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Copper-chalcogenides are promising candidates for thin film photovoltaics due to their ideal electronic structure and potential for defect tolerance. To this end, we have theoretically investigated the optoelectronic properties of Cu₂SiSe₃, due to its simple ternary composition, and the favorable difference in charge and size between the cation species, limiting antisite defects and cation disorder. We find it to have an ideal, direct bandgap of 1.52 eV and a maximum efficiency of 30% for a 1.5 μm-thick film at the radiative limit. Using hybrid density functional theory, the formation energies of all intrinsic defects are calculated, revealing the p-type copper vacancy as the dominant defect species, which forms a perturbed host state. Overall, defect concentrations are predicted to be low and have limited impact on non-radiative recombination, as a consequence of the p - d coupling and antibonding character at the valence band maxima. Therefore, we propose that Cu₂SiSe₃ should be investigated further as a potential defect-tolerant photovoltaic absorber.

High-nuclearity Mn complexes have attracted significant scientific attention due to their fascinating magnetic properties and their relevance to bioinorganic systems and catalysis. In this work, we demonstrate how the strong binding characteristics of phosphonate ligands can be coupled with sterically hindered carboxylate groups to influence the symmetry of Mn coordination clusters. We describe the structure of two high-nuclearity Mn coordination cages, {Mn12} and {Mn15}, synthesized using this approach. These cages are structurally related to the truncated tetrahedral geometry and adopt rare topological features of Archimedean and Johnson-type solids. Their structural attributes distinctively influence their magnetic properties and electrocatalytic H2O oxidation characteristics.

The dependence of the global population on ammonia means that the Haber–Bosch process is one of the most studied and optimised processes in chemistry. Despite this focus, the reaction still requires harsh conditions, which has prompted substantial research efforts to enable the electroreduction of N2 at ambient conditions. The literature regarding this reaction is plagued with reports of competition with the hydrogen evolution reaction and large potentials required for N2 dissociation. Cyanide, isoelectronic with N2, has a significantly lower bond dissociation energy which could enable a route to sustainable ammonia production. Herein, we present the first mechanistic study of the cyanide electroreduction on a Ni cathode, experimentally shown to produce methylamine as a major product, and CH4 and NH3 as minor products. Theoretical calculations reveal that the dominance of methylamine in the products is due to the weak binding of this species, which desorbs from the surface preventing further hydrogenation. We also present an alternative CNRR pathway which involves the hydrogen atoms comprising the predicted surface coverage at relevant reaction conditions. Interestingly, this new pathway circumvents the formation of methylamine, exclusively producing CH4 and NH3, although it is hindered by the presence of a large energy barrier. Strategies to favour this alternative pathway and the prospects of CNRR for the sustainable production of ammonia under ambient conditions are also outlined.

Two novel Ru(II) photosensitisers sporting ethynyl-Nile Red chromophores are shown to absorb strongly in the visible region, and to have two distinct but weakly emissive states (1ILCT* and 3MLCT*). In addition a long-lived, lower energy ‘dark’ (non-emissive) triplet excited state is identified (3ILCT*) and successfully exploited for singlet oxygen generation.

Solid oxide fuel cells (SOFCs) are highly efficient fuel-flexible energy conversion devices. In this review, we present the latest advances in the computational modelling of SOFC components. The combination of first principle calculations and classical molecular dynamics (MD) simulations can provide an accurate and complete description of the materials being investigated — from their electronic structure and related properties to the thermodynamic and kinetics behind catalytic reactions or diffusion processes. Computational modelling is, therefore, an essential tool in developing or improving SOFC components, allowing researchers to predict, understand and explain the mechanisms behind the experimentally observed properties.

The 4-amino-1,8-naphthalimide-Tröger's base fluorophore, TBNap-TPy, adorned with phenyl-terpyridine moiety was synthesised and assessed for its aggregation-induced emission (AIE) behaviour. TBNap-TPy was further employed as a fluorescent sensor for the discriminative sensing of π-electron-deficient nitroaromatic; the TBNap-TPy displaying the largest fluorescence quenching with high selectivity for picric acid, a harmful environmental pollutant widely used in the dye industries.

Interfaces are a type of extended defect which govern the properties of materials. As the nanostructuring of materials becomes more prevalent the impact of interfaces such as grain boundaries (GBs) becomes more important. Computational modelling of GBs is vital to the improvement of our understanding of these defects as it allows us to isolate specific structures and understand resulting properties. The first step to accurately modelling GBs is to generate accurate descriptions of the structures. In this paper, we present low angle mirror tilt GB structures for fluorite structured materials (calcium fluoride and ceria). We compare specific GB structures which are generated computationally to experimentally known structures, wherein we see excellent agreement. The high accuracy of the method which we present for predicting these structures can be used in the future to predict interfaces which have not already been experimentally identified and can also be applied to heterointerfaces.

