Charge generation during the synthesis of doped lanthanum manganites via combustion of organo-inorganic precursors

Synthesis of lanthanum manganite powders via combustion reactions: some aspects of the influence of magnetic field and charge generation in precursors on the formation of properties

“…Certain regularity can be observed in the spatial arrangement of the particles. The difference in powders obtained from precursors with different charge generation intensities is clearly seen when comparing their intense sintering temperature [57,59]. This difference is also clearly seen in the dependence of the specific surface area on the value of the generated potential difference ground -precursor (Fig.…”

“…In this case, during the precursor (PVA, ϕ = 1) combustion in a magnetic field (H = 3 kOe), the potential difference U of the order of +60 V was determined while this value was about −8 V when the combustion of the same precursor occurred in the absence of a magnetic field. It should be noted that the value of U reached +100 V and even more when the combustion occurs under the influence of an electromagnetic field [59]. Consequently, a constant magnetic field prevented the removal of negatively charged paramagnetic molecular groups like H 2 O − , CO − 3 during combustion, whereas the application of an alternating electromagnetic field, on the contrary, promoted it [50,59].…”

“…Mixing the solutions resulted in the formation of precursors. The ratio of the organic part to the nitrates was stoichiometric (ϕ = 1) according to the combustion reaction [59] with the formation of water, carbon dioxide and nitrogen as the main gaseous products, or exceeded it (ϕ > 1). The following starting reagents (analytical grade) were used: lanthanum (III) nitrate hexahydrate La(NO For the preparation of precursors, two solutions were prepared separately in distilled water containing nitrates of the corresponding metals and an organic component.…”

“…The properties of complex oxide materials obtained via combustion reactions are influenced by such conditions as process temperature, composition and concentration of the gases formed. One of the important phenomena accompanying the synthesis processes of complex oxides by combustion of nitrate-organic precursors [5,16,19, is the generation of high-density electric charges in the precursors and nanoparticles [45,[56][57][58][59][60][61][62][63]. The possibility of charge formation is associated with the release of ionized molecular groups into the gaseous environment and also with the lability of the oxidation state of transition metal ions which are the part of the precursors and the resulting material.…”

“…In many cases, the presence of charges during SCS determines the morphology of the synthesized complex oxides and has a significant impact on powder sintering processes. The temperature interval of intense sintering can be reduced by hundreds of degrees in the presence of high charges [57,59]. The presence of high charges leads to mutual repulsion of nanoparticles, formation of small contact area between them, which significantly increases the reserve of excess surface energy of particles.…”