Quadrupole Interaction Frequency Research Articles

Probing electronic environment in gamma irradiated sodium borosilicate glass and simulated waste glass: a perturbed angular correlation spectroscopy study

Time Differential Perturbed Angular Correlation (TDPAC) has been used to investigate the local structural changes (if any) in Sodium borosilicate (NBS) Glass and Simulated Waste Oxide loaded sodium borosilicate glass (SNBS) used for immobilization of high-level liquid waste at Trombay, Mumbai. The glasses were doped with 181Hf tracer as TDPAC probe and irradiated with varying dose (1–50 MGy) of gamma radiation using 60Co (average γ energy 1.25 MeV) source. Hyperfine interaction parameters (quadrupole interaction frequency, its distribution and asymmetry of electric field gradient) were obtained for irradiated NBS and SNBS glasses from fitting of TDPAC data using DPAC software. The data was compared with the corresponding unirradiated glasses. Results do not show any micro-crystallinity upon irradiation in both the NBS and SNBS glass even at the highest gamma dose of 50 MGy even though small changes were observed in quadrupole interaction frequency at doses beyond 30 MGy. This suggests that the sodium borosilicate glass used for immobilization of high-level waste at Trombay is stable towards gamma radiation at least up to a gamma dose of 50 MGy.

Search for ferromagnetism in Hf2Co7: An investigation by perturbed angular correlation (PAC) spectroscopy

Perturbed angular correlation (PAC) measurements in Hf2Co7 have been performed in the temperature range 77–973 K using the 181Hf probe to observe ferromagnetism in this intermetallic alloy. From present measurements, no magnetic interaction is observed at any temperature in the above temperature range. Only two quadrupole interaction frequencies have been found. At room temperature, values of quadrupole frequency and asymmetry parameter are found to be ωQ=15.7(4)Mrad/s, η=0, δ=0 for site 1 (∼71%) and ωQ=46(1)Mrad/s, η=0.74(5), δ=5(3)% for site 2 (∼29%). Present results contradict with the earlier reported results where a room temperature ferromagnetism was found with a Curie temperature of ∼400 K. X-ray diffraction measurement in Hf2Co7 has also been performed. From the measured XRD pattern, an almost pure phase of Hf2Co7 was observed.

TDPAC study of Fe-implanted titanium dioxide thin films

Fe-doping in TiO2 has been proven to improve several of its properties, including the photocatalytic activity. Time-differential perturbed angular correlation (TDPAC) as the applied spectroscopy method is particularly interesting because it can probe the electric and magnetic interactions on a local atomic scale. In this work the hyperfine interactions on 111Cd atoms substituting Ti atoms in TiO2 due to nearby Fe atoms also diluted within the TiO2 lattice were measured as a function of temperature. The results review two fractions with distinct quadrupole interaction parameters. One site, occupied by the 111Cd probes, presents the smaller quadrupole interaction frequency, namely υq1 = 45 MHz, and can be ascribed to sites that are more distant from the Fe substitutional site whereas the second site characterized with υq2 = 62 MHz is related to Cd probe atoms that are closer to the Fe defect. Additionally, the system has been characterized using electron dispersive spectroscopy.

Hyperfine interaction study of pressure induced phase transformations in Hafnia

Time Differential Perturbed Angular correlation (TDPAC) study of pressure dependent phase transition in HfO2 has been performed for the first time to reveal the change in local structure around Hf atom. The results show that the nuclear hyperfine interaction parameters namely, quadrupole interaction frequency and asymmetry parameter at atmospheric pressure are in agreement with literature while that at 45 GPa are significantly different from that at atmospheric pressure.

Ab-initio calculations of electric field gradient in Ru compounds and their implication on the nuclear quadrupole moments of $$^{99}\hbox {Ru}$$ 99 Ru and $$^{101}\hbox {Ru}$$ 101 Ru

