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Solid-state electrolytes (SSEs) with high ion conductivity are pivotal for the development and large-scale adoption of green-energy conversion and storage technologies such as fuel cells, electrocatalysts and solid-state batteries. Yet, SSEs are extremely complex materials for which general rational design principles remain indeterminate. Here, we combine first-principles materials modelling, computational power and modern data analysis techniques to advance towards the solution of such a fundamental and technologically pressing problem. Our data-driven survey reveals that the correlations between ion diffusivity and other materials descriptors in general are monotonic, although not necessarily linear, and largest when the latter are of vibrational nature and explicitly incorporate anharmonic effects. Surprisingly, principal component and k-means clustering analyses show that elastic and vibrational descriptors, rather than the usual ones related to chemical composition and ion mobility, are best suited for reducing the high complexity of SSEs and classifying them into universal classes. Our findings highlight the need for considering databases that incorporate temperature effects to improve our understanding of SSEs and point towards a generalized approach to the design of energy materials., We acknowledge financial support from the MCIN/AEI/10.13039/501100011033 under Grant no. PID2020-119777GB-I00, the “Ramón y Cajal” fellowship RYC2018-024947-I, the Severo Ochoa Centres of Excellence Program (CEX2019-000917-S), the Generalitat de Catalunya under Grant no. 2017SGR1506, and the CSIC under the “JAE Intro SOMdM 2021” grant program. The authors acknowledge computational support from the Red Española de Supercomputación (RES) under the grants FI-2022-1-0006, FI-2022-2-0003 and FI-2022-3-0014., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).

This document is the Accepted Manuscript version of a Published Work that appeared in final form inACS Sustainable Chemistry and Engineering, copyright © 2023 American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acssuschemeng.2c06573. Hydrogen is a promising fossil-fuel alternative fuel owing to its environmentally neutral emissions and high energy density. However, the need for purified water and external power are critical hindrances to the implementation of hydrogen production. The present work demonstrates the potential to overcome these shortcomings through piezo-photocatalysis of seawater using defective BaTiO3–x (BTO) nanoparticles. This material was made piezoelectrically active by a straightforward annealing process under different atmospheres, including O2, N2, Ar, or H2, the latter of which caused Ti4+ ¿ Ti(4–x)+ multiple reductions and structural distortions that stabilize piezoelectric tetragonal domains. A suite of experimental techniques was employed to reveal the effects of reduction on the energy band structure. A substantial piezoelectric effect and the presence of self-polarization were confirmed by piezoresponse force microscopy, while simulation work clarified the role of vibrations on band bending deriving from the self-polarization. The hydrogen evolution through photocatalysis, piezocatalysis, and piezo-photocatalysis over the defective BaTiO3–x nanoparticles was characterized with deionized (DI) water, simulated seawater, and natural seawater. A promising HER with a rate of 132.4 µmol/g/h was achieved using DI water through piezo-photocatalysis without a cocatalyst. In contrast, a substantial HER rate of 48.7 µmol/g/h was obtained for natural seawater, despite the deleterious impact of dissolved ions. The present work offers new perspectives for large-scale green H2 production using abundant natural resources with a conventional piezoelectric material that is readily available but still affected by the ions dissolved in seawater.

Ni-rich layered oxides, such as LiNi0.8Co0.1Mn0.1O2 (NCM811), are promising cathode materials for high-energy lithium-ion batteries. However, the relatively high reactivity of Ni in NCM811 cathodes results in severe capacity fading originating from the undesired side reactions that occur at the cathode-electrolyte interface during prolonged cycling. Therefore, the trade-off between high capacity and long cycle life can obstruct the commercialization process of Ni-rich cathodes in modern lithium-ion batteries (LIBs). In addition, high sensitivity toward air upon storage greatly limits the commercial application. Herein, a facile surface modification strategy is introduced to enhance the cycling and in-air storage stability of NCM811. The NCM811 with a uniform SrTiO3 (STO) nano-coating layer exhibited outstanding electrochemical performances that could deliver a high discharge capacity of 173.5 mAh·g-1 after 200 cycles under 1C with a capacity retention of 90%. In contrast, the uncoated NCM811 only provided 65% capacity retention of 130.8 mAh·g-1 under the same conditions. Structural evolution analysis suggested that the STO coating acted as a buffer layer to suppress the dissolution of transition metal ions caused by the HF attack from the electrolyte and promote the lithium diffusion during the charge–discharge process. In addition, the constructed STO layer prevented the exposure of NCM811 to H2O and CO2 and thus effectively improved the in-air storage stability. This work offers an effective way to enhance the performance stability of Ni-rich oxides for high-performance cathodes of lithium-ion batteries.

