Electric field gradients at Os nuclei in the hexagonal transition metals Os and Re

The electric field gradient eq at Os nuclei in Os and Re single crystals has been determined by Mössbauer transmission experiments with the 137 keV resonance in ¹⁸⁶Os as -4.5 (3) × 10¹⁷ V/cm² and - 3.8 (3) × 10¹⁷ V/cm², respectively.     

The electric field gradient for Gd in gadolinium metal

We have examined the temperture dependence of the efg for GdGd above the Curie point. Using anI =10⁺ isomer in¹⁴⁴Gd as a probe nucleus, we find a weakT ^3/2 dependence withB=(1.5±0.4) 10^–5 K^–3/2. The absolute value of the efg at 332 K was measured by Coulomb excitation of 2⁺ states in^{156, 158, 160}Gd, yielding |eq(332 K)|=(3.43±0.14) 10¹⁷ V/cm². A possible small deviation from theT ^3/2 temperature dependence of the efg for ferromagnetic Gd is discussed.     

New levels observed in188Os from the decay of188Re

The level structure of¹⁸⁸Os has been investigated following the decay of 17h¹⁸⁸Re. The energies and relative intensities of 41 gamma rays were determined using large volume high resolution Ge(Li) detectors. The decay was observed to populate the 0⁺ states at 1478 and 1704 keV which were recently observed in (p, t) reaction studies. Additional states at 1414 and 1843 keV were also observed in the decay.     

The magnetic hyperfine field and the electric field gradient at181Ta impurities in Gd metal

The magnetic hyperfine fieldH _hf and the electric field gradientV _zz at¹⁸¹Ta impurties in metallic Gd were determined by time differential perturbed angular correlation measurements with the 133 keV K-conversion electron 482 keV -cascade of¹⁸¹Ta. The sources for these measurements were prepared by implantation of radioactive¹⁸¹Hf ions into Gd. The results are: |H _hf(TaGd; 77 K)|=285(14)kG, and |V _zz(TaGd; 330 K)|=5.32(15)·10¹⁷V/cm². The value ofH _hf fits well into the systematics for 5d impurities in Gd and indicates a positive core polarisation contribution, which is expected if the conduction electrons of Gd have to a large extent d-character. The electric field gradients of the 5d impurities in Gd are not consistent with a proportionality between the ionic and the electronic contribution.     

Temperature dependence of the electric field gradient at Ta nuclei in hafnium pyrovanadate

The electric field gradient EFG in hafnium pyrovanadate has been measured at Hf sites at different temperatures with the time-differential perturbed angular correlation method. The results obtained show the existence of a phase transition around 110°C.     

The electric field gradient at tantalum in yttrium

A uniform, axially symmetric electric field gradient at ¹⁸¹Ta in hcp Y of |eq| = (5.9 ± 0.3) × 10¹⁷V/cm² at 300 K, increasing by 11% upon cooling to 4.2 K, was found using the time differential perturbed angular correlation technique.     

The temperature dependence of the electric field gradient in ruthenium metal

The electric field gradient in ruthenium metal was studied between 15 K and 863 K. In contradiction to a recently proposed theory [1] the EFG was found to decrease with increasing temperature.     

Temperature variation of electric field gradient in scandium metal

Electric field gradient (EFG) in scandium metal has been evaluated at temperatures 11 K and 293 K using band wave functions determined in the temperature dependent model potentials. The results of net EFG obtained are −3.756×10¹³ esu/cm³ and −8.009×10¹³esu/cm³ at 11 K and 293 K respectively. The agreement with available experimental result is reasonably good.     

The sign of the electric field gradient at the nuclear site of Zn in Zn metal

By use of low temperature nuclear quadrupole orientation the quadrupole coupling constant of^69mZn in a Zn single crystal has been determined asv _Q=eQV _zz/h=–28(3) MHz.A positive sign forV _zzat the nuclear site of Zn in Zn is deduced. The half-life of^69mZn has been remeasured asT _1/2=13.756 (18)h.     

