Abstract
Four batches of cerium oxide powders (with nanocrystallite size of
6.9 nm–572 nm) were prepared from four precursor nanopowders by thermal
decomposition of Ce-propionate and annealing in air between
250 °C–1200 °C for 10 min–240 min. Ceria formation reactions, structure,
vibrational, luminescence and magnetic properties were investigated by
differential scanning calorimetry, x-ray diffraction, electron
microscopy, infrared spectroscopy, photoluminescence and SQUID. All the
samples exhibit room temperature ferromagnetism, RTFM, (with coercivity,
Hc, of 8 Oe - 121 Oe and saturation magnetization, Ms, of up to 6.7*10−3
emu/g) and a broad defect-related photoluminescence, PL, emission in
the visible range. The samples derived from the same precursor show Ms
proportional to the peak area of defect-related PL emission whereas
this is not valid for the samples derived from the different precursors.
An improvement of ferromagnetism and intensity of defect-related PL
emission was observed when annealing the products in which
nanocrystalline cerium oxide coexists with Ce - oxicarbonate traces, Ce2O2CO3.
The experimental results were explained based on the following
considerations: room temperature ferromagnetism was induced by the
defective ceria with high concentration of oxygen vacancies generated by
decomposition of Ce-propionate; oxygen vacancies of the starting
precursor nanopowders could be redistributed (at the surfaces/grain
boundaries, GBs) upon heating under conditions that promote an inert
local environment; the decomposition of Ce2O2CO3
residues can provide an excess of oxygen vacancies at the nanoparticles
surfaces or GBs, which can induce or enhance ferromagnetism;
surfaces/GBs rather than bulk defects appear responsible for RTFM – this
can explain the (often reported in literature) inconsistency between
oxygen vacancies concentration and Ms.
Original language | English |
---|---|
Journal | Materials Chemistry and Physics |
Volume | 209 |
Pages (from-to) | 121-133 |
ISSN | 0254-0584 |
DOIs | |
Publication status | Published - 2018 |
Keywords
- Cerium oxide nanopowders
- Ce - propionate
- Ce2 O2 CO3
- Ferromagnetism
- Photoluminescence