Ag 5s Research Articles

Incommensurately Modulated Structure in AgCuSe-Based Thermoelectric Materials for Intriguing Electrical, Thermal, and Mechanical Properties.

AgCuSe-based materials have attracted great attentions recently in thermoelectric(TE) field due to their extremely high electron mobility, ultralow lattice thermal conductivity, and abnormal "brittle-ductile" transition at room temperature. However, although the investigation on the crystal structure of AgCuSe low-temperature phase (named as β-AgCuSe) wasstarted more than half a century before, it is still in controversy yet, which greatly limits the understanding of its intriguing electrical, thermal, and mechanical performance. In this work, via adopting the advanced three-dimensionalelectron diffraction technique, this study finds that the AgCuSe-based materials crystalize in an incommensurately modulated structure with an orthorhombic Pmmn(0β1/2)s00 superspace group. The local lattice distortion in the incommensurately modulated structure has weak effects on the conduction band minimum due to the delocalized and isotropic feature of Ag 5s states, leading to high carrier mobility. Likewise, the inhomogeneous, weak, and anisotropic Ag-Se bonds result in the high degree of anharmonicity and ultralow lattice thermal conductivity. Furthermore, alloying S in AgCuSe reinforces the interaction between the adjacent Ag-Se layers, yielding the "brittle-ductile" transition at room temperature. This work well interprets the structure-performance relationship of AgCuSe-based materials and sheds light on the future investigation of this class of promising TE materials.

Na3Ti3O3(SeO3)4F: A Phase-Matchable Nonlinear-Optical Crystal with Enlarged Second-Harmonic-Generation Intensity and Band Gap.

A new phase-matchable nonlinear-optical material, Na3Ti3O3(SeO3)4F, has been achieved by a facile hydrothermal reaction. The anionic skeleton displays a honeycombed 3D structure with Ti6Se6 12-member polyhedral ring tunnels along the c axis. Na3Ti3O3(SeO3)4F presents a strong second-harmonic-generation (SHG) response of about 6 × KDP, which is twice that of its isostructural Ag compound. Interestingly, the band gap of Na3Ti3O3(SeO3)4F is also broader than that of the isomorph. Also, the powder laser-induced damage threshold of Na3Ti3O3(SeO3)4F is even 5.5 times larger than that of Ag3Ti3O3(SeO3)4F. Theoretical calculations revealed that the fully filled Ag 4d and empty Ag 5s states have made the difference in the band gap and SHG response of the two isostructural compounds. Our work has provided a practical way of improving the SHG efficiency and band gap simultaneously, which is usually considered to be a pair of negatively correlated parameters.

Superatomic Signature and Reactivity of Silver Clusters with Oxygen: Double Magic Ag 17 – with Geometric and Electronic Shell Closure

Understanding the stability and reactivity of silver clusters toward oxygen provides insights to design new materials of coinage metals with atomic precision. Herein, we report a systematic study o...

Reaction Behavior of the NO Molecule on the Surface of an Mn Particle (M = Ru, Rh, Pd, and Ag; n = 13 and 55): Theoretical Study of Its Dependence on Transition-Metal Element.