The nuclear quadrupole moments, Q, for the ground and first excited states in \(^{99}\hbox {Ru}\) and ground state of \(^{101}\hbox {Ru}\) have been determined by comparing the experimentally observed quadrupole interaction frequencies \(\nu _Q\) with calculated electric field gradient (EFG) for a large number of Ru-based compounds. The ab-initio calculations of EFG were performed using the all-electron augmented plane wave \(+\) local orbital (APW \(+\) lo) method of the density functional theory (DFT). From the slope of the linear correlation between theoretically calculated EFGs and experimentally observed \(\nu _Q\), we obtain the quadrupole moment for the (\(5/2^+\)) ground state in \(^{99}\hbox {Ru}\) and \(^{101}\hbox {Ru}\) as 0.0734(17) b and 0.431(14) b respectively, showing excellent agreement with the values reported in literature. For \(3/2^+\), the quadrupole moment of the first excited state in \(^{99}\hbox {Ru}\) is obtained as \(+\)0.203(3) b, which is considerably lower than the commonly accepted literature value of \(+\)0.231(12) b. The results presented in this paper would be useful for the precise determination of quadrupole moment of high spin states in other Ru isotopes and is likely to stimulate further shell model calculations for an improved understanding of nuclear shape in these nuclei.

Identification of phase components in Zr-Ni and Hf-Ni intermetallic compounds; investigations by perturbed angular correlation spectroscopy and first principles calculations

Time-differential perturbed angular correlation (TDPAC) measurements have been carried out in stoichiometric ZrNi3 and HfNi3 intermetallic compounds using 181Ta probe in the temperature range 77–1073 K considering the immense technological applications of Zr-Ni and Hf-Ni intermetallic compounds. In ZrNi3, four components due to the production of Zr2Ni7, Zr8Ni21, Zr7Ni10 and ZrNi3 have been found at room temperature. The HfNi3 sample produces five electric quadrupole interaction frequencies at room temperature. The phase HfNi3 is strongly produced in stoichiometric sample of HfNi3 where two non-equivalent Hf sites are found to be present. Besides this phase, two other phases due to Hf2Ni7 and Hf8Ni21 have been found but, we do not observe any phase due to Hf7Ni10. X-ray diffraction, TEM/energy dispersive X-ray spectroscopy (EDX) and TEM-selected area electron diffraction (SAED) measurements were used to further characterize the investigated materials and it was found that these results agree with the TDPAC results. In order to confirm findings from TDPAC measurements, density functional theory (DFT) based calculations of electric field gradients (EFG) and asymmetry parameters at the sites of 181 Ta probe nucleus were performed. Our calculated results are found to be in excellent agreement with the experimental results.

Effects of Zr impurity on microscopic behavior of Hf metal

Hf metal with ∼ 3 wt% Zr impurity has been reinvestigated by perturbed angular correlation (PAC) spectroscopy using a LaBr3(Ce)–BaF2 detector set up to understand the microscopic behavior of this metal with temperature. From present measurements, five quadrupole interaction frequencies have been found at room temperature where both pure hcp fraction (∼33%) with 12 nearest neighbor Hf surrounding the probe 181Hf atom and the probe–impurity fraction (∼33%) corresponding to 11 nearest neighbor Hf plus one dissimilar Zr atom are clearly distinguished. At room temperature, the results for quadrupole frequency and asymmetry parameter are found to be ωQ=51.6(4)Mrad/s, η=0.20(4) for the impurity fraction and ωQ=46.8(2)Mrad/s, η=0 for the pure fraction with values of frequency distribution width δ=0 for both components. At 77K, only 1NN Zr impurity (∼93%) and pure hcp (∼7%) components have been found with a value of δ ∼ 10% for the impurity fraction. A drastic change in microstructural configuration of Hf metal is observed at 473K where the impurity fraction increases to ∼ 50% and the pure hcp fraction reduces to ∼ 15% with abrupt changes in quadrupole frequencies for both components. The pure fraction then increases with temperature and enhances to ∼50% at 973K. In the temperature range 473–973K, quadrupole frequencies for both components are found to decrease slowly with temperature. Using the Arrhenius relation, binding energy (B) for the probe–impurity pair and the entropy of formation are measured from temperature dependent fractions of probe–impurity and pure hcp in the temperature range 473–773K. The three other minor components found at different temperatures are attributed to crystalline defects.

Low temperature structural modification in Rb2ZrF6: Investigations by perturbed angular correlation spectroscopy

Temperature dependent perturbed angular correlation (PAC) measurements in crystalline compounds Rb2ZrF6 and Cs2HfF6 have been performed in the temperature range 298–753K. In Rb2ZrF6, four discrete quadrupole interaction frequencies have been observed at room temperature which correspond to four minor structural modifications. From previous measurements, on the other hand, two structural modifications of this compound were known. A displacive phase transition, probably, occurs at low temperature due to rotation of the ZrF62− octahedron and produces different structural modifications. From present measurements in Rb2ZrF6, two quadrupole interaction frequencies [ωQ=26.1(3)Mrad/s, η=0.55(2), δ=5(1)% and ωQ=148.7(3)Mrad/s, η=0.538(5), δ=1.2%] have been found at room temperature which were not found from previous studies. In Cs2HfF6, these new structural modifications have not been observed.

