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Transition metal dichalcogenide (TMDC) monolayers exhibit great photocatalytic performances and tunabilities. By using first-principles simulations based on density functional theory, we demonstrate here that external electric bias can be employed to further improve the photocatalytic hydrogen production efficiencies of the six AB2 (A = Mo, W and B = S, Se, Te) TMDC monolayers since these are influenced by their piezoelectric response. In particular, when subjected to a proper amount of electrically induced tensile biaxial strain, most TMDC monolayers turn into potentially ideal photocatalysts toward the hydrogen evolution reaction (HER). The beneficial effects of introducing tensile biaxial strain on the TMDC monolayers are not limited to the reduction of the band gap and proper adjustment of the band edge positions; the concomitant hydrogen adsorption free energies are also modified in such a way that the HER reaction is noticeably favored.

This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Applied Materials and Interfaces, copyright © 2022 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/acsami.2c02675. Metallic 1T-phase MoS2 exhibits superior hydrogen evolution reaction (HER) performance than natural 2H-phase MoS2 owing to its higher electrical conductivity and abundance of active sites. However, the reported 1T-MoS2 catalysts usually suffer from extreme instability, which results in quick phase transformation at ambient conditions. Herein, we present a facile approach to engineer the phase of MoS2 by introducing intercalated hydrazine. Interestingly, the as-synthesized 1T-dominant MoS2 sample demonstrates excellent ambient stability without noticeable degradation for 3 months. Additionally, the 1T-dominant MoS2 exhibits superior electrical conductivity (~700 times higher than that of 2H-MoS2) and improved electrochemical catalytic performance (current density ~12 times larger than that of 2H-MoS2 at an overpotential of 300 mV vs the reversible hydrogen electrode, RHE). Through experimental characterizations and density functional theory (DFT) calculation, we conclude that the stabilization of the metallic phase could be attributed to the electron donation from hydrazine molecules to the adjacent Mo atoms. The phase control strategy in this work provides a guideline to develop other highly efficient and stable two-dimensional (2D) electrocatalysts.

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).

Organic electrochemical transistors (OECTs) for bioelectronic applications require the design of conjugated polymers that are stable in aqueous environments and afford high energy efficiency and good performance in OECTs. Polymers based on poly(ethylenedioxythiophene) (PEDOT) are promising in this area due to their low oxidation potential and reversible redox, but they often require cross-linking to prevent dissolution and yield OECTs operating in the less efficient depletion mode. In this work, a new conjugated polymer PEDOT-Phos is presented, which combines a conjugated poly(ethylenedioxythiophene) (PEDOT) backbone with alkyl-protected phosphonate groups. PEDOT-Phos exhibits a low oxidation onset potential (-0.157 V vs Ag/AgCl) and its nanoporous morphology affords it a high volumetric capacitance (282 ± 62 F cm–3). Without any cross-linking, additives, or post-treatment, PEDOT-Phos can be used in aqueous OECTs with efficient accumulation mode operation, long-term stability when immersed in aqueous media, low threshold voltages (-0.161 ± 0.005 V), good transconductances (9.3 ± 1.8 mS), and ON/OFF current ratios (618 ± 54) comparable to other PEDOT-based materials in OECTs. These results highlight the great promise of PEDOT-Phos as a stand-alone channel material for energy-efficient, bioelectronic devices.

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.

Perovskite oxides are regarded as promising electrocatalysts for water splitting due to their cost-effectiveness, high efficiency and durability in the oxygen evolution reaction (OER). Despite these advantages, a fundamental understanding of how critical structural parameters of perovskite electrocatalysts influence their activity and stability is lacking. Here, we investigate the impact of structural defects on OER performance for representative LaNiO3 perovskite electrocatalysts. Hydrogen reduction of 700¿°C calcined LaNiO3 induces a high density of surface oxygen vacancies, and confers significantly enhanced OER activity and stability compared to unreduced LaNiO3; the former exhibit a low onset overpotential of 380 mV at 10 mA¿cm-2 and a small Tafel slope of 70.8 mV¿dec-1. Oxygen vacancy formation is accompanied by mixed Ni2+/Ni3+ valence states, which quantum-chemical DFT calculations reveal modify the perovskite electronic structure. Further, it reveals that the formation of oxygen vacancies is thermodynamically more favourable on the surface than in the bulk; it increases the electronic conductivity of reduced LaNiO3 in accordance with the enhanced OER activity that is observed.

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.

Ruddlesden–Popper phase 2D perovskite solar cells (PSCs) exhibit improved lifetime while still facing challenges such as phase alignment and up-scaling to module-level devices. Herein, polyelectrolytes are explored to tackle this issue. The contact between perovskite and hole-transport layer (HTL) is important for decreasing interfacial non-radiative recombination and scalable fabrication of uniform 2D perovskite films. Through exploring compatible butylamine cations, we first demonstrate poly(3-(4-carboxybutyl)thiophene-2,5-diyl)-butylamine (P3CT-BA) as an efficient HTL for 2D PSCs due to its great hydrophilicity, relatively high hole mobility and uniform surface. More importantly, the tailored P3CT-BA has an anchoring effect and acts as the buried passivator for 2D perovskites. Consequently, a best efficiency approaching 18¿% was achieved and we further first report large-area (2×3 cm2, 5×5 cm2) 2D perovskite minimodules with an impressive efficiency of 14.81¿% and 11.13¿%, respectively.

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.

