Structural and magnetic properties of Zn x Mn 3-x O 4 spinels

To study structural and magnetic properties of spinels a series of ceramic samples with a different ZnMn ratio was prepared by high-temperature annealing in air followed by quenching in liquid nitrogen. The spinels with nominal composition of Zn x Mn 3-x O 4 (x=0-1.29) were characterized by means of X-ray diffraction, Raman spectroscopy, scanning electron microscopy and SQUID magnetometry. Two tetragonal spinels of the same I4 1 /amd space-group were identified based on the crystallographic, vibrational and grain-morphology point of view and described in detail. The unit-cell parameters and phase ratio of the spinel phases were determined using Rietveld refinement. According to the factor-group analysis the majority of the vibrational modes were identified in the Raman spectra. The magnetic properties of Zn x Mn 3-x O 4 spinels are in agreement with a model of nanoscale ferrimagnetic Mn 3 O 4 clusters in the antiferromagnetic ZnMn 2 O 4 matrix (T N ≈60 K). New features are a constricted hysteresis loop for x=0.3, and the effect of defects on magnetic properties for high Zn content which points to a good quality of the samples prepared by a solid state reaction. © 2016 Elsevier B.V. All rights reserved

Structural and magnetic properties of Zn x Mn 3-x O 4 spinels

International audienceTo study structural and magnetic properties of spinels a series of ceramic samples with a different ZnMn ratio was prepared by high-temperature annealing in air followed by quenching in liquid nitrogen. The spinels with nominal composition of Zn x Mn 3-x O 4 (x=0-1.29) were characterized by means of X-ray diffraction, Raman spectroscopy, scanning electron microscopy and SQUID magnetometry. Two tetragonal spinels of the same I4 1 /amd space-group were identified based on the crystallographic, vibrational and grain-morphology point of view and described in detail. The unit-cell parameters and phase ratio of the spinel phases were determined using Rietveld refinement. According to the factor-group analysis the majority of the vibrational modes were identified in the Raman spectra. The magnetic properties of Zn x Mn 3-x O 4 spinels are in agreement with a model of nanoscale ferrimagnetic Mn 3 O 4 clusters in the antiferromagnetic ZnMn 2 O 4 matrix (T N ≈60 K). New features are a constricted hysteresis loop for x=0.3, and the effect of defects on magnetic properties for high Zn content which points to a good quality of the samples prepared by a solid state reaction. © 2016 Elsevier B.V. All rights reserved

ZnO thin films prepared by spray-pyrolysis technique from organo-metallic precursor

Presented experiments utilize methanolic solution of zinc acetyl-acetonate as a precursor and sapphire (001) as a substrate for deposition of thin films of ZnO. The X-ray diffraction analysis revealed polycrystalline character of prepared films with preferential growth orientation along c-axis. The roughness of prepared films was assessed by AFM microscopy and represented by roughness root mean square (RMS) value in range of 1.8 - 433 nm. The surface morphology was mapped by scanning electron microscopy showing periodical structure with several local defects. The optical transmittance spectrum of ZnO films was measured in wavelength range of 200-1000 nm. Prepared films are transparent in visible range with sharp ultra-violet cut-off at approximately 370 nm. Raman spectroscopy confirmed wurtzite structure and the presence of compressive stress within its structure as well as the occurrence of oxygen vacancies. The four-point Van der Pauw method was used to study the transport prosperities. The resistivity of presented ZnO films was found 8 × 10–2 Ω cm with carrier density of 1.3 × 1018 cm–3 and electron mobility of 40 cm2 V–1 s–1

Phase equilibria in the Zn-Mn-O system

International audienceDifferent ratios of ZnO and MnCO3 were mixed and processed by ceramic route to investigate phase relations in the Zn-Mn-O system using differential thermal analysis and X-ray powder diffraction techniques. Except for Zn1-xMnxO we detected two different spinel phases in this system. FactSage program was used for the construction of the Zn-Mn-O phase diagram in air and oxygen atmosphere. To verify the composition in several parts of the diagram at the temperature of interest, a number of high-temperature annealings followed by quenching was performed. © 2014 Elsevier Ltd

Phase equilibria in the Zn-Mn-O system

Different ratios of ZnO and MnCO3 were mixed and processed by ceramic route to investigate phase relations in the Zn-Mn-O system using differential thermal analysis and X-ray powder diffraction techniques. Except for Zn1-xMnxO we detected two different spinel phases in this system. FactSage program was used for the construction of the Zn-Mn-O phase diagram in air and oxygen atmosphere. To verify the composition in several parts of the diagram at the temperature of interest, a number of high-temperature annealings followed by quenching was performed. © 2014 Elsevier Ltd