Effect of U substitution on the magnetism in the geometrically frustrated antiferromagnet YMn2 studied through TDPAC spectroscopy

Temperature dependence of hyperfine fields for 111Cd in (Y 1−xUx)Mn 2 alloys have been studied by perturbed angular correlation spectroscopy. Single phase alloys having C-15 cubic structure synthesized for x < 0.1 show contraction of the unit cell. The magnetic hyperfine field as well as the transition temperature show steep decline with increasing U content, while the quadrupole interaction frequency show the opposite behavior. As an important feature our results reveal that doping U in YMn 2 changes the nature of the magnetic phase transition from first to second order.

Perturbed Angular Correlation Study of the Static and Dynamic Aspects of Cadmium and Mercury Atoms Inside and Attached to a C60 Fullerene Cage

Abstract 30 keV 111mCd and 50 keV 199mHg beams from ISOLDE were used to implant on preformed targets of C60 with a thickness of 1 mg cm-2. Endofullerene compounds, viz. 111mCd@C60 and 199mHg@C60 formed during implantation were separated by filtration through micropore filter paper followed by solvent extraction. Dried samples of the endofullerene compounds were counted for the time differential perturbed angular correlation (TDPAC) measurement using the coincidence of the 151 - 245 keV cascade of 111mCd and the 374 - 158 keV cascade of 199mHg on a six LaBr3(Ce) detector system coupled with digital electronics. The results for 111mCd@C60 indicate a single static component (27%) and a fast relaxing component (73%), the latter implying that the cadmium atom moves rapidly inside the cage at room temperature. The quadrupole interaction frequency and asymmetry parameter of the cadmium atom occupying the static site in C60 are wQ=8.21(36) Mrad s-1 and η = 0.41(9), respectively. The fast relaxation constant is 0.0031(4) ns-1. Similarly, mercury atoms also exhibit a single static and a fast component. The static site has a quadrupole frequency wQ=283.0(12.4) Mrad s-1 and η =0 with a fraction of 30%. The fast relaxation constant is 0.045(8) ns-1 with a fraction of 70%, very similar to that of cadmium.

Unusual temperature dependence of quadrupole interaction at 111Cd in UMn2⋅

We report the temperature dependence of electric quadrupole interaction frequency of 111Cd probe in UMn2 measured by time differential perturbed angular correlation spectroscopy. The measurements carried out in the temperature range do not show any indication of magnetic ordering. Interestingly the quadropole frequency νQ decrease at low temperatures, quite in contrast with the usual phonon associated increase observed in metals and alloys. We believe, this unusual feature may be related to dynamic lattice distortion driven by spin fluctuation.

Hydrogen behavior in Pd0.75Ag0.25H x studied by PAC and PAS

Hydrogen behavior in Pd0.75Ag0.25Hx has been investigated by both perturbed angular correlation (PAC) and positron annihilation lifetime spectroscopy (PAS) techniques. The PAC measurements with the 111Ag/111Cd probe nuclei were conducted at room temperature as a function of the hydrogen concentration x up to 0.35. At x = 0 the probe nuclei experienced no quadrupole perturbation, while a distinct perturbation was observed after hydrogen charging. The quadrupole interaction frequency ω1 and its distribution width σ1 and relative fraction f1 all decrease with increasing hydrogen concentration, indicating size growth and concentration reduction of the hydrogen induced vacancy clusters. The measured frequency distribution width σ1 reveals hydrogen diffusion. The PAS measurements were also performed at room temperature. The obtained lifetimes and their variation with hydrogen concentration strongly support the PAC results. The experimental results can be explained by the appearance of the β-phase in the Pd0.75Ag0.25Hx samples. The α-phase is the major phase in the Pd0.75Ag0.25Hx samples. Charging of the hydrogen leads to the formation of the β-phase and the fraction of the β-phase increases with increasing hydrogen concentration. The present PAC and PAS results show that as the fraction of the β-phase increases, hydrogen induced vacancy clusters are formed and become larger and larger, while the cluster density reduces due to the combination of the vacancy clusters into larger size vacancy clusters.