Reaction of NO molecule on M13 and M55 clusters (M = Ru, Rh, Pd, and Ag) was theoretically investigated to elucidate why its reaction behavior depends on the position of metal element in the periodic table. DFT computations show that NO dissociative adsorption occurs on M = Ru and Rh, NO molecular adsorption occurs on M = Pd, and NO dimerization occurs on M = Ag, which agree with experimental findings. The d-band center and d-band top become lower in energy following the order Ru > Rh > Pd > Ag; this is one of the characteristic features of the periodic table. In the Ag cluster, the valence band-top consists of Ag 5s orbital and its energy is higher than the d-band top of Pd. For NO dissociative adsorption, the M-N and M-O bond strengths are crucially important at the transition state and the product, to which the metal d orbital contributes very much. Ru and Rh clusters have a high energy d-band center and d-valence band top, leading to the formation of strong M-N and M-O bonds. Pd and Ag clusters have a low energy d-band center and d-band top, leading to the formation of weak M-N and M-O bonds. Because the Ag cluster has a high energy 5s valence band that can overlap well with the π* + π* MO of ONNO (NO dimer) moiety due to the same symmetry, charge transfer (CT) occurs from the Ag cluster to the π* + π* MO, which is indispensable for NO dimerization. The 4d-valence band top of Ru and Rh clusters does not fit to the π* + π* MO because of the different symmetry. Though the d-valence band top of the Pd cluster can overlap with the π* + π* MO, its energy is low, which is not good for the CT. Thus, the reactivity of metal cluster for NO is determined by the energy and type (4d or 5s) of the valence band top, which both depend on the position of element in the periodic table; accordingly, Ru and Rh clusters are reactive for NO dissociative adsorption, the Ag cluster is reactive for NO dimerization, but the Pd cluster is not reactive for both and only NO molecular adsorption is possible.

Structural and optical evolution in Pb100-xAgxSe (x = 3, 6, 9 and 12) thin films by chemical bath deposition

We developed a simple room-temperature synthetic route that achieves well-crystallized Pb100−xAgxSe alloy thin films by chemical bath deposition (CBD). The strategy provides a new paradigm to synthesize Ag doped PbSe thin films in one-step. We show that uniform distributed Pb100−xAgxSe thin films can be produced, whose crystal structure, morphology, and optical properties could be tailored with Ag concentration. With increasing x, both the shape and size of crystals are changing. Besides, the growth mechanism transits from cluster to ion by ion (IBI). The optical band gap (Eg) of the thin films is found to linearly increase with x values, from 0.26 eV to 0.31 eV. The density of states (DOS) and energy band structure of Pb100−xAgxSe are calculated using the first principle method. The calculation shows that Se 4p hybrids with Ag 4d at the valance band maximum, and the contribution to the conduction band minimum is mainly from Pb 6p and Ag 5s. The energy band gap shows the same tendency with Ag concentration as that in the experiment.

Solid-Solution-Like o-C3N4/Ag2SO4 Nanocomposite as a Direct Z-Scheme Photocatalytic System for Photosynthesis of Active Oxygen Species

Efficient photosynthesis of active oxygen species (e.g., •OH, •O2–, and H2O2) is of cardinal significance for environmental science and biochemistry. We report a system of o-C3N4/Ag2SO4 with solid-solution-like structure synthesized by coordinating the 5s orbit of Ag+ with surface 2p lone electrons of o-C3N4. The as-synthesized o-C3N4/Ag2SO4 demonstrates a unique electronic structure, as illuminated high light absorption, perfect redox potentials, large BET specific area, abundant active sites, and efficient interfacial charge transfer. Electron paramagnetic resonance spectra and Mott–Schottky measurements confirm that o-C3N4/Ag2SO4 photocatalysts demonstrate highly efficient activity for yielding •OH, •O2–, and H2O2 species with the Z-scheme photocatalytic principle. Experimental and DFT calculation reveal that the transferred electrons on the conduction band (CB) made up of Ag 5s were favorably shifted into the valence band (VB) composed of N 2p with the formed coordination under irradiation, greatly pr...

A novel open–framework spheniscidite photocatalyst with excellent visible light photocatalytic activity: Silver sensitization effect and DFT study

