Search results for "AMA"
showing 10 items of 8558 documents
High-pressure study of the infrared active modes in wurtzite and rocksalt ZnO
2011
International audience; We present a high-pressure study of ZnO carried out in the mid- to far-infrared frequency domain with the aim of characterizing the optic modes of wurtzite and rocksalt ZnO. We obtained the pressure coefficients of the E1(TO), E1(LO), A1(TO), and A1(LO) modes of the low-pressure wurtzite phase and compare them with previous Raman measurements. The optical modes of the high-pressure rocksalt phase are infrared active, so we were able to determine their wave numbers and pressure dependencies. In the wurtzite phase, high pressure induces a slight decrease in both longitudinal and transverse effective charges. The decrease is more pronounced in the rocksalt phase.
Acoustic vibrations of monoclinic zirconia nanocrystals
2011
International audience; Polarized low-frequency Raman spectra originating from confined acoustic vibrations are reported for monoclinic ZrO2 nanoparticles with a narrow size distribution synthesized from a continuous supercritical water process. The monoclinic lattice structure is taken into account for the interpretation of the spectra by comparing with isotropic and anisotropic continuum elasticity calculations for monodomain nanocrystals. The various mechanisms leading to the broadening of the Raman peaks are discussed. We demonstrate that an accurate determination of the size distribution of the nanoparticles is possible using the Raman peak due to the fundamental breathing vibration wh…
Magnetization reversal of the domain structure in the anti-perovskite nitride Co3FeN investigated by high-resolution X-ray microscopy
2016
We performed X-ray magnetic circular dichroism (XMCD) photoemission electron microscopy imaging to reveal the magnetic domain structure of anti-perovskite nitride Co3FeN exhibiting a negative spin polarization. In square and disc patterns, we systematically and quantitatively determined the statistics of the stable states as a function of geometry. By direct imaging during the application of a magnetic field, we revealed the magnetic reversal process in a spatially resolved manner. We compared the hysteresis on the continuous area and the square patterns from the magnetic field-dependent XMCD ratio, which can be explained as resulting from the effect of the shape anisotropy, present in nano…
The influence of Cr and Ni doping on the microstructure of oxygen containing diamond-like carbon films
2021
Abstract Non-hydrogenated diamond-like carbon (DLC) films doped with metals and oxygen were deposited by direct current magnetron sputtering. The influence of chromium and nickel on the surface morphology, elemental composition, bonding structure, adhesion force, optical transmittance and nanohardness of the films was characterized by atomic force microscopy (AFM), energy dispersive X-ray spectroscopy (EDX), multi-wavelength Raman spectroscopy, UV–VIS–NIR spectrophotometry and nanoindenter. The surface roughness was reduced with the addition of Cr (7.4 at. %) or Ni (8.9 at. %) into DLC films. The EDX measurements indicated that the addition of Cr increased the oxygen content by ~37%, while …
EPR in glass ceramics
2019
Abstract The development of novel materials requires a profound understanding of the relationship between a material's performance and its structural properties. Electron paramagnetic resonance (EPR) is a well-established technique for a direct detection and identification of paramagnetic defects in solids. This chapter provides an overview of the applicability of continuous wave EPR spectroscopy in the studies of glass ceramics focusing on transition metal (Mn2 +, Cu2 +, Cr3 +) and rare earth (Gd3 +, Eu2 +, Er3 +, Yb3 +) ion local structure analysis. EPR spectra features of the above-mentioned paramagnetic probes in glasses and glass ceramics are compared and discussed in detail. The chapt…
Static and dynamic structure of $ZnWO_4$ nanoparticles
2011
Abstract Static and dynamic structure of ZnWO 4 nanoparticles, synthesized by co-precipitation technique, has been studied by temperature dependent x-ray absorption spectroscopy at the Zn K-edge and W L 3 -edge. Complementary experimental techniques, such as x-ray powder diffraction, Raman and photoluminescence spectroscopies, have been used to understand the variation of vibrational, optical, and structural properties of nanoparticles, compared to microcrystalline ZnWO 4 . Our results indicate that the structure of nanoparticles experiences strong relaxation leading to the significant distortions of the WO 6 and ZnO 6 octahedra, being responsible for the changes in optical and vibrational …
Ab initio calculations of structural, electronic and vibrational properties of BaTiO3 and SrTiO3 perovskite crystals with oxygen vacancies
2020
The first-principles (ab initio) computations of the structural, electronic, and phonon properties have been performed for cubic and low-temperature tetragonal phases of BaTiO3 and SrTiO3 perovskite crystals, both stoichiometric and non-stoichiometric (with neutral oxygen vacancies). Calculations were performed with the CRYSTAL17 computer code within the linear combination of atomic orbitals approximation, using the B1WC advanced hybrid exchange-correlation functional of the density-functional-theory (DFT) and the periodic supercell approach. Various possible spin states of the defective systems were considered by means of unrestricted (open shell) DFT calculations. It was demonstrated that…
Effect of Mn doping on the low-temperature synthesis of tricalcium phosphate (TCP) polymorphs
2019
Abstract Effect of Mn doping on the low-temperature synthesis of tricalcium phosphate (TCP) polymorphs was demonstrated in α- and β-TCP polymorphs prepared by wet precipitation method under identical conditions and annealed at 700 °C. Calcium phosphates with Mn doping level in the range from 1 to 5 mol% were studied and the formation of desired polymorph was controlled by varying Mn content in as-prepared precipitates. It was found that increasing Mn content resulted in the formation of β-TCP, while α-TCP was obtained with low Mn doping level, whereas a mixture of two polymorphs was obtained for intermediate Mn concentrations. Moreover, doping with Mn ions allowed the synthesis of β-TCP at …
Fluence effect on ion-implanted As diffusion in relaxed SiGe
2005
A systematic study on the fluence (5 × 108 − 4 × 1014 cm−2) dependence of ion-implanted As diffusion in relaxed Si1 − xGex alloys (with x = 0.2, 0.35 and 0.5) and silicon has been performed by the modified radiotracer and secondary ion mass spectrometry techniques. With fluences above 4 × 1011 cm−2 a clear fluence-dependent enhancement in arsenic diffusion was noted for Si1 − xGex. In case of arsenic-implanted silicon such fluence dependency was not observed. This can be assigned to enhanced implantation-induced damage formation and more deficient radiation damage recovery of SiGe.
Raman characterization of Pb2Na1−xLaxNb5−xFexO15 and Pb0.5(5−x)LaxNb5−xFexO15 (0≤x≤1) solid solutions
2011
Abstract The ferroelectric compounds Pb 2 Na 1− x La x Nb 5− x Fe x O 15 and Pb 0.5(5− x ) La x Nb 5− x Fe x O 15 (0≤ x ≤1) with the tungsten bronze type structure have been investigated using Raman spectroscopy. The evolution of the spectra as a function of composition at room temperature is reported. In the frequency range 200–1000 cm −1 three main A 1 phonons around 240 ( υ 1 ), 630 ( υ 2 ) and 816 ( υ 3 ) cm −1 were observed. The broadening of the Raman lines for high values of x originates from a significant structural disorder. This is in good agreement with the relaxor character of these compositions. The lowest-frequency part of the spectra, below 180 cm −1 , reveals a structural ch…