Lead-free organic–inorganic halide perovskites have gained much attention as nontoxic alternatives to CH3NH3PbI3 in next-generation solar cells. In this study, we have examined the geometric and electronic properties of methylammonium germanium iodide CH3NH3GeI3 using density functional theory. Identifying a suitable functional to accurately model the germanium halide perovskites is crucial to allow the theoretical investigation for tuning the optoelectronic properties. The performance of various functionals (PBE, PBE+D3, PBEsol, PBEsol+D3, HSE06, and HSE06+D3) has been evaluated for modelling the structure and properties. The calculation of electronic properties was further refined by using the quasiparticle GW method on the optimized geometries, and that has an excellent agreement with the experiment. We report from our GW calculations that the characteristic of the density of states for CH3NH3GeI3 resembles the density of states for CH3NH3PbI3 and the effective masses of the charge carriers of CH3NH3GeI3 are comparable to the effective masses of CH3NH3PbI3 as well as silicon used in commercially available solar cells.

Summary: n-type transparent conductors (TCs) are key materials in the modern optoelectronics industry. Despite years of research, the development of a high-performance p-type TC has lagged far behind that of its n-type counterparts, delaying the advent of “transparent electronics”-based p-n junctions. Here, we propose the layered oxysulfide [Cu 2S 2][Sr 3Sc 2O 5] as a structural motif for discovering p-type TCs. We have used density functional theory to screen 24 compositions based on this motif in terms of their thermodynamic and dynamic stability and their electronic structure, thus predicting two p-type TCs and eight other stable systems with semiconductor properties. Following our predictions, we have successfully synthesized our best candidate p-type TC, [Cu 2S 2][Ba 3Sc 2O 5], which displays structural and optical properties that validate our computational models. It is expected that the design principles emanating from this analysis will move the field closer to the realization of a high figure-of-merit p-type TC.Progress and Potential: This work has predicted and experimentally realized the p-type transparent conductor [Cu 2S 2][Ba 3Sc 2O 5], and at the same time has developed design principles for layered oxychalcogenide materials of this structure type. The layered oxychalcogenide materials offer a large configurational space of potentially stable compounds with tunable functional properties for a wide range of applications. The longer-term ambitions of the research are to use the combined methods of density functional theory and experiments to search for and understand further layered oxychalcogenide structure types and configurations for different semiconductor applications. This research has the potential to affect the types of electronic devices by bringing us closer to the realism of transparent electronics. The research presented will also further the development of applications for which transparent conductors are essential, such as solar cells. Abstract: The realization of transparent electronics is hindered by the lack of a suitable high-mobility p-type transparent conductor (TC). This work used ab initio simulations to search for a p-type TC based on the layered oxychalcogenide [Cu 2S 2][A 3M 2O 5] structure. The main result of this study was the discovery of the optimum p-type oxychalcogenide TC, [Cu 2S 2][Ba 3Sc 2O 5], predicted to have a higher optical band gap, better hole mobility, and greater stability than its parent compound [Cu 2S 2][Ba 3Sc 2O 5]; this was verified experimentally.

Polynuclear transition metal complexes have continuously attracted interest owing to their peculiar electronic and magnetic properties which are influenced by the symmetry and connectivity of the metal centres. Understanding the full electronic picture in such cases often becomes difficult owing to the presence of multiple bridges between metal centres. We have investigated the electronic structure of a {Mn6} cage complex using computational and experimental approaches with the aim to understand the coupling between the manganese centres. The nature of the various coupling pathways has been determined using a novel methodology that involves perturbing the system while retaining the symmetry and analysing the effect on the coupling strength due to the perturbation. Furthermore, we have investigated the magnetic properties of this complex in higher oxidation states which reveals a switch in the nature of coupling from antiferromagnetic to ferromagnetic in addition to stabilisation of intermediate spin states.

A new hyper-crosslinked 4-amino-1,8-naphthalimide Tröger’s base containing pyridinium covalent organic polymer, TBNap-COP, was synthesised and employed as a ‘turn-off’ fluorescent chemosensor for nitroaromatic explosives. TBNap-COP was synthesised in quantitative yield using a one-step nucleophilic substitution reaction between a dipyridyl scaffold (TBNap, bis-[N-(2-(pyridine-4-yl)ethyl)]-9,18-methano-1,8-naphthalimide-[b,f][1,5]diazocine) and 1,3,5-tris(bromomethyl)benzene by heating in DMF for 3 days. The formation and phase-purity of TBNap-COP were fully characterised by using various spectroscopic and microscopy analyses. The suspension of TBNap-COP in water showed strong fluorescence emission characteristics owing to the ‘push-pull’ based ICT transition and it was used as a fluorescent sensor for discriminative detection of nitroaromatic explosives. TBNap-COP displayed selective fluorescence quenching responses for phenolic-nitroaromatics, with particularly high sensitivity for picric acid which is a powerful secondary chemical explosive and a harmful environmental pollutant widely used in the dye industries.