We report a novel silver modified spheniscidite (SPH–Ag) visible light responsive photocatalyst with open–framework structure. The SPH–Ag photocatalyst was firstly synthesized by one step hydrothermal method. Meanwhile, the contribution of silver sensitization to the visible light photocatalytic property of SPH–Ag was confirmed by characterization results and DFT calculation. Ag+ is demonstrated to enter into the spheniscidite cavities and replace one NH4+ per unit cell without destroying the structure. Noteworthy, compared to SPH, the pure phase SPH–Ag catalyst equipped with larger specific surface area, broader visible light response region, stronger oxidizing ability and lower recombination rate of electrons and holes. Meanwhile, the valence electrons are rearranged and the unoccupied Ag 5s orbital hybridizes with Fe 3d and O 2p orbitals at valance band, which greatly improves the SPH–Ag’s ability of gaining electrons and the separation of photo generated charge carriers. As expected, the SPH–Ag catalyst exhibited enhanced photocatalytic activity for ARG degradation under visible light irradiation, which is mainly attributed to the generation of h+ and O2− species. Furthermore, its photocatalytic property was highly maintained as well as its structure and surface chemical properties after five recycles. This work may provide insight into the design of new–type Ag–based photocatalysts and their photocatalytic mechanism.

Toughness enhancement and tribochemistry of the Nb-Ag-N films actuated by solute Ag

The high-hardness nature of transition metal nitrides (TMN) has been widely exploited for industrial applications ranging from wear-resistance and cutting tools to scratch-resistant films. To design TMN-based films displaying a further improved toughness and a reduced friction represent urgent challenges. Up to now, creating a nanocomposite structure by introducing a very small content of the metal phase has been considered as a common strategy to enhance hardness and toughness. Herein, we present a new approach to incorporate few solute Ag atoms (∼1.5 at.%) into NbN film to form a Nb-Ag-N solid solution structure, achieving enhanced hardness and toughness, coupled with improved wear-resistance ability and remarkable drop in coefficient of friction (CoF). Hardness and toughness enhancement as well as the tribochemistry actuated by solute Ag have been investigated by combined experimental and density functional theory (DFT) analyses. Results show that the hardness enhancement induced by solute Ag stems from the combination of variation in microstructure and increment in bulk modulus B and C44. DFT calculations and electronic structure analyses further reveal that the presence of hybridizations between Ag 5s, 4d orbitals and N p-electrons is responsible for increment in B and C44; furthermore, the appearance of additional Ag eg states contributes to the improved toughness. Additionally, solute Ag can activate self-oxidation by forming Ag2O + Nb2O5 at the surface, which is beneficial for the formation of silver niobate (AgNbO3) during the sliding, thereby triggering the falling of the CoF at only 1.5 at.% Ag. Incorporation of few solute Ag atoms into TMN may provide a new strategy to improve the comprehensive properties including hardness, toughness, friction and wear-resistance.

General Assembly of Twisted Trigonal-Prismatic Nonanuclear Silver(I) Clusters.

A general class of C3 -symmetric Ag9 clusters, [Ag9 S(tBuC6 H4 S)6 (dpph)3 (CF3 SO3 )] (1), [Ag9 (tBuC6 H4 S)6 (dpph)3 (CF3 SO3 )2 ]⋅CF3 SO3 (2), [Ag9 (tBuC6 H4 S)6 (dpph)3 (NO3 )2 ] ⋅NO3 (3), and [Ag9 (tBuC6 H4 S)7 (dpph)3 (Mo2 O7 )0.5 ]2 ⋅2 CF3 COO (4) (dpph=1,6-bis(diphenylphosphino)hexane), with a twisted trigonal-prism geometry was isolated by the reaction of polymeric {(HNEt3 )2 [Ag10 (tBuC6 H4 S)12 ]}n , 1,6-bis(diphenylphosphino)hexane, and various silver salts under solvothermal conditions. The structures consist of discrete clusters constructed from a girdling Ag9 twisted trigonal prism with the top and bottom trigonal faces capped by diverse anions (i.e., S(2-) and CF3 SO3 (-) for compound 1, 2×CF3 SO3 (-) for compound 2, 2×NO3 (-) for compound 3, and tBuC6 H4 S(-) and Mo2 O7 (2-) for compound 4). This trigonal prism is bisected by another shrunken Ag3 trigon at its waist position. Interestingly, two inversion-related Ag9 trigonal-prismatic clusters are dimerized by the Mo2 O7 (2-) ion in compound 4. The twist is amplified by the bulkier thiolate, which also introduces high steric-hindrance for the capping ligand, that is, the longer dpph ligand. Four more silver-sulfur clusters (namely, compounds 5-8) with their nuclearity ranging from 6-10 were solely characterized by single-crystal X-ray diffraction to verify the above-described synergetic effect of mixed ligands in the construction of Ag9 twisted trigonal prisms. Surprisingly, only cluster 1 emits yellow luminescence at λ=584 nm at room temperature, which may be attributed to a charge transfer from the S 3p orbital to the Ag 5s orbital, or mixed with metal-centered (MC) d(10) →d(9) s(1) transitions. Upon cooling from 300 to 80 K, the emission intensity was enhanced along with a hypsochromic shift. The good linear relationship between the maximum emission intensity and the temperature for compound 1 in the range of 180-300 K indicates that this is a promising molecular luminescent thermometer. Furthermore, cyclic voltammetric studies indicated that the diffusion- and surface-controlled redox processes were determined for compounds 1 and 3 as well as compound 4, respectively.

