 IDEALS Home
 →
 College of Engineering
 →
 Dept. of Physics
 →
 Dissertations and Theses  Physics
 →
 View Item
Files in this item
Files  Description  Format 

application/pdf 1993_weilert.pdf (6MB)  1993_weilert 
Description
Title:  Phonon scattering by ferroelectric domain walls in potassium dihydrogen phosphate 
Author(s):  Weilert, Mark Anthony 
Doctoral Committee Chair(s):  Anderson, A.C. 
Department / Program:  Physics 
Discipline:  Physics 
Degree:  Ph.D. 
Genre:  Dissertation 
Subject(s):  phonon scattering
ferroelectric domain walls potassium dihydrogen phosphate 
Abstract:  I have studied phonon scattering by ferroelectric domain walls in KH2P04 (KDP) using thermal conductivity and phonon imaging measurements of samples in both singledomain (poled) and multidomain states. Domains were eliminated by applying a 2 3kV /em field using evaporated electrodes. Phonon images of a poled (001) sample (at 1.7K) show twofold symmetric focusing patterns that clearly show the small orthorhombic distortion of the lattice. Poled images are qualitatively reproduced by calculations using continuum acoustics with room temperature tetragonal elastic moduli split to orthorhombic symmetry; a rough set of low temperature orthorhombic moduli is thereby determined. The presence of domains causes a large change in ST focusing structures but little change in L and FT patterns. There is an apparent decrease in overall intensity for all modes. The images show strongly mode and polarization dependent phonon scattering. Monte Carlo simulations using acoustic mismatch (phonon reflection) to model phonon/domain wall interactions accurately reproduce the changes seen in the domained images. The low temperature (0.033K) thermal conductivity, K, of [100], [110], and [001] (tetragonal basis) oriented samples was measured. K in poled samples shows typical surfacelimited behavior which is predicted to 13% by calculations including finite length and anisotropy and using elastic constants from the imaging simulations. Domain walls produce a 40% conductivity decrease in a [110] sample and a 30% decrease in [100) samples which is nearly independent of sample size, suggesting strong scattering of only a subset of phonons. Domain wall scattering is nearly temperature independent between 0.3K and 1K, but decreases at lower temperatures, and increases above 1K. The [001] sample couldn't be poled, but the domained K is higher than that expected from sample surface scattering. Domains parallel to the heat flow may be channeling phonons and increasing K. Acoustic mismatch calculations applied to K predict the right order of scattering, but do not reproduce the sample size effects. Orientation effects can be partially explained. The probability of diffuse scattering at the domain boundaries (often seen in Kapitza resistance studies) is at most 1%. 
Issue Date:  1993 
Genre:  Dissertation / Thesis 
Type:  Text 
Language:  English 
URI:  http://hdl.handle.net/2142/28682 
Rights Information:  1993 Mark Anthony Weilert 
Date Available in IDEALS:  20120123 
This item appears in the following Collection(s)

Dissertations and Theses  Physics
Dissertations in Physics 
Graduate Dissertations and Theses at Illinois
Graduate Theses and Dissertations at Illinois