Disputas: Nalini Vajeeston
M.Phil Nalini Vajeeston ved vil forsvare sin avhandling for graden ph.d. (philosophiae doctor): Synthesis, Structure, and Proton Conductivity of Meta- and Pyrophosphates
Professor Ani V. Virkar, Dept. of Material Sciences and Egineering, University of Utah, USA
Associate Professor Irina Animitsa Chemical Dept., Ural State University, Russia
Professor Eddy Walter Hansen, Department of Chemistry University of Oslo
Leder av disputas: Professor Harald Walderhaug
Veileder: Prof. Truls Norby og Prof. Helmer Fjellvåg
A proton conducting ceramic is one of the promising advanced materials for energy saving and environmental conservation in the future, since it can be applied to many devices for energy conversion, production and separation of hydrogen, synthesis of chemicals and sensing of hydrogen-containing compounds. Stable as well as high proton conducting electrolytes are essential for good performance of protonic devices. The main aim of this study is to synthesize and characterize a number of materials in which proton conduction may be envisaged and to test the protonic defects and the models they are based on. As a practical goal it is desirable to identify materials with high proton conductivity at some temperature between 300 and 600°C, that have pure protonic or mixed protonic and electronic conduction, and that are stable in wet hydrogen as well as in air.
This thesis focuses on phosphates, more specifically on LaP3O9 and tetravalent metal pyrophosphate (Ti, Zr and Sn) systems. In metaphosphate, the proton conductivity is increased by acceptor doping, as it is in oxides, and the proton transport takes place by the Grotthus mechanism. In pyrophosphates, the acceptor doping appears not to be significant for the defect structure and we derived a defect chemical model in which protons are charge compensated by oxygen interstitials.
Structural characterization was done with XRD and other techniques such as electron diffraction (TEM) and neutron powder diffraction. The microstructure and homogeneity were analyzed with SEM and the content of protons was determined using thermogravimetry. Proton conductivity was characterized using impedance spectroscopy and transport number measurements. The outcome of these investigations are modest proton conductivity and useful for a better understanding of the conduction mechanism and also defect structures.
The research was carried out at the Functional Energy Related Materials in Oslo (FERMiO), Centre for Materials Science and Nanotechnology, Department of Chemistry, University of Oslo.
For mer informasjon, kontakt Raul Boris Farina Briceno.