Phase transitions into multidomain states in ferroelectric thin films with depletion charges and partial electrode screening
Çöloğlu, Hale Nur (2011) Phase transitions into multidomain states in ferroelectric thin films with depletion charges and partial electrode screening. [Thesis]
Official URL: http://192.168.1.20/record=b1379261 (Table of Contents)
This study addresses the limit of ferroelectric functionality for (001) BaTiO3 thin films grown on (001) SrTiO3 substrates sandwiched between pseudomorphic metallic electrodes having perfect and partial screening in the presence of homogeneously distributed ionized impurities for various film thicknesses. The role of thickness, depletion charge density and dead layers on domain formation and phase transition temperatures of ferroelectric films are investigated using the Landau-Ginzburg- Devonshire (LGD) phenomenological approach along with equations of electrostatics and electrostatic boundary conditions. It is well known that dead layers due to finite screening at the ferroelectric-electrode interfaces trigger electrical domain formation. It is demonstrated that depletion charges in the presence of ideal electrodes where polarization charges are fully compensated can also induce a saw-tooth type domain structure. In the presence of dead layers, moderate charge densities result only in a slight tilting of domain walls with respect to the film surface normal while high charge densities stabilize saw-tooth domains. Phase transition temperatures are found to decrease due to depletion charges especially in relatively thick films while this reduction is negligible in thinner films and their phase transition temperatures are nearly the same as charge-free films with dead layers. Comparison with an analytical approach for the phase transition temperature and domain period also supports the results extracted from the numerical approach reported in this thesis. Applied electric fieldpolarization simulations show that high depletion charges lead to disappearance of the hystereses but this does not necessarily mean disappearance of ferroelectric behavior.
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