Atomic coordination and the distribution of electric field gradients in amorphous solids

Czjzek, G.; Fink, J.; Götz, F. W. Paul; Schmidt, Helmut; Coey, J. M. D.; Rebouillat, J.P.; Liénard, A.

doi:10.1103/physrevb.23.2513

Cited by 369 publications

(315 citation statements)

References 30 publications

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“…Concerning the quadrupolar splitting, , the values of the parameter q=< 2 >/<> 2 , are 1.5 for both alloys, in agreement with Pizarro et al for FeZr [8]. However, this value is higher than those corresponding to Czjzek distributions in the frame of random packing of hard spheres model [10]. The third contribution used in Zr alloy corresponds to a magnetic phase which could be Fe 2 Zr or Fe 3 Zr formed in an earlier stage of the milling process and which fraction decreases as milling progresses in the studied range.…”

Section: Journal Of Alloys and Compounds 536s1 (2012) 9-12supporting

confidence: 88%

Comparison of equivalent ball milling processes on Fe70Zr30 and Fe70Nb30

Blázquez¹,

Ipus²,

Conde³

et al. 2012

Journal of Alloys and Compounds

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Dynamical analysis of the movement of a single ball in a planetary ball mill yields a cubic law with the frequency of the mill for the power released during the process. This fact has been explored for two binary compositions: Fe 70 Zr 30 and Fe 70 Nb 30 using two different milling frequencies. The experimental techniques used, in general, support the predictions of the equivalent milling time model. However, some deviations appear which could be ascribed to differences in the temperature inside the vial during milling. Journal of Alloys and Compounds, 536S1 (2012) and approximately the same amount of sample ~0.2 g was extracted in argon atmosphere for each composition. This process was done six times and, in the following, they will be named as milling steps from 1 to 6 (4, 8, 12, 16, 20 and 24 h milling at 360 rpm and 8, 16, 24, 32, 40 and 48 h milling at 286 rpm, respectively). At the first milling step no powder could be recover for the Zr alloy but the starting material stuck on the ball and vial surfaces forming a shiny layer.Samples were analyzed using differential scanning calorimetry (DSC) in a PerkinElmer DSC7; X-ray diffraction (XRD) using Cu-K wavelength, scanning electron microscopy (SEM) in a Jeol JSM-6460 LV and Mössbauer spectrometry (MS) in a transmission geometry using a 57 Co(Rh) source. Values of the hyperfine parameters were obtained by fitting with NORMOS program [6]. The isomer shift, IS, was quoted relative to the Mössbauer spectrum of an -Fe foil at room temperature. 3Results and discussion Figure 1 shows the XRD patterns of several samples. The amorphous phase of the asmilled samples is evidenced by a broad amorphous halo. Figure 2 shows the DSC scans at 40 K/min of the different studied samples. All the features observed in the curves are irreversible as they disappear in a second scan, which was used as the corresponding baseline. A general agreement can be found for the two samples of each composition obtained at the same milling step. This is especially clear concerning the broad exothermic peak ascribed to the release of the energy stored during milling (structural and strain relaxation phenomena at low temperatures and grain growth and crystallization phenomena at high temperatures). For allJournal of Alloys and Compounds, 536S1 (2012) 9-12 http://dx.doi.org/10.1016/j.jallcom.2011.11.084 the samples, a deviation from the baseline occurs about 400 K which coincides with a slight decrease of the mass of the sample observed by thermomagnetic gravimetry, TG (both experiments, DSC and TG were performed under argon flow). Thus this feature should be ascribed to some gas desorption from the powders.However, concerning endothermic processes some differences arise between the two set of experiments performed at different frequencies and depending on the studied composition. For Nb alloy, there is an endothermic peak about 625 K which appears only for the samples milled at 360 rpm. Similar endothermic peaks were found in FeGeNb powders being ascribed to solving intermetallic(...

