- From the TGA
trace provided, determine the composition just before cooling, the maximum
oxygen content on cooling and the composition of the room temperature product.
Use these data to account for the preparative conditions used in the experiment.
Why is the sample not superconducting after stage 1?
- Identify any
impurities in your X-ray diffraction profile and determine whether the orthorhombic
or tetragonal phase predominates.
- Show that the
average charge q on the copper in your compound is given by
where v1 is the titre in the determination of the Cu(III) content,
v2 the titre obtained when analysing the total copper content,
and w1, w2 the corresponding weights of sample. Calculate
q and hence determine the oxygen stoichiometry of the product. Suggest
another method of measuring the oxygen content.
- Examine the
cell diagram and answer the following questions:
- How many
distinct copper coordination sites are there, and what are their geometies?
- How are
these units linked together into an infinite array?
- What are
the coordination numbers of yttrium and barium?
- Which structure
is formed if the vacant oxygen sites (broken circles) are also filled?
- Comment on
the fact that the superconducting properties of the materials can deteriorate
on standing for long periods.
adopts the K2NiF4 structure in which the Cu(II) cation
has a Jahn-Teller distorted, quasi-octahedral coordination with four short
bonds in the equatorial plane and two long axial bonds. The distorted octahedra
share vertices in two dimensions. Explain whether simple band theory can correctly
describe the observation that La2CuO4 is an insulator.
Why does the substitution of strontium for lanthanum in La2-xSrxCuO4
produce metallic conductivity?
© Copyright 1996 Oxford University