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In this work, we show how to obtain internal monodispersed gold nanoparticles inside polydopamine (PDA) nanospheres that are also externally decorated with gold. The number of internal nanoparticles is affected by the size of the PDA nanosphere used, and the lower limit in the number of gold nanoparticles in the center of decorated nanospheres, one single gold nanoparticle, has been reached. In addition, extensive molecular dynamics simulations of PDA nanospheres based on four different chemical motifs, in the presence of water and with different sizes, have been performed to gain insight into the arrangements capable of accommodating cavities. In particular, PDA nanospheres based on pyranoacridinotrione (PYR) units provide good agreement with the experimental attainment of internal metal nanoparticles. In these, the stacking of PYR units leads to a particular morphology, with large portions of space occupied by the solvent, that would explain the observed formation of gold nanoparticles inside the PDA nanosphere.

The doping strategy of hybrid perovskites is being extensively explored not only for higher efficiency but also to overcome issues in photovoltaic materials such as self-degradation pathways in an ambient atmosphere or under visible irradiation. Here, BiI3 is introduced in the synthesis of MAPbI3 films (MA: CH3–NH3+) to stabilize the material. Around 25% of nominal Bi3+ is accommodated in the perovskite structure, producing a shrinking of the unit cell and a small increase of the band gap. The presence of empty Bi gap states quenches the 770 nm red interband emission and results in a near-infrared emission at 1100 nm. However, high enough visible irradiation density induces a progressive segregation of Bi3+ out of the perovskite lattice and promotes the re-emergence of the red emission. This emission is blue-shifted, and its intensity increases strongly with time until it reaches a saturation value which remains stable in the transformed films for extremely high power densities, around 1000 times higher t...

The relatively low stability of solar cells based on hybrid halide perovskites is the main issue to be solved for the implementation in real life of these extraordinary materials. Degradation is accelerated by temperature, moisture, oxygen, and light and mediated by halide easy hopping. The approach here is to incorporate pristine graphene, which is hydrophobic and impermeable to gases and likely limits ionic diffusion while maintaining adequate electronic conductivity. Low concentrations of few-layer graphene platelets (up to 24 × 10–3 wt %) were incorporated to MAPbI3 films for a detailed structural, optical, and transport study whose results are then used to fabricate solar cells with graphene-doped active layers. The lowest graphene content delays the degradation of films with time and light irradiation and leads to enhanced photovoltaic performance and stability of the solar cells, with relative improvement over devices without graphene of 15% in the power conversion efficiency, PCE. A higher graphene content further stabilizes the perovskite films but is detrimental for in-operation devices. A trade-off between the possible sealing effect of the perovskite grains by graphene, that limits ionic diffusion, and the reduction of the crystalline domain size that reduces electronic transport, and, especially, the detected increase of film porosity, that facilitates the access to atmospheric gases, is proposed to be at the origin of the observed trends. This work demonstrated how the synergy between these materials can help to develop cost-effective routes to overcome the stability barrier of metal halide perovskites, introducing active layer design strategies that allow commercialization to take off. We acknowledge financial support by the Spanish Ministry of Science and Innovation under Projects PID2020-115514RB-I00 (C.C.), MAT2015-65356-C3-2-R (A.A), and PID2019-107314RB-I00 (I.M-S). This work was partially supported by European Research Council (ERC) via Consolidator Grant (724424-No-LIMIT) (I.M-S), AYUDA PUENTE 2020 URJC (C.C.). Associated Lab LABCADIO belonging to Community of Madrid, CM, net laboratories ref 351 is also acknowledged (C.C.). T.S.R. acknowledges funding from CM and European Social Fund (ESF) under the Talento fellowship 2017-T2/IND-5586 and project F660 financed by CM and Rey Juan Carlos University under action 1, “Encouragement of Young Phd students investigation". C.R-O. acknowledges funding from the Spanish Ministry of Science and Innovation under a FPI predoctoral contract (PRE2019-088433).