Interfacial properties of the enhanced visible-light plasmonic Ag/Bi2WO6 (0 0 1) nanocomposite

First principle calculations are performed to study the interfacial photoelectric properties of Agn/Bi2WO6 (001) (n=1, 2, 3, 4) hybrid photocatalyst. The parallel adsorption of Ag cluster leads to more energetic favorable structures due to stronger interfacial interactions. The positive charged Ag cluster may act as excited electron traps and facilitate the electron⿿hole separation. In particular, hybridization between Ag 5s and O 2p leads to the formation of isolated energy levels above the valence bands, and they become more dispersed with broader bandwidth with the increment of silver cluster size, which is responsible for the enhanced absorption in visible-light region. In the deep valence region, Ag 4d orbital turns more delocalized and hybrid with O 2p states as the cluster size increases, which contributes to more covalent bond feature of Ag⿿O. Moreover, optical spectra demonstrate obvious red-shifts of the absorption edge with the increment of silver content, which enhances efficiently the visible-light photocatalytic activities of Bi2WO6 (001). The study provides insights into the enhanced photocatalyic mechanism of Ag/Bi2WO6 (001) and aids in the design of noble metal loaded visible-light plasmonic photocatalyst.

Crystal structure and optical properties of the [Ag62S12(SBu(t))32](2+) nanocluster with a complete face-centered cubic kernel.

The crystal structure of the [Ag62S12(SBu(t))32](2+) nanocluster (denoted as NC-I) has been successfully determined, and it shows a complete face-centered-cubic (FCC) Ag14 core structure with a Ag48(SBu(t))32 shell configuration interconnected by 12 sulfide ions, which is similar to the [Ag62S13(SBu(t))32](4+) structure (denoted as NC-II for short) reported by Wang. Interestingly, NC-I exhibits prominent differences in the optical properties in comparison with the case of the NC-II nanocluster. We employed femtosecond transient absorption spectroscopy to further identify the differences between the two nanoclusters. The results show that the quenching of photoluminescence in NC-I in comparison to that of NC-II is caused by the free valence electrons, which dramatically change the ligand to metal charge transfer (LMCT, S 3p → Ag 5s). To get further insight into these, we carried out time-dependent density functional theory (TDDFT) calculations on the electronic structure and optical absorption spectra of NC-I and NC-II. These findings offer a new insight into the structure and property evolution of silver cluster materials.

