetrafluorides and group V trifluorides. The value of the efg for the F 2 -molecule is in good agreement with recent theoretical calculations. The results for the tetra- and trifluorides are discussed in the framework of the Townes and Dailey theory.

The temperature dependence of quadrupole interactions at cadmium impurities in Arsenic metal

We have performed time differential perturbed angular correlation measurements over a temperature range from 77 K to 763 K to investigate the static electric quadrupole interaction of111Cd in rhombohedral Arsenic metal. The observed quadrupole interaction frequency decreases with increasing temperature and is consistent with the well knownT3/2 relation, valid for metals.

The electric hyperfine interaction in the F2-Molecule and in some tri- and tetrafluorides

The quadrupole coupling constants in the fluorine molecule and in the group V trifluorides and the group IV tetrafluorides have been measured. In the case of fluorine the value of the resulting efg is in good agreement with recent theoretical calculations; the other results are discussed in the framework of the Townes and Dai1ey theory.

Electric field gradients in interhalogenic compounds

The time differential perturbed angular distribution me thod has been applied to investigate the electric field gradient in the interhalogenic compunds C1F, BrF3 and 1F5 Measurements at different temperatures revealed an unexpected behaviour of the modulation amplitude. Since for this behaviour no consistent explanation can be given yet, data are reported only.

Lattice defects in CaF2 and SrF2 after proton irradiation

The time differential perturbed angular distribution method (TDPAD) has been applied to investigate the electric field gradient produced by radiation induced defects in the cubic lattices of CaF2 and SrF2. In mixed crystals of the alkaline-earth difluorides CaF2 or SrF2 and the rare earth trifluorides PrF3, NdF3 or SmF3 the amplitudesA22exp in the TDPAD spectra strongly depend on the rare earth trifluoride concentration. From the fact that the observed amplitudes are well described by a simple statistical model the conclusion can be drawn that the defects produced in CaF2 and SrF2 after proton irradiation are F− interstitials.

The Electric Quadrupole Interaction in Noncubic Fluorides and of Radiation Induced Lattice Defects in Cubic Fluorides

The electric quadrupole interaction at the 19F site was investigated for several fluorides, especially in the transition metal and rare earth fluorides, using the TDPAD-method.