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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 Associate Advisor: Prof. P. Gao Associate Advisor: Prof. G. Rossetti, Jr. Ph.D. Dissertation Proposal
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ABO 3 -type Perovskite structure A B O
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Novel polarization states in ABO 3 nanowires (p,T) surface phase diagrams of ABO 3 surfaces “Vortex” v/s “axial” polarization states Effect of size, surface termination and axial strain on the polarization states Outline Methodology to construct surface phase diagrams Calculated (p,T) surface phase diagrams for LaMnO 3 and PbTiO 3 (001) surfaces Remaining work Impact of work
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Novel polarization states in ABO 3 nanowires
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Ferroelectricity in bulk perovskites Ferroelectricity: a collective phenomena A balance between long range Coulombic force (favor ferroelectric state) short range repulsive forces (resist ferroelectric state) Dipole moment per unit volume = Polarization T Tc Ferroelectric Paraelectric ABO 3 perovskite Energy P Paraelectric state ABO 3 perovskite Ferroelectric Well Energy P Paraelectric state Energy P Ferroelectric state Energy P
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Ferroelectricity in Nanostructures Thin film Depolarizing Field +++++++++ - - - - - - - - - Bulk Aguado-Puente et al. (PRL, 2008) C. Kittel, Phys. Rev. 70, 965 1946. Ferromagnetic closure domains
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Ferroelectricity in Nanostructures P + + + - - - Depolarizing Field P No depolarizing Field No depolarizing Field Closure domain Prosendeev & Bellaiche (PRB 2007) PFM results indicate possible presence of non- rectilinear polarization in PZT nanodots Rodriguez et al (Nanoletters, 2009)
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ABO 3 Nanowires – Our DFT Study 2x2-AO-terminated nanowire 2x2-BO 2 -terminated nanowire AO-plane BO 2 -plane AO-plane BO 2 -plane Construction of ABO 3 nanowires
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BaTiO 3 Nanowires – Our DFT Study Axial polarization instability above 1.2 nm ferroelectricparaelectric 4x4-TiO 2 P 4x4-BaO τ =rxP Vortex polarization instability above 1.6 nm Geneste et. al, APL 88, 112906 (2006);
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Spanier et al, Nano Lett. 6, 735 (2006) 0.8 nm Off-axis Polarization in BaTiO 3 nanowires BaTiO 3 Nanowires – Experimental Study
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PbTiO 3 Nanowires – Our DFT Study c (Å) FaFa FaFa FaFa FaFa P 1x1 to 4x4-PbO FvFv Shimada et al, PRB 79, 024102 (2009) c tetragonal Bulk a cubic Bulk P P P 4x4-TiO 2 τ =rxP Unit cell decomposed dipole moments
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PbTiO 3 Nanowires vs. Terminations Strain-induced phase transition: vortex axial polarization 4x4-TiO 2 -terminated nanowire [001] Axial compressive Strain Axial Tensile Strain 4x4-PbO-terminated nanowire Four possible switchable polarization states Vortex (clockwise/counter-clockwise), Axial (positive/negative)
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PbTiO 3 nanowires display switchable rectilinear (axial) and non-rectilinear (vortex) polarization configurations Control of polarization states axial Strain and surface terminations
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(T, p) surface phase diagrams of ABO 3 systems
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Flexibility Versatility Less expensive Thermal stability Excellent oxygen exchange properties Why are they important? Perovskite Surfaces in Catalysis
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R. J. H. Voorhoeve, D. W. Johnson, Jr., J. P. Remeika, P. K. Gallagher SO 4 -2 Dead site Active site Sulfur poisoning 26 MARCH 2010 VOL 327 SCIENCE Chang Hwan Kim, Gongshin Qi, Kevin Dahlberg, Wei Li Perovskite Surfaces in Catalysis
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Suprafacial v/s Intrafacial
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Surface-O* ↔ Surface + ½ O 2 (g) Cubic LaMnO 3 and PbTiO 3 surface phase diagrams
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+ N/2 O 2 Cubic LaMnO 3 and PbTiO 3 surface phase diagrams
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(1x1) AO-terminated(1x1) BO 2 -terminated Formation Energies Cubic LaMnO 3 and PbTiO 3 surface phase diagrams A
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Relaxed geometries for most favored adsorption sites Cubic LaMnO 3 and PbTiO 3 surface phase diagrams
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Perovskite surfaces in contact with O 2 (g) Assuming ideal gas behavior for O 2 Surface-O* ↔ Surface + ½ O 2 (g)
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Surface phase diagrams for surfaces in contact with O 2 PbTiO 3 (001) TiO 2 -terminated log P O2 100% O ad-atom coverage Partial O vacancy coverage Partial coverage of O ad-atom Clean surface 100% O vacancy T (K) LaMnO 3 (001) MnO 2 -terminated 100% O vacancy Partial coverage of O ad-atom Partial O vacancy coverage 100% O ad-atom coverage log P O2 T (K)
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Remaining Work Electric field response of the vortex polarization state in PbTiO 3 nanowires E field ? Dielectric tensor of ferroelectric nanowires 4x4-PbO terminated nanowire (axial polarization) 4x4-TiO 2 terminated nanowire (vortex polarization) Effect of surface passivation (by various species such as –OH, H, -CH 3 etc.) on polarization states in PbTiO 3 nanowires
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Thermodynamics of environment dependent interaction of various gases on the (001) surface of ABO 3 type perovskites NO, NO 2, N 2, O 2 (gases) Adsorption site Equilibrium geometry Electronic structure Energetics Kinetics ?? Remaining Work
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Impact of Work 0 1 0 0 Non volatile Ferroelectric memory Potential to increase present memory storage density by five order of magnitude How to shrink the hard drive?!!
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Impact of Work DeNO x processes NO + CO + unburned hydrocarbons catalytic converter catalytic converter CO CO 2 NO x N 2 + O 2 CnHmCnHm CO 2 +H 2 O LaCoO 3 (○) La 0.9 Sr 0.1 CoO 3 (●) LaMnO 3 (□) La 0.9 Sr 0.1 MnO 3 (■) commercial DOC (▲)
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List of Publications G. Pilania, S. P. Alpay and R. Ramprasad, "Ab initio study of ferroelectricity in BaTiO 3 nanowires", Phys. Rev. B 80, 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 PbZrO 3 (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 PbTiO 3 nanowires”, under review. G. Pilania and R. Ramprasad “Thermodynamics of environment dependent oxygen adsorption and vacancy formation on cubic PbTiO 3 and LaMnO 3 (001) surfaces”, In preparation.
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Acknowledgments Group Members : Ning, Tang, Tom, Hong, Satyesh, Chenchen, Yenny Committee members: Profs. Rampi Ramprasad, Puxian Gao and George A. Rossetti, Jr. Profs. Rainer Hebert and Pamir S. Alpay Computational resources: IMS computation clusters; SGI supercomputer in SoE and Teragrid Funding: NSF & ONR
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Thanks!
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Back-up slides
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[001] 4x4-TiO 2 -terminated nanowire 4x4-TiO 2 terminated Nanowire Atomic relaxations in the vortex state
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Cubic LaMnO 3 and PbTiO 3 surface phase diagrams ∆γ=∆γ=
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Effect of vibrational free energy (1x1)-MnO 2 -terminated (001) LaMnO 3 surface O ad-atoms % change in ∆ γ T (k) O vacancies % change in ∆ γ T (k)
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