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MATERIALS SCIENCE AND ENGINEERING

SEMINAR

Texture and Anisotropy in the Bismuth Sodium Titanate System

By:

Christopher M. Fancher

Ph.D. Final Examination

Co-Advisors:

Prof. K. J. Bowman and Prof. J. E. Blendell

ABSTRACT

Bi_0.5Na_0.5TiO₃ has received interest as a potential replacement for lead containing ferroelectrics. However, the piezoelectric response of pure Bi_0.5Na_0.5TiO₃ does not compare to the strong piezoelectric response of lead based piezoelectrics. To increase the piezoelectric response, Bi_0.5Na_0.5TiO₃ has been alloyed with BaTiO₃ and K_0.5Na_0.5NbO₃. Another route to enhance the response is to take advantage of the anisotropic properties by inducing a preferred crystallographic orientation. Both routes were used to investigate the effect a crystallographic texture has on the strain response of Bi_0.5Na_0.5TiO₃-based ceramics.

A crystallographic texture was induced by templated grain growth of pure phase Bi_0.5Na_0.5TiO₃ templates using the tape casting method to orient template particles relative to the tape cast normal. Sintered Bi_0.5Na_0.5TiO₃ based materials developed a strong (00l)_pc fiber texture relative to the tape cast normal, with no preferential alignment relative to the tape cast plane. Textured Bi_0.5Na_0.5TiO₃-(5)BaTiO₃ showed a piezoelectric response of 245 pC/N, a better than 50% enhancement from the 150 pC/N response of randomly oriented samples.

The Bi_0.5Na_0.5TiO₃-(x)BaTiO₃-(y)K_0.5Na_0.5NbO₃ (x,y) system has been shown to undergo electric-field-induced phase transformation from a pseudocubic to polar phase. For (7,2) a strong 8.67 multiples of a random distribution (MRD) crystallographic texture increased the macroscopic strain response by 50%. Applying the electric field perpendicular to the fiber texture axis reduces the macroscopic strain response of textured (7,2) by 17%. The affect field direction has on the electric-field-induced phase transformations of textured (7,2) was investigated using in situ electric field dependent diffraction. In situ diffraction data showed the high strain response of textured (7,2) can be attributed to a reversible pseudocubic to tetragonal transformation. The field-induced tetragonal phase nucleates preferentially with a strong c-axis alignment in the electric field direction, ferroelastic domain texture. In situ diffraction data suggests the origin of the reduction in strain associated with a field applied perpendicular to the fiber texture axis is the result of a shorter induced lattice spacing and lower domain texture.

Date:         Thursday, April 4, 2013

Time:      9:30 A.M.

Place:        HAMP 1113

Lisa Stacey

Secretary/Development Assistant

Purdue University

School of Materials Engineering

765/494-4100