Structural studies of apatite-type oxide ion conductors doped with cobalt.
A series of Co doped lanthanum silicate apatite-type phases, La9.83Si4.5Co1.5O26, La9.66Si5CoO26, La10Si5CoO26.5 and La8BaCoSi6O26, have been synthesised, and neutron diffraction, EXAFS and XANES used to investigate their structures in detail. All compositions were shown to possess the hexagonal apatite structure, and the results confirmed that cobalt can be doped onto both the La and Si sites within the structure depending on the starting composition. The Co doping is shown to cause considerable local distortions within the apatite structure. In the case of Si site doping two compositions showed anisotropic peak broadening, which has been attributed to incommensurate ordering of oxygen within the apatite channels.
Low temperature crystal structures of apatite oxygen-conductors containing interstitial oxygen.
Oxygen-stoichiometric La(9.33) square(0.67)(Si(6)O(24))O2 and oxygen-excess La(8.65)Sr(1.35)(Ge(6)O(24))O(2.32) and La(8.65)Sr(1.35)(Si(6)O(24))O(2.32) oxy-apatites have been structurally characterized at low temperatures by the Rietveld method. Oxygen-interstitial distribution has been studied at 15 K for La(9.33) square(0.67)(Si(6)O(24))O2 and La(8.65)Sr(1.35)(Ge(6)O(24))O(2.32) by time-of-flight neutron powder diffraction and at 4 K for La(8.65)Sr(1.35)(Si(6)O(24))O(2.32) by constant-wavelength neutron powder diffraction. The low temperature structural study was undertaken in order to distinguish between the effects of static disorder, originated mainly from the presence of interstitial oxygens, and the anisotropic thermal vibrations. At such low temperatures, the influence of the anisotropic thermal vibrations is minimised. This structural study has firmly established the existence of interstitial oxygens in these materials, which may be useful as electrolytes for solid oxide fuel cells.
Axonal sensorimotor neuropathy in patients with β-thalassaemia
Objective: The purpose of this study was to investigate the prevalence of peripheral neuropathy in patients with β-thalassaemia. Methods: Thirty six patients with a mean age of 29.2±8.2 years and 17 healthy controls with a mean age of 27.6±9.1 were included in this study. Measurements included the neuropathy symptoms score (NSS), the neuropathy disability score (NDS) as well as nerve conduction studies of two motor (ulnar and peroneal) and two sensory (ulnar and sural) nerves of the right limbs. Results: A mainly sensory axonal polyneuropathy was present in 19 out of 36 patients (52.7%). Eight out of these 19 patients also had abnormal NDS values. The neuropathy correlated significantly with the age of the patients and the hematocrit. However, it did not correlate with the presence of antibodies against HCV, the ferritin levels, or with a history of transfusions, desferrioxamine treatment, or splenectomy. Conclusions: This study showed a high prevalence of a predominantly sensory neuropathy in patients with β-thalassaemia. The electrophysiological data suggest that the underlying pathology is an axonopathy. Chronic hypoxia of the nerves resulting from severe anaemia may contribute to the pathogenesis of this neuropathy.