The role of local chemical environments in the electron energy loss spectra of complex multiferroic oxides was studied using computational and experimental techniques. The evolution of the O K-edge across an interface between bismuth ferrite (BFO) and lanthanum strontium manganate (LSMO) was considered through spectral averaging over crystallographically equivalent positions to capture the periodicity of the local O environments. Computational techniques were used to investigate the contribution of individual atomic environments to the overall spectrum, and the role of doping and strain was considered. Chemical variation, even at the low level, was found to have a major impact on the spectral features, whereas strain only induced a small chemical shift to the edge onset energy. Through a combination of these methods, it was possible to explain experimentally observed effects such as spectral flattening near the interface as the combination of spectral responses from multiple local atomic environments.

Lithium-rich manganese-based oxides (LRMO) are regarded as promising cathode materials for powering electric applications due to their high capacity (250 mAh g–1) and energy density (~900 Wh kg–1). However, poor cycle stability and capacity fading have impeded the commercialization of this family of materials as battery components. Surface modification based on coating has proven successful in mitigating some of these problems, but a microscopic understanding of how such improvements are attained is still lacking, thus impeding systematic and rational design of LRMO-based cathodes. In this work, first-principles density functional theory (DFT) calculations are carried out to fill out such a knowledge gap and to propose a promising LRMO-coating material. It is found that SrTiO3 (STO), an archetypal and highly stable oxide perovskite, represents an excellent coating material for Li1.2Ni0.2Mn0.6O2 (LNMO), a prototypical member of the LRMO family. An accomplished atomistic model is constructed to theoretically estimate the structural, electronic, oxygen vacancy formation energy, and lithium-transport properties of the LNMO/STO interface system, thus providing insightful comparisons with the two integrating bulk materials. It is found that (i) electronic transport in the LNMO cathode is enhanced due to partial closure of the LNMO band gap (~0.4 eV) and (ii) the lithium ions can easily diffuse near the LNMO/STO interface and within STO due to the small size of the involved ion-hopping energy barriers. Furthermore, the formation energy of oxygen vacancies notably increases close to the LNMO/STO interface, thus indicating a reduction in oxygen loss at the cathode surface and a potential inhibition of undesirable structural phase transitions. This theoretical work therefore opens up new routes for the practical improvement of cost-affordable lithium-rich cathode materials based on highly stable oxide perovskite coatings.

A high-throughput screening of piezo-photocatalytic materials based on first-principles calculations and a simple electrostatic model is presented that identifies new bulk compounds able to catalyse the water splitting reaction under sunlight.

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of physical chemistry C, copyright © 2022 American Chemical Society, after peer review and technical editing by the publisher. To access the final edited and published work see 10.1021/acs.jpcc.2c04297. Multiferroic BiFe0.5Cr0.5O3 (BFCO) thin films are promising candidates for emerging optoelectronics and all-oxide solar absorbers. Yet, a thorough understanding of the structural evolution and associated changes in the functional properties of BFCO is lacking. Here, we explore thickness-dependent structural phase transitions in epitaxial BFCO films and ascertain the impact of the accompanying crystallographic distortions on their photoresponse. The results show that the strain imposed by the substrate changes the crystal symmetry, inducing a transition from a tetragonal-like to rhombohedral-like phase through a rather complex strain relaxation mechanism upon increasing film thickness. This change in crystallographic distortion also induces a shift of ~150 meV in the bandgap. Moreover, wavelength-resolved photocurrent measurements reveal that the absorption onset is redshifted for the tetragonal-like structure, implying light absorption up to wavelengths of 800 nm. First-principles calculations shed further light on the symmetry-induced changes in the electronic structure of the BFCO films, where the crystallographic symmetry is shown to be a decisive factor for modifying the characteristics of the valence band maximum and conduction band minimum in the perovskite oxides, revealing a new type of Mott multiferroic in BFCO system. This work provides a new strategy to further engineer the optoelectronic properties of the multiferroic oxide films through thickness-induced phase transitions.