Tin oxide materials are technologically important materials with applications including catalysis, transparent conducting oxides, and battery materials. The structure and electronic structure of these materials play a key role in determining their properties and applications. In this chapter, we discuss the crystalline structure of SnO2, SnO, and Sn3O4, using both experimental data and data calculated from density functional theory (DFT). We discuss the electronic structure of these tin oxide materials by studying data from existing experimental studies using methods such as X-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy (XES), hard X-ray photoelectron spectroscopy (HAXPES), and X-ray absorption spectroscopy (XAS). The electronic structure is further studied using different levels of DFT (generalized gradient approximation and hybrid DFT), wherein band structures and densities of states are used to elucidate the specific attributes of the electronic structure and compare to experimental data. The lone pair effects in SnO and Sn3O4 are also highlighted and discussed.

Summary n-type transparent conductors (TCs) are key materials in the modern optoelectronics industry. Despite years of research, the development of a high-performance p-type TC has lagged far behind that of its n-type counterparts, delaying the advent of “transparent electronics”-based p-n junctions. Here, we propose the layered oxysulfide [Cu2S2][Sr3Sc2O5] as a structural motif for discovering p-type TCs. We have used density functional theory to screen 24 compositions based on this motif in terms of their thermodynamic and dynamic stability and their electronic structure, thus predicting two p-type TCs and eight other stable systems with semiconductor properties. Following our predictions, we have successfully synthesized our best candidate p-type TC, [Cu2S2][Ba3Sc2O5], which displays structural and optical properties that validate our computational models. It is expected that the design principles emanating from this analysis will move the field closer to the realization of a high figure-of-merit p-type TC., Graphical Abstract, Highlights • 24 compounds were screened based on the [Cu2S2][A3M2O5] (I4/mmm) structure • Of the compounds, [Cu2S2][Ba3Sc2O5] was predicted to be the optimum p-type TC • [Cu2S2][Ba3Sc2O5] had a theoretical conductivity of 2,058 S cm−1 at 1 × 1021 cm−3 • Successful synthesis of [Cu2S2][Ba3Sc2O5] was achieved experimentally, Progress and Potential This work has predicted and experimentally realized the p-type transparent conductor [Cu2S2][Ba3Sc2O5], and at the same time has developed design principles for layered oxychalcogenide materials of this structure type. The layered oxychalcogenide materials offer a large configurational space of potentially stable compounds with tunable functional properties for a wide range of applications. The longer-term ambitions of the research are to use the combined methods of density functional theory and experiments to search for and understand further layered oxychalcogenide structure types and configurations for different semiconductor applications. This research has the potential to affect the types of electronic devices by bringing us closer to the realism of transparent electronics. The research presented will also further the development of applications for which transparent conductors are essential, such as solar cells., The realization of transparent electronics is hindered by the lack of a suitable high-mobility p-type transparent conductor (TC). This work used ab initio simulations to search for a p-type TC based on the layered oxychalcogenide [Cu2S2][A3M2O5] structure. The main result of this study was the discovery of the optimum p-type oxychalcogenide TC, [Cu2S2][Ba3Sc2O5], predicted to have a higher optical band gap, better hole mobility, and greater stability than its parent compound [Cu2S2][Ba3Sc2O5]; this was verified experimentally.

The ionic and electronic conductivity of orthorhombic LaMnO3 can be modified by introducing lower valence dopants at both the La and Mn sites. Alkaline earth doped perovskites, such as LaMnO3, have a variety of applications in catalysis, for nitrogen storage and reduction, and oxidation of volatile organic compounds, and as the oxygen electrode in solid oxide fuel cells. Here, we investigate doping with the divalent alkaline earth metals Mg, Ca, Sr and Ba, and the charge compensation mechanism. The energies of formation of isolated defects and clustered pairs were investigated at both La and Mn sites to establish the most probable site at which they will be introduced. The charge compensation mechanism for the introduction of alkaline earth dopants was examined by considering both ionic (formation of an oxygen vacancy for every two alkaline earth dopants introduced) and electronic compensation (a hole localised at the Mn site for each dopant introduced). Larger cations (Ca, Sr and Ba) were found to have lower defect formation energies when introduced at the La site, while the smaller Mg defect had lower formation energies when introduced to the Mn site. For all defects introduced, electronic compensation for the defect was found to be more energetically favourable, which will result in improved electronic conductivity of the material.

