Author
Juan Rodríquez-Carvajal
Bio: Juan Rodríquez-Carvajal is an academic researcher. The author has contributed to research in topics: Powder diffraction & Magnetic structure. The author has an hindex of 6, co-authored 9 publications receiving 1648 citations.
Papers
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TL;DR: WinPLOTR is a graphic program for the analysis of powder diffraction patterns that has been developed for a Windows 9x/2k/NT environment and can be used as a Graphic User Interface for programs defined by the user.
Abstract: WinPLOTR is a graphic program for the analysis of powder diffraction patterns. It has been developed for a Windows 9x/2k/NT environment. It takes advantage of this graphical environment to offer a powerful and user-friendly powder diffraction tool. The program is able to display and analyse many different kinds of diffraction patterns as well as calculated and observed profiles coming from the Windows/DOS version of the program FullProf. It can also be used as a Graphic User Interface (GUI) for programs defined by the user.
1,638 citations
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TL;DR: In this article, a short account of the methodology used within FullProf to extract average micro-structural properties from the analysis of broadened lines of constant wavelength diffraction patterns is presented.
Abstract: A short account of the methodology used within FullProf to extract average micro-structural properties from the analysis of broadened lines of constant wavelength diffraction patterns is presented. The approach is based on the Voigt approximation and can be combined with the Rietveld method as well as with the profile matching (Le Bail fit) procedure. Both the instrumental and sample profiles are supposed to be well described by Voigt functions. To get reliable sample parameters a good knowledge of the Instrumental Resolution Function (IRF) is needed. Only a phenomenological treatment, in terms of coherent size domains and strains due to structural defects, is performed.
151 citations
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16 citations
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TL;DR: In this article, the authors reviewed the techniques for magnetic structure determination from NPD data and provided a review of the classical approach for solving magnetic structures, the TE method is unable to provide appropriate results and other methods have to be used.
Abstract: The classical approach for solving magnetic structures is the “trial and error” (TE) method The reason is that many studies have been performed on relatively simple systems and the fact that the dominant isotropic exchange interactions, in absence of frustration, favour simple collinear structures The improvement of the resolution of neutron powder diffractometers has allowed handling complex incommensurate magnetic systems For solving complex magnetic structures the TE method is unable to provide appropriate results and other methods have to be used In this communication the techniques for magnetic structure determination from neutron powder diffraction (NPD) data are reviewed In the general case the magnetic moment of an atom in the crystal is given as a Fourier series The Fourier coefficients, S , are complex vectors constituting the “unknowns” to be determined These vectors define the magnetic structure and they correspond to the “atom positions” of an unknown crystal structure The steps for solving magnetic structures from NPD are the following: i) Search for the propagation vector(s) {k} The set {k} provides the translation symmetry of the spin configuration ii) Symmetry analysis is needed to find the smallest set of free parameters In general the vectors S are linear combinations of the basis functions of the irreducible representations of the wave vector group G j k
16 citations
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TL;DR: In this paper, the surface lattice structures of LiNi0.5Co0.2Mn0.3O2 were investigated under various cutoff voltage conditions, and it was shown that the pristine rhombohedral phase tends to transform into a mixture of spinel and rock salt phases.
Abstract: LiNixCoyMnzO2 (NCM, 0 ≤ x,y,z 4.3 V) required for high capacity is inevitably accompanied by a more rapid capacity fade over numerous cycles. Here, the degradation mechanisms of LiNi0.5Co0.2Mn0.3O2 are investigated during cycling under various cutoff voltage conditions. The surface lattice structures of LiNi0.5Co0.2Mn0.3O2 are observed to suffer from an irreversible transformation; the type of transformation depends on the cutoff voltage conditions. The surface of the pristine rhombohedral phase tends to transform into a mixture of spinel and rock salt phases. Moreover, the formation of the rock salt phase is more dominant under a higher voltage operation (≈4.8 V), which is attributable to the highly oxidative environment that triggers the oxygen loss from the surface of the material. The presence of the ionically insulating rock salt phase may result in sluggish kinetics, thus deteriorating the capacity retention. This implies that the prevention of surface structural degradation can provide the means to produce and retain high capacity, as well as stabilize the cycle life of LiNi0.5Co0.2Mn0.3O2 during high-voltage operations.