Introducing large oxygen deficiencies while retaining low resistivity is important for enhancing the overall thermoelectric properties in 3d transition-metal oxides. In this study, a new synthesis route to reconstruct the insulating brownmillerite SrCoO2.5 is adapted. Through a step-by-step nano-blocks modification, a series of highly-conductive layered structures is evolved, which are [Sr2O2H2]0.5CoO2, [Sr2O2]0.4CoO2, and [Sr2CoO3]0.57CoO2, while still retaining considerable Seebeck coefficient (˜100 µV K-1). Coexistence of low resistivity and high oxygen deficiency is realized in the latter two polymorphs by forming a majority of sintered oxygen vacancies in the rock-salt layer and a minority of normal oxygen vacancies in the CoO2 layer. A room-temperature in-plane power factor of 3.6 mW K-2 m-1, power output density of 4.5 W m-2 at a temperature difference of 28 K, and an out-of-plane thermal conductivity of 0.33 W K-1 m-1 are obtained in the [Sr2O2]0.4CoO2 thin film that exhibits the highest oxygen deficiency (d = 2.95), which is on par with Bi2Te3, the benchmark. It is pointed out that proper distribution of oxygen vacancy is essential in tailoring the physical and chemical properties of transition-metal oxides. The sintered/normal oxygen vacancy layer model provides guidance to the exploration of materials with both low electric resistivity and thermal conductivity.

Multiferroics in which giant ferroelectric polarization and magnetism coexist are of tremendous potential for engineering disruptive applications in information storage and energy conversion. Yet the functional properties of multiferroics are thought to be affected detrimentally by the presence of point defects, which may be abundant due to the volatile nature of some constituent atoms and high temperatures involved in materials preparation. Here, we demonstrate with theoretical methods that oxygen vacancies may enhance the functionality of multiferroics by radically changing their magnetic interactions in thin films. Specifically, oxygen vacancies may restore missing magnetic super-exchange interactions in large axial ratio phases, leading to full antiferromagnetic spin ordering, and induce the stabilization of ferrimagnetic states with a significant net magnetization of 0.5 uB per formula unit. Our theoretical study should help to clarify the origins of long-standing controversies in bismuth ferrite and improve the design of technological applications based on multiferroics., Comment: 11 pages, 5 figures

Organic–inorganic hybrid lead halide perovskite solar cells have made unprecedented progress in improving photovoltaic efficiency during the past decade, while still facing critical stability challenges. Herein, the natural organic dye Indigo is explored for the first time to be an efficient molecular passivator that assists in the preparation of high-quality hybrid perovskite film with reduced defects and enhanced stability. The Indigo molecule with both carbonyl and amino groups can provide bifunctional chemical passivation for defects. In-depth theoretical and experimental studies show that the Indigo molecules firmly binds to the perovskite surfaces, enhancing the crystallization of perovskite films with improved morphology. Consequently, the Indigo-passivated perovskite film exhibits increased grain size with better uniformity, reduced grain boundaries, lowered defect density, and retarded ion migration, boosting the device efficiency up to 23.22%, and ˜21% for large-area device (1 cm2). Furthermore, the Indigo passivation can enhance device stability in terms of both humidity and thermal stress. These results provide not only new insights into the multipassivation role of natural organic dyes but also a simple and low-cost strategy to prepare high-quality hybrid perovskite films for optoelectronic applications based on Indigo derivatives.