LaMnO 3 -based perovskites have been widely studied as the oxygen electrode for high temperature solid oxide fuel cells, and may be optimised for use at lower temperatures by introduction of dopants at the La and Mn sites. In order to examine defective LaMnO 3 , a good model of the parent compound is required. The performance of a range of functionals is assessed for modelling the bulk physical and electronic properties of the distorted perovskite LaMnO 3 . The effect of correcting for the self-interaction error is examined, by inclusion of a + U correction, or by use of a hybrid functional. The PBEsol functional, with a + U correction applied to Mn 3 d and O 2 p states is found to give a good description of both the structural and electronic properties of LaMnO 3 .

LaMnO3-based perovskites, which have been extensively studied as cathodes for high temperature solid oxide fuel cells (SOFCs), are also of interest for intermediate temperature SOFCs (T = 600-1000 K). Oxygen vacancy formation is required in LaMnO3 for oxygen diffusion, therefore a low vacancy formation energy is preferable. The stability of the low index surfaces of orthorhombic LaMnO3 has been investigated, with the {010} surface found to be the most stable. Surface stability was found to be affected by the La and Mn coordination, and the Mn-O bonds cleaved on surface formation. The crystal morphology has been predicted, in order to determine the most likely terminations to be present. The formation of oxygen vacancies in bulk LaMnO3 and at all of its low index surfaces has been examined, and it has been found that formation of vacancies in the bulk has a high energy, while there is a large variation in formation energies at the low index surfaces, which is likely to lead to segregation of vacancies to the surface of orthorhombic LaMnO3.

A Troger's base-functionalised covalent organic polymer (TB-COP) was synthesised and used as an adsorbent for the efficient removal of picric acid (PA) from water through the use of weak and reversible supramolecular interactions such as hydrogen bonding and π–π interactions. TB-COP was readily synthesised in quantitative yield using a one-pot metal-free polymerisation reaction strategy between a semi-flexible aromatic triamine [L; benzene-1,3-5-tricarboxylic acid-tris-(4-amino-phenyl-amide)] and dimethoxymethane. The molecular structure, physicochemical and morphological characteristics of TB-COP were analysed by using various spectroscopic and imaging techniques. Thermogravimetric analysis showed TB-COP to be thermally stable up to 380 °C; while the calculated Brunauer–Emmett–Teller (BET) surface area was found to be 34 m2 g−1 at 273 K. The picric acid adsorption study of the activated TB-COP showed an excellent adsorption capacity of ca. 90% within 60 minutes of contact time at 298 K (Langmuir isotherm model: KL = 0.0541 ± 6 L mg−1, R2 = 0.9962); the adsorption efficiency being shown to improve with increasing temperature. The extraction of PA was also clearly visible to the naked eye, where the yellow colored PA solution became transparent upon addition of TB-COP. Other interfering phenolic organic pollutants showed poor to moderate adsorption efficiency. Importantly, TB-COP could be used to store PA over a long period of time in a safe manner, without any leakage or any significant loss in extraction efficiency. Moreover, the polymer could be reused for several adsorption cycles, as PA could be released back into the solution by simply changing the pH of the aqueous media. This makes TB-COP an extremely promising material for the selective and efficient removal of picric acid from water, and TB-COP can be considered as being a ‘fast’ and naked eye colorimetric indicator for such analytes.

The 4-amino-1,8-naphthalimide Troger's base functionalized triazine covalent organic polymer TB-TZ-COP was synthesised and employed as a “turn-on” fluorescent and a colorimetric sensor for the discriminative sensing of volatile organic compounds; the TB-TZ-COP displaying the largest fluorescent enhancement and high sensitivity for 1,4-dioxane, a harmful environmental pollutant classified as a Group 2B carcinogen.

We report the synthesis and characterization of two photoactive metal-organic frameworks (MOFs)

n-Type transparent conductors (TCs) are key materials in the modern optoelectronics industry. Despite years of research, the development of a high performance p-type TC has lagged far behind that of its n-type counterparts delaying the advent of “transparent electronics” based on fully transparent p-n junctions. Here, we propose the layered oxysulfide [Cu2S2][Sr3Sc2O5] as a structural motif for discovering novel p-type TCs. We have used density functional theory to screen the thermodynamic and dynamical stability and electronic structure of 24 compositions based on this motif, predicting 2 new p-type TCs and 8 other stable systems with semiconductor properties. Following our predictions, we have successfully synthesized our best candidate p-type TC, [Cu2S2][Ba3Sc2O5], which displays structural and optical properties that validate our computational models. It is expected that the design principles emanating from this analysis will move the field closer to the realization of a high figure-of-merit p-type TC.

The chemical accessibility of the Ce

We report the synthesis and characterization of two photoactive metal–organic frameworks (MOFs), TCM-14 and TCM-15. The compounds were synthesized by incorporating 4,4′-azopyridine auxiliary ligand...

