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Physics and Chemistry of ABO 3 Nanostructures from First Principles

Ph.D. Dissertation Proposal. Physics and Chemistry of ABO 3 Nanostructures from First Principles. Ghanshyam Pilania Chemical, Materials & Biomolecular Engineering Institute of Materials Science University of Connecticut Principal Advisor: Prof. R. Ramprasad

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Physics and Chemistry of ABO 3 Nanostructures from First Principles

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  1. Ph.D. Dissertation Proposal Physics and Chemistry of ABO3 Nanostructures from First Principles GhanshyamPilania Chemical, Materials & Biomolecular Engineering Institute of Materials Science University of Connecticut Principal Advisor: Prof. R. Ramprasad Associate Advisor: Prof. P. Gao Associate Advisor: Prof. G. Rossetti, Jr.

  2. ABO3-type Perovskite structure A B O

  3. Outline Novel polarization states in ABO3 nanowires “Vortex” v/s “axial” polarization states Effect of size, surface termination and axial strain on the polarization states (p,T) surface phase diagrams of ABO3 surfaces Methodology to construct surface phase diagrams Calculated (p,T) surface phase diagrams for LaMnO3 and PbTiO3 (001) surfaces Remaining work Impact of work

  4. Novel polarization states in ABO3 nanowires

  5. Ferroelectricity in bulk perovskites ABO3 perovskite ABO3 perovskite Ferroelectric Well Energy Energy Energy Energy P P P P Paraelectric state Paraelectric state Ferroelectric state Dipole moment per unit volume = Polarization Ferroelectricity: a collective phenomena A balance between long range Coulombic force (favor ferroelectric state) short range repulsive forces (resist ferroelectric state) T Paraelectric Tc Ferroelectric

  6. Ferroelectricity in Nanostructures Bulk Thin film +++++++++ Depolarizing Field - - - - - - - - - Ferromagnetic closure domains C. Kittel, Phys. Rev. 70, 965 1946. Aguado-Puente et al. (PRL, 2008)

  7. Ferroelectricity in Nanostructures Closure domain No depolarizing Field No depolarizing Field P P PFM results indicate possible presence of non-rectilinear polarization in PZT nanodots Prosendeev & Bellaiche (PRB 2007) - - - + + + Depolarizing Field Rodriguez et al (Nanoletters, 2009)

  8. ABO3 Nanowires – Our DFT Study Construction of ABO3 nanowires AO-plane 2x2-AO-terminated nanowire BO2-plane 2x2-BO2-terminated nanowire AO-plane BO2-plane

  9. paraelectric ferroelectric BaTiO3 Nanowires – Our DFT Study Axial polarization instability above 1.2 nm Vortex polarization instability above 1.6 nm 4x4-TiO2 P 4x4-BaO τ=rxP Geneste et. al, APL 88, 112906 (2006);

  10. BaTiO3 Nanowires – Experimental Study Off-axis Polarization in BaTiO3 nanowires 0.8 nm Spanieret al, NanoLett. 6, 735 (2006)

  11. PbTiO3 Nanowires – Our DFT Study c tetragonal Bulk Fa Fa Fa 4x4-TiO2 Fa P acubic Bulk τ=rxP P c (Å) Fv P Unit cell decomposed dipole moments P 1x1 to 4x4-PbO Shimada et al, PRB 79, 024102 (2009)

  12. PbTiO3 Nanowires vs. TerminationsStrain-induced phase transition: vortex  axial polarization 4x4-TiO2-terminated nanowire 4x4-PbO-terminated nanowire Axial compressive Strain Axial Tensile Strain [001] Four possible switchable polarization states Vortex (clockwise/counter-clockwise), Axial (positive/negative)

  13. Control of polarization statesaxial Strain and surface terminations PbTiO3 nanowires display switchable rectilinear (axial) and non-rectilinear (vortex) polarization configurations

  14. (T, p) surface phase diagrams of ABO3 systems

  15. Perovskite Surfaces in Catalysis Why are they important? Versatility Flexibility Less expensive Thermal stability Excellent oxygen exchange properties

  16. Sulfur poisoning Perovskite Surfaces in Catalysis SO4-2 Dead site Active site 26 MARCH 2010 VOL 327 SCIENCE Chang Hwan Kim, Gongshin Qi, Kevin Dahlberg, Wei Li R. J. H. Voorhoeve, D. W. Johnson, Jr., J. P. Remeika, P. K. Gallagher