[EN] In spite of the outstanding properties of metal halide perovskites, its polycrystalline nature induces a wide range of structural defects that results in charge losses that affect the final device performance and stability. Herein, a surface treatment is used to passivate interfacial vacancies and improve moisture tolerance. A functional organic molecule, phenylethyl ammonium iodide (PEAI) salt, is dissolved with the antisolvent step. The additive used at low concentration does not induce formation of low-dimensional perovskites species. Instead, the organic halide species passivate the surface of the perovskite and grain boundaries, which results in an effective passivation. For sake of generality, this facile solution-processed synthesis was studied for halide perovskite with different compositions, the standard perovskite MAPbI, and double cation perovskites, MACsPbI and MAFAPbI, increasing the average photoconversion efficiency compared to the reference cell by 18%, 32%, and 4% respectively, observed for regular, n-i-p, and inverted, p-i-n, solar cell configurations. This analysis highlights the generality of this approach for halide perovskite materials in order to reduce nonradiative recombination as observed by impedance spectroscopy., T.S.R. acknowledges funding from Community of Madrid under the Talentfellowship 2017-T2/IND-5586 and project F660 financed by Community of Madrid and Rey Juan Carlos University. The authors acknowledgefinancialsupport by the Spanish Ministry of Science and Innovation under Projects PID2020-115514RB-I00, MAT2015-65356-C3-2-R, and PID2019-107314RB-I00. This work was partially supported by AYUDA PUENTE 2020 URJC.Associated Lab LABCADIO belonging to CM net laboratories ref 351are also acknowledge. C.R.O. acknowledges funding from the Spanish Ministry of Science and Innovation under a FPI pre-doctoral contract(PRE2019-088433)

Size, shape and hot spots are crucial to optimize Raman amplification from metallic nanoparticle (NPs). The amplification from radius = 1.8 ± 0.4 nm ultra-small silver NPs was explored. Increasing NP density redshifts and widens their plasmon that, according to simulations for NPs arrays, is originated by the reduction of the interparticle distance, d, becoming remarkable for d ≤ R. Inter-particle interaction red-shifts (>130 nm) and widens (>90 nm) the standard plasmon of non-interacting spherical particles. Graphene partly delocalizes the carriers enhancing the NIR spectral weight. Raman amplification of graphene phonons is moderate and depends smoothly on d while that of Rhodamine 6G (R6G) varies almost exponentially due to their location at hot-spots that depend strongly on d. The experimental correlation between amplification and plasmon position is well reproduced by simulations. The amplification originated by the ultra-small NPs is compared to that of larger particles, granular silver films with 7 < R < 15 nm grains, with similar extinction values. The amplification is found to be larger for the 1.8 nm NPs due to the higher surface/volume ration that allows higher density of hot spots. It is demonstrated that Raman amplification can be efficiently increased by depositing low density layers of ultra-small NPs on top of granular films. The research leading to these results has received funding from Ministerio de Ciencia, Innovación y Universidades (RTI2018-096918-B-C41). S.C. acknowledges the grant BES-2016-076440 from MINECO. L.M. acknowledges the European Union (grant number ERC-2013-SyG 610256 NANOCOSMOS).

