Two perovskite-like catalysts (LaFeO3 and La2NiO4) have been prepared, characterised by high thermal stability and phase purity. SEM analysis showed that they consisted of 20-60 nm spheroids, generally clustered into one order of magnitude larger particles. A temperature-dependent EPR pattern was obtained with LaFeO3. In particular, at 110 K the spectrum was formed of an asymmetric pattern attributable to an axially symmetric paramagnetic system with gx = gy = 2, gz = 3.2. This feature became progressively more symmetric with increasing temperature, the apparent gz value decreasing down to 2.3 at 480 K. The EPR spectrum of La2NiO4 was even more temperature-dependent than that of LaFeO3. However, the EPR line of the former became more symmetric than that of the latter at high temperature. Indeed, gx = gy = 2.13 at any temperature and gz decreased from 5.5 down to 2.9 when increasing temperature from 110 K up to 380 K. The results show that both samples possess superparamagnetic properties, connected with particles ca. 20 nm in size. Furthermore, the EPR patterns were broader with La2NiO4, than with LaFeO3, indicating a greater amount of local disorder in the former. This was attributed to the presence of more oxygen vacancies in the Ni-based with respect to the Fe-based sample, in line with what elsewhere hypothesised on the base of catalytic properties of the two samples for the flameless combustion of methane.
|Titolo:||EPR investigation of superparamagnetism in nanometer-size LaFeO(3+d) and La(2)NiO(4+d) perovskites|
OLIVA, CESARE (Primo)
FORNI, LUCIO (Ultimo)
|Data di pubblicazione:||2001|
|Settore Scientifico Disciplinare:||Settore CHIM/02 - Chimica Fisica|
|Citazione:||EPR investigation of superparamagnetism in nanometer-size LaFeO(3+d) and La(2)NiO(4+d) perovskites / C.Oliva, L.Forni. ((Intervento presentato al convegno 34th Annual International Meeting ESR Group of RSC tenutosi a Bristol (U.K.) nel 2001.|
|Appare nelle tipologie:||14 - Intervento a convegno non pubblicato|