The electric field gradient at111Cd in vanadium oxides

The electric field gradient (efg) of¹¹¹Cd in polycrystalline V₂O₅ was studied using perturbed angular correlation (PAC) spectroscopy, with the¹¹¹In activity ion-implanted at 400 keV. Between the individual steps of an isochronal annealing program, a distinct efg (v _Q 1=88.1(3) MHz, ₁=0.62(2)) was recorded the contribution of which increased with annealing temperature up to 74% at 870 K. Corresponding X-ray analysis of inactive V₂O₅ samples, which underwent the same annealing treatment, proved that the sample always stayed as V₂O₅. Since V₂O₅ has only one equivalent cation site, it is concluded that this efg belongs to¹¹¹Cd at this site. Oxidation of a vanadium foil atT=675 and 800 K at =200 mbar also yielded this efg. From PAC measurements in VO₂, two well-defined efg's were found above and below the metal-semiconductor transition at 340 K, which are tentatively attributed to the monoclinic and the tetragonal phase.Supported by Deutsche Forschungsgemeinschaft and DAAD.On leave from the University of Durban-Westville, South Africa.     

Temperature dependence of the electric field gradient in Er metal

The method of perturbed angular distributions was used to measure the temperature dependence of the electric field gradient in Er single crystal for 98 KT156 K. The I=11^– isomer in Er¹⁵⁴) was used as a probe. ₀ increases monotonically for 98 KT259 K and then decreases. A possible cause for this effect may be short range interactions between the f electrons above the Neel point.Visitor from the Weizmann Institute, Rehovoth, Israel.     

The electric field gradient at the iron sites inβFeOOH

The temperature behaviour of the hyperfine parameters of iron in paramagnetic chlorine containingΒFeOOH is studied by⁵⁷Fe Mössbauer spectroscopy. Applying external magnetic fields, the sign and asymmetry parameterη of the electric field gradient (EFG) at the compound's two iron sites is determined. It is shown that an external field enhances the distributive character of the hyperfine parameters. Finally, heat treatment experiments allow new data on the nature of both iron coordination types to be presented.     

The electric field gradient at iodine impurities in zinc and cadmium

The electric quadrupole interaction at iodine implanted in zinc and cadmium single crystals is investigated, using the - perturbed angular correlation technique. The results show that the implanted¹²⁹Te and¹³²Te isotopes occupy two well-defined sites, identified by the electric field gradient parameters. One fraction of the impurities is substitutionally implanted, witheq _zz=–1.49(9)10¹⁸ and –1.58(15)10¹⁸V/cm², in Zn and Cd respectively. The other fraction is identified as an impurity-divacancy configuration with |eq _zz |=3.81(8)10¹⁸V/cm²; =0.72(4) for Zn and |eq _zz |=3.55(11)10¹⁸V/cm²; =0.53(13) for Cd. The electronic enhancement in the electric fieldgradient at the substitutional site equalsK=–0.66 and –0.56 respectively and follows the empirical trend ofK versus the impurity valence for the s-p elements in Zinc.     

The electric field gradient at Ta in HfB2

Using the time-differential perturbed-angular correlation technique, we have observed the nuclear electric quadrupole interaction at ¹⁸¹Ta (482 keV) as an impurity in the refractory compound HfB₂. The measured interaction frequency is ν_Q=730±5 MHz which corresponds to an electric field gradient of |eq|=(1·19±0·05)×10¹⁸ V/cm² at room temperature. By considering a second measurement at 4·2°K, which yields the same results as above, and by comparison with available results for Hf in HfB₂, we conclude that the d-electron density of states at the Fermi level is quite small in agreement with trends observed by others.     

Electric field gradients at probe nuclei in Ti and Re hosts

The electric field gradients (EFGs) at different probe nuclei in Ti and Re hosts are compared with the predictions of the conduction electron charge shift model. It is found that this model is successful in predicting the sign and, to a zero-order approximation, the magnitude of the EFG when the localized d-contributions are small and the universal correlation is obeyed.     

Temperature and pressure variation of the electric field gradient in arsenic metal

The variation of the NQR frequency ⁷⁵v_Q for arsenic metal has been measured at 195 and 295 K for pressures up to 2 kbar and at atmospheric pressure between 77 and 525 K. The data are compared with those for other metallic elements.     

Temperature dependence of the surface electric field gradient for indium metal

The electric field gradient at indium surfaces was studied with¹¹¹In PAC-probes as a function of temperature. The surface field gradient was determined to be temperature independent up to 100 K and the fraction of¹¹¹In surface sites shows a pronounced annealing behaviour between 150 K and 250 K.