M. C. Caracoche’s research while affiliated with National University of La Plata and other places

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Publications (57)


Stabilization and Hyperfine Characterization of Metastable Tetragonal ZrO2
  • Article

September 1990

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14 Reads

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10 Citations

Journal of Materials Research

M. C. Caracoche

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M. T. Dova

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A. R. López García

Hydrolyzed ZrCl4 and ZrO2 · nH2O have been used as starting compounds in a time-differential perturbed-angular correlation (TDPAC) investigation on the stabilization and thermal evolution of the metastable tetragonal form of ZrO2. This phase, of quadrupole parameters very similar to those reported for the high temperature tetragonal form, emerges at moderate temperatures previous to the monoclinic phase, when starting from hydrolyzed ZrCl4 and from ZrO2 · 2H2O treated previously at 673 K. Though in all cases zirconia appears initially as an amorphous compound characterized by unique hyperfine parameters, two different precursors have been observed to exist immediately previous to the occurrence of either the monoclinic or the metastable tetragonal crystal phases. Each of them exhibits a quadrupole frequency identical with and an asymmetry parameter higher than the ones characterizing the forthcoming corresponding crystal phases. A crystallization enthalpy of (33 ± 5) kJ/mol has been determined for the formation of the metastable tetragonal phase out of its precursor.


TDPAC characterization of Ni 2 HfF 8 ·12H 2 O and its decomposition products

June 1990

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14 Reads

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2 Citations

Hyperfine Interactions

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[...]

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H. Saitovitch

The hyperfine interaction in Ni2HfF812H2O has been determined between 77 K and 1100 K by means of the time-differential perturbed angular correlation technique. From 200 K on, the one-site phase existing at lower temperatures undergoes a gradual phase transition until, at room temperature, the populations of both phases attain a 2:1 ratio. While the quadrupole frequencies characterizing them exhibit aT 3/2 thermal dependence, their population ratio seems to obey a Boltzmann distribution. At 350 K, when the η-value of the high temperature phase electric field gradient approaches its maximum value, the starting compound decomposes to NiHfF66H2O. A kinetics study of the Ni2HfF812H2O recovery at room temperature seems to indicate that a tri-dimensional diffusion mechanism is responsible for the corresponding reaction process. The first decomposition product of NiHfF66H2O left to atmospheric pressure is found to be NiHfF64H2O at 368 K and, between 414 K and 590 K, the high temperature cubic phase of NiHfF6 and Hf2OF6 can be simultaneously observed. Finally, monoclinic HfO2 appears from 1020 K on, having been preceded by an interaction which can be though of as depicting a preliminary stage in hafnia formation.


Time-differential perturbed-angular-correlation study of phase transitions and molecular motions in K 3 (Hf,Zr) F 7

January 1990

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17 Reads

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10 Citations

Physical review. B, Condensed matter

Using time-differential perturbed-angular correlation, two thermal reversible phase transitions have been observed in both isostructural compounds K3HfF7 and K3ZrF7: the orthorhombic-to-tetragonal transition, occurring in K3HfF7 around 275 K, and the tetragonal-to-disordered cubic transition, which developed from room temperature (RT) over a wide thermal range. It has been inferred that ionic complexes MF73- in the tetragonal and cubic phases have the same structure, and that the cubic phase appears due to the onset of their reorientational motion. The detailed investigation performed on K3HfF7 has allowed the determination of a two-stage mechanism for this movement: a slow diffusional reorientation near RT and an isotropic fast relaxation at higher temperatures. Activation energies for different thermal ranges have been calculated.


Hyperfine Interaction of ZrO2-Tetragonal Phase

June 1988

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23 Reads

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31 Citations

Hyperfine Interactions

The quadrupole hyperfine interaction of the tetragonal phase of the zirconium oxide has been measured at 1523 K using the time-differential perturbed angular correlation technique. The electric field gradient at zirconium sites was determined to beV zz =(17.50.4)1017 Vcm−2 and axially symmetric.


Quadrupole hyperfine interaction and thermal stability of ZrF 4 .3H 2 O

June 1988

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5 Reads

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6 Citations

Hyperfine Interactions

The quadrupole hyperfine interaction of ZrF4.3H2O is reported. This compound is observed to dehydrate to ZrF4 at 325 K. Spectra taken on cooling were observed to be time dependent, and the rehydration process involved was investigated at 293, 298 and 302 K. Contrary to what had previously been determined in HfF4.3H2O, no intermediate compound was observed to participate in the reaction investigated, thus confirming structural differences already reported to exist between these isoformulae compounds.


