Electric quadrupole interaction measurements in YBa2Cu3O x and related compounds

In this work we present Electric Quadrupole Interaction (EQI) measurements, made by Time Differential Perturbed Angular Correlation (TDPAC), on¹¹¹Cd in YBa₂Cu₃O _x and some related compounds. These studies were intended to determine the relationship between the EQI and the actual probe site. The probes were introduced into the materials as a diluted¹¹¹In-complex or via In(¹¹¹In)₂O₃. Our observations indicated that there is no need to suppose the presence of many probe sites in YBa₂Cu₃O _x to explain the experimental results.     

Muonium quadrupole interaction in ferroelectric substances KDP and KHCO3

The muonium quadrupole interaction is determined in KDP and KHCO₃. Using single crystal the field gradient tensor was obtained from muonium precession under the transverse field at room temperature. The muonium signal relaxes very fast at lower temperature, from this temperature dependence the dynamics of muonium was obtained. This revised version was published online in August 2006 with corrections to the Cover Date.     

Hyperfine interaction of 25Al in α-Al2O3 and its quadrupole moment

A brief review is presented of recent work with the Precision Penning Trap Mass Spectrometer, formerly at MIT, now at Florida State University. This includes atomic mass comparisons using single trapped ions; mass comparisons using two simultaneously trapped ions alternated between large and small cyclotron radii; and measurement of the dipole moment of a molecular ion using the polarizability-induced shift in cyclotron frequency.     

Skyrme's interaction and the role of the effective mass for the isoscalar giant quadrupole resonance

Using Skyrme's interactions various models for the isoscalar giant quadrupole resonance are compared and the equality of their results are shown. The dependence of the excitation energy on the parameters of the interaction is shown to originate essentially from the different single particle effective masses. The validity of the approaches is tested by comparison with RPA results. Uncertainties due to the discretization of the continuum are discussed.     

Electric quadrupole interactions in the CdTiO3 perovskite2

The TDPAC technique has been used to measure the EFG at the Cd site in the perovskite CdTiO₃. The experimental results obtained at 293 K are compared with ionic lattice sum calculations of the EFG. In addition measurements at 16 and 77 K show that no considerable modification of the EFG is observed at the Cd site at temperatures below and above the previously described phase transition at 50 K.     

Temperature dependence of the electric quadrupole interaction in PbHfO3

The temperature dependence of the Electric Field Gradient (EFG) in PbHfO₃ was studied in the temperature range 25–225°C by the Differential Perturbed Angular Correlation method. In the two anti-ferroelectric phases below 215°C, not too close to either transition temperature, the EFG decreases as the temperature increases toward T_c. Just above T_c an abrupt rise of EFG was observed indicating a critically behaving contribution to EFG. The results are interpreted in terms of a model based on the local static as well as time-dependent changes of the electric environment, at a lattice site. In accord with the predictions of this model the results exhibit qualitatively the P²_s temperature dependence of EFG far from T_c, where P_s is the sub-lattice polarization, while in close proximity to T_c the dominant contribution to EFG is due to the susceptibility X_q connected with the soft-mode fluctuations. The derived critical exponents are in agreement with previous experimental results on related compounds and with theoretical predictions. A hitherto unobserved additional component of V_zz was established, behaving critically at the antiferro-paraelectric transition at 215°C. This new component is interpreted to originate in local fluctuations connected with the central mode.     

Comment on the magnetic interaction in nuclei

The contributions of the relativistic electromagnetic corrections to the Coulomb energy shifts are examined carefully in this note. In previous calculations, some of the terms were neglected or their contributions were not evaluated properly. In this note, we consider the appropriate expressions of the electromagnetic interactions and discuss their contributions to Coulomb energy shifts.     

