A.G. Bibiloni

• National University of La Plata

We present Perturbed Angular Correlation (PAC) results of the electric-nuclear quadrupole interaction at 181Ta located at the nonequivalent cation sites of cubic C-Sm2O3 and monoclinic B-Sm2O3 free of defects. The application of the empirical Cd/Ta correlation found in binary oxides allowed us to correlate the interactions with each site and to ide...

Time Differential Perturbed Angular Correlation (TDPAC) experiments using 111In as probe were performed in order to determine the nature of In-sites in In-ferrierite (In/FER), before and after the incorporation of Pt through the hyperfine interaction between the nuclear quadrupole moment of the probe's nucleus and the extranuclear electric field gr...

A new method for analysing Time-Differential Perturbed Angular Correlation spectra is presented and applied to study the hyperfine interaction of ¹⁰⁰ Rh in the high temperature modification of niobium pentoxide. The measured quadrupole interactions are assigned to about 80% of the radiactive probes replacing niobium atoms in the lattice and about 2...

For the first time a well defined correlation between local and lattice contributions of the electric field gradient in semiconductors and insulators is presented. The local component of the electric field gradient in binary oxides, originated in extraionic contributions, is extracted from all quadrupole coupling constants measured in Perturbed Ang...

The Perturbed-Angular-Correlation technique was used to study the impurity cationic-site population and electric-field gradients in scandium and samarium sesquioxides implanted with 181Hf → 181Ta. We found a departure of the tantalum (hafnium) relative occupancy of the crystallographic sites C and D in the bixbyite structure from the natural abunda...

Perturbed angular correlation (PAC) measurements were performed in pure cerium dioxide using 181Hf as the probe. The activity was introduced by ionic implantation on pure CeO2 pressed powder. The substitutional replacement of Ce by Hf and the removal of radiation damage due to the ion implantation were achieved through thermal treatments in air at...

We present, for the first time, clear experimental evidence of the influence of the electronic configuration of probe-atoms on the temperature dependence of the electric-field gradient (EFG) tensor at impurity sites. We measured the EFG at 111In→111Cd and 181Hf→ 181Ta impurity sites in a complete series of semiconducting and insulating compounds wi...

Internal oxidation of indium in a silver matrix is studied by time-differential perturbed angular correlations. The oxidizer treatments were performed in air at 1 atm. Our results are consistent with the formation of different In-O complexes.

This paper presents strong evidence for the influence of the density of oxide particles on the internal oxidation kinetics of silver based alloys. Measurements performed by Mbssbauer Spectroscopy, on 1 at% Sn in Ag alloys oxidized at temperatures between 523 and 823K, clearly indicate that the oxidation kinetics are described by a power law of the...

The ionic exchange of Hf donor impurities in substitutional cationic sites of the cubic (bixbyite) phase of the wide-gap semiconductor Tm2O3 was studied. The doping process was performed by ball-milling-assisted solid-state reaction of Tm2O3 and neutron-activated m-HfO2. 181Ta atoms, obtained by the β-decay of the 181Hf-isotope, were used as probes...

A highly efficient, reliable, and low-cost μ-μ TDPAC spectrometer, PACAr, optimized for 181Hf-implanted low-activity samples, is presented. A versatile EPROM-based routing/coincidence unit was developed and implemented to be use with the memory-card-based multichannel analyzer hosted in a personal computer. The excellent energy resolution and very...

The combination of hyperfine techniques and ab initio calculations has been shown to be a powerful tool to unravel structural and electronic characterizations of impurities in solids. A recent example has been the study of Cd-doped SnO, where ab initio calculations questioned previous TDPAC assignments of the electric-field gradient (EFG) in 111In-...

In this paper, the beginnings of the Laboratory of Nuclear Spectroscopy and Hyperfine Interactions (LENIH) at the Department of Physics of the National University of La Plata and the evolution of the principal ideas involved and the main goals achieved are reviewed. Special attention is devoted to the relationships between the LENIH members and the...

