M.Sc Thesis

M.Sc StudentAvram Ya'akobovich
SubjectFormation of pn or pin Junction in Mixed Ionic-Electronic
Conductor as a Result of Oxygen Activity Gradient
DepartmentDepartment of Chemical Engineering
Supervisor Professor Tsur Yoed
Full Thesis textFull thesis text - English Version


In this research a pn junction was formed in BaTiO3 (BT), with oxygen chemical potential gradient as the only driving force. BT is able to conduct electrons and oxygen ions at elevated temperatures; hence it can be treated as an MIEC (mixed ionic and electronic conductor) although the ionic transference number is low. The formation of a pn junction was achieved by applying a gradient in PO2 on a BT pellet by using an in-house built unique experimental system. The experimental system was built in order to allow both the formation of the junction and quenching the pellet in order to view hue changes which will provide evidence of pn junction formation. The process was monitored by means of computerized data recording. The recorded parameters were the PO2 and the temperature. Later the experimental system was modified to allow monitoring of the conductance of the BT pellet and I-V relations in the BT pellet.

In order to achieve better conductance of the p side of the pellet, the BT pellets were doped with acceptors. Unusual and unexpected I-V relations under PO2 gradient and other experimental results suggest possible mobility of metal vacancies in the BT pellet under PO2 gradient at elevated temperatures. This movement of metal vacancies was related to the large electrochemical gradient formed within the pellet which produced the driving force.