K. Lagarec's research while affiliated with University of Ottawa and other places
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Publications (15)
We report the first direct observation of a high-moment (HM)/low-moment (LM) transition occurring in face centered cubic (FCC) Fe-Ni alloys. 57 Fe Mössbauer isomer shifts (ISs) give local electronic densities that exhibit a large discontinuity of , 0.4 el./ $ a_{0}^3 $ at the transition that spans the concentration range 65-75 apc (atomic percent)...
We report the first conclusive observation of a high-moment (HM)/low-moment (LM) transition occurring in face centered cubic Fe–Ni alloys. 57Fe Mössbauer isomer shifts give local electronic densities that exhibit a large discontinuity of ∼0.4 el./a03 at the transition that spans the concentration range ∼60–80 at% Fe, in agreement with ab initio pre...
[Rejected article. Had been submitted as a Scientific Correspondence to Nature, in August 1999.] -- All authors who have performed T = 0 K electronic structure calculations in an effort to elucidate lnvar behaviour, including the authors of a recent Letter to Nature and the author of the associated News and Views, have discussed their results in te...
A new model, developed by Lagarec and Rancourt, for distributions of hyperfine parameters in Mossbauer spectroscopy is briefly described and is applied to the spectrum of a synthetic taenite. The model extends from the Voigt-based fitting (VB F) method introduced by Rancourt and Ping (1991) and generalizes VBF to handle the more realistic cases of...
On the basis of Raman spectra and x-ray-diffraction patterns, we show
that both dense zirconium and hafnium dioxides adopt the same structural
phases, in similar pressure ranges. Furthermore both dioxides may be
quenched at room conditions from high pressure to give polycrystalline
solids which present optical transparency. From energy dispersive a...
We provide an experimental proof that the so-called `paramagnetic phase’ seen in Fe–Ni-bearing meteorites has a very different electronic structure from that of all other known Fe–Ni minerals, in support of the recent proposal that it is a low moment phase and a new meteoritic mineral. Mössbauer isomer shift measurements, corrected for second-order...
1998 International Union of Crystallography The cristallographic problem: XRDA (Desgreniers & Lagarec, 1994) provides the necessary tools to carry out the analysis of X-ray diffraction patterns in a simple and, in our opinion, very productive manner. Method of solution: XRDA3.1 is meant to accomplish the complete handling and analysis of X-ray diff...
This is the user manual for the Mossbauer spectral analysis software "Recoil", developed in the research group of Professor Denis G. Rancourt, Department of Physics, University of Ottawa, Ottawa, Canada.
We present a model of the total Probability Density Distribution (PDD) of static hyperfine parameters for 57Fe Mössbauer spectroscopy that permits the analysis of independent, partially or fully correlated arbitrary-shape partial distributions of center shift (δ) and quadrupole splitting (Δ) or center shift, quadrupole shift (ϵ) and hyperfine magne...
A single crystal of anatase TiO2 was studied by Raman spectroscopy at quasi-hydrostatic pressures up to 70 GPa. The crystallinity of the sample shortens the pressure range of the transition to an α-PbO2 structure to between 4.5 and 7 GPa. The resulting polycrystalline sample then transforms to a baddeleyite structure between 13 and 17 GPa. The Rama...
PRESSURE-induced amorphization of solids has been much studied since it was first observed in 19841. It was found recently2,3 that some materials can be amorphized reversibly under pressure, reverting back to the original crystalline structure and orientation when the pressure is decreased. It has been suggested4 that the presence of non-deformable...
XRDA, an analysis software for energy-dispersive X-ray diffraction data obtained from samples compressed in a diamond-anvil cell using synchrotron radiation, is described. The code takes advantage of the recent availability of inexpensive fast PC's and the widespread Windows graphical environment. The program offers an efficient way to analyze the...
Citations
... More accurately, one of the components exhibits δ values much greater than the observed in the respective component of those sam- ples belonging to the steady state. Such difference from around 0.44 mm/s for the early stages, down to 0.14 mm/s for the steady state, resembles a high spin (HS) to low spin (LS) transition, and it is almost two times larger than that observed in γ -FeNi alloys at the Invar composition [16,17]. As is well established, isomer shifts are very sensitive to interatomic distance, which strongly affects the 4s-electron charge density. ...
