NIRT Active Electromechanical Nanostructures Without the Use of

NIRT: Active Electromechanical Nanostructures Without the Use of Piezoelectric Constituents Working Definition of Piezoelectricity A uniform strain causes polarization and vice-versa - A + + . + C - + - A + . + C P P + B Odd order tensor cannot be sustained by centrosymmetric crystal—hence piezoelectricity is restricted to noncentrosymmetric crystals B Beyond Uniform Strain and Polarization---Flexoelectricity In principle, flexoelectric coefficients are non-zero for all dielectrics (although may be negligibly small in some cases)—experimentally verified for many materials! Na. Cl will exhibit an apparent piezoelectric effect when subjected to strain gradients Apparent Piezoelectric Behavior at Nanoscale Without Using Piezoelectric Materials Electric Fields Around the Spherical Inclusion for Different Sizes PI: Pradeep Sharma (University of Houston) Boris Yakobson (Rice University) Ramanan Krishnamoorti (University of Houston) Zoubeida Ounaies (Texas A&M University) Program Manager: Clark V. Cooper (CMMI Division, Engineering Directorate) Experimental Results: Enhancement of Dielectric Constant and Electric Conductivity at Low Vol% Centrosymmetr ic Inclusion Decreasing Size The phenomenon is nonlinear due to percolation, while quadratic trend is observed for displacement – input voltage data. Noncentrosymmetric inclusion For a In. As-Ga. As system, we obtain electric fields at the interface of ~ 750 k. V/m Apparently Piezoelectric Composites without Piezoelectric Constituents Volume Fraction = 6. 25% σxx Alignment & Electrokinetic Interactions E Various dominant electrokinetic regimes based on electric field magnitude and frequency identified dielectrophoresis vs electrophoresis. Hole Size = 3 nm σxx Apparent piezoelectric behavior upto 80% of bulk Quartz at 3 nm hole size in paraelectric Ba. Ti. O 3. Giant Piezoelectricity in Nanostructures Uniform Stress Conclusions and Summary: §Developed complete mathematical framework for the phenomenon. § Demonstrated feasibility of piezoelectric materials without using piezoelectric materials. § Demonstrated the “Giant” apparent piezoelectric coefficient for nanostructures. a § Experimental evaluation of the response of SWNT nanocomposites to electrical input is in progress. § Publication highlights (sample): Directio n of Strain Gradien t Giant apparent piezoelectric enhancement 80% of Due to flexoelectricity, the requirement of material nonbulk at 3 nm beam size in paraelectric Ba. Ti. O. 3 centrosymmetry has been transferred to shape non-centrosymmetry. M. S. Majdoub, P. Sharma and T. Cagin, Physical Review B, 77, 125424 (2008). Invited review article at MRS Bulletin, 2009