Graphene is grown by chemical vapour deposition on ruthenium ultrathin films down to a nominal thickness of 5 nm. While at 910 °C multilayer graphitic films are obtained, single layer defective graphene is formed at 1000 °C. The extremely thin Ru films allow the formation of a novel nano-crystalline ruthenium carbide phase to be discerned by combining synchrotron X-ray diffraction, synchrotron X-ray absorption spectroscopy and electron diffraction. The ruthenium carbide (Ru-C) phase formed at or above 1000 °C presents cubic symmetry (cP) with a lattice parameter of 2.927 Å and a Ru-C distance of around 2.31 Å. The increase of C solubility in ruthenium seems to be sufficient to trigger the stabilization of the Ru-C phase during graphene growth preferentially in grains with orientation different to (0001). The structural transition from hcp Ru to cP Ru-C is not limited to a shell; it occurs for the whole grain. The formation of the carbide seems to favour the synthesis of single layer graphene by hindering the segregation of carbon to the surface during cooling. This simple method allows nano-crystalline ruthenium-carbide films to be obtained as well as graphene covered Ru nanograins, both with size control. These new materials are foreseen to present interesting mechanical, catalytic and sensing properties.http://doi.org/10.1039/C7TC02855E, Funding by the Spanish Ministerio de Economía y Competitividad (MINECO) under Project MAT2015-65356-C3-1-R and Comunidad de Madrid Excellence Network under Project S2013/MIT-2740 is acknowledged. We also acknowledge the MINECO for financial support and provision of synchrotron radiation facilities at the BM25 SpLine of The Spanish CRG Beamline at the ESRF. L. A.-F. acknowledges a FPI grant (BES-2013-062759) from MINECO.

Poly(3,4-ethylenedioxythiophene):poly (styrene sulfonate) (PEDOT:PSS) plays a relevant role in the device performance as hole extraction layer (HTL) of inverted perovskite solar cells. Here, we show a simple low-temperature spin coating method for obtaining homogenous graphene-doped thin films of PEDOT:PSS with improved electrical conductivity without decreasing optical transmittance. Moreover, the crystallinity and stability in ambient conditions of the perovskite grown on it are enhanced. The hydrophobic character of graphene probably blocks undesirable reactions hampering degradation. By impedance spectroscopy it is demonstrated better charge extraction and reduction of recombination mechanisms at the doped-HTL/perovskite interface, resulting in improved photovoltaic parameters of the solar cell and greater stability at room operation conditions thus providing a simple and cost-effective method of preparing solar cells based on hybrid perovskites.

La2−xSrxCoTiO6 (0.6 ≤ x ≤ 1.0) compound series is prepared by Sr-substitution in the A-site of the perovskite by a modified Pechini procedure under air. Charge compensation as Sr2+ content increase occurs by Co2+ oxidation to Co3+. Reduced samples are obtained by further treatment under 5%H2/Ar and characterized by Neutron Powder Diffraction. Upon redution, Co3+ to Co2+ reduction and oxygen vacancies creation are detected. Dependence of total conductivity with temperature and pO2 exhibits a typical p-type semiconducting behaviour. Results show that the higher the Sr content, the higher holes (Co3+) concentration and consequently, La2−xSrxCoTiO6 (x = 1.0) shows the highest conductivity (13.23 S/cm at 1073 K in air). The negligible reactivity with YSZ, used as the electrolyte, of symmetrical cells under oxidant conditions and the moderate thermal expansion found by XRD point to their possible use as SOFC cathodes. Thus, La1.2Sr0.8CoTiO6-based cathodes display polarization resistance of 0.9 Ω cm2 at 1073 K in oxygen, only slightly above than the current state-of-the-art.

The topotactic Li/H exchange in LiLaTiO has been studied in different aqueous and non-aqueous media with different acidity. With this purpose, aqueous hydrochloric and nitric acid solutions and benzoic acid/ethanol solution were employed. The pristine and exchanged samples have been characterized by H and Li MAS-NMR, TGA and XRD techniques. Aqueous hydrochloric and nitric acid solutions produce the powders degradation and the subsequent formation of LiTiO and LaTiO phases. A detailed analysis of the H MAS NMR spectra of exchanged samples indicate that Li/H exchange reaction in pure water produced formation of LiOH at the particles surface, band at 0 ppm, that could subsequently carbonated after exposition in air. Furthermore the presence of other OH signals at 8, 6 and 2 ppm has been related to differences on octahedral Ti-O distances, produced by La/vacancy ordering in alternating planes of perovskites. In samples immersed into benzoic acid/ethanol solution results are similar, however the amount of LiOH species in particle surface is considerable lower. The exchange degree improved when increasing exchange temperature. The mechanical grinding of powders decreases the particle size improving exchange reactions; however, grinding treatments eliminated specific NMR bands of perovskite. In ground materials new H NMR bands at 6 and 4 ppm were ascribed to an amorphous phase., This work has been supported by Projects funded by the Regional Government (Comunidad de Madrid through MATERYENER3 CM S2013/MIT-2753) and the Spanish Government, (MICINN through MAT2013-46452-C4-3R Project). The authors also thank the European Programme-IRSES (NANOLICOM) for financial support.

