Dimensional crossover of correlated anion disorder in oxynitride perovskites

A simple crossover from two-dimensional to three-dimensional correlated disorder of O and N atoms on a cubic lattice has been discovered within the Ba1xSrxTaO2N series of perovskite oxynitrides. The crossover is driven by lattice expansion as x decreases, and provides a rapid increase in entropy due to a change from subextensive to extensive configurational entropy regimes.We thank STFC, UK for support for H. J. and provision of ISIS beamtime, and EPSRC for additional support. This work was also supported by the Ministerio de Economia y Competitividad (MINECO), Spain through Project MAT2017-86616-R, the Severo Ochoa Program SEV-2015-0496, and Fellowship support to AB (MAT2011-24757). We thank the ALBA synchrotron for the provision of beamtime and Prof. Rosa Palacin, Dr Carlos Frontera (ICMAB-CSIC) and Dr F. Fauth (ALBA) for assistance with data collection.Peer reviewe

A new intermediate intercalate in superconducting sodium-doped hafnium nitride chloride

Anew phase has been observed during the sodiumintercalation of hafnium nitride chloride as intermediate between the host β-HfNCl and the already reported Na 0.29 HfNCl with Tc of 24 K; the new intermediate shows interlayer spacings ranging from 9.48 to 9.67 A°, corresponds to a second stage intercalate of HfNCl and is superconducting with a critical temperature of 20 K.Beltran Porter, Daniel, [email protected]

On the strange case of divalent ions intercalation in V2O5

International audienceVanadium pentoxide has been investigated for multivalent ion battery technologies but the structural characterization of inserted phases is poor, and conflicting reports exist in the literature. This study presents a critical overview of controversial aspects related to Mg and Ca insertion in α-V2O5 under diverse conditions by combined electrochemical and ex-situ XRD experiments. Galvanostatic tests are carried out in dry and wet alkyl carbonate-based electrolytes at RT and 100 °C. The formation of protonated phases with negligible divalent ion content if any is evidenced by Rietveld refinements of the XRD data, unambiguously dismissing the presence of AV2O5 (A: Mg, Ca) as electrochemical reduction products. Furthermore, thermal instability of V2O5 at 100 °C in alkyl carbonate solvents is demonstrated by XRD and TEM analysis and the formation of an orthorhombic phase with increased a parameter, most likely due to degradation favored by both water and temperature, is observed for both Mg and Ca. In order to assess the feasibility of the reverse reaction, fully intercalated AV2O5 (A = Ca, Mg) phases were also prepared by solid state reaction and oxidation attempted both electrochemically and chemically without evidence of any significant amount of Mg2+ or Ca2+ extraction, further corroborating the sluggish diffusion kinetics of divalent cations in α-V2O5

Nitride tuning of lanthanide chromites

LnCrO3−xNx compounds with Ln = La, Pr and Nd represent one of the few examples of chromium oxynitrides and the first chromium oxynitride perovskites. Hole-doping of LnCrO3 through O2−/N3− anion substitution suppresses the antiferromagnetic transition far less drastically than cation substitutions.</p

Engineering Polar Oxynitrides: Hexagonal Perovskite BaWON2

Non-centrosymmetric polar compounds have important technological properties. Reported perovskite oxy- nitrides show centrosymmetric structures, and for some of them high permittivities have been observed and ascribed to local dipoles induced by partial order of nitride and oxide. Reported here is the first hexagonal perovskite oxynitride BaWON2, which shows a polar 6H polytype. Synchrotron X-ray and neutron powder diffraction, and annular bright-field in scan- ning transmission electron microscopy indicate that it crystal- izes in the non-centrosymmetric space group P63mc, with a total order of nitride and oxide at two distinct coordination environments in cubic and hexagonal packed BaX3 layers. A synergetic second-order Jahn-Teller effect, supported by first principle calculations, anion order, and electrostatic repulsions between W6+ cations, induce large distortions at two inequiva- lent face-sharing octahedra that lead to long-range ordered dipoles and spontaneous polarization along the c axis. The new oxynitride is a semiconductor with a band gap of 1.1 eV and a large permittivity

Reduced graphene oxide nanocomposites decorated with superparamagnetic iron oxide nanoparticles