The time-differential γ–γ perturbed-angular-correlation (PAC) technique with ion-implanted 181Hf tracers has been applied to study the hyperfine interactions of 181Ta impurities in the cubic bixbyite structure of Ho2O3 and Eu2O3. The PAC experiments were performed in air in the temperature range 300–1373 K (in the case of Ho2O3) and 77–1273 K (in t...

We report an ab initio study of the temperature dependence of the electric-field gradient (EFG) tensor at Cd impurities replacing cations in Lu2O3. Calculations were performed with the Full-Potential Linearized-Augmented Plane Wave method that allows us to treat the electronic structure and the processes induced by the impurity in the host-lattice...

The time-differential perturbed-angular-correlation (TDPAC) technique was applied to the study of the internal electric-field gradient (EFG) in Eu- and Ho-sesquioxides in their cubic bixbyite phases. The results, as well as previous characterizations of the EFG at $^{181}$Ta sites in oxides with the bixbyite structure, were compared to those obtain...

An In(4 wt%)-impregnated H-ZSM5 catalyst was characterized under wet and dry conditions by time-differential perturbed angular correlation (PAC) and by temperature-programmed reduction (TPR). Different indium species were quantified, correlating their structure with the catalyst deactivation due to the presence of water during the NO selective cata...

The effect of reduction treatments in H2 at 500 °C in both wet and dry atmosphere on mono and bimetallic In−zeolite supported catalysts has been studied using the perturbed angular correlation technique. The relaxation in the observed hyperfine interaction has been associated with the formation of oxygen vacancies in the indium sesquioxide particle...

The time-differential-perturbed γ-γ angular-correlation technique (TDPAC) with ion-implanted 181Hf tracers has been applied to study the hyperfine interactions of 181Ta impurities in the cubic bixbyite structure of Er 2 O 3 and Gd 2 O 3 . The TDPAC experiments were performed in air in the temperature range 300-1073 K (in the case of Er 2 O...

Time Differential Perturbed Angular Correlation (TDPAC) experiments using 111In as probe were performed in order to determine the nature of In-sites in In-ferrierite (In/FER), before and after the incorporation of Pt through the hyperfine interaction between the nuclear quadrupole moment of the probe's nucleus and the extranuclear electric field gr...

Two indium-containing silicalite zeolites (In/H–ZSM5) catalysts prepared by wet impregnation and ionic exchange were characterized by the Perturbed Angular Correlation (PAC) technique using 111In as probe to determine the nature of the indium species. Some of these species take part in the catalytic reaction of the selective reduction (SCR) of NOx...

We report here first Perturbed Angular Correlation (PAC) results of the electric field gradient (EFG) characterisation at 111Cd impurities located at both non-equivalent cation sites of the bixbyite structure of Lutetium sesquioxide, between room temperature (RT) and 1273 K. The comparison with results coming from a systematic 111Cd PAC study in bi...

Thin Sn-O films were prepared by thermal evaporation of high-purity tin in a low-pressure oxygen atmosphere. The films were monitored by conversion electron Mossbauer spectroscopy (CEMS). Radioactive 111In+-ions were implanted into the films and perturbed angular correlation (PAC) measurements were carried out in air after different annealings up t...

Two series of room temperature X-ray and Mossbauer spectroscopy (MS) measurements were performed on powder SnO samples after 1 h annealing in air and Ar at temperatures between 473 and 1073 K in 100 K steps. Complementary measurements on one SnO sample treated in vacuum in this sequence were performed after the thermal treatment at 773 K. In the th...

Physics has made many contributions to health care and illness prevention. With the help of advanced technology european and american investigators surprise us every day with the results of their research. Contributions made by argentinian physicists to this field of knowledge are, however, much less known. The aim of the present article is to resc...