Facile in-suit synthesis of Ag/AgVO3 one-dimensional hybrid nanoribbons with enhanced performance of plasmonic visible-light photocatalysis

The novel one-dimension Ag/AgVO3 plasmonic photocatalysts were synthesized via in situ reduction of AgVO3 by NaBH4 at room temperature. The morphologies, optical properties and electronic structures of the synthesized Ag/AgVO3 plasmonic photocatalysts were systematically characterized using a combination of theoretical calculations and experimental techniques. The photocatalytic activities of Ag/AgVO3 photocatalysts were evaluated using photocatalytic degradation of basic fuchsin (BF) dye. The results showed that the photocatalytic efficiency of Ag/AgVO3 was better than that of AgVO3. Ag/AgVO3 demonstrated a high photocatalytic activity with 93.6% of BF decomposed within 90min. Such enhanced photocatalytic performance could be attributed to the relatively high conductivity and electron-storing capacity of Ag nanoparticles coated on AgVO3 surfaces. These Ag nanoparticles facilitate charge transfer between AgVO3 and Ag nanoparticles, and induce the localized surface plasmon resonance (SPR) that increases electric field and absorption of visible light. The results of the FDTD simulation confirmed that the SPR and the electric field enhancement were caused by the Ag nanoparticles. The theoretical calculation based on DFT indicates that Ag formed could narrow the bandgap of AgVO3 due to the fact that the Ag 5s orbital by association with Ag nanoparticles moves down the CB after hybridization. Meanwhile, the hybridization of O 2p and Ag 4d orbits of Ag/AgVO3 is weak, which is beneficial for valence band electrons to excite into the conduction band. The combined experimental results and characterizations of Ag/AgVO3 suggest that h+ and O2− are the main reactive species for degradation of BF in the visible light-catalyzed oxidation.

Theoretical insights into the adsorption of monatomic Ag on the (2 × 2) BiOCl (0 0 1) surfaces

The adsorption energies, geometric structures, electronic properties, work functions and surface dipole moments of monatomic Ag adsorption on the (2×2) BiOCl (001) surfaces, including the 1Cl-, BiO- and 2Cl-terminated BiOCl (001) surfaces, have been investigated using first-principles calculations based on density functional theory. The most energetically favorable adsorption configuration of single Ag atom is at the fourfold hollow site, with the minimum adsorption energies of −0.465, −2.954 and −8.080eV for the 1Cl-, BiO- and 2Cl-terminated BiOCl (001) surfaces, respectively. The analysis results of electronic properties indicate that there are new intermediate energy states mainly contributed to Ag 4d and Cl 3p states for 2Cl-terminated (001) surface, and Ag 5s states for 1Cl- and BiO-terminations. In addition, Ag adsorption can induce the formation of surface dipole moment and change in work function by the interfacial charge transfer. Combined with the previously reported experiments, the charge transport mechanism and effective separation processes of photo-induced electron–hole pairs of Ag/BiOCl photocatalytic system are built up and discussed. More importantly, our calculated findings could afford the theoretical basic knowledge for further understanding the microscopic structures, electronic properties, and photocatalytic reaction mechanism of Ag/BiOCl photocatalyst, providing a new analysis calculation for potential application in the investigation on the Ag/BiOBr and Ag/BiOI as well as other noble metals/BiOCl catalytic systems.

Theoretical aspects of graphene-like group IV semiconductors

Silicene and germanene are the silicon and germanium counterparts of graphene, respectively. Recent experimental works have reported the growth of silicene on (111)Ag surfaces with different atomic configurations, depending on the growth temperature and surface coverage. We first theoretically study the structural and electronic properties of silicene on (111)Ag surfaces, focusing on the (4×4)silicene/Ag structure. Due to symmetry breaking in the silicene layer (nonequivalent number of top and bottom Si atoms), the corrugated silicene layer, with the Ag substrate removed, is predicted to be semiconducting, with a computed energy bandgap of about 0.3eV. However, the hybridization between the Si 3p orbitals and the Ag 5s orbital in the silicene/(111)Ag slab model leads to an overall metallic system, with a distribution of local electronic density of states, which is related to the slightly disordered structure of the silicene layer on the (111)Ag surface. We next study the interaction of silicene and germanene with different hexagonal non-metallic substrates, namely ZnS and ZnSe. On reconstructed (0001)ZnS or ZnSe surfaces, which should be more energetically stable for very thin layers, silicene and germanene are found to be semiconducting. Remarkably, the nature and magnitude of their energy bandgap can be controlled by an out-of-plane electric field, an important finding for the potential use of these materials in nanoelectronic devices.