Time-differential perturbed-angular-correlation study of K_ {2} HfF_ {6} polymorphism

August 1986

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19 Reads

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3 Citations

Physical review. B, Condensed matter

The thermal behavior of the hyperfine interaction in K2HfF6 was investigated by means of the time-differential perturbed-angular-correlation technique between 293 and 750 K. The quadrupole parameters associated with the monoclinic, orthorhombic, cubic, and trigonal phases have been determined. An activation energy Ea=86±16 kJ/mol could be calculated for the monoclinic-to-orthorhombic phase transition taking place between 384 and 466 K. An analogy with the hyperfine interaction of the isomorphous compound K2ZrF6 could be established.


Hyperfine interactions in Li 2 ZrF 6 and Li 2 HfF 6

August 1986

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9 Reads

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3 Citations

Hyperfine Interactions

The quadrupole hyperfine interaction in Li2ZrF6 and Li2HfF6 has been studied as a function of temperature. Both lattices are characterized by very similar low and symmetric electric field gradients at probe sites and no phase transitions were observed up to 770 K. On heating, between 700 and 830 K, the Li2ZrF6 undergoes chemical reactions which give rise to ZrO2 and then to Li3ZrF7 (high temperature α-phase) and Li2ZrO3. On cooling, below 750 K, the α→β transition in Li3 ZrF7 already reported is found to take place. An analogous behaviour is determined for Li2HfF6. Accordingly, the same decomposition steps and exstence of high and low temperature phases for Li3HfF7 can be inferred.


Anomalous thermal behaviour of β-(NH4)2HfF6

August 1986

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19 Reads

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3 Citations

Hyperfine Interactions

It has been determined that the thermally activated alpha-->beta transition occurring in (NH4)2HfF6 at about 370 K is not always reversible. The beta-phase hysteresis was investigated between 14 and 400 K. It was possible to explain previously published results without considering the Goldanskii-Karyagin effect.


The thermal behaviour of the quadrupole hyperfine interaction in (NH 4 ) 2 HfF 6

March 1986

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12 Reads

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7 Citations

Hyperfine Interactions

A TDPAC investigation has been accomplished on (NH4)2 HfF6 between 14 and 620 K. A phase transition was observed below 390 K. The low temperature phase is characterized by two non-equivalent sites for hafnium atoms in a 1∶1 ratio. The high temperature phase, on the other hand, is depicted by a unique quadrupole interaction. Above 400 K, the compound decomposes successively to NH4 HfF5, NH4 Hf2F9 and HfF4. An enthalpy of 764 kJ/mol could be determined for the (NH4)2 HfF6→NH4 HfF5+NH4F chemical reaction. The hyperfine interaction and thermal evolution of (NH4)2 HfF6 was found to be quite similar to that of (NH4)2 ZrF6.


TDPAC study on the thermal stability of zirconium tetrafluoride

March 1986

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6 Reads

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10 Citations

Hyperfine Interactions

The thermal evolution of the hyperfine interaction in α-ZrF4 is investigated between 293 K and 788 K. The first change, observed ay 534 K, is attributed to the appearance of the non-stoichiometric compound ZrO1.3F1.4. During the transformation, the relative fraction of the latter shows an Arrhenius behaviour with an activation energyE a=(22.6±5.5) kJ/mol. At approximately 700 K, ZrO1.3F1.4 gives rise to the monoclinic phase of ZrO2 and to β-ZrF4.


Citations (21)


... In effect, divalent and trivalent dopants introduce oxygen vacancies into the structure of HfO 2 which in turn, stabilize a high temperature phase of HfO 2 such as the cubic phase [5][6][7]. Some of the well-known dopants to stabilize the cubic phase of HfO 2 include CaO, CeO 2 , MgO and Y 2 O 3 [8]. In fact, the latter three crystallize into the fluorite cubic structure and when used as dopants, compel HfO 2 to stabilize also into its inherent fluorite cubic structure. ...

Reference:

Probing the electronic structure of HfO2 polymorphs with Electron Energy Loss Spectroscopy
Thermal evolution of CaO-doped HfO 2 films and powders
  • Citing Article
  • Full-text available
  • May 2009

Journal of Physics Conference Series

... Different dopants are generally added to the PSZ solution to stabilize the composite system. Sol-gel method is one of the most adopted methods to develop doped cubic zirconia nanocrystalline powders [5][6][7]. However, the high cost of production makes it commercially unsuitable. ...

Phase structure and thermal evolution in coatings and powders obtained by the sol-gel process: Part I. ZrO2−11.3 mol% Y2O3

Journal of Materials Research

... However, there is no report of the thermal decomposition of (NH 4 ) 3 ZrF 7 in air. The thermal behavior of (NH 4 ) 2 ZrF 6 and NH 4 Zr 2 F 9 in air was analyzed but a great difference is observed [22][23][24][25], as listed in Table 1. For example, Yamada et al. [22] and Rodrfguez et al. [23] indicated that NH 4 ZrF 9 lost NH 4 F to form ZrF 4 at 347°C and then converted to ZrO 2 at 400 and 487°C, respectively. ...