Strategies for tuning the thermal conductivity of crystals by means of external fields are rare. Here, we predict the existence of large magnetophononic effects in materials that undergo antiferromagnetic (AFM) ↔ ferromagnetic (FM) phase transitions, which allow for the modulation of the lattice heat conductivity, κL, via the application of magnetic fields. Specifically, by using first-principles methods we predict a large and anomalous κL increase of ≈40% for the metamagnetic phase transition occurring in bulk FeRh near room temperature. The disclosed magnetophononic effects are caused by large anharmonic spin-phonon couplings, namely, significant differences in the phase space of allowed phonon-phonon collision processes taking place in the respective AFM and FM phases., We acknowledge financial support by MCIN/AEI/10.13039/501100011033 under Grant No. PID2020-119777GB-I00, the “Ramón y Cajal” fellowship RYC2018-024947-I, and the Severo Ochoa Centres of Excellence Program (CEX2019-000917-S), and by the Generalitat de Catalunya under Grant No. 2017 SGR 1506. Calculations were performed at the Centro de Supercomputación de Galicia (CESGA) within action FI-2021-1-0007 of the Red Española de Supercomputación (RES). We thank Michael Wolloch and Jesús Carrete for useful discussions., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).

All-inorganic CsPbX3 (X = Cl, Br, I, or mixed halides) perovskite quantum dots (QDs) exhibit tunable optical bandgaps and narrow emission peaks, which have received worldwide interest in the field of both photovoltaics (PVs) and light-emitting diodes (LEDs). Herein, it is reported a discovery that CsPbI3 perovskite QD solar cell can simultaneously deliver high PV performance and intense electroluminescence. In specific, the multifunctional CsPbI3 QD film is fabricated through a simple yet efficient solid-state-ligand exchange process using a tailored organic ligand triphenyl phosphite (TPPI). The function of QD surface manipulation using TPPI here is proven to be twofold, balancing the carrier transport and effectively passivating the QD surface to produce conductive and emissive QD film. The CsPbI3 perovskite QD solar cell delivers a champion efficiency of 15.21% with improved open circuit voltage and high fill factor. Concurrently functioning as a red LED, the CsPbI3 perovskite QD solar cell outputs electric power to light conversion efficiency approaching 4%, a record value for QD electroluminescent PVs. The results here indicate that these versatile perovskite QDs may be a promising candidate for fabricating multifunctional optoelectronic devices.

The structural and electronic properties of MnO2 based electrocatalysts are key factors determining their electrochemical performance. To date, it is still challenging to synergistically tune the crystal structure, morphology, and electronic band (i.e., band gap and band alignments) of MnO2 through facile synthesis approaches. This study has reported a one-step hydrothermal method to synthesize a prototypical MnO2 electrocatalyst with optimized structural and electrochemical properties. By simply adjusting the hydrothermal time, the phase transition from polymorphic d to a can be induced in MnO2. The obtained nanowires on nanosheets structure grown in-situ on nickel foam provides a large surface area, great accessible active sites, and good mass/charge transfer efficiency. Further investigation through first-principles calculations reveals that compared to d-MnO2, the a-MnO2 polymorph with rich oxygen vacancies has better band-alignment tunability, which is also beneficial for improving the electrochemical performance. The a phase MnO2 exhibits superior catalytic performance for both OER and HER (OER overpotential of 0.45 V at 50 mA cm-2 and HER overpotential of 0.14 V at 50 mA cm-2). The developed synthesis method can be extended to catalyst designs that require precise control of phase and morphology evolution in a wide range of applications.

Structural defects are ubiquitous for polycrystalline perovskite films, compromising device performance and stability. Herein, a universal method is developed to overcome this issue by incorporating halide perovskite quantum dots (QDs) into perovskite polycrystalline films. CsPbBr3 QDs are deposited on four types of halide perovskite films (CsPbBr3, CsPbIBr2, CsPbBrI2, and MAPbI3) and the interactions are triggered by annealing. The ions in the CsPbBr3 QDs are released into the thin films to passivate defects, and concurrently the hydrophobic ligands of QDs self‐assemble on the film surfaces and grain boundaries to reduce the defect density and enhance the film stability. For all QD‐treated films, PL emission intensity and carrier lifetime are significantly improved, and surface morphology and composition uniformity are also optimized. Furthermore, after the QD treatment, light‐induced phase segregation and degradation in mixed‐halide perovskite films are suppressed, and the efficiency of mixed‐halide CsPbIBr2 solar cells is remarkably improved to over 11% from 8.7%. Overall, this work provides a general approach to achieving high‐quality halide perovskite films with suppressed phase segregation, reduced defects, and enhanced stability for optoelectronic applications., A universal approach is reported to fabricate perovskite films by incorporating inorganic CsPbBr3 quantum dots (QDs) into halide perovskite bulk films. Upon post‐annealing, the released elements from QDs compensate vacancies, and hydrophobic ligands on QDs passivate under‐charged Pb atoms and self‐assemble on surface. Therefore, the resulting films with reduced trap density, suppressed phase segregation, improved surface uniformity and enhanced stability are enabled.