Nuclear quadrupole interaction in the low dimensional hf-trichalcogenides

We report on Time Differential Perturbed Angular Correlation measurements of the nuclear quadrupole interaction of¹⁸¹Hf(β⁻)¹⁸¹ and its temperature dependence in the low dimensional Hf- trichalcogenides HfS₃, HfSe₃ and HfTe₃. In HfS₃ the temperature dependence of the precession frequency is a slowly decreasing function with a negative curvature, the deviation from axial symmetry of the electric field gradient is practically temperature independent. In HfSe₃ the NQI shows a peculiar behaviour; between 10K and 300K the quadrupole frequency and the asymmetry parameter increase, between 300K and 400K the frequency decreases while the deviation from axial symmetry increases, indicating a structural phase transition near room temperature. In HfTe₃ the quadrupole frequency is practically temperature independent below 600K and increases linearely at higher temperatures, the asymmetry parameter increases steadily in the temperature range from 10K to 600K and then decreases. There is a strong correlation between the strength and the asymmetry of the electric field gradient so that the system depends on one control parameter only.     

Electric quadrupole interaction in hafnium sulphates

A coincidence system is developed which gives a time resolution of =0,8 ns for the 133–482 keV -ray cascade of¹⁸¹Hf. It is applied to the study of EQI in hafnium sulphate salts. In the case of Hf(SO₄)₂ the interaction strength of _Q = 157.8 ± 0.5 MHz is obtained, together with the assymetry parameter =0.531±0.005 and the field distribution parameter =0.003±0.001. The data are compared with point-charge model calculations.A similar set of EQI data is also derived for another unstable and unidentified hafnium sulphate structure.     

Zr-doped rutile TiO2: a nuclear quadrupole interaction study

Role of Zr atom on the quadrupole interaction of ¹⁸¹Ta in rutile TiO₂ has been investigated by time differential perturbed angular correlation (TDPAC) study. The quadrupole frequency remains same as that in the pure rutile TiO₂ but its distribution increases with the amount of Zr. This indicates a metal-metal interaction between probe atom and Zr-atom in the nearest neighbour.     

Temperature dependence of electric quadrupole interaction of181Ta in HfO2

High-resolution TDPAC determination of EQI of¹⁸¹Ta in HfO₂ is performed. Room temperature parameters of ω_Q = 111 (1) MHz and η=0.36(1) are obtained. The temperature dependence of ω_Q and η in the range 78–1100 K is established. An explanation of the observed phenomena in a dielectric lattice is discussed.     

Magnetic and quadrupole interaction studies at 111Cd in GdMn2 and TbMn2

The temperature dependence of the electric quadrupole interaction and the magnetic hyperfine field at ¹¹¹Cd probe sites in RMn₂ (R=Gd, Tb) has been studied by TDPAC method. In the paramagnetic region the quadrupole interaction frequency ν_Q in both compounds varies linearly with temperature. Below the Neel temperature, we find an abrupt decrease in the magnitude of ν_Q which is consistent with an expansion of the unit cell. As an important feature, the data near T_N shows the coexistence of localized and itinerant magnetism of Mn atoms. This revised version was published online in August 2006 with corrections to the Cover Date.     

Temperature dependence of the quadrupole interaction in potassium heptafluohafnate

The quadrupole interaction between the tantalum nucleus and its environment in potassium heptafluohafnate incorporating radioactive¹⁸¹Hf has been studied over the temperature range from 77 K to 318 K. A discontinuity in the field gradient tensor is observed at 250 K together with a more gradual alteration with midpoint temperature of approximately 210 K. Below 250 K, the data indicate two inequivalent sites for the tantalum nuclei. The values obtained for the electric field gradient tensor suggest that motional averaging may be significant in this compound.     

Study of the structure and electric quadrupole interaction in the intermetallic compound Hf2Fe

The electric quadrupole interactions at¹⁸¹Ta probe nuclei in a cubic Hf₂Fe lattice were studied by the TDPAC method. In addition, the crystalline structure study of the Hf₂Fe compound was performed. The results of the EQI measurement show the presence of two independent interactions, one at low frequency, characterized by ω _Q ⁽¹⁾ =33 Mrad/s and δ=30%, and the other at high frequency described by ω _Q ⁽²⁾ =207 ± 2 Mrad/s and δ=4%. Both interactions are found to be compatible with the crystalline structure established in this investigation. The large temperature dependence of the electric field gradient of the second interaction in the range from 78K to 1183K was determined. The change in the EFG follows the empiricalT ^3/2 -relation.