Off-campus FIU users: To download campus-access content, please use the following link to log in to our proxy server with your FIU library username and password.

Non-FIU users: Please talk to your librarian about requesting this content through interlibrary loan.

Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Mechanical Engineering

Advisor's Name

Arvind Agarwal

Advisor's Title

Committee Member

Advisor's Name

Chunlei (Peggy) Wang

Advisor's Title

Committee Member

Advisor's Name

Jiandi Zhang

Advisor's Title

Committee Member

Advisor's Name

Surendra K. Saxena

Advisor's Title

Committee Member

Advisor's Name

W. Kinzy Jones

Advisor's Title

Committee Member

Keywords

Barium Strontium Titanate, Sintering, Semiconductive, Positive Tempertaure Coefficient Resistivity

Date of Defense

11-21-2007

Abstract

Low temperature sintering has become a very important research area in ceramics processing and sintering as a promising process to obtain grain size below 100nm. For electronic ceramics, low temperature sintering is particularly difficult, because not only the required microstructure but also the desired electronic properties should be obtained.

In this dissertation, the effect of liquid sintering aids and particle size (micrometer and nanometer) on sintering temperature and Positive Temperature Coefficient Resistivity (PTCR) property are investigated for Ba1-xSrxTiO3 (BST) doped with 0.2-0.3mol% Sb3+ (x = 0.1,0.2,0.3,0.4 and 0.5). Different sintering aids with low melting point are used as sintering aids to decrease the sintering temperature for micrometer size BST particles. Micrometer size and nanometer size Ba1-xSrxTiO3 (BST) particles are used to demonstrate the particle size effect on the sintering temperature for semiconducting BST. To reduce the sintering temperature, three processes are developed, i.e. 1 using sol-gel nanometer size Sb3+ doped powders with a sintering aid; 2 using micrometer size powders plus a sintering aid; and 3 using nanometer size Sb3+ doped powders with sintering aids.

Grain size effect on PTCR characteristics is investigated through comparison between micrometer size powder sintered pellets and nanometer size powder sintered pellets. The former has lower resistivity at temperatures below the Curie temperature (Tc) and high resistivity at temperatures above the Curie temperature (Tc) along with higher ñmax/ñmin ratio (ñmax is the highest resistivity at temperatures above Tc, ñmin is the lowest resistivity at temperatures below Tc), whereas the latter has both higher ñmax and ñmin. Also, ñmax/ñmin is smaller than that of pellets with larger grain size. The reason is that the solid with small grain size has more grain boundaries than the solid with large grain size. The contribution z at room temperature and high temperature and a lower ñmax/ñmin ratio value.

Share

COinS