We demonstrate that the heat capacity Boson peak (BP)-like anomaly appearing in fully ordered anharmonic molecular crystals emerges as a result of the strong interactions between propagating (acoustic) and low-energy quasi-localized (optical) phonons. In particular, we experimentally determine the low-temperature (

The new class of oxide heterojunctions with mixed dimensionalities holds great promise for energy and environmental applications. However, the existing fabrication strategies typically involve low-yield and multistep processes leading to the formation of powders that necessitate binding agents when used for electrochemical applications; thereby, the durability and performance of the resultant electrode may be adversely impacted. To address these challenges, the present work first reports a high-temperature counter-current gas flow technique for rapid fabrication (5–10 min) of centimetre-size, self-adhesive, free-standing 3D patches made of ZnO-based woven nanowires. Furthermore, the high applicability of the method was shown by layer-by-layer assembly of the ZnO and layers of 0D heteroatoms including Bi2O3, CdO, SnO2, and carbon forming stratified oxide heterojunction (SOH) nanostructures with midgap states within their electronic bandgap region. This work is innovative in that the ZnO and the fabricated SOHs are synthesised through a sustainable and large-scale method based on microrecycling of waste materials. The engineering of the electronic band positions can modify the functionality of the SOH patches by optimising the potentials required for catalytic reactions. As a representative, the SOH nanostructures were tested for anodic electrocatalytic water oxidation to H2O2. The results showed that the ZnO–CdO patch has the lowest overpotential of 150 mV and outstanding stability at 2.33 V vs. RHE. Furthermore, the results of first-principles density functional theory (DFT) calculations (i) confirmed realignments of the band position due to the formation of midgap states, and (ii) revealed that significant improvements in the electrocatalytic H2O2 performance can be achieved with overpotentials as low as 0.19 and 0.31 V for ZnO–CdO and ZnO–Bi2O3, respectively. This work offers an ultrafast fabrication strategy to synthesise binder-free SOH nanostructures with an engineered electronic structure that can be an alternative to state-of-the-art noble metal electrocatalysts such as Pt.

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.

Thermoelectric materials create an electric potential when subjected to a temperature gradient and vice versa; hence they can be used to harvest waste heat into electricity and in thermal management applications. However, finding highly efficient thermoelectrics with high figures of merit, zT ≥ 1, is very challenging because the combination of a high power factor and low thermal conductivity is rare in materials. Here, we use first-principles methods to analyze the thermoelectric properties of Li2SnX3 (X = S, and Se), a recently synthesized class of lithium fast-ion conductors presenting high thermal stability. In p-type Li2SnX3, we estimate highly flat electronic valence bands that produce high Seebeck coefficients exceeding 400 μV K−1 at 700 K. In n-type Li2SnX3, the electronic conduction bands are slightly dispersive; however, the accompanying electron–acoustic phonon scattering is weak, which induces high electrical conductivity. The combination of a high Seebeck coefficient and electrical conductivity gives rise to high power factors, reaching a maximum of ∼4.5 mW m−1 K−2 at 300 K in both n-type Li2SnS3 and Li2SnSe3. Likewise, the thermal conductivity in Li2SnX3 is low as compared to conventional thermoelectric materials, 1.35–4.65 W m−1 K−1 at room temperature. As a result, we estimate a maximum zT of 1.1 in n-type Li2SnS3 at 700 K and of 2.1 (1.1) in n-type Li2SnSe3 at the same temperature (300 K). Our findings of large zT in Li2SnX3 suggest that lithium fast-ion conductors, typically employed as electrolytes in solid-state batteries, hold exceptional promise as thermoelectric materials.

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.

Epitaxially grown $$\hbox {SrTiO}_{{3}}$$ SrTiO 3 (STO) thin films are material enablers for a number of critical energy-conversion and information-storage technologies like electrochemical electrode coatings, solid oxide fuel cells and random access memories. Oxygen vacancies ($${\mathrm{V}_{{\mathrm{O}}}}$$ V O ), on the other hand, are key defects to understand and tailor many of the unique functionalities realized in oxide perovskite thin films. Here, we present a comprehensive and technically sound ab initio description of $${\mathrm{V}_{{\mathrm{O}}}}$$ V O in epitaxially strained (001) STO thin films. The novelty of our first-principles study lies in the incorporation of lattice thermal excitations on the formation energy and diffusion properties of $${\mathrm{V}_{{\mathrm{O}}}}$$ V O over wide epitaxial strain conditions ($$-4 \le \eta \le +4$$ - 4 ≤ η ≤ + 4 %). We found that thermal lattice excitations are necessary to obtain a satisfactory agreement between first-principles calculations and the available experimental data for the formation energy of $${\mathrm{V}_{{\mathrm{O}}}}$$ V O . Furthermore, it is shown that thermal lattice excitations noticeably affect the energy barriers for oxygen ion diffusion, which strongly depend on $$\eta $$ η and are significantly reduced (increased) under tensile (compressive) strain. The present work demonstrates that for a realistic theoretical description of oxygen vacancies in STO thin films is necessary to consider lattice thermal excitations, thus going beyond standard zero-temperature ab initio approaches.

We measured the specific heat Cp of normal (C4H4S) and deuterated (C4D4S) thiophene in the temperature interval of 1 = T, K = 25. C4H4S exhibits a metastable phase II2 and a stable phase V, both with frozen orientational disorder (OD), whereas C4D4S exhibits a metastable phase II2, which is analogous to the OD phase II2 of C4H4S and a fully ordered stable phase V. Our measurements demonstrate the existence of a large bump in the heat capacity of both stable and metastable C4D4S and C4H4S phases at temperatures of ~10 K, which significantly departs from the expected Debye temperature behavior of Cp ˜ T3. This case study demonstrates that the identified low-temperature Cp anomaly, typically referred to as a “Boson-peak” in the context of glassy crystals, is not exclusive of disordered materials.

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.