Direct in situ observation of the electron-driven synthesis of Ag filaments on -Ag2WO4 crystals

E. Longo1,*,L.S. Cavalcante1, D.P. Volanti1, A.F. Gouveia2, V.M. Longo1, J.A. Varela1M.O. Orlandi1, J. Andrés3

1Institute of Chemistry, São Paulo State University, Interdisciplinary Laboratory of Electrochemistry and Ceramics, Francisco Degni 55, Araraquara 14800-900, Brazil

2Department of Chemistry, University Federal of São Carlos, Interdisciplinary Laboratory of Electrochemistry and Ceramics, Rod. Washington Luís 235, São Carlos 13565-905, Brazil

3Department of Physical and Analytical Chemistry, Universitat Jaume I, Theoretical and Computational Chemistry Group, Av. de Vicent Sos Baynat, s/n, Castelló de la Plana12071, Spain

*Corresponding author

Correspondence to: Elson Longo ()

Supporting Information:

Details of the orthorhombic structure with space group. The -Ag2WO4 crystals have an orthorhombic structure and distorted [WO6] clusters with an octahedral configuration. There are four types of coordination for the Ag+ ion, including: distorted deltahedral [AgO7], octahedral [AgO6], tetrahedral [AgO4] and angular [AgO2]clusters. These clusters are bonded through different Ag−O distance and angles (see Table S1).Therefore, the -Ag2WO4 orthorhombic structure has four different types of coordination for the Ag+ ion and six possible configurations for the [AgOx] x=2, 4, 6 or 7 clusters. For the tetrahedral [AgO4] and deltahedral [AgO7] clusters, there are two possible configurations, as shown by the different bonds, distances and angles(see Table S2). By analysing the Ag3 structure in more detail, the octahedral [AgO6] is located in the centre with the [AgOx] and octahedral [WO6] clusters surrounding it. The distances between [AgO6] and the other clusters can be measured (see Fig. S2) which suggests a core-shell system in the -Ag2WO4 orthorhombic structure (see Fig. S3).

Density of states forthe -Ag2WO4 crystals. Fig. S4 shows the electron density maps obtained usingfirst-principles calculations of the -Ag2WO4 crystal along the exposed [110] plane. This face displays Ag atoms belonging to external [AgO4] and [AgO2] clusters. The contour plot reveals that the bonding between Ag and O exhibits a covalent nature, which is due to hybridisation between the O (2p) and Ag (4d) orbitals. Fig. S5shows the electronic diagrams illustrating the density of states (DOS) for the -Ag2WO4 structure. The DOS projected on the atoms indicates that the valence band (VB) maximum is derived from Ag (4d orbitals) with a contribution from O (2p orbitals). The conduction band (CB) is derived from W 5d orbitals and from Ag4d orbitals(Ag contributes to VBs and CBs). Therefore, the Ag behaves in manner similar to an electron (VB) and a hole (CB).

Computational method and periodic model of the -Ag2WO4 crystals. The simulation was performed using a periodic approximation as implemented in the CRYSTAL09 computer code1. The computational method is based on DFT in conjunction with Becke’s three-parameter hybrid non-local exchange functional2, combined with the Lee–Yang–Parr gradient-corrected correlation functional, B3LYP3. The hybrid density-functional method has been extensively used for molecules and provides an accurate description of crystalline structures, bond lengths, binding energies, and band-gap values4. The diagonalization of the Fock matrix was performed at adequate k-point grids (Pack–Monkhorst 1976) in the reciprocal space5. The thresholds controlling the accuracy of the calculation of the Coulomb and exchange integrals were set to 10-8 (ITOL1 to ITOL4) and 10-14 (ITOL5), and the percent of Fock/Kohn–Sham matrix mixing was set to 30 (IPMIX 1⁄4 30). The dynamical matrix was computed by the numerical evaluation of the first derivative of the analytical atomic gradient. The point group symmetry of the system was fully exploited to reduce the number of points considered. For each numerical step, the residual symmetry was preserved during the self-consistent field (SCF) and gradient calculations. The atomic centres for Ag and W atoms have been described by basis sets (PS-11d3G pseudopotential basis sets) provided by the CRYSTAL basis set library, and the O atoms have been described by the standard 6-31G*.6 k-point sampling was chosen as 36 points within the irreducible part of the Brillouin zone. The XcrysDen program was used to design the band structure diagrams7.

References

1. R. Dovesi, V. R. Saunders, C. Roetti, R. Orlando, C. M. Zicovich- Wilson, F. Pascale, B. Civalleri, K. Doll, N. M. Harrison, I. J. Bush, P. D. Arco, M. Llunell, CRYSTAL06 Users Manual, University of Torino, 2006.

2. Becke, A. D. Density-functional thermochemistry.3. The role of exact exchange. J. Chem. Phys.98, 5648-5652, (1993).

3. Lee, C. T., Yang, W. T. & Parr, R. G. Development of the Colle-Salvetti correlation-energy formula into a functional of the electron-density. Physical Review B37, 785-789, (1988).

