Aron Walsh PhD Supervisor: Prof. Graeme Watson School of Chemistry, University of Dublin, Trinity College, Ireland The Origin of Structural Distortions in Post Transition Metal Ceramics

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Watson group (TCD) • Thin film amorphisation and recrystalisation. • Oxide catalysis. • Adrenoceptors. • Supramolecular excited states.

Watson group (TCD) • Thin film amorphisation and recrystalisation. • Oxide catalysis. • Adrenoceptors. • Supramolecular excited states.

Watson group (TCD) • Thin film amorphisation and recrystalisation. • Oxide catalysis. • Adrenoceptors. • Supramolecular excited states.

Kr H N O Cl F Ar Ne Xe Rn He Cf No Am Lr Cm Fm Pu Pm Np Bk Md Es Ds Bh ub Mt uq Sg Rf Tc Hs uu Db Hg Br Se S P C Be Mg Ca Sr Ba Ra Li Na K Rb Cs Fr Sc Y Ti Zr Hf V Cr Mn Fe Co Ni Cu Zn Nb Mo Ru Rh Pd Ag Cd Ta W Re Os Ir Pt Au Ga In Tl Pb Bi Sn Al Ge As B Si Sb Te Po I At La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Ac Th Pa U O Hg Tl Pb Bi Sn

Kr H N O Cl F Ar Ne Xe Rn He Cf No Am Lr Cm Fm Pu Pm Np Bk Md Es Ds Bh ub Mt uq Sg Rf Tc Hs uu Db Hg Br Se S P C Be Mg Ca Sr Ba Ra Li Na K Rb Cs Fr Sc Y Ti Zr Hf V Cr Mn Fe Co Ni Cu Zn Nb Mo Ru Rh Pd Ag Cd Ta W Re Os Ir Pt Au Ga In Tl Pb Bi Sn Al Ge As B Si Sb Te Po I At La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Ac Th Pa U O Hg Tl Pb Bi Sn

Introduction ★ Unusual properties of metal ceramics Symmetric and asymmetric crystal structures. ★ What is a lone pair? “Pair of electrons residing in the outer shell of one atom and not shared by other atoms”. ★ Lone pairs in ceramics Considered as resulting from ns2 electronic configuration e.g. Bi(III), Pb(II), Sn(II), Tl(I). Stereochemical models: Bonding (Lewis, JACS 1916), VSEPR (Gillespe, Molecular Geometry 1972). Intra-atomic hybridization (L. E. Orgel, J. Chem. Soc. 1959).

Figure: Crystal structures of (a) litharge PbO, (b) rocksalt PbS, (c) herzenbergite SnS and (d) monoclinic Bi2 O3. (a) (b) (c) (d)

Applications ★ Pb(II), Sn(II) ceramics Gas sensors, light sensitive diodes, solar cells, batteries, anticorrosive paints, acid batteries. ★ Bi(III) ceramics Fast ion conductors, fuel cell electrolytes. ★ Hg(II), Tl(III) Components in high Tc superconductors. ★ Ternary compounds Catalysts, transparent conducting oxides.

Computational Methods ★ Density Functional Theory Gradient corrected PBE functional. ★ Plane Wave Basis Set PAW used to represent the core electrons. ★ Convergence Tests Plane wave cutoff and k-point sampling. ★ Structural Optimizations Cell vectors, angles and volume.

Experimental Methods High resolution synchrotron based spectroscopies. ★ X-ray Photoemission (1500eV) Target valence band, measure ejected electrons → Total EDOS. ★ Soft X-ray Emission Eject core electron, measure photon from valence relaxation. Strict selection rules → PEDOS. ★ Hard X-ray Photoemission (8000eV) Enhance the metal s contribution to the EDOS[1]. [1] D.J. Payne, R.G. Egdell, G. Paolicelli, F. Offi, G. Pannacione, P. Lacovig, G. Monaco, G. Vanko, A. Walsh, G.W. Watson, J. Guo, P.-A. Glans, T. Learmonth and K.E. Smith, Physical Review B (2007).

I. Pb(II) PbO Litharge PbS Rocksalt PbSe Rocksalt PbTe Rocksalt A.Walsh and G.W.Watson, Journal Of Solid State Chemistry 178, 1422 (2005). D.J.Payne, R.G.Egdell, A.Walsh, G.W.Watson, J.Guo, P.-A.Glans, T.Learmonth and K.E.Smith, Physical Review Letters 96, 157403 (2006).

Optimization PbO PbS Rocksalt Litharge Rocksalt Litharge Litharge (fixed a:c) E (eV) +0.37 - - +0.10 +0.51 a 5.27 4.06 6.01 5.13 5.08 b - 4.06 - 5.13 5.08 c - 5.39 - 4.21 7.08 Pb-O 2.64 2.35 (+1%) 3.01 (+1%) 2.86 2.82 Table 1 Calculated and experimental data for litharge and rocksalt PbO and PbS.

Figure: Electron density maps of rocksalt structured (a) PbO, (b) PbS and litharge structured (c) PbO and (d)PbS.