La preparaci&oacute; i caracteritzaci&oacute;, r&agrave;pides i senzilles per&ograve; alhora acurades, de nanocomp&ograve;sits s&oacute;n punts clau per a la seva transfer&egrave;ncia al mercat. Aquest article presenta la s&iacute;ntesi de nanocomp&ograve;sits d&rsquo;&ograve;xid de graf&egrave; redu&iuml;t (RGO) decorat amb nanopart&iacute;cules d&rsquo;&ograve;xid de ferro superparamagn&egrave;tiques (SPION), amb control de la mida i la quantitat de nanopart&iacute;cules sobre les l&agrave;mines d&rsquo;RGO, per mitj&agrave; d&rsquo;un proc&eacute;s in situ d&rsquo;una sola etapa assistit per microones. La descomposici&oacute; d&rsquo;oleat de ferro en pres&egrave;ncia d&rsquo;&agrave;cid oleic com a estabilitzant est&egrave;ric ha adre&ccedil;at el problema de l&rsquo;elevada aglomeraci&oacute; de les nanopart&iacute;cules que apareix en estudis anteriors i n&rsquo;ha millorat la monodispersitat d&rsquo;una manera substancial. Aquests resultats s&rsquo;han comparat amb els d&rsquo;un m&egrave;tode t&iacute;pic sense estabilitzaci&oacute; est&egrave;rica. Finalment s&rsquo;ha provat que l&rsquo;ajust d&rsquo;un model nucli-closca (core-shell) de nanopart&iacute;cula a les corbes d&rsquo;imantaci&oacute; mesurades mitjan&ccedil;ant un dispositiu SQUID, considerant una distribuci&oacute; log-normal, &eacute;s un m&egrave;tode de determinaci&oacute; de mida de part&iacute;cula preferible enfront del t&iacute;pic mesurament directe d&rsquo;histogrames en imatges de microsc&ograve;pia electr&ograve;nica de transmissi&oacute; (TEM), per la rapidesa i millor representativitat que suposa del conjunt de la mostra.Paraules clau: &Ograve;xid de graf&egrave; redu&iuml;t, nanopart&iacute;cules d&rsquo;&ograve;xid de ferro, superparamagnetisme, s&iacute;ntesi assistida per microones.The preparation and characterization of composite nanomaterials in a fast and easy manner are essential for their transfer to market. This paper discusses the synthesis of reduced graphene oxide (RGO) nanocomposites decorated with superparamagnetic iron oxide nanoparticles (SPIONs), with control of sizes and coverages through a one-step in situ microwave-assisted process. The decomposition of iron oleate in the presence of oleic acid as a steric stabilizer has addressed the problem of the high degree of nanoparticle agglomeration observed in previous reports, and it has significantly improved monodispersity. These results have been compared with those of a typical method without steric stabilizers. Lastly, the particle size determination method based on the fitting of a core-shell nanoparticle model to the magnetization curves measured by SQUID, assuming a log-normal distribution, has been shown to be a good alternative to the typical direct measurement of nanoparticles on TEM micrographs, thanks to its speed and better sample representativity.Keywords: Reduced graphene oxide, iron oxide nanoparticles, superparamagnetism, microwave-assisted synthesis

Microwave-assisted synthesis of SPION-reduced graphene oxide hybrids for magnetic resonance imaging (MRI)

Magnetic resonance imaging (MRI) is a useful tool for disease diagnosis and treatment monitoring. Superparamagnetic iron oxide nanoparticles (SPION) show good performance as transverse relaxation (T) contrast agents, thus facilitating the interpretation of the acquired images. Attachment of SPION onto nanocarriers prevents their agglomeration, improving the circulation time and efficiency. Graphene derivatives, such as graphene oxide (GO) and reduced graphene oxide (RGO), are appealing nanocarriers since they have both high surface area and functional moieties that make them ideal substrates for the attachment of nanoparticles. We have employed a fast, simple and environmentally friendly microwave-assisted approach for the synthesis of SPION-RGO hybrids. Different iron precursor/GO ratios were used leading to SPION, with a median diameter of 7.1 nm, homogeneously distributed along the RGO surface. Good relaxivity (r*) values were obtained in MRI studies and no significant toxicity was detected within in vitro tests following GL261 glioma and J774 macrophage-like cells for 24 h with SPION-RGO, demonstrating the applicability of the hybrids as T-weighted MRI contrast agents