The doping of CeO2 with trivalent cations is a common technique for enhancing ionic conductivity in electrolytes for solid oxide fuel cell applications. However, the local defect structure in these materials is yet to be fully explored. Furthermore, many studies have overlooked the effect of the dopants on the reducibility of CeO2, which is important as electronic conductivity can short-circuit the fuel cell. Density functional theory (DFT)+U calculations have been performed on a series of CeO2 systems doped with trivalent cations. The most stable configuration and the relative attraction between dopant cations and oxygen vacancies were determined, and it was found that the defect structure is principally dependent on the ionic radius of the dopant cations. The reduction energy was found to be dependent on the structure around the dopants but did not vary significantly between dopants of similar ionic radii. From these results, it is possible to suggest which trivalent cations would be most suitable to en...

The electronic and atomic structures of amorphous transparent tin oxides have been investigated by a combination of X-ray spectroscopy and atomistic calculations. Crystalline SnO is a promising p-type transparent oxide semiconductor due to a complex lone-pair hybridization that affords both optical transparency despite a small electronic band gap and spherical s-orbital character at the valence band edge. We find that both of these desirable properties (transparency and s-orbital valence band character) are retained upon amorphization despite the disruption of the layered lone-pair states by structural disorder. We explain the anomalously large band gap widening necessary to maintain transparency in terms of lone-pair stabilization via atomic clustering. Our understanding of this mechanism suggests that continuous hole conduction pathways along extended lone pair clusters should be possible under certain stoichiometries. Moreover, these findings should be applicable to other lone-pair active semiconductors.

V2O5 aerogels are capable of reversibly intercalating more than 5 Li(+)/V2O5 but suffer from lifetime issues due to their poor capacity retention upon cycling. We employed a range of material characterization and electrochemical techniques along with atomic pair distribution function, X-ray photoelectron spectroscopy, and density functional theory to determine the origin of the capacity fading in V2O5 aerogel cathodes. In addition to the expected vanadium redox due to intercalation, we observed LiOH species that formed upon discharge and were only partially removed after charging, resulting in an accumulation of electrochemically inactive LiOH over each cycle. Our results indicate that the tightly bound water that is necessary for maintaining the aerogel structure is also inherently responsible for the capacity fade.

The ionic and electronic conductivity of orthorhombic LaMnO3 can be modified by introducing lower valence dopants at both the La and Mn sites. Alkaline earth doped perovskites, such as LaMnO3, have a variety of applications in catalysis, for nitrogen storage and reduction, and oxidation of volatile organic compounds, and as the oxygen electrode in solid oxide fuel cells. Here, we investigate doping with the divalent alkaline earth metals Mg, Ca, Sr and Ba, and the charge compensation mechanism. The energies of formation of isolated defects and clustered pairs were investigated at both La and Mn sites to establish the most probable site at which they will be introduced. The charge compensation mechanism for the introduction of alkaline earth dopants was examined by considering both ionic (formation of an oxygen vacancy for every two alkaline earth dopants introduced) and electronic compensation (a hole localised at the Mn site for each dopant introduced). Larger cations (Ca, Sr and Ba) were found to have lower defect formation energies when introduced at the La site, while the smaller Mg defect had lower formation energies when introduced to the Mn site. For all defects introduced, electronic compensation for the defect was found to be more energetically favourable, which will result in improved electronic conductivity of the material.

Ceria (CeO 2 ) doped with trivalent cations has been shown to be a technologically important material for use as solid electrolytes in solid oxide fuel cells and electrolysis cells. To fully understand and optimize these materials for use it is necessary to elucidate their behavior on an atomic scale. In this work, we perform both density functional theory and force field based molecular dynamics simulations of bulk and interfaces in doped CeO 2 .

The synthesis, photophysics and biological investigation of fluorescent 4-amino-1,8-naphthalimide Troger's bases (TB-1–TB-3) and a new Troger's base p-cymene–Ru(II)–curcumin organometallic conjugate (TB–Ru–Cur) are described; these compounds showed fast cellular uptake and displayed good luminescence and cytotoxicity against cervical cancer cells.

p-Type transparent conductors and semiconductors still suffer from remarkably low performance compared to their more widespread n-type counterparts, despite extensive investigation into their development. In this contribution, we present a comparative study on the defect chemistry of potential p-type transparent conducting oxides Mg-doped and Ni-doped Cr2O3. Conductivities as high as 28 S cm−1 were achieved by Ni-doping. By benchmarking crystallography and spectroscopy characterization against density functional theory calculations, we show that the incorporation of Ni into Cr2O3 contributes to the composition of the valence band, making the formed holes more delocalized, while Mg states do not interact with the valence band in Mg-doped Cr2O3. Furthermore, it is experimentally proven that Ni has a higher solubility in Cr2O3 than Mg, at least in the highly non-thermodynamic deposition conditions used for these experiments, which directly translates into a higher acceptor concentration. The combination of these two effects means that Ni is a more effective acceptor in Cr2O3 than Mg and explains the improved conductivity observed for the former.

