**3. Preparation of calcium ferrite nanoparticles**

*Nanocrystalline Materials*

well as high-frequency dielectric properties.

the Pb- and Ni-doped BiFeO3 nanoparticles.

**2. Preparation of hematite (α-Fe2O3) nanoparticles**

techniques to improve their performance. In the case of the enhancing magnetization induced by doping, it has been suggested that this is probably due to increasing distortion of local structure, increasing the effect of Dzyaloshinskii-Moriya (DM) interaction, distortion of Fe and O bonding, destruction of spin cycloid structure, and the presence of impurity phase in the BiFeO3 systems [53, 57]. Besides affecting the magnetic properties, introduction of doping in BiFeO3 leads to the improvement of dielectric and ferroelectric properties [50, 58, 59]. Yuan et al. [54] have found that a sufficient amount of Sr/Pb doping can improve the magnetic properties as

In addition, the dielectric properties of pure BiFeO3 phase strongly depend on the atmospheric condition during the powder synthesis. Liu et al. [60] have found a higher spontaneous polarization and lower breakdown field based on polarizationelectrical field (P-E) hysteresis loops in the samples annealed in H2 and N2 atmospheres. In this chapter, BiFeO3 nanoparticles were synthesized by sol-gel method using natural iron sand as one of the raw materials and calcined in air atmosphere. Then, the ferroelectric and the dielectric properties were intensively investigated in

Prior to the preparation of α-Fe2O3 nanoparticles, at first, Fe3O4 nanoparticles were synthesized from natural iron sand as the raw material by coprecipitation technique using HCl as dissolving agent and NH4OH as precipitating agent. The detail of experimental procedure to synthesize Fe3O4 nanoparticles was also described in elsewhere [3]. First of all, the extracted iron sand was collected and dissolved in 12 M HCl at ~70°C under continuous and constant stirring of 600 rpm. The obtained solution from the reaction process was filtered and added slowly with 6.49 M NH4OH under the same temperature and stirring speed for 30 minutes. Then, the black precipitates were formed. The precipitate (Fe3O4 phase) was initially washed with distilled water until pH 7 and then dried at 70°C for 5 h. In order to get α-Fe2O3 phase, the dried nanopowder (Fe3O4 phase) was calcined at 800°C for 2 h, as shown in **Figure 1**. Finally, the Fe2O3 powders from this calcination were continued by performing coprecipitation process again with the same experimental procedure as before until the precipitation process. A reddish

*Hematite (α-Fe2O3) synthesized from natural iron sand (Fe3O4) by coprecipitation method followed by* 

**36**

**Figure 1.**

*calcination process at 800°C for 2 h.*

Calcium biferrite (CaFe4O7) nanoparticles were synthesized by the so-called chemically dissolved method using precipitated CaCO3 and Fe2O3 as Ca2+ and Fe3+ ion sources, respectively. Fe2O3 powders were obtained as described previously from natural iron sand, whereas the precipitated CaCO3 particles were synthesized from natural limestone through carbonation process. First, the natural limestone was extracted from the existing impurities, such as silica, and then it was calcined at 900°C for 6 h to produce CaO. The CaO powder was dissolved into distilled water to produce Ca(OH)2 solution. The carbonation process using CO2 gas flow was performed until it formed a precipitation at pH around 7. The precipitated CaCO3 was filtered and dried for further synthesis. The detail procedure was also explained in the former paper by Arifin et al. [61].

In the synthesis of the calcium ferrite nanoparticles using the chemically dissolved method, the obtained Fe2O3 and precipitated CaCO3 were dissolved in HNO3 to get Fe(NO)3 and Ca(NO)2 solutions, respectively, with a molar ratio of 1:6. Both solutions were mixed homogeneously and heated at constant temperature (80°C) and stirring rate (600 rpm) until it formed slurry precipitates. The precipitates were washed using distilled water and dried at 80°C for 10 h. The resulted powders were collected and then sintered at 800°C for 3 h.