The new scheelite form of SmCrO4 oxide was obtained by heating the zircon-type SmCrO4 oxide at 4 GPa and 803 K. X-ray diffraction revealed that this scheelite SmCrO4 phase crystallized with tetragonal symmetry, S.G. I41/a and lattice parameters: a=0.50776(3) nm and c=1.15606(2) nm. This structural phase transition from zircon to scheelite involved a decreasing of around 10% in the unit cell volume. Although the Cr-O and Sm-O distances did not change very much in both zircon and scheelite polymorphs, the changes occurred in the bond angles were remarkable that appear to support the proposed reconstructive model to explain this structural zircon-scheelite phase transition. Magnetic susceptibility and magnetization measurements revealed that the scheelite SmCrO4 oxide behaved an antiferromagnetic material, where the Sm3+ and Cr5+ were simultaneously ordered. The estimated Neel temperature, TN, was 16 K and the critical field at 12 K associated with the metamagnetic transition was 3.2 T.

EuNbO 2 N oxynitride was synthesized by nitridation of the EuNbO 4 precursor oxide at 1113 K in ammonia flow for 12 h. X-ray powder diffraction data revealed that the EuNbO 2 N oxynitride crystallizes with the cubic perovskite-type structure, S.G. P m 3 ¯ m and a lattice constant of a = 4.03244(10) A. Thermogravimetric studies reveal that the oxynitride decomposes around 513 K under oxygen atmosphere, giving as a final product of decomposition the EuNbO 4 oxide. The extremely low value obtained for remanence and coercive field fully agrees the isotropic character of the 8 S 7/2 ground state associated to the Eu 2+ . Magnetic susceptibility measurements indicate that EuNbO 2 N behaves as paramagnetic over temperature range 10–300 K, the sudden increase in the susceptibility observed below 10 K, is characteristic of the onset of a ferromagnetic behaviour with an estimated T c = 6.2 K. The saturation moment of 6.48 μ B which is smaller than 7 μ B expected for Eu 2+ can be due to the presence of Eu 3 NbO 7 impurity, confirmed by the X-ray powder diffraction data.

EuNbO 2 N oxynitride was synthesized by nitridation of the EuNbO 4 precursor oxide at 1113 K in ammonia flow for 12 h. X-ray powder diffraction data revealed that the EuNbO 2 N oxynitride crystallizes with the cubic perovskite-type structure, S.G. P m 3 ¯ m and a lattice constant of a = 4.03244(10) A. Thermogravimetric studies reveal that the oxynitride decomposes around 513 K under oxygen atmosphere, giving as a final product of decomposition the EuNbO 4 oxide. The extremely low value obtained for remanence and coercive field fully agrees the isotropic character of the 8 S 7/2 ground state associated to the Eu 2+ . Magnetic susceptibility measurements indicate that EuNbO 2 N behaves as paramagnetic over temperature range 10–300 K, the sudden increase in the susceptibility observed below 10 K, is characteristic of the onset of a ferromagnetic behaviour with an estimated T c = 6.2 K. The saturation moment of 6.48 μ B which is smaller than 7 μ B expected for Eu 2+ can be due to the presence of Eu 3 NbO 7 impurity, confirmed by the X-ray powder diffraction data.