In situ capture of active species and oxidation mechanism of RhB and MB dyes over sunlight-driven Ag/Ag3PO4 plasmonic nanocatalyst

Sunlight-driven Ag/Ag3PO4 plasmonic nanocatalysts have been successfully prepared using an in situ ethylene glycol reduction method. The photocatalysts showed strong photocatalytic activity for decomposition of RhB and MB dyes under visible light irradiation (λ>420nm). The excellent photocatalytic performance of Ag/Ag3PO4 came from the sensitivity of Ag3PO4 and the high separation efficiency of electron–hole pairs, which resulted in a large number of holes participating in the photocatalytic oxidation process. The results of density function theory calculation revealed that the visible-light absorption band in the Ag3PO4 catalyst is attributed to the band transition from the hybrid orbital of O 2p and Ag 4d to the Ag 5s and 5p orbital. The generation of active species in the photocatalytic system was evaluated using the fluorescence (FL) and electron spin resonance (ESR) techniques as well as in situ capture of active species by t-butanol and EDTA. The results indicated that the free hydroxyl radicals were not the major active oxidizing species in the photocatalytic process. The photocatalytic reaction process of the pollutants was mainly governed by the direct oxidation by the holes.

Electronic structure and optical properties of Ag3PO4 photocatalyst calculated by hybrid density functional method

The electronic structure and optical properties of Ag3PO4 were studied by hybrid density functional theory. The results indicated that the band gap is 2.43 eV, which agrees well with the experimental value of 2.45 eV. The conduction bands of Ag3PO4 are mainly attributable to Ag 5s and 5p states, while the valence bands are dominated by O 2p and Ag 4d states. The highest valence band edge potential was 2.67 V (vs. normal hydrogen electrode), which has enough driving force for photocatalytic water oxidation and pollutants degradation. The optical absorption spectrum showed that Ag3PO4 is a visible light response photocatalyst.

On the Reactivity of Sulfosalts in Cyanide Aqueous Media: Structural, Bonding and Electronic Aspects

The reactivity of the ruby silver minerals proustite (3Ag(2)S⋅As(2)S(3)) and pyrargyrite (3Ag(2)S⋅Sb(2)S(3)) was studied with two types of electrodes: a carbon-paste electroactive electrode (CPEE) and a paraffin-impregnated graphite electrode (PIGE). Polycrystalline samples of α-Ag(2)S (acanthite), As(2)S(3) (orpiment), Sb(2)S(3) (stibnite), Ag(3)AsS(3) (proustite), Ag(3)SbS(3) (pyrargyrite), and three samples of the proustite-pyrargyrite solid solution series were synthesized from pure elements by a solid-state reaction method. Phase identification of samples was carried out by XRD and chemical homogeneity was checked by SEM-EDS. Besides, sulfosalts were characterized by diffuse reflectance spectroscopy (DRS). Flat-band and formal potentials of sulfosalts were determined by the Mott-Schottky method and differential pulse abrasive stripping voltammetry, respectively. Band structure, bonding and solid-state structure are considered to investigate the oxidation and reduction of the solids. A ligand-to-metal charge transfer (LMCT) transition from the AsS(3) (or SbS(3)) group to Ag is related to ease of reducing the pyrargyrite-proustite series. Despite the increase in the amount of As (Sb) in Ag(3)SbS(3) (Ag(3)AsS(3)), reactivity is similar due to the similarity of the solid-state structures, and the same oxidation states of S, As, Sb and Ag species in the lattice. However, the nature of the pnictogen (As or Sb) changes the position of the conduction and valence band edges and modulates the reactivity of the pyrargyrite-proustite series. Anodic dissolution occurs by hole transfer from the top of the valence band that is formed mainly by the states of the AsS(3) and SbS(3) groups. Meanwhile, silver reduction occurs by electron transfer from the Ag 5s orbitals located at the bottom of the conduction band. The difficulty in dissolving proustite and pyrargyrite in cyanide is related to the presence of pyramidal AsS(3) and SbS(3) groups in these sulfosalts.