Production of 62Zn radioactive nuclear beam and on-line PAC investigation of quadrupole interaction in nano-magnetic material Fe73.5Cu1Nb3Si13.5B9

An Isotope Separator On-Line (ISOL), dedicated to on-line perturbed angular correlation (PAC) and positron annihilation spectroscopy (PAS), has been constructed at CIAE based on the HI-13 tandem accelerator, and a 30 keV radioactive beam of 62Zn with intensity of 2 ×107/s produced by it. Using the 62Zn radioactive beam the investigation of the nano-crystalline soft magnetic Fe73.5Cu1Nb3Si13.5B9 materials has been fulfiled for the first time by the on-line time differential PAC technique. Two quadrupole interaction frequencies ω01 ( = 440 Mrad/s) and ω02 ( = 90 Mrad/s) were gained, indicating there are two implantation sites of 62Zn. The frequency ω02 shows a fluctuation of the crystal lattice constants and proves the characteristic distribution model of nano-crystalline grain boundary. The frequency ω01 demonstrates that the implanted 62Zn occupies the site of the ordered grain core. The fractions of ω01 and ω02 are f01 = 38 % and f02 = 62 %, respectively.

Determination of the crystal structures of In70-Ni30 and In70-Pd30 using perturbed angular correlation

According to phase diagrams based on x-ray measurements, In70-Pt30 has the cubic Sn7Ir3 crystal structure (D8f, cI40) but the alloys In70-Ni30 and In70-Pd30 have been variously reported to have either a cubic gamma-brass (D81-3, cI52) or the Sn7Ir3 structures. In this study, hyperfine interaction measurements are applied as an alternate method to identify phases. Perturbed angular correlation (PAC) measurements were made of characteristic nuclear quadrupole interactions of 111In/Cd probe atoms, and demonstrated a common, characteristic "signature" of the Sn7Ir3 structure in all three alloys. The Sn7Ir3 structure has two inequivalent Sn-sites with a 3:4 ratio of atoms and point symmetries indicate that the electric-field gradients at both sites should be axially symmetric. Measured perturbation functions for all three alloys exhibited two axially symmetric quadrupole interaction signals having the expected 3:4 ratio of amplitudes, as expected for the structure. Furthermore, ratios of the two quadrupole interaction frequencies in each alloy were characteristically large, with frequencies for probe atoms on In(3) sites roughly five times greater than on In(4) sites. Taken together, these observations confirm that all three phases have the Sn7Ir3 structure. Quadrupole interaction frequencies are also reported for isostructural alloys of gallium with Pt, Pd and Ni. Negligible inhomogeneous broadening was observed in measurements near room temperature in all six phases, indicating excellent atomic ordering at the stoichiometric 70:30 compositions.

The ab initio Calculation of Electric Field Gradient at the Site of P Impurity in α-Al3O2

An ab initio calculation of the electric-field gradient (EFG) at the site of a phosphorous impurity substituting an Al atom in α-Al2O3 is carried out using the WIEN2k code with the full-potential linearized augmented plane wave plus local orbital method (LAPW+lo) in the frame of density functional theory. The atomic lattice relaxations caused by the implanted impurities were calculated for two different charged states to well describe the electronic structure of the doped system. The EFG at the site of the phosphorous impurity in the charged supercell calculated with the exchange-correlation potential of the Wu-Cohen generalized gradient approximation (WC-GGA) is 0.573 × 1021 V/m2. Then, the nuclear quadrupole moment of the I = 3 state in 28P is deduced to be 137 mb from the quadrupole interaction frequency of 190 kHz measured recently by the β-NQR method.

Study of cation-localisation in apatite and orthophosphate structures using 181Hf/181Ta probe

Nuclear quadrupole interaction study using Time Differential Perturbed Angular Correlation technique has been carried out to identify the sites where hafnium can reside in hydroxyapatite in order to mimic the behavior of plutonium adsorption on hydroxyapatite. Hf(IV) has been found to occupy three sites with the quadrupole interaction frequency(ωQ) and its asymmetry(η): (i) ωQ = 136.7(5) Mrad/s, η = 0.54(1); (ii) ωQ = 300.1(9) Mrad/s, η = 0.35(2); (iii) ωQ = 124.6(5), η = 0.0(1). Narrow frequency distributions indicate the sites are well-defined. This study has been extended to barium orthophosphate to confirm our inference for the apatite structure.