Harvesting energy from ubiquitous moisture is attracting growing interest for directly powering electronic devices. However, it is still challenging to fabricate high-performing moisture-electric generators (MEGs) with high and stable electric output. Herein, we report a simple strategy to modify the oxygen-based groups of graphene oxide using hydrochloric acid treatment, which boosts the electric output based on the device structure of graphene oxide/polyvinyl alcohol (GO/PVA) MEGs. The resulting MEG enables a stable voltage of 0.85 V and a current of 9.28 µA (92.8 µA·cm-2), which are among the highest values reported so far. More excitingly, electric output gets further improved by simply assembling four MEG units in series or parallel. Moreover, the MEG shows great commercial potential for flexible and wearable applications. Driven by these advancements, the assembled MEGs can successfully power sensors and calculators. This work opens a new era of advance for a new energy conversion technology able to directly powering electronic devices. C.C. acknowledges support from the Spanish Ministry of Science, Innovation and Universities under the "Ramon y Cajal" fellowship RYC2018-024947-I

This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Materials Letters, copyright © 2021 American Chemical Societ, after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acsmaterialslett.1c00592. A cost-effective and environmentally friendly Pb source is a prerequisite for achieving large-scale, low-cost perovskite photovoltaic devices. Currently, the commonly used method to prepare the lead source is based on a fire smelting process, requiring a high temperature of more than 1000 °C, which results in environmental pollution. Spent car lead acid batteries are an environmentally hazardous waste; however, they can alternatively serve as an abundant and inexpensive Pb source. Due to “self-purification”, quantum dots feature a high tolerance of impurities in the precursor since the impurities tend to be expelled from the small crystalline cores during colloidal nucleation. Herein, PbI2 recycled from spent lead acid batteries via a facile low-temperature solution process is used to synthesize CsPbI3 quantum dots, which simultaneously brings multiple benefits including (1) avoiding pollution originating from the fire smelting process; (2) recycling the Pb waste from batteries; and (3) synthesizing high-quality quantum dots. The resulting CsPbI3 quantum dots have photophysical properties such as PLQY and carrier lifetimes on par with those synthesized from the commercial PbI2 due to expelling of the impurity Na atoms. The resulting solar cells deliver comparable power conversion efficiencies: 14.0% for the cells fabricated using recycled PbI2 and 14.7% for the cells constructed using commercial PbI2. This work paves a new and feasible path to applying recycled Pb sources in perovskite photovoltaics.

Protonated 3d transition-metal oxides often display low electronic conduction, which hampers their application in electric, magnetic, thermoelectric, and catalytic fields. Electronic conduction can be enhanced by co-inserting oxygen acceptors simultaneously. However, the currently used redox approaches hinder protons and oxygen ions co-insertion due to the selective switching issues. Here, a thermal hydration strategy for systematically exploring the synthesis of conductive protonated oxides from 3d transition-metal oxides is introduced. This strategy is illustrated by synthesizing a novel layered-oxide SrCoO3H from the brownmillerite SrCoO2.5. Compared to the insulating SrCoO2.5, SrCoO3H exhibits an unprecedented high electronic conductivity above room temperature, water uptake at 250 °C, and a thermoelectric power factor of up to 1.2 mW K-2 m-1 at 300 K. These findings open up opportunities for creating high-conductive protonated layered oxides by protons and oxygen ions co-doping. CC acknowledges support from the Spanish Ministry of Science, Innovation, and Universities under the “Ramón y Cajal” fellowship RYC2018-024947-I.