We present, for the first time, clear experimental evidence of the influence of the electronic configuration of probe-atoms on the temperature dependence of the electric-field gradient (EFG) tensor at impurity sites. We measured the EFG at 111In-->111Cd and 181Hf--> 181Ta impurity sites in a complete series of semiconducting and insulating compound...

We studied the hyperfine interactions of 181Ta in In2O3 by means of perturbed-angular-correlation (PAC) measurements. We prepared thin films of indium sesquioxide with different degrees of initial amorphism and implanted them with 181Hf. Chemically prepared indium-sesquioxide powder samples were also made starting from neutron-irradiated HfCl4, whi...

The dispersion of metal oxides on supports is a problem currently being investigated in supported catalysts. On the other hand, a nuclear spectroscopy technique, namely time differential perturbed angular correlation (TDPAC), has been used in extensive investigations on Mo-based catalysts. This technique, through the measurement of the local electr...

The TDPAC (time differential perturbed angular correlation) technique, already applied to the study of molybdenum oxide species supported on alumina, is used to investigate the same oxide on the novel support TiO2/Al2O3. 99Mo obtained by neutron irradiation of natural molybdenum in the samples is used as a TDPAC probe. Measurements in the range fro...

The electric-field gradient (EFG) at the probe-atom site in binary oxides has been theoretically estimated, assuming it is composed of two terms. The first term is local, due to deformation of the valence orbitals of the probe atom, and was calculated by methods of quantum chemistry. The second term is due to the rest of the lattice ions, and these...

The perturbed-angular-correlation (PAC) technique has been applied to the study of the internal electric-field gradients (EFG) in Yb, Y, and Dy sesquioxides. The 181Ta PAC probes were introduced in the oxide lattices by means of 181Hf implantation, which decays to the Ta impurity by beta emission. The tracer 181Ta was used and the results were comp...

We present a perturbed-angular-correlation measurement of the hyperfine interaction at 181Ta in indium sesquioxide, giving the hyperfine characterization of 181-->181Ta in substitutional cation sites of the lattice. Our results indicate that the probes produce a distortion of the oxygen next-neighbors arrangement.

Thermal evaporated thin Sn−O films subjected to annealing treatments in air in the range 473–1173 K and in Ar in the range 473–773 K followed by annealings in air up to 1373 K were studied by CEMS (Conversion Electron Mössbauer Spectroscopy). Complementary Mössbauer and X-ray measurements were also performed on SnO powder that underwent the same se...

In connection with a general study of the evolution of tin-oxygen thin films, we report here on the hyperfine interactions of181Ta substitutionally replacting tin in the isolated phases SnO and SnO2. For this purpose, pure SnO pressed powder and a thin SnO2 film were implanted with181Hf. In both cases, unique quadrupole frequencies were found after...

We present here a study, through perturbed angular correlation (PAC), of a 181implanted Sn-O thin film prepared by thermal evaporation of tin in a 10-3-Torr oxygen atmosphere. The film, as prepared, was characterized by conversion-electron Mössbauer spectroscopy (CEMS). These data revealed the two oxidation states, namely, 2+ and 4+, for 119Sn. The...

TDPAC measurements were carried out on111In-implanted α-Nb2O5 samples at room temperature, after isochronal annealings up to 1270 K in 200 mbar oxygen and up to 1070 K in 10−5 mbar, respectively. The observed hyperfine interactions were compared to point charge model calculations which predict 15 and 2 equivalent cation sites in α-Nb2O5 and NbO2. T...

Perturbed angular correlation studies of molybdenum trioxide powder are carried out in the presence of lattice defects at room and higher temperatures. The activity, 99Mo, is introduced by neutron irradiation of natural MoO3. The defects, namely oxygen vacancies, are produced by the correspondent radiation damage and by reduction in ammonium atmosp...

The time-differential perturbed angular correlation technique has been applied using 111In probes, which decay through electron capture to 111Cd, to study the hyperfine interaction in cubic cadmium oxide, in the temperature range RT–740 °C (RT denotes room temperature). The main fraction of probes are located in perfect-lattice sites, with null ele...