Figure: Electronic density of states of litharge PbO. -10.00 -5.00 0.00 5.00 Energy (eV) n(e) Pb(6s) O(2p). Pb(6pz ) Pb(6px+y )

Figure: Electronic density of states of litharge PbO. -10.00 -5.00 0.00 5.00 Energy (eV) n(e) Pb(6s) O(2p). Pb(6pz ) Pb(6px+y ) I II III

-10.00 -5.00 0.00 5.00 Energy (eV) n(e) Pb(6s) O(2p). Pb(6pz ) Pb(6px+y )

-10.00 -5.00 0.00 5.00 Energy (eV) n(e) Pb(6s) O(2p). Pb(6pz ) Pb(6px+y ) Bonding interaction Oxygen based Source of asymmetry

O O O O Pb

O O O O Pb O O O O Pb

O O O O Pb O O O O Pb O O O O Pb

Figure: Electronic density of states of litharge PbS. -10.00 -5.00 0.00 5.00 Energy (eV) n(e) Pb(6s) S(3p). Pb(6px+y ) Pb(6pz )

Figure: Electronic density of states of litharge PbS. -10.00 -5.00 0.00 5.00 Energy (eV) n(e) Pb(6s) S(3p). Pb(6px+y ) Pb(6pz ) I II III

-10.00 -5.00 0.00 5.00 Energy (eV) n(e) Pb(6s) S(3p). Pb(6px+y ) Pb(6pz )

-10.00 -5.00 0.00 5.00 Energy (eV) n(e) Pb(6s) S(3p). Pb(6px+y ) Pb(6pz ) Unchanged Reduced bonding Reduced Asymmetry

Lone Pair? ★ The directed asymmetric density in Pb(II) is a result of the interaction of anti-bonding Pb(6s) and anion p states with Pb(6pz). ★ The anion is directly involved in the states producing the asymmetric density. ★ However, interaction with anion p states of appropriate energy is needed. ★ The 3p states of sulphur are too high in energy!

Experimental Evidence ★ Comparison of the X-ray absorption and emission spectra confirm that the Pb 6s states are concentrated at the bottom of the valence band.

II. Sn(II) SnO Litharge SnS Herzenbergite SnSe Herzenbergite SnTe Rocksalt A.Walsh and G.W.Watson, Physical Review B 70, 235114 (2004). A.Walsh and G.W.Watson, Journal Of Physical Chemistry B 109, 18868 (2005).

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Overlap between anion p and cation s Circle: DFT Calculations. Triangle: Experiment (XPS and XES).

III. Bi(III) Low T Monoclinic α High T Cubic δ A.Walsh, G.W.Watson, D.J.Payne, R.G.Edgell. J.Guo, P.-A.Glans, T.Learmonth, K.E.Smith, Physical Review B 73, 235104 (2006). D.J.Payne, R.G.Egdell, A.Walsh, G.W.Watson, J.Guo, P.-A.Glans, T.Learmonth and K.E.Smith, Physical Review Letters 96, 157403 (2006).

Vacancy configurations in the high temperature defective fluorite Phase ★ <100>: density functional theory. ★ <110>: forcefield, LMTO calculations. ★ <111>: electrostatics, diffraction studies. ★ Anion disorder: diffraction studies.

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Electron Density Maps (a) <100> (b) <110> (c) <111>

Electronic Density of states (a) Alpha phase. (b) (100) delta phase. (c) (110) delta phase. (d) (111) delta phase. (red metal s, green metal p and blue anion p)

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IV. Bi2Sn2O7 ★One of the most complex solved oxide structures. ★Bi(III) and Sn(IV) atoms. ★Increased catalytic activity over similar pyrochlore oxides. A.Walsh, G.W.Watson, D.J.Payne, G.Atkinson, R.G.Edgell, Journal of materials chemistry 16, 3452 (2006).

Electronic density of states Electronic distributions indicative of the binary SnO2 and Bi2O3 layers..

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V. Group XII/XIII Oxides HgO and Tl2O3 ★Key components in the current highest temperature superconductors. ★Electronic structure of binary oxides had been neglected. ★Observed significant bonding of the shallow core d states with oxygen p states. P.-A.Glans, T.Learmonth, C.McGuiness, K.E.Smith, J.Guo, A.Walsh, G.W.Watson and R.G.Egdell, Chemical Physics Letters 399, 98 (2004). P.-A.Glans, T.Learmonth, C.McGuiness, K.E.Smith, J.Guo, A.Walsh, G.W.Watson and R.G.Egdell, Physical Review B 71, 235109 (2005).

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Conclusions ★ The anion plays a key role in determining the electronic structure and properties of heavy metal ceramics. ★ The lone pair associated with the ns2 electronic configuration is clearly more than a stereo- chemical feature. ★ These results have major implications for the chemical understanding and tuning the properties of current and future materials.

Acknowledgments TCD for a Trinity College Postgraduate Studentship. HEA for a PRTLI (Cycle III) grant. TCHPC for support of the IITAC cluster. Prof. Graeme Watson, Dr. Joanne Fearon, Dr. Gemma Kinsella, Berry Matijssen, Dr. James Hilton, Dr. Ben Morgan, Dr. Michael Nolan, David Scanlon, Kate Godinho and Dr. Oscar Rubio for their enlightening discussions and support.