Thermoelectric properties of AgSbO 3 with defect pyrochlore structure

The thermoelectric oxide AgSbO 3 has been prepared by the conventional solid state reaction (CSSR) method combined with spark plasma sintering (SPS) technique. The electrical resistivity ρ and the Seebeck coefficient S were measured simultaneously from 323 to 873 K. It was found that ρ decreased monotonically from 3.75 to 7.20 × 10 −4 Ω m as the temperature was increased. The highest absolute value of the Seebeck coefficient | S| ( S < 0) reached 209 μV K −1 at 873 K. In addition to the large thermopower, a rather low thermal conductivity of 0.825 W m −1 K −1 at 873 K has been observed. Better thermoelectric performance at higher temperatures may origin from the change in hybridization of the Ag 4d–O 2p orbital and the Ag 5s–Sb 5s orbital, which are responsible for engineering energy positions and shapes of the valence-band (VB) top and the conduction band (CB) bottom, respectively.

Theoretical study of Au(I)–Ag(I) metallophilic attractions and luminescence of [Au 2(carb) 2Ag(μ-3,5-Ph 2pz)] (with Ph = phenyl, pz = pyrazolate) and [Au(im)CH 3(pz)Ag 2(μ-3,5-H 2pz) 2] (with im = imidazole) complexes

The study of trimeric mixed-metal complexes is of great importance for their potential use in sensor devices and nanoparticle design, due to the fascinating luminescent and catalytic activity properties. The goal of this work is to understand the Au(I)–Ag(I) closed-shell metallophilic attraction and phosphorescent character in the representative Au–Ag complexes [Au 2(carb) 2Ag(μ-3,5-Ph 2pz)] ( 1) and [Au(im)CH 3(pz)Ag 2(μ-3,5-H 2pz) 2] ( 2) through ab initio and DFT techniques. The metal–metal intramolecular interactions are ruled by a Au 5d and Ag 4d mixing, while the intermolecular attractions are governed by a Au 6s and Ag 5s mixing, by π-stacking attractions coming from pz groups and dispersion interactions in complex 2. The phosphorescence reported experimentally may be addressed to MLCT transitions, with intrametallic contributions, where a distortion of the lowest-energy excited state geometry of the monomer and dimer are also involved.

Crystallographic phase stabilities and electronic structures in AgNbO3 by first-principles calculation

Silver niobate (AgNbO3) assumes several phases that crystallise in the perovskite structure similar to sodium niobate (NaNbO3). In order to investigate the phase stability of AgNbO3, the formation enthalpies of both physically the realised (real) cubic , tetragonal (P4/mbm) and orthorhombic (Cmcm, Pbcm) phases as well as the virtual phases, the orthorhombic (Pc21 b) and rhombohedral (R3cR) phases, which are observed in NaNbO3, have been obtained using a plane-wave pseudopotential method. Although the orthorhombic (Pbcm) phase has the lowest formation enthalpy among the real phases, the virtual rhombohedral (R3cR) phase has the lowest symmetry as well as the lowest formation enthalpy among all phases. We thus speculate that the rhombohedral (R3cR) phase may be stable at extremely low temperatures provided that it is accessible kinetically. In addition, the electronic structures of the various phases of AgNbO3 are calculated within the generalised gradient approximation with the Perdew–Burke–Ernzerhof correction (GGA-PBE). The valence band top was found to consist of predominately localised Ag 4d and O 2p orbitals constituting the O 2p–Nb 4d bonding orbital, while the bottom of the conduction band was found to mainly consist of the anti-bonding orbital of Nb 4d–O 2p under the Ag 5s orbital.