A pressure-induced structural phase transition and its intimate link with the superconducting transition was studied for the first time in TiSe2 up to 40 GPa at room temperature using X-ray diffraction, transport measurement, and first-principles calculations. We demonstrate the occurrence of a first-order structural phase transition at 4 GPa from the standard trigonal structure (S.G.P3¯m1) to another trigonal structure (S-G-P3¯c1). Additionally, at 16 GPa, the P3¯c1 phase spontaneously transforms into a monoclinic C2/m phase, and above 24 GPa, the C2/m phase returns to the initial P3¯m1 phase. Electrical transport results show that metallization occurs above 6 GPa. The charge density wave observed at ambient pressure is suppressed upon compression up to 2 GPa with the emergence of superconductivity at 2.5 GPa, with a critical temperature (Tc) of 2 K. A structural transition accompanies the emergence of superconductivity that persists up to 4 GPa. The results demonstrate that the pressure-induced phase transitions explored by the experiments along with the theoretical predictions may open the door to a new path for searching and controlling the phase diagrams of transition metal dichalcogenides. C.C. acknowledges support from the Spanish Ministry of Science, Innovation, and Universities under the “Ramon y Cajal” fellowship RYC2018-024947-I.

The high-pressure and high-temperature structural and chemical stability of ruthenium has been investigated via synchrotron X-ray diffraction using a resistively heated diamond anvil cell. In the present experiment, ruthenium remains stable in the hcp phase up to 150 GPa and 960 K. The thermal equation of state has been determined based upon the data collected following four different isotherms. A quasi-hydrostatic equation of state at ambient temperature has also been characterized up to 150 GPa. The measured equation of state and structural parameters have been compared to the results of ab initio simulations performed with several exchange-correlation functionals. The agreement between theory and experiments is generally quite good. Phonon calculations were also carried out to show that hcp ruthenium is not only structurally but also dynamically stable up to extreme pressures. These calculations also allow the pressure dependence of the Raman-active E2g mode and the silent B1g mode of Ru to be determined.

The morphologies of ceria nanocrystals play an essential role in determining their redox and catalytic performances in many applications, yet the effects of synthesis variables on the formation of ceria nanoparticles of different morphologies and their related growth mechanisms have not been systematised. The design of these morphologies is underpinned by a range of fundamental parameters, including crystallography, optical mineralogy, the stabilities of exposed crystallographic planes, CeO2-x stoichiometry, phase equilibria, thermodynamics, defect equilibria, and the crystal growth mechanisms. These features are formalised and the key analytical methods used for analysing defects, particularly the critical oxygen vacancies, are surveyed, with the aim of providing a source of design parameters for the synthesis of nanocrystals, specifically CeO2-x. However, the most important aspect in the design of CeO2-x nanocrystals is an understanding of the roles of the main variables used for synthesis. While there is a substantial body of data on CeO2-x morphologies fabricated using low cerium concentrations ([Ce]) under different experimental conditions, the present work fully maps the effects of the relevant variables on the resultant CeO2-x morphologies in terms of the commonly used raw materials [Ce] (and [NO3-] in Ce(NO3)3·6H2O) as feedstock, [NaOH] as precipitating agent, temperature, and time (as well as the complementary vapour pressure). Through the combination of consideration of the published literature and the generation of key experimental data to fill in the gaps, a complete mechanistic description of the development of the main CeO2-x morphologies is illustrated. Further, the mechanisms of the conversion of nanochains into the two variants of nanorods, square and hexagonal, have been elucidated through crystallographic reasoning. Other key conclusions for the crystal growth process are the critical roles of (1) the formation of Ce(OH)4 crystallite nanochains as the precursors of nanorods and (2) the disassembly of the nanorods into Ce(OH)4 crystallites and NO3--assisted reassembly into nanocubes (and nanospheres) as an unrecognised intermediate stage of crystal growth.