Absence of room temperature ferromagnetism in transition metal doped ZnO nanocrystalline powders from PAC spectroscopy

Local structural and electronic environment around 111In probe atoms in transition metal doped Zn1 − xTxO (T=Mn, Co, V and Ni; x = 0.01, 0.02, 0.05) and Cu co-doped Zn1 − xCoxCu0.01O (x = 0.01–0.04) have been monitored on an atomic scale by Perturbed Angular Correlation (PAC) spectroscopy. Single phase nanocrystalline powders were synthesized at low annealing temperatures by sol-gel method. PAC measurements exhibited the well known quadrupole interaction frequency, $\upnu_{\rm Q} =$ 31 MHz, which have been attributed to the substitutional incorporation of 111In in ZnO matrix. PAC results did not reveal any evidence of magnetic ordering down to 77 K in pure and doped ZnO, which is consistent with the recent observation of paramagnetic behavior in transition metal doped ZnO with synchrotron based studies.

Evidence of palladium-defect pairing in intrinsic germanium

Time Differential Perturbed Angular Correlation measurements were performed in intrinsic germanium with the 100Pd/100Rh probe. The probe was produced via 92Zr(12C, 4n)100Pd and recoil-implanted into samples. Parallel measurements with the 111In/111Cd probe confirmed the quality of the germanium studied. The measurements with the 100Pd/100Rh probe show a modulation pattern in the ratio function with a quadrupole interaction frequency of 8.3(2) Mrad/s. The pattern depends on sample orientation and it is most pronounced after annealing at 500°C. After annealing at 700°C the effect vanishes due to strong damping of the ratio function. The pattern may be caused, similar to what has been observed for highly doped n-type silicon, by the pairing of the Pd-atom with a vacancy located in the direction. The disappearance of the pattern would indicate the dissociation of this pair. Pair formation and dissociation may be relevant to palladium-induced-crystallization processing of germanium.

Growth of germanium–carbide thin film on crystal substrate

The formation of germanium-carbide in crystalline germanium substrate is studied using the perturbed γ–γ angular correlation (PAC) method. The growth of Ge–C micro-crystalline system in the host matrix was observed after annealing the sample above 450°C in vacuum. The Ge–C complexes have been detected at high dose carbon implantation in germanium (≥1 × 1015cm −2). Information about the lattice locations of the carbon atoms in the host lattice can be obtained via the interaction between carbon atoms with unstable probe nucleus (111In). Several carbon related complexes have been detected in this investigations which can be characterized by unique quadrupole interaction frequencies. The parameters of the hyperfine interactions drawn from the time spectra provide additional information about the formation of Ge–C system in germanium.

PAC investigations of radiation damage annealing in 111In implanted ZnO

The structural and electronic environment about implanted radioactive 111In(→ 111Cd) probe atoms as a function of annealing temperature in a single crystal of ZnO(0 0 0 1) has been monitored on an atomic scale using perturbed angular correlation technique, a nuclear hyperfine method. This technique is based upon the hyperfine interaction of the nuclear electric quadrupole moment or magnetic moment of the probes, respectively, with the electric field gradient or magnetic hyperfine field arising from the extra-nuclear electronic charges and spin distributions. The probe atoms 111In were recoil-implanted at room temperature following heavy-ion nuclear reactions. The electric quadrupole interaction was measured at room temperature for as-implanted and annealed samples. The thermal annealing in ambient nitrogen up to 1000 °C showed a progressive reduction of disorder around the probe atom as evidenced via continual decrease in width of the distribution of quadrupole interaction frequencies. Present measurements suggested that annealing at 800 °C for 30 min in flowing nitrogen is enough to produce an optimum recovery of crystallinity. After annealing of radiation damage at 1000 °C we observed an axially symmetric electric field gradient which is characterized by the unique quadrupole interaction frequency of 30.6(3) MHz and a frequency distribution of width nearly zero. The observed electric field gradient was attributed to substitutional incorporation of probe atoms at cation-sites of ZnO. In contrast to annealing in ambient nitrogen at 1000 °C, air annealing of 111In implanted ZnO samples revealed change in local stoichiometry about probe atoms which is attributed to the internal oxidation of the indium probes. The measured electric field gradient and asymmetry parameter at cation-sites of ZnO have been compared with theoretical calculations using a simple point charge model.