The limit of solubility of Ga2O3 in the cubic bixbyite In2O3 phase was established by X-ray diffraction and Raman spectroscopy to correspond to replacement of around 6% of In cations by Ga for samples prepared at 1250 °C. Density functional theory calculations suggest that Ga substitution should lead to widening of the bulk bandgap, as expected from the much larger gap of Ga2O3 as compared to In2O3. However both diffuse reflectance spectroscopy and valence band X-ray photoemission reveal an apparent narrowing of the gap with Ga doping. It is tentatively concluded that this anomaly arises from introduction of Ga+ surface lone pair states at the top of the valence band and structure at the top of the valence band in Ga-segregated samples is assigned to these lone pair states. In addition photoemission reveals a broadening of the valence band edge. Core X-ray photoemission spectra and low energy ion scattering spectroscopy both reveal pronounced segregation of Ga to the ceramic surface, which may be linked to both relief of strain in the bulk and the preferential occupation of surface sites by lone pair cations. Surprisingly Ga segregation is not accompanied by the development of chemically shifted structure in Ga 2p core XPS associated with Ga+. However experiments on ion bombarded Ga2O3, where a shoulder at the top edge of the valence band spectra provide a clear signature of Ga+ at the surface, show that the chemical shift between Ga+ and Ga3+ is too small to be resolved in Ga 2p core level spectra. Thus the failure to observe chemically shifted structure associated with Ga+ is not inconsistent with the proposal that band gap narrowing is associated with lone pair states at surfaces and interfaces.

The electronic structure of a family of ternary copper chalcogenide systems Cu3MCh4 (M = V, Nb, Ta; Ch = S, Se, Te) has been explored to ascertain the compounds' potential for optoelectronic device applications. The lattice parameters, density of states, band gap, optical absorption, and effective mass of each of the nine systems were determined with PBEsol+U, and a valence band alignment was performed to assess the doping limits of the series. The calculated optical band gaps of the materials range from 1.19 eV for Cu3VTe4 to 2.60 eV for Cu3TaS4, with the former also predicted to have the highest valence band maximum and the lowest hole effective mass of the series, indicative of a p-type material with photovoltaic potential. The wide range of band gap energies predicted in this series of isostructural materials evidences how selective combination of elements in ternary systems can be used to tune electronic properties through alloying and thus target ideal values for specific applications. Five materials in the series are predicted to have optical band gaps suitable for solar cell absorbers, with Cu3NbTe4 and Cu3TaTe4 being of particular interest due not only to their respective band gaps of 1.46 eV and 1.69 eV but also their potential to be alloyed based on their similar lattice constants and valence band energies.

The oxygen states on CeO 2 surfaces were investigated with DFT + U calculations. The results reveal the variable nature of the oxygen states, including the never before modeled intrinsic peroxide surface defect. Under O-rich conditions, the peroxide defects on the (1 0 0) and (1 1 0) surfaces is more stable than oxygen vacancies. On surfaces doped with La (III) it is found that under O-rich conditions the (1 0 0) and (1 1 0) surface will preferentially form peroxide ions in response to the presence of the dopants while the (1 1 1) surface prefers oxygen vacancies. Calculated shifts in core levels match experimental binding energies, further suggesting the presence of peroxide species.

This paper reports the synthesis of highly conductive niobium doped titanium dioxide (Nb:TiO 2 ) fi lms from the decomposition of Ti(OEt) 4 with dopant quantities of Nb(OEt) 5 by aerosol -assisted chemical vapor deposition (AACVD). Doping Nb into the Ti sites results in n -type conductivity, as determined by Hall effect measurements. The doped fi lms display signifi cantly improved electrical properties compared to pristine TiO 2 fi lms. For 5 at.% Nb in the fi lms, the charge carrier concentration was 2 × 10 21 cm −3 with a mobility of 2 cm 2 V ‐1 s ‐1 . The corresponding sheet resistance was as low as 6.5 Ω sq ‐1 making the fi lms suitable candidates for transparent conducting oxide (TCO) materials. This is, to the best of our knowledge, the lowest reported sheet resistance for Nb:TiO 2 fi lms synthesized by vapour deposition. The doped fi lms were also blue in colour, with the intensity dependent on the Nb concentration in the fi lms. A combination of synchrotron, laboratory and theoretical techniques confi rmed niobium doping into the anatase TiO 2 lattice. Computational methods also confi rmed experimental results of both delocalized (Ti 4+ ) and localized polaronic states (Ti 3+ ) states. Additionally, the doped fi lms also functioned as photocatalysts. Thus, Nb:TiO 2 combines four functional properties (photocatalysis, electrical conductivity, optical transparency and blue colouration) within the same layer, making it a promising alternative to conventional TCO materials.