Compositional engineering of BiFeO3 can significantly boost its photovoltaic performance. Therefore, controlling site substitution and understanding how it affects the optical and electronic properties while achieving robust and stable phases is essential to continue progressing in this field. Here the influence of cation co-substitution in BiFeO3 on phase purity, optical and electronic properties is investigated by means of X-ray diffraction, spectroscopic ellipsometry and X-ray absorption spectroscopy, respectively. Piezoelectric force microscopy and ferroelectric characterization at room temperature has been carried out in co-doped BiFeO3 films. First-principles calculations are also performed and compared to the experimental observations. It is shown that the incorporation of La3+ in Bi(Fe,Co)O3 films improves phase purity and stability while preserving the reduced band gap achieved in metastable Bi(Fe,Co)O3. Moreover, it is suggested that the changes in the optoelectronic properties are mainly dictated by the hybridisation between unoccupied Co 3d and O 2p states along with the presence of Co3+/Co2+ species. This thorough study on (Bi,La)(Fe,Co)O3 thin films coupled with the use of a cost-effective and facile solution deposition synthesis increases the motivation to continue exploiting the potential of these perovskite materials., This research was supported by the Spanish Ministerio de Ciencia, Innovación y Universidades (“Severo Ochoa” Programme for Centres of Excellence in R&D CEX2019-000917-S, MAT2017-83169-R, RTI2018-093996-B-C32, PID2019-107727RB-I00 (AEI/FEDER, EU)). P. M. thanks financial support from FPI fellowship (PRE2018-084618). C. M. and C. C. acknowledge computational resources and technical assistance from the Australian Government and the Government of Western Australia through the National Computational Infrastructure (NCI) and Magnus under the National Computational Merit Allocation Scheme and The Pawsey Supercomputing Centre. The authors acknowledge Prof. J. Fontcuberta for providing access to his experimental facilities and the support of ALBA staff for the successful performance of the measurements at CIRCE beamline of the ALBA Synchrotron Light Source. I. F. and C. C. acknowledge support from the Spanish Ministry of Science, Innovation and Universities under the “Ramón y Cajal” fellowship RYC2017-226531 and RYC2018-024947-I, respectively. M. C and I. F acknowledge Beca Leonardo from fundación BBVA. H. T is financially supported by China Scholarship Council (CSC) with no. 201906050014. The work of P. M. and H. T have been done in the framework of the doctorate in Materials Science of the Autonomous University of Barcelona.

Disorder–disorder phase transitions are rare in nature. Here, we present a comprehensive low-temperature experimental and theoretical study of the heat capacity and vibrational density of states of 1-fluoro-adamantane (C10H15F), an intriguing molecular crystal that presents a continuous disorder–disorder phase transition at T = 180 K and a low-temperature tetragonal phase that exhibits fractional fluorine occupancy. It is shown that fluorine occupancy disorder in the low-T phase of 1-fluoro-adamantane gives rise to the appearance of low-temperature glassy features in the corresponding specific heat (i.e., “boson peak” -BP-) and vibrational density of states. We identify the inflation of low-energy optical modes as the main responsible for the appearance of such glassy heat-capacity features and propose a straightforward correlation between the first localized optical mode and maximum BP temperature for disordered molecular crystals (either occupational or orientational). Thus, the present study provides new physical insights into the possible origins of the BP appearing in disordered materials and expands the set of molecular crystals in which “glassy-like” heat-capacity features have been observed.

Metal oxide pseudocapacitors are limited by low electrical and ionic conductivities. The present work integrates defect engineering and architectural design to exhibit, for the first time, intercalation pseudocapacitance in CeO2–x. An engineered chronoamperometric electrochemical deposition is used to synthesize 2D CeO2–x nanoflakes as thin as ~12 nm. Through simultaneous regulation of intrinsic and extrinsic defect concentrations, charge transfer and charge–discharge kinetics with redox and intercalation capacitances together are optimized, where reduction increases the gravimetric capacitance by 77% to 583 F g–1, exceeding the theoretical capacitance (562 F g–1). Mo ion implantation and reduction processes increase the specific capacitance by 133%, while the capacitance retention increases from 89 to 95%. The role of ion-implanted Mo6+ is critical through its interstitial solid solubility, which is not to alter the energy band diagram but to facilitate the generation of electrons and to establish the midgap states for color centers, which facilitate electron transfer across the band gap, thus enhancing n-type semiconductivity. Critically, density functional theory simulations reveal, for the first time, that the reduction causes the formation of ordered oxygen vacancies that provide an atomic channel for ion intercalation. These channels enable intercalation pseudocapacitance but also increase electrical and ionic conductivities. In addition, the associated increased active site density enhances the redox such that the 10% of the Ce3+ available for redox (surface only) increases to 35% by oxygen vacancy channels. These findings are critical for any oxide system used for energy storage systems, as they offer both architectural design and structural engineering of materials to maximize the capacitance performance by achieving accumulative surface redox and intercalation-based redox reactions during the charge/discharge process.