  17. Suprafacial v/s Intrafacial

  18. Cubic LaMnO3 and PbTiO3 surface phase diagrams Surface-O*↔ Surface + ½ O2 (g)

  19. Cubic LaMnO3 and PbTiO3 surface phase diagrams + N/2 O2

  20. Cubic LaMnO3 and PbTiO3 surface phase diagrams (1x1) AO-terminated (1x1) BO2-terminated A Formation Energies

  21. Cubic LaMnO3 and PbTiO3 surface phase diagrams Relaxed geometries for most favored adsorption sites

  22. Perovskite surfaces in contact with O2 (g) Surface-O*↔ Surface + ½ O2 (g) Assuming ideal gas behavior for O2

  23. Surface phase diagrams for surfaces in contact with O2 LaMnO3 (001) MnO2-terminated PbTiO3 (001) TiO2-terminated 100% O ad-atom coverage 100% O ad-atom coverage log PO2 log PO2 Partial coverage of O ad-atom T (K) T (K) Partial coverage of O ad-atom Clean surface Partial O vacancy coverage 100% O vacancy 100% O vacancy Partial O vacancy coverage

  24. Remaining Work Effect of surface passivation (by various species such as –OH, H, -CH3 etc.) on polarization states in PbTiO3 nanowires ? Efield Electric field response of the vortex polarization state in PbTiO3 nanowires Dielectric tensor of ferroelectric nanowires 4x4-PbO terminated nanowire (axial polarization) 4x4-TiO2 terminated nanowire (vortex polarization)

  25. Remaining Work Thermodynamics of environment dependent interaction of various gases on the (001) surface of ABO3 type perovskites Adsorption site Equilibrium geometry Electronic structure Energetics NO, NO2, N2, O2 (gases) Kinetics ??

  26. Impact of Work 0 0 1 0 How to shrink the hard drive?!! Non volatile Ferroelectric memory Potential to increase present memory storage density by five order of magnitude

  27. Impact of Work DeNOxprocesses NO + CO + unburned hydrocarbons LaCoO3 (○) La0.9Sr0.1CoO3 (●) CO2 CO catalytic converter CO2+H2O CnHm LaMnO3 (□) N2 + O2 NOx La0.9Sr0.1MnO3 (■) commercial DOC (▲)

  28. List of Publications G. Pilania, S. P. Alpay and R. Ramprasad, "Ab initio study of ferroelectricity in BaTiO3 nanowires", Phys. Rev. B80, 014113(1)-014113(7)- (2009). G. Pilania, D. Q. Tan, Y. Cao, V. S. Venkataramani, Q. Chen and R. Ramprasad, "Ab initio study of antiferroelectric PbZrO3 (001) surfaces", J. Mater. Sci. 44, 5249-5255 (2009). G. Pilania, T. Sadowski and R. Ramprasad, "Oxygen adsorption on CdSe Surfaces: A case study of asymmetric anisotropic growth through Ab initio computations", J. Phys. Chem. C. 113(5), 1863-1871 (2009). J. D. Doll, G. Pilania, R. Ramprasad and F. Papadimitrakopoulos, "Oxygen-Assisted Unidirectional Growth of CdSe Nanorods Using a Low-Temperature Redox Process", Nano Lett., 10 (2), 680-685 (2010). G. Pilania and R. Ramprasad “Vortex -Polarization Instability in PbTiO3 nanowires”, under review. G. Pilania and R. Ramprasad “Thermodynamics of environment dependent oxygen adsorption and vacancy formation on cubic PbTiO3 and LaMnO3 (001) surfaces”, In preparation.

  29. Acknowledgments Committee members: Profs. Rampi Ramprasad, Puxian Gao and George A. Rossetti, Jr. Profs. Rainer Hebert and Pamir S. Alpay Group Members : Ning, Tang, Tom, Hong, Satyesh, Chenchen, Yenny Computational resources: IMS computation clusters; SGI supercomputer in SoE and Teragrid Funding: NSF & ONR

  30. Thanks!

  31. Back-up slides

  32. 4x4-TiO2 terminated Nanowire Atomic relaxations in the vortex state 4x4-TiO2-terminated nanowire [001]

  33. Cubic LaMnO3 and PbTiO3 surface phase diagrams ∆γ=

  34. Effect of vibrational free energy (1x1)-MnO2-terminated (001) LaMnO3 surface O ad-atoms O vacancies T (k) % change in ∆γ % change in ∆γ T (k)

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