The time-differential perturbed angular-correlation technique is applied to study stoichiometric and reduced molybdenum trioxides. Hyperfine characterization of 111Cd-probes substitutionally replacing Mo in the perfect crystalline lattice is presented. The trapping of doubly ionized oxygen vacancies in the most weakly bond site of the cation next n...

Time-differential perturbed-angular-correlation measurements made using 111In probes, which decay through electron capture to 111Cd, have been performed on SnO2 films in order to check the existence of electron-capture aftereffects. Two different substrates were employed for the SnO2 films: an insulating quartz plate and a silver film. Measurements...

The time-differential perturbed-angular-correlation technique is applied to study the hyperfine interaction of 111In atoms in stannic oxide. Two different preparation procedures were employed to obtain high-purity samples. With both of them two static quadrupole interactions are observed, characterized at room temperature by the parameters ω1=31.1...

The time-differential perturbed-angular-correlation technique has been applied to study Cu2O and CuO compounds using 111In probes. The hyperfine interaction of 111Cd substitutionally replacing copper has been characterized in both oxides. The temperature dependence of the electric field gradient (EFG) has been studied in the region 17-1170 K for Cu...

We present here preliminary TDPAC results on the semiconductors SnO2 and Cu2O in the temperature range 17–1200K, using111Cd. We discuss the presence of a time-dependent interaction associated to EC aftereffects processes in terms of the specific character (acceptor/donnor) of the impurity.

We present a new analysis of a series of measurements of the static and time-dependent interactions in the angular correlation of gamma rays from 111Cd following electron capture in 111In, in InCl3, InCl2, InCl1.8, InCl1.5, and InCl compounds. The time-dependent hyperfine interaction arising from the electronic rearrangements which follow the nucle...

The electric field gradient at Zr sites has been measured by time-differential perturbed angular correlations in amorphous and crystalline Zr68Hf2Cu30 alloys. The results support a dense random packing of atoms and discard any kind of regular atomic arrangements in the amorphous alloy.

We present a series of time-differential perturbed angular correlation measurements of the time-dependent interaction associated with the aftereffects processes which follow the electron capture decay of the111In embedded in In2O3 precipitates in a silver matrix. The In2O3 precipitates were obtained by internal oxidation of indium-silver alloys. We...

The compound CdCl2 was investigated by TDPAC searching for aftereffects at111Cd probes. In opposition to previous results, we do not find such effects. This confirms that, as previously suggested, the probe must be a non-isovalent impurity in the compound, so that the atomic disturbances following electron-capture persist long enough to produce det...

We present a series of measurements of the static and time-dependent interactions in the angular correlation of 111In (electron capture to 111Cd) in pure and Sn-doped In2O3. Results on the static electric field gradient are consistent with mainly ionic bonds and confirm the s character of the conduction band. The temperature and free-electron-densi...

The hyperfine interactions at In and Sn sites of In2O3Sn (ITO) were measured through time-differential perturbed angular correlations and Mssbauer spectroscopy, respectively. Polycrystalline samples prepared by co-precipitation with nominal 0.025, 1 and 5 at.% Sn were studied. They all showed the cubic bixbyite structure characteristic of In2O3 aft...

The results show that it is possible, by controlling the oxide particle size and the average distance between them, to modify the internal oxidation kinetics, indicating that oxygen diffusion can be altered. There is indirect evidence that inhomogeneous elastic fields are responsible for the rapid access channels for diffusion when the oxide comple...

A Mssbauer study of internally formed oxides as a function of oxidation temperatures between 200 dCaSnO3 /RT\delta _{CaSnO_3 /RT} = 0.00 0.01 mm/s, dCaSnO3 /RT\delta _{CaSnO_3 /RT} = 0.29 0.02 mm/s and Q=0.32 0.03 mm/s, and could be in the form of one-Sn-atom oxide complexes in the silver matrix. From the measured isomer shifts in the range 400 t...