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Section: Journal Of Alloys and Compounds 536s1 (2012) 9-12supporting

confidence: 88%

Comparison of equivalent ball milling processes on Fe70Zr30 and Fe70Nb30

Blázquez¹,

Ipus²,

Conde³

et al. 2012

Journal of Alloys and Compounds

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“…NaCl 1M was used as reference. The 23 Na NMR spectra were simulated with the Dmfit software [13] using the Czjzek [14] distribution models.…”

Section: Glass Characterizationmentioning

confidence: 99%

“…Simulations have thus been carried out using the Czjzek model [14]. The NMR parameters deduced from the spectra simulation, such as chemical shift and quadrupolar constant (C Q ), are reported in Table 1.…”

Section: Single Fibre Tensile Test (Sftt)mentioning

confidence: 99%

Structure–properties relationships in fibre drawing of bioactive phosphate glasses

et al. 2017

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New bioactive phosphate glasses suitable for continuous fibre production are investigated in this work. The structure of both bulk and fibres from Na 2 O-CaO-MgO-P 2 O 5 glasses has been studied by means of Raman and 31 P and 23 Na Nuclear Magnetic Resonance spectroscopies, and the structural results have been correlated with the mechanical properties of the fibres and the dissolution rate of the bulk glasses. It has been observed that the mechanical properties of the phosphate glass fibres are influenced by the glass network connectivity, whilst the dissolution rates are governed by the Q i speciation of the PO 4 units. As seen in previous studies, molar volume seems to play an important role in the fragility behaviour of phosphate glasses. Here, a lower molar volume resulting from the increase in the oxygen packing density, hinders the cooperative flow of the PO 4 units throughout the glass network and, therefore, causes a reduction in the kinetic fragility.

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“…As mentioned earlier, model distributions reflect the underlying stochastic nature of bonding in a disordered material. There is significant evidence [52,53,54] to suggest that a more general electric field gradient model for disordered systems as probed by 27 Al NMR is given by the Czjzek model [19]. Future work will be devoted to the incorporation of models such as these into the approach outlined here.…”

Section: Gcc -O4 -O Mqmas Opt Mqmas Optc -Lm -Lgslcblas -Lgsl -Fopenmpmentioning

confidence: 98%

“…In the case of disordered chemical environments [14,15,16,17], calculations of powdered lineshapes for MQMAS becomes a formidable task. This is due to the fact that parameters relevant to simulation take on a distributed nature [18,19]. The focus of this paper is devoted to the optimized simulation of multiple quantum magic angle spinning spectra, in the presence of low to significant disorder.…”

Section: Introductionmentioning

confidence: 99%

Optimized multiple quantum MAS lineshape simulations in solid state NMR

Brouwer

Davis

Mueller

2009

Computer Physics Communications

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The majority of nuclei available for study in solid state Nuclear Magnetic Resonance have half-integer spin I > 1/2, with corresponding electric quadrupole moment. As such, they may couple with a surrounding electric field gradient. This effect introduces anisotropic line broadening to spectra, arising from distinct chemical species within polycrystalline solids. In Multiple Quantum Magic Angle Spinning (MQ-MAS) experiments, a second frequency dimension is created, devoid of quadrupolar anisotropy. As a result, the center of gravity of peaks in the high resolution dimension is a function of isotropic second order quadrupole and chemical shift alone. However, for complex materials, these parameters take on a stochastic nature due in turn to structural and chemical disorder. Lineshapes may still overlap in the isotropic dimension, complicating the task of assignment and interpretation. A distributed computational approach is presented here which permits simulation of the two-dimensional MQMAS spectrum, generated by random variates from model distributions of isotropic chemical and quadrupole shifts. Owing to the non-convex nature of the residual sum of squares (RSS) function between experimental and simulated spectra, simulated annealing is used to optimize the simulation parameters. In this manner, local chemical environments for disordered materials may be characterized, and via a re-sampling approach, error estimates for parameters produced.

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Atomic coordination and the distribution of electric field gradients in amorphous solids

Cited by 369 publications

References 30 publications

Comparison of equivalent ball milling processes on Fe70Zr30 and Fe70Nb30

Comparison of equivalent ball milling processes on Fe70Zr30 and Fe70Nb30

Structure–properties relationships in fibre drawing of bioactive phosphate glasses

Optimized multiple quantum MAS lineshape simulations in solid state NMR

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