*2.1.4 Auto-combustion synthesis*

In this process, Bi(NO3)3.5H2O and Fe(NO3)3.9H2O are frequentlyutilized as the oxidizer, whereas glycine (C2H5NO2), sucrose (C12H22O11), ethylene glycol (C2H6O2), ethanolamine (C2H7NO), citric acid (C6H8O7.6H2O), urea (CON2H4), stearic acid (C18H36O2), etc. may be utlized as fuels. To begin, the metal nitrates are dissolved in dilute HNO3 [55] or distilled water [56] to form an aqueous solution, and then the fuels are added to the solution while constantly stirring. Then, the resulting starting material is moved to a container that can be heated to between 80 and 200 degrees Celsius [55, 56] to form a densify gel-like product. Then, the gels are heated in a furnace to above 300°C to initiate the auto combustion reaction, which produces the final bismuth ferrite nanomaterials [55]. The combustion reactions with glycine and sucrose as fuels are demonstrated below, where bismuth ferrite as the only solid metal oxide product and carbon dioxide, water and dinitrogen simply illuminated during or after the reaction.

$$\text{Bi (NO}\_3\text{)}\_3 \text{ + Fe (NO}\_3\text{)}\_3 + \text{3.33}\text{C}\_2\text{H}\_3\text{NO}\_2 \rightarrow \text{BiFeO}\_3 + \text{6.66}\text{CO}\_2 + \text{8.33}\text{H}\_2\text{O}\_{4.66}\text{N}\_2\tag{4}$$

$$\text{Bi (NO}\_3\text{)}\_3 \star \text{Fe (NO}\_3\text{)}\_3 \star \text{C}\_{12}\text{H}\_{21}\text{O}\_{11} \star \text{4.5O}\_2 \rightarrow \text{BiFeO}\_3 \star \text{12CO}\_2 \star \text{3 N}\_2 \star \text{11H}\_2\text{O} \tag{5}$$

Nevertheless, because secondary phases are frequently constructed with bismuth ferrite, the procedure would be much more complicated. Despite this, Farhadi et al. [57]. Later conducted a study by Yang et al. [55] utilized sucrose (C12H22O11) to acquire phase-pure nanoscale BFO powders. The influence of fuel composition on the resulting bismuth ferrite phases discovered that glycine (C2H5NO2) or ethanolamine

(C2H7NO) performs better. Throughout overall, the perovskite bismuth ferrite phase is acquired with some secondary phases, making control over the combustion process for phase pure bismuth ferrite difficult.
