Download Local structure of proton conducting Y

Local structure of proton conducting Y-doped AZrO3 (A=Ba, Sr, Ca)
perovskites investigated with vibrational spectroscopy
By
Caroline Wanjiru Mburu
Abstracts
Fuel cells convert chemical energy directly into electrical energy and have an advantage over
conventional means of power generation due to their high-energy conversion efficiency besides
being environmentally friendly. The first fuel cell was demonstrated over 160 years ago but
development continued inhibited by lack of attractive materials, which have high conductivity in
the intermediate temperature region (200-500 ˚C).
This thesis concerns experimental studies done on perovskite structured yttrium doped barium
zirconate, calcium zirconate and strontium zirconate systems. The main work has included
synthesis of yttrium doped barium zirconate with different Y concentrations and to study the
local structure of this system as a function of Y concentration, and to study the influence of
protons on the local structure surrounding the Y ions. The experiments were performed using xray powder diffraction (XRD), to study the average structure of the perovskite lattice, and
infrared (IR) and luminescence spectroscopy to study the local structure of the material.
The results indicate that increasing Y concentration leads to a slight, but clear, distortion of the
local structure of the perovskite structure and we also find a dependence on hydration.
Moreover, the results show that the symmetry around the Y atom is more distorted in the dry
sample than in the hydrated. For the 20% Y doped BaZrO3 material in particular, spectral
differences could not be resolved with the techniques used, which would motivate a further study
of the local ordering of the dopant atoms.
Aims:
1. Synthesize yttrium doped barium zirconate, calcium zirconate and strontium zirconate
with different Y concentrations.
2. Study the local structure of yttrium doped BaZrO3 as a function of Y concentration.
3. Study the local structure of AZrO3 as a function of A site cation.
4. Study the influence of hydration on the local structure of the above mentioned materials.