Towards graphene bromide : bromination of graphite oxide

Halogenated graphene derivatives are interesting for their outstanding physical and chemical properties. In this paper, we present various methods for the synthesis of brominated graphene derivatives by the bromination of graphite oxides. Graphite oxides, prepared according to either the Hummers or Hofmann method, were brominated using bromine or hydrobromic acid under reflux or in an autoclave at elevated temperatures and pressures. The influence of both graphite oxide precursors on the resulting brominated graphenes was investigated by characterization of the graphenes, which was carried out using various techniques, including SEM, SEM-EDS, high-resolution XPS, FTIR, STA and Raman spectroscopy. In addition, the resistivity of the brominated graphenes was measured and the electrochemical properties were investigated by cyclic voltammetry. Although the brominated graphenes were structurally similar, they had remarkably different bromine concentrations. The most highly brominated graphene (bromine concentration above 26 wt%) exhibited a C/O ratio above 44 and partial hydrogenation. Brominated graphenes with such properties could be used for reversible bromine storage or as a starting material for further chemical modifications.Published versio

Flux growth of ZnO crystals doped by transition metals

ZnO crystals doped with Cr, Mn, Fe and Co were grown by the flux method. The prepared crystals revealed no phase separation detectable by X-ray diffraction. Structure properties were characterized by Raman and photoluminescence spectroscopy. For ZnO:Co, Mn and Cr, no spontaneous ferromagnetic moment was observed up to T=2 K whereas for the ZnO:Fe crystals the m(H) curves suggest the existence of 5 nm superparamagnetic iron clusters. At low temperatures the m(H) curves can be interpreted as a superposition of major paramagnetic and minor antiferromagnetic contribution. The paramagnetic part corresponds to the presence of Co2+, Fe3+, Mn2+ ions and small Cr atom clusters. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved

A study of the structural properties of GaN implanted by various rare-earth ions

GaN layers with h0001i crystallographic orientation, grown by low-pressure metal-organic vapourphase epitaxy (MOVPE) on c-plane sapphire substrates, were implanted with 200 and 400 keV Sm+, Tm+, Eu+, Tb+ and Ho+ ions at fluencies of 1 1015–1 1016 cm2. The composition of the ion-implanted layers and concentration profiles of the implanted atoms were studied by Rutherford Back-Scattering spectrometry (RBS). The profiles were compared to SRIM 2008 simulations. The structural properties of the ion-implanted layers were characterised by RBS-channelling and Raman spectroscopy. Changes in the surface morphology caused by the ion implantation were examined by Atomic Force Microscopy (AFM). A structural analysis showed a high disorder of the atoms close to the amorphised structure at the surface layer above an implantation fluence of 5 1015 cm2 while lower disorder density was observed in the bulk according to the projected range of 400 keV ions. The post-implantation annealing induced significant changes only in the Sm and Eu depth profiles; a diffusion of rare-earths implanted at a fluence of 5 1015 cm2 to the surface was observed. The annealing caused the reconstruction of the surface layer accompanied by surface-roughness enhancement

A study of the structural and magnetic properties of ZnO implanted by Gd ions

GaN layers with 〈0 0 0 1〉 crystallographic orientation, grown by low-pressure metal-organic vapour-phase epitaxy (MOVPE) on c-plane sapphire substrates, were implanted with 200 and 400 keV Sm+, Tm+, Eu+, Tb+ and Ho+ ions at fluencies of 1 × 1015–1 × 1016 cm−2. The composition of the ion-implanted layers and concentration profiles of the implanted atoms were studied by Rutherford Back-Scattering spectrometry (RBS). The profiles were compared to SRIM 2008 simulations. The structural properties of the ion-implanted layers were characterised by RBS-channelling and Raman spectroscopy. Changes in the surface morphology caused by the ion implantation were examined by Atomic Force Microscopy (AFM). A structural analysis showed a high disorder of the atoms close to the amorphised structure at the surface layer above an implantation fluence of 5 × 1015 cm−2 while lower disorder density was observed in the bulk according to the projected range of 400 keV ions. The post-implantation annealing induced significant changes only in the Sm and Eu depth profiles; a diffusion of rare-earths implanted at a fluence of 5 × 1015 cm−2 to the surface was observed. The annealing caused the reconstruction of the surface layer accompanied by surface-roughness enhancement