4. F. Cora, M. Alfredsson, G. Mallia, D. S. Middlemiss, W. Mackrodt,R. Dovesi, R. Orlando, Structure and Bonding, Springer-Verlag, Berlin, 2004. p. 113.

5. Monkhorst, H. J. & Pack, J. D. Special points for Brillouin-zone integrations. Physical Review B13, 5188-5192, (1976).

6.

7. A. Kokalj, J. Mol. Graphics Modell., 1999, 17, 176.

Figures Legends:

Figure S1: Rietveld refinement plot of α-Ag2WO4crystals prepared by the injection of ions into a hot aqueous solution (IIHAS) method at 90ºC for 1 min.

Figure S2: Core-shell system in α-Ag2WO4.

Figure S3: Distances between [AgOx] and [WO6] clusters.

Figure S4: Electron density maps for the α-Ag2WO4 crystals with vertical plane in the [110] direction containing Ag and O atoms.

Figure S5:Total DOS of α-Ag2WO4 structure.

Tables Legends:

Table S1: Lattice parameters, unit cell volume, atomic coordinates and site occupation obtained by Rietveld refinement data for α-Ag2WO4 microcrystals prepared by the injection of ions into a hot aqueous solution (IIHAS) method at 90ºC for 1 min.

Table S2: Ag−O distance and angles of the α-Ag2WO4 crystals.

Figures

Figures S1:

Figures S2:

Figures S3:

Figures S4:

Figures S5:

Tables

Table S1:

Atoms / Wyckoff / Site / x / y / z
W1 / 4c / 1 / 0.2533 / 0 / 0.5261
W2 / 2b / 2 / 0 / 0.8203 / 0.5
W3 / 2b / 2 / 0 / 0.1222 / 0.5
Ag1 / 4c / 1 / 0.7392 / 0.1388 / 0.9431
Ag2 / 4c / 1 / 0.2467 / 0.8022 / 0.0092
Ag3 / 2a / 2 / 0 / 0.9634 / 0
Ag4 / 2a / 2 / 0 / 0.6506 / 0
Ag5 / 2a / 2 / 0 / 0.3139 / 0
Ag6 / 2a / 2 / 0 / 0.49371 / 0.5
O1 / 4c / 1 / 0.3658 / 0.7004 / 0.1826
O2 / 4c / 1 / 0.3625 / 0.3947 / 0.1921
O3 / 4c / 1 / 0.3334 / 0.7414 / 0.7778
O4 / 4c / 1 / 0.4441 / 0.2743 / 0.7867
O5 / 4c / 1 / 0.1335 / 0.5024 / 0.2912
O6 / 4c / 1 / 0.4288 / 0.5036 / 0.7917
O7 / 4c / 1 / 0.2001 / 0.5987 / 0.8322
O8 / 4c / 1 / 0.1911 / 0.3722 / 0.8851
a = 11.058(2)Å, b = 12.215(2)Å, c = 5.995(3)Å; V = 809.77(4)Å3; Z = 2; Crystal strucuture: orthorhombic; Space-group: Pn2n (Nº. 34); Point-group symmetry: (); Rw= 6.43%; Rwnb= 5.52%; RB= 4.97%; Rexp= 5.04%; and σ = 1.66

Table S2:

Atom types / (No.) / Distance / Cluster / Angle
Ag(1) / O1 / (1) / 2.354 (2.37) /
[AgO7] – Deltahedral
O2 / (1) / 3.314 (2.99) / O1-Ag-O4 103.272
O3 / (1) / 2.663 (2.67)
O4 / (1) / 2.468 (2.56) / O1-Ag-O2 140.289
O5 / (1) / 2.633 (2.70)
O7 / (1) / 2.413 (2.25) / O7-Ag-O4 101.294
O8 / (1) / 2.806 (2.76)
Ag(2) / O1 / (1) / 3.312 (3.06) /
[AgO7] – Deltahedral
O2 / (1) / 2.356 (2.32) / O2-Ag-O4 103.401
O3 / (1) / 2.471 (2.52)
O4 / (1) / 2.726 (2.50) / O2-Ag-O8 145.478
O5 / (1) / 2.580 (2.75)
O7 / (1) / 2.960 (2.68) / O4-Ag-O8 72.624
O8 / (1) / 2.394 (2.57)
Ag(3) / O1 / (2) / 2.581 (2.75) /
[AgO6] – Octahedral / O1-Ag-O1 111.531
O2 / (2) / 2. 562 (2.68) / O2-Ag-O2 109.759
O6 / (2) / 2.369 (2.25) / O6-Ag-O6 179.492
Ag(4) / O4 / (2) / 2.371 (2.32) /
[AgO4] – Tetrahedral / O4-Ag-O4 131.433
O7 / (2) / 2.283 (2.28) / O7-Ag-O7 141.566
Ag(5) / O3 / (2) / 2.430 (2.26) /
[AgO4]–Tetrahedral / O3-Ag-O3 122.742
O8 / (2) / 2.246 (2.36) / O8-Ag-O8 155.026
Ag(6) / O5 / (2) / 2.339 (2.20) /
[AgO2] – Angular / O5-Ag-O5 177.368

1