893 citations
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TL;DR: In this paper, the authors describe the development of a class of lead-free (0.94−x)Bi0.5Na 0.5TiO3-0.06BaTiO 3−xK0.4NbO3 ceramics.
Abstract: Piezoelectric actuators convert electrical into mechanical energy and are implemented for many large-scale applications such as piezoinjectors and ink jet printers. The performance of these devices is governed by the electric-field-induced strain. Here, the authors describe the development of a class of lead-free (0.94−x)Bi0.5Na0.5TiO3–0.06BaTiO3–xK0.5Na0.5NbO3 ceramics. These can deliver a giant strain (0.45%) under both unipolar and bipolar field loadings, which is even higher than the strain obtained with established ferroelectric Pb(Zr,Ti)O3 ceramics and is comparable to strains obtained in Pb-based antiferroelectrics.
784 citations
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TL;DR: The International Tables for X-ray Crystallography (ITC) as mentioned in this paper were published by the International Union of Crystallographers (IUC) for the first time in 1952.
Abstract: International Tables for X-Ray Crystallography (Published for the International Union of Crystallography.) Vol. 1: Symmetry Groups. Edited by Norman F. M. Henry and Kathleen Lonsdale. Pp. xi + 558. (Birmingham: Kynoch Press, 1952.) 105s.
691 citations
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TL;DR: The genesis of the modern whole powder pattern decomposition methods (the so-called Pawley and Le Bail methods) is detailed and their importance and domains of application are decoded from the most cited papers citing them.
Abstract: A modern definition for whole powder pattern decomposition WPPD methods would be that they simultaneously have to refine the unit-cell parameters and extract the best estimations of the Bragg peak intensities from a complete diffractogram. This is done very fast nowadays, irrespective of the number of Bragg peaks present in a powder diffraction pattern, but we did not attain this comfortable situation without some past efforts. The WPPD methods’ introduction occurred slowly and progressively thanks to the increase in computer power, the improvements in graphical user interfaces, the diffractometer data digitalization, the availability of synchrotron and neutron radiation, and last but not least, the proposition of new algorithms. Innovations were not instantly accepted this being true for all the whole powder pattern fitting methods including the Rietveld and the decomposition methods or could not be applied immediately to every radiation source or diffractometer the hardware before adaptations made by an essential category of crystallographers being conceivers and developers of the software. Ancestors of the WPPD methods extracted peak intensities without the cell restraint, so that each peak position was a parameter to be refined as well as the peak intensity, the peak shape and its width. This is still useful if the aim is the search for the peak positions for indexing, though derivative methods can make that peak-position-hunting job faster. Taking advantage of the indexing see a recent review paper by Bergmann et al. 2004, new WPPD methods, applying cell restraint to the peak position, opened the door to a long list of new possibilities and applications including first indexing confirmation which are detailed in this paper. However, only some selected application references will be provided because the number of papers involved is quite high and increasing more than 2000 texts specify the use of WPPD methods. Contributions from Rennes by Louer’s group from 1987 to 1993 will be especially enlightened, not forgetting the other players during that same time, restraining generally to the structure determinations by powder diffractometry SDPD applications published in the early stages of this retrospection because the subsequent activity increased too considerably, by more than 850 SDPDs in the last ten years. If only a partial review of applications can be given, the evolution of the methods will be discussed as completely as possible.
625 citations
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10 Jan 2014-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the effect of annealing on microstructure and related tensile properties is examined and the results demonstrate that the mechanical behavior of the Al-12Si SLM samples can be tuned within a wide range of strength and ductility through proper annesaling treatment.
Abstract: Al-12Si specimens are produced by selective laser melting (SLM) from gas atomized powders. An extremely fine cellular structure is observed with residual free Si along the cellular boundaries. Room temperature tensile tests reveal a remarkable mechanical behavior: the samples show yield and tensile strengths of about 260. MPa and 380. MPa, respectively, along with fracture strain of ~3%. The effect of annealing on microstructure and related tensile properties is examined and the results demonstrate that the mechanical behavior of the Al-12Si SLM samples can be tuned within a wide range of strength and ductility through proper annealing treatment.
612 citations