Traditional refrigeration technologies based on compression cycles of greenhouse gases pose serious threats to the environment and cannot be downscaled to electronic device dimensions. Solid-state cooling exploits the thermal response of caloric materials to external fields and represents a promising alternative to current refrigeration methods. However, most of the caloric materials known to date present relatively small adiabatic temperature changes ($|\Delta T| \sim 1$ K) and/or limiting irreversibility issues resulting from significant phase-transition hysteresis. Here, we predict the existence of colossal barocaloric effects (isothermal entropy changes of $|\Delta S| \sim 100$ JK$^{-1}$kg$^{-1}$) in the energy material Li$_{2}$B$_{12}$H$_{12}$ by means of molecular dynamics simulations. Specifically, we estimate $|\Delta S| = 387$ JK$^{-1}$kg$^{-1}$ and $|\Delta T| = 26$ K for an applied pressure of $P = 0.4$ GPa at $T = 475$ K. The disclosed colossal barocaloric effects are originated by an order-disorder phase transformation that exhibits a fair degree of reversibility and involves coexisting Li$^{+}$ diffusion and (BH)$_{12}^{-2}$ reorientational motion at high temperatures., Comment: 8 pages, 3 figures, 1 table

Controlling the size and shape of metallic colloids is crucial for a number of nanotechnological applications ranging from medical diagnosis to electronics. Yet, achieving tunability of morphological changes at the nanoscale is technically difficult and the structural modifications made on nanoparticles generally are irreversible. Here, we present a simple nonchemical method for controlling the size of metallic colloids in a reversible manner. Our strategy consists of applying hydrostatic pressure on a Ca cationic sublattice embedded in the irradiated matrix of CaF2 containing a large concentration of defects. Application of our method to CaF2 along with in situ optical absorption of the Ca plasmon shows that the radii of the Ca nanoparticles can be reduced with an almost constant rate of −1.2 nm/GPa up to a threshold pressure of ∼9.4 GPa. We demonstrate recovery of the original nanoparticles upon decompression of the irradiated matrix. The mechanisms for reversible nanocolloid-size variation are analyzed with first-principles simulations. We show that a pressure-driven increase in the binding energy between fluorine centers is responsible for the observed nanoparticle shrinkage. We argue that the same method can be used to generate other metallic colloids (Li, K, Sr, and Cs) with tailored dimensions by simply selecting an appropriate matrix., J.R.-F. and V.M. acknowledge the Spanish Ministry of Science, Innovation and Universities for the Juan de la Cierva program IJCI-2014-20513 and FJCI-2016-27921, respectively. C.C. acknowledges support from the Australian Research Council under the Future Fellowship funding scheme (No. FT140100135). Computational resources and technical assistance were provided by the Australian Government and the Government of Western Australia through the National Computational Infrastructure (NCI) and Magnus under the National Computational Merit Allocation Scheme and The Pawsey Supercomputing Centre. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 829161.

International audience; As the world shifts toward renewable energy, the need for an effective energy carrier is pressing. Hydrogen has often been touted as a universal clean energy vector and the fuel of the future. Unfortunately, mass adoption of the hydrogen economy is slow due to a lack of incentives and technical difficulties in storing hydrogen. Better materials capable of reversible hydrogen uptake/release with hydrogen capacity surpassing 5 mass% at the ambient must emerge. So far, finding such materials has been elusive; alloys capable of ambient hydrogen uptake/release have a low storage capacity while high capacity hydrides have a very high hydrogen release temperature. From metal alloys to complex hydrides, a better understanding of the behavior of hydrogen in hydrides is essential to fine-tune their properties toward application. Herein, the latest approaches to design hydrogen storage materials based on known hydrides are reviewed with the aim to facilitate the emergence of alternative thinking toward the design of better hydrogen storage materials. Synthetic methods and conceptual approaches to achieve particular hydrogen thermodynamics and kinetics are discussed. These include metallurgical alloying, mechanochemical modification, chemical destabilization, the nanosizing approach, and theoretical modeling and machine learning techniques to guide experimental work.