We present a description of the probe-impurity distant neighbours configuration for repulsive systems in a cubic lattice, using a continuous charge distribution around the probe nuclei. We propose a simple model for the charge distribution shape and its dependence with the impurity concentration. TDPAC measurements performed on111Cd probes in 1, 4,...

We present a series of measurements of a fluctuating perturbation in the angular correlation of $^{111}\mathrm{Cd}$ in ${\mathrm{In}}_{2}$${\mathrm{O}}_{3}$ powder samples. We analyze the temperature dependence of the associated hyperfine parameters and conclude that this perturbation arises from "aftereffects" following the electron capture of $^{...

The internal oxidation of AgIn alloys has been investigated by time-differential perturbed angular correlation technique on 111In probes. We studied the oxidation kinetics of dilute (a few ppm) AgIn alloys at 300°C under different annealing conditions and 1 at.% indium alloys at 300°C and 550°C. In some cases, the time dependence of the oxidation-f...

The first quantitative results on internal oxidation of impurities in a noble-metal host, using the time-differential perturbed angular-correlation technique, are reported here. The system studied was indium-silver, with a few ppm of indium. The existence of a well-defined oxidation front is found for this highly dilute alloy. The kinetics of oxida...

Through the time differential perturbed angular correlation investigation of the system In in Ag, the applicability of the technique to the study of the internal oxidation process is proved. An unusually high electric quadrupole interaction for this system is found. On leave from Departamento de Física, UNLP, Argentina.

The general problem of anomalous diffusion is discussed in connection with the way in which the TDPAC (time differential perturbed angular correlation) technique may help determine the relative fraction of substitutional or interstitial positions of the diffusing atoms. The TDPAC technique referred to the Ag-In system is outlined. The present measu...

The hyperfine interaction of140Ce in nickel has been investigated by the time-differential perturbed-angular-correlation technique (TDPAC). The probe was produced by isotope separator implantation of the fission product140Xe, the β- decay chain of which finally populates excited states of140Ce. Different spin rotation spectra were observed before a...

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 110C.

The quadrupole interaction frequency |v q| = |eQV zz /h|0 = 8.71 ± 0.11 MHz was measured for the 75 keV state of100Rh in a polycrystalline cadmium matrix by use of the γ-e− and γ-γ time differential perturbed angular correlation (TDPAC) techniques. The temperature dependence of the electric quadrupole coupling constant for100Rh in Cd is similar to...

The electric quadrupole coupling constants of the lowest excited 5/2– state in197Hg have been measured by the e–- TDPAC method for the hosts Ti and Sn at room temperature and for Zn and Cd at various temperatures. The observed temperature dependences are approximately the same as those known for other impurities in the same host lattices. They are...

The100Pd radioactivity was implanted into a pure Zn host with the help of an isotope separator. The temperature dependence of the quadrupole interaction was studied by time-differential measurements of the 84 keV?- 75 keVK-conversion angular correlation. We conclude that electrons contribute significantly to the electric field gradient at the Rh si...

It is shown that for the determination of the quadrupole splitting (ω0 = 28.5 ± 1.0 MHz) of the first excited 23.8 keV state of 119Sn in β-tin the e- -γ time-differential perturbed angular correlation technique is superior to the Mössbauer method.

The 197mHg radioactivity was implanted into pure-Fe, -Co, and -Ni hosts with the help of an isotope separator. These ferromagnetic hosts produce strong magnetic hyperfine interactions at the nuclear site of the Hg atoms. These hyperfine interactions were studied by time-differential measurements of the 165-keV L-conversion e--134-keV γ angular corr...

The influence of an internal magnetic field and an axially symmetric electric field gradient on differential angular correlations has been investigated previously. It is the purpose of this paper to extend such calculations to: a) the axially symmetric electric field axis not parallel to the magnetic axis; b) a non-axially symmetric electric field...