Page 10 - PR 2014 2016 07 Nuclear Science and Technology

152 Nuclear Science and Technology | Progress Report

Rietveld analyses of neutron and Ba Sr Co0.80Fe0.20O2.427 (δ = 0.573).
X-ray diffraction patterns 0.45 0.55

The Neutron Diffraction Laboratory is also
involved in studies that employ the Rietveld
quantitative phase analysis using neutron and
X-ray diffraction patterns. The studies present-
ed below were all made in cooperation with
other groups. The X-ray diffraction patterns
were measured at different laboratories, inside
and outside IPEN, and the neutron diffraction
ones in the high-resolution diffractometer
Aurora.

Oxygen stoichiometry in BSCF

In a co-operative study between the Science
and Technology of Materials Centre and the
Neutron Diffraction Laboratory, the compound
Ba Sr Co Fe O (BSCF) has been stud-
0.50 0.50 0.80 0.20 3-δ
ied. BSCF is a candidate for air electrodes in
Intermediate Temperature Solid Oxide Fuel
Cells (ITSOFC). This work deals with the oxygen
vacancy in BSCF. The EDTA- Citrate method
was applied to a solution of barium, strontium,
cobalt and ferrite nitrate salts to synthesize Fig 6. X-ray (a) and neutron (b) diffraction patterns employed
in the combined X-ray and neutron Rietveld refinement.
the compound. Three portions of the product
were calcinated at 700, 800 and 900 °C, for five
hours in air. Rietveld phase analyses applied Thermal analysis and phase relations
to the three samples found that only that cal- in the system La W O -Li W O 7
2
2
9
2
2
cinated at 900 °C showed to be a single-phase
BSCF. Use of neutrons was fundamental for the The pseudobinary phase diagram La W O -
2 2 9
determination of the oxygen stoichiometry Li W O has been described, for the first
2 2 7
in the sample. As a matter of fact, oxygen is a time, in a co-operative work done in the
light atom and it becomes ‘invisible’ to X rays Crystal Growth and the Neutron Diffraction
when associated to heavy atoms, like those Laboratories, both at IPEN, and in the Leibniz
in the formula of BSCF. This is a classical case Institute for Crystal Growth, IKZ- Berlin,
where neutrons shall be used instead of X rays. Germany. The phase diagram contains
Actually, a combination of X rays and neutrons the intermediate tungstate LiLa(WO )
4 2
was applied to this case. The stoichiometry in which has been studied as a prospective
the single-phase sample was then determined laser host material. Li CO , La O and WO
2 3 2 3 3
by using a combined X-ray and neutron Riet- powders were used as starting materials
veld refinement. The stoichiometric formula to synthesize the compounds La W O and
2 2 9
for the single-phase BSCF sample resulted Li W O . These two compounds were mixed
2 2 7

Instituto de Pesquisas Energéticas e Nucleares