Title

Misfit Strain-Temperature Phase Diagram of Ferroelectric BaTiO3/SrTiO3 Superlattices

Publication Date

5-1-2013

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Materials Science and Engineering

Department

Materials Science and Engineering

Major Advisor

Dmitri Tenne, Ph.D.

Advisor

William B. Knowlton, Ph.D.

Advisor

Rick Ubic, Ph.D.

Abstract

Thin films of ferroelectric barium titanate (BaTiO3) and strontium titanate (SrTiO3) [(BaTiO3)8(SrTiO3)4]x40 superlattice structures are epitaxially grown on novel rare-earth scandate substrates in order to induce a systematically varied strain in the superlattice. Strained thin-film superlattices exhibit phase transition temperatures that differ from the same materials in their bulk form. A thorough understanding of the misfit strain-temperature phase diagram is needed to engineer the material parameters and physical properties of these superlattices. Ultraviolet Raman spectroscopy, transmission electron microscopy, and x-ray diffraction are utilized to develop a misfit strain-temperature phase diagram for BaTiO3/ SrTiO3 superlattices. Results indicate that the superlattices experience strain- and temperature-dependent phase transitions from rhombohedral-like phases to tetragonal or orthorhombic-like phases and then again to paraelectric cubic phases. Once the misfit strain-temperature relationship is understood, phases of the superlattices can be engineered based on the chosen substrate, the film thickness, and number of layers in a superlattice.

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