Time Differential Perturbed Angular Correlations Investigation of the (NH4)2ZrF6 Thermal Decomposition
  • Citing Article
  • February 1985

... Though the proton-and deuteron-induced reactions are most accessible to the majority of modern cyclotrons, there are alternative routes utilizing helium-4 ions, neutrons, or helium-3 nucleus with comparable cross sections [75][76][77]. Alpha beams afford a particularly attractive reaction route using monoisotopic manganese targets via 55 Mn(α,n) 58m Co. The measured excitation functions are shown below in Figure 12a. ...

Cross-section ratios for the isomeric pair 58mCo, 58Co produced by the (d, t) reaction
  • Citing Article
  • August 1965

Journal of Inorganic and Nuclear Chemistry

... Mocoroa studied isomeric ratios for the 133 Cs(d,2n) and 133 Cs(d,p) reactions in the 9.4-28.5 MeV energy range (Mocoroa et al., 1966). Natowitz measured 134m Cs/ 134g Cs isomeric and yield ratios in the 2.5-19.4 ...

Isomeric cross-section ratios for 134mCs, 134Cs and 133mBa, 133Ba formed in (d, p) and (d, 2n) reactions
  • Citing Article
  • January 1966

Journal of Inorganic and Nuclear Chemistry

... Details of the atomic arrangements of materials of technological uses were studied using short range methods as extended X-ray absorption fine structure (EXAFS) [22] and the perturbed angular correlations (PAC) [23,24] techniques. In particular, PAC technique has proved to be an efficient tool in the investigation of the milling effect of the monoclinic zirconia by showing the quadrupole interactions of special atomic arrays through which the monoclinic phase transforms into the tetragonal form [25]. ...

Phase transformations in monoclinic zirconia caused by milling and subsequent annealing
  • Citing Article
  • June 1994

Journal of the American Ceramic Society

... This observation is contrary to what has been reported for structural-charge-compensating vacancies that are inherent to doped stabilized zirconias. 12,13,18 The DTA/TGA and XRD results can be correlated to some extent with the evolution of the structure of the Zr environments that are revealed in detail by the PAC experiments. This correlation can be performed despite the dissimilar thermal treatments of the experiments that have been conducted in this work (10°C/min in DTA/TGA, at least 2 d at each temperature in in situ PAC measurements and after annealing at increasing temperatures in XRD). ...

Characterization of metastable tetragonal forms in ZrO{sub 2}-2.8 mol% Y{sub 2}O{sub 3} ceramics
  • Citing Article
  • April 1996

Journal of the American Ceramic Society

... It is interesting to note that for HfF 4 ·3H 2 O we observe about 2/3 of a discrete signal and about 1/3 of the anisotropy is lost rapidly [8]. A previous study [13] of this compound did not quote A eff 22 , but the spectra looked like ours and started with about −15% anisotropy which, compared to assumed A eff 22 = −23.0(1)% as in [4], would also give about 2/3 of the total anisotropy for the discrete component. ...

On the kinetics of chemical reactions in hafnium tetrafluorides using time differential-perturbed angular correlations
  • Citing Article
  • November 1983

Chemical Physics Letters

... The agreement of orientations of the principal systems and the values of angle from the relation of Casabella et al (1959) and the assumptions involved enable us to state that the first assumption is not so critical, as the molecule of NbCls possesses m and 2/m symmetries. In GaCI a dimer (Peterson and Bridenbaugh 1969; Satyanandam 1974 ) also, the results are in good agreement, although the true symmetry of the molecule is "i. In conclusion, the high value of ~7 and the low value of the NQR frequency in NbCI 5, which are the general characteristics of an ionic compound, and the agreement of the various calculated quantities from the point-charge model, with the experimental frequency and the predicted values of the other NQR parameters are consistent with the ionic nature of NbCI 5. ...

Nuclear quadrupole interactions in HfGeO4
  • Citing Article
  • May 1979

physica status solidi (a)

... It is probably the cubic phase stabilized by a small amount of impurities [6]. The characteristic hyperfine parameters for this phase have been reported for different aliovalent impurities and typical values are in the following ranges: ω Q = 90-100 Mrad/s, Á 1 = 0.75-1 and ı 1 = 5-15% [7][8][9]. This phase contains many oxygen vacancies, which produce a nonzero EFG at the probe site. ...

PAC Experiments for a Short Range Study of the Zr(10%Pr)O2 Solid Solution
  • Citing Article
  • July 2006

Hyperfine Interactions