In this study, density functional theory is used to evaluate the electronic structure of the antimony chalcogenide series. Analysis of the electronic density of states and charge density shows that asymmetric density, or ‘lone pairs’, forms on the SbIII cations in the distorted oxide, sulphide and selenide materials. The asymmetric density progressively weakens down the series, due to the increase in energy of valence p states from O to Te, and is absent for Sb2Te3. The fundamental and optical band gaps were calculated and Sb2O3, Sb2S3 and Sb2Se3 have indirect band gaps, while Sb2Te3 was calculated to have a direct band gap at Γ. The band gaps are also seen to reduce from Sb2O3 to Sb2Te3. The optical band gap for Sb2O3 makes it a candidate as a transparent conducting oxide, while Sb2S3 and Sb2Se3 have suitable band gaps for thin film solar cell absorbers.

The failure to develop a degenerate, wide band gap, p-type oxide material has been a stumbling block for the optoelectronics industry for decades. Mg-doped LaCuOSe has recently emerged as a very promising p-type anode layer for optoelectronic devices, displaying high conductivities and low hole injection barriers. Despite these promising results, many questions regarding the defect chemistry of this system remain unanswered, namely (i) why does this degenerate semiconductor not display a Moss–Burnstein shift?, (ii) what is the origin of conductivity in doped and un-doped samples?, and (iii) why is Mg reported to be the best dopant, despite the large cation size mismatch between Mg and La? In this article we use screened hybrid density functional theory to study both intrinsic and extrinsic defects in LaCuOSe, and identify for the first time the source of charge carriers in this system. We successfully explain why LaCuOSe does not exhibit a Moss–Burstein shift, and we identify the source of the subgap optical absorption reported in experiments. Lastly we demonstrate that Mg doping is not the most efficient mechanism for p-type doping LaCuOSe, and propose an experimental reinvestigation of this system.

Since the original discovery of the water-splitting activity of silver orthophosphate (Ag3PO4), considerable effort has been devoted to improving its photocatalytic activity and stability through morphology control and the design of multi-component electrode systems. Relatively little attention, however, has been paid to understanding the fundamental electronic properties of this material. Using X-ray photoelectron spectroscopy and hybrid density functional theory (DFT) calculations, we have studied the electronic structure of Ag3PO4. Our results indicate that hybrid DFT calculations closely reproduce the structural, electronic, and optical properties of Ag3PO4. From further analysis of the experimental and theoretical electronic structure data we have constructed a revised molecular orbital diagram for Ag3PO4 that highlights the strong covalent interactions formed in the tetrahedral PO4 structural units.

In this paper we report a computational study of the effects of strain on the conductivity of Y-doped ceria (YDC). This material was chosen as it is of technological interest in the field of Solid Oxide Fuel Cells (SOFCs). The simulations were performed under realistic operational temperatures and strain (𝜖) levels. For bulk and thin film YDC, the results show that tensile strain leads to conductivity enhancements of up to 3.5 × and 1.44 × , respectively. The magnitude of these enhancements is in agreement with recent experimental and computational evidence. In addition, the methods presented herein allowed us to identify enhanced ionic conductivity in the surface regions of YDC slabs and its anisotropic character.

Non-stoichiometric oxides are frequently used in SOFC electrodes due to the ease with which they exchange oxygen with the atmosphere over their entire surface, as compared to composites limited to three phase boundaries (i.e. LSM/YSZ). The large fluctuations in oxygen content these materials exhibit during operation lead, not only to significant changes in transport properties, but also to a defect induced expansion, known as chemical expansion, potentially contributing to mechanical failure. In this presentation, new insights into the origins of chemical expansion, with consequent development of methods for reducing its impact in non-stoichiometric oxides, facilitated by collaborations of the authors, will be discussed.

The origin of the almost unique combination of optical transparency and the ability to bipolar dope tin monoxide is explained using a combination of soft and hard X-ray photoemission spectroscopy, ...

The most widely used oxide for photocatalytic applications owing to its low cost and high activity is TiO2. The discovery of the photolysis of water on the surface of TiO2 in 19721 launched four decades of intensive research into the underlying chemical and physical processes involved2, 3, 4, 5. Despite much collected evidence, a thoroughly convincing explanation of why mixed-phase samples of anatase and rutile outperform the individual polymorphs has remained elusive6. One long-standing controversy is the energetic alignment of the band edges of the rutile and anatase polymorphs of TiO2 (ref. 7). We demonstrate, through a combination of state-of-the-art materials simulation techniques and X-ray photoemission experiments, that a type-II, staggered, band alignment of ~ 0.4 eV exists between anatase and rutile with anatase possessing the higher electron affinity, or work function. Our results help to explain the robust separation of photoexcited charge carriers between the two phases and highlight a route to improved photocatalysts.