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... In other words, the slow transformation between crystalline fcc ↔ bcc arrangements serves as a phenomenological background of "quasi-bistability" which is observed in the form of T C am changes, traditionally known as "reversible" relaxation. As the ferromagnetic coupling is weaker in the fcc phase than in the bcc FeNi structure [85], the incomplete transformations are reflected in the shape of thermomagnetic curves. In order to demonstrate the origin of the "bi-stable" nature of the T c changes in Fe(Ni)-based glasses, the phenomenon is investigated by the hysteretic behavior of T c in crystalline Fe 90 Ni 10 alloys [86]. ...
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... The Raman spectrum of TNT 45 /Ti well coincides with that of the reference TiO 2 P25 (Evonik). Four Raman peaks at 144, 398, 518 and 640 cm − 1 are present, which can be assigned to E g (phononic mode ʋ6), B 1g (phononic mode ʋ4), A 1g (B 1g ) (phononic mode ʋ2) and E g (phononic mode ʋ3), respectively [51][52][53]. ...
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... The 57 Fe absorption spectrum was collected at 298 K in transmission mode over 24 h with the velocity scale at ± 4 mm/s, and was recorded in a multichannel analyzer (Takes 269) using 512 channels. After velocity calibration against a spectrum of highpurity α-iron foil (25-μm thick), raw data were folded to 256 channels and the experimental spectrum was fitted to Lorentzian line-shapes using Recoil 1.04 fitting program (Rancourt and Ping 1991;Lagarec and Rancourt 1999). The final fitting model consisted of two doublets, one for Fe 2+ and one for Fe 3+ . ...
... For each studied sample, about 100 mg of material was grinded and used as Mössbauer absorber. Spectral analysis was performed with the two-dimensional extended Voigt-based fitting method (x-VBF) developed by Lagarec and Rancourt (1997). This method provides the total Probability Density Distribution (PDD) of static hyperfine parameters allowing the analysis of independent, partially or fully correlated arbitraryshape partial distributions of isomer shift (δ), quadrupole splitting ( ) and, for magnetically ordered materials, hyperfine magnetic Zeeman splitting (z). ...
... Amorphization was found to be fully (dodecasil-3C) or partially (decadodecasil-3R) reversible only when guest molecules were present. [542] Hence, the guests acted as "organizing centers", making the lattice resilient to much higher pressures compared to guest-free clathrasils. [542] A surprisingly simple architecture of water and cations is hosted inside a mineral called bikitaite. ...
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... These values corresponded to the α-Fe(Ni, Co) phase (kamacite). In contrast, the Mössbauer spectrum of Santa Catharina IAB-ung measured in [69] was similar to the spectrum of Twin City (compare Figures 23b and 24b). Santa Catharina ataxite contained the highest known Ni content (35 wt.% Ni). ...
... The sc-XRDp procedure for the data acquisition from microcrystals and their analysis has previously been successfully employed (Laniel et al., 2019a(Laniel et al., ,b, 2020a and the details can research papers be found elsewhere (Bykova, 2015). Powder X-ray diffraction was also performed, and the pXRD data were integrated with Dioptas (Prescher & Prakapenka, 2015) and analyzed with the XRDA software (Desgreniers & Lagarec, 1994). A Le Bail unit-cell parameters refinement employing a pXRD pattern from NO + NO 3 À at 3.9 GPa was accomplished with the FullProf software (Rodríguez-Carvajal, 1993). ...
... First-principles simulations predict that SiO 2 adopts the cotunnite structure at pressures greater than ∼700 GPa, which corresponds to the conditions of a super-Earth's deep interior [10]. Numerous metal oxides such as TiO 2 , SnO 2 , PbO 2 , ZrO 2 , HfO 2 , CeO 2 , and TeO 2 also adopt the cotunnite structure under high pressure [11][12][13][14][15][16][17]. A theoretical study predicts that the postcotunnite phase of PbF 2 adopts the hexagonal Ni 2 In-type structure (space group: P6 3 /mmc, CN = 11), similar to that of CaF 2 , BaF 2 , and SrF 2 [6]. ...
... 56 The unit-cell volume and lattice parameters of C 4 N 2 were obtained through full profile fitting using the Le Bail 58 method, as implemented in GSAS with EXPGUI. [59][60] Single-crystal X-ray diffraction studies for C 4 N 2 were carried out at the Advanced Photon Source, sector 16-BMD. Monochromatic X-rays (λ = 0.30998 Å) with a beam size of (~15 × 30 µm 2 ) were focused on the sample and room-temperature diffraction was collected using a MAR image plate. ...