A combination of soft and hard synchrotron-based spectroscopy with first-principles density functional theory within the GGA + U framework is used to investigate the distortion of the Mn local environment of LixMnPO4 as a function of electrochemical delithiation (x = 1.0, 0.75, 0.5, 0.25) and its effect on the electron and hole polaron formation. Analysis of the soft X-ray absorption spectroscopy (XAS) of the Mn L3,2-edges confirmed the evolution from the Mn2+ to the Mn3+ charge state as a two-phase reaction upon delithiation; the corresponding Mn K-edge extended X-ray fine structure measurements clearly revealed a splitting of the Mn–O nearest-neighbor distances with increasing Mn3+ character. In addition, the O K-edge absorption and emission spectra confirmed the corresponding orbital lifting of degeneracy accompanying the distortion of the MnO6 octahedra in the Mn3+ state. Our GGA + U calculations show that the distortion is not a strict Jahn–Teller distortion but is instead a preferential elongation o...

Due to its high dielectric constant, large band gap, and very small lattice mismatch with Si, CeO2 has been proposed as a promising candidate high-κ dielectric material. The performance of CeO2 as a dielectric material, however, is severely limited due its propensity for facile reduction (oxygen vacancy formation), which causes a high interface state density, and subsequent decreased drain currents. In this article we use density functional theory (DFT) to screen for trivalent dopants which could decrease the concentration of defects in CeO2 samples. We demonstrate that La and Y are the most soluble trivalent dopants in CeO2, and can reduce the number of the electrons in the system both ionically (formation of [MCe–VO–MCe] clusters) or to a lesser extent electronically (hole formation). La doping also increases the lattice constant of CeO2, improving the lattice match with Si.

Efficient modulation of the bandgap of In2O3 will open up a route to improved electronic properties. We demonstrate using ab initio calculations that Tl incorporation into In2O3 reduces the band gap and confirm that narrowing of the gap is observed by X-ray photoemission spectroscopy on ceramic surfaces. Incorporation of Tl does not break the symmetry of the allowed optical transitions, meaning that the doped thin films should retain optical transparency in the visible region, in combination with a lowering of the conduction band effective mass. We propose that Tl-doping may be an efficient way to increase the dopability and carrier mobility of In2O3. © 2013 AIP Publishing LLC.

Ce is one of the few lanthanide elements to exhibit well-defined (III) and (IV) oxidation states in solid-state environments, and there is therefore ambiguity as to whether CeVO4 should be formulated as Ce(III)V(V)O4 or Ce(IV)V(IV)O4. To address this question, CeVO4 and Ce0.5Bi0.5VO4 have been studied by density functional theory calculations and X-ray photoemission spectroscopy. A peak above the main O 2p valence band in photoemission is attributed to localized Ce 4f states, in agreement with the calculations which show occupation of Ce 4f states. The Ce 3d core level spectrum is diagnostic of Ce(III) with no sign of a peak associated with 4f0 final states that are characteristic of Ce(IV) compounds. The experimental and theoretical results thus confirm that both compounds contain Ce(III) and V(V), rather than Ce(IV) and V(IV). In agreement with experiment, the calculations also show that the tetragonal zircon phase adopted by CeVO4 is more stable for Ce0.5Bi0.5VO4 than the monoclinic clinobisvanite phase adopted by BiVO4, so that the formation of the stereochemically active Bi(III) lone pairs is suppressed by Ce doping. (Figure Presented).

The defect structure and ionic diffusion processes within the anion-deficient, fluorite structured system Ce 1-xY xO 2-x/2 have been investigated at high temperatures (873 K-1073 K) as a function of dopant concentration, x, using a combination of neutron diffraction studies, impedance spectroscopy measurements, and molecular dynamics (MD) simulations using interionic potentials developed from ab initio calculations. Particular attention is paid to the short-range ion-ion correlations, with no strong evidence that the anion vacancies prefer, at high temperature, to reside in the vicinity of either cationic species. However, the vacancy-vacancy interactions play a more important role, with preferential ordering of vacancy pairs along the «111» directions, driven by their strong repulsion at closer distances, becoming dominant at high values of x. This effect explains the presence of a maximum in the ionic conductivity in the intermediate temperature range as a function of increasing x. The wider implications of these conclusions for understanding the structure-property relationships within anion-deficient fluorite structured oxides are briefly discussed, with reference to complementary studies of yttria and/or scandia doped zirconia published previously. © 2011 American Chemical Society.