Figure 1. Shows X-ray diffraction patterns of unradiated LSCF powder calcinated at 900 º C and 1100º C. It revealed that at the calcination temperature of 900° C a minor secondary phase is present and formation of perovskite phase was not complete [15, 16], but after raising calcination temperature up to 1100º C, it led to formation of pure perovskite.
Figure 2. shows the diffraction patterns of (a) un-radiated and irradiated samples (b) 20 kGy, (c) 250 kGy and (d) 500 kGy after calcination at 1100 º C for 6 h. All cases produced pure perovskite phase (JCPSD no. 48–0125) .
Mean crystallite size of (a), (b), (c) and (d) samples were determined by X-ray line broadening of diffraction patterns and the values of 19,18,27 and 42 nm were obtained, respectively.
The curves represent TGA results of unradiated and radiated LSCF powder are shown in Fig. 3. It shows weight changes in different stages. The maximum weight loss for unradiated and radiated samples was about 55% and 50% in the temperature range 25-327o C, this loss may be due to the dehydration of the gel. The loss of about 20% for unradiated sample and radiated one in the temperature range 327oC-540o C is correlated to nitrates. Above 540o C, no weight loss has been observed and the curves represent TGA results become horizontal . It was observed also that the weight loss in case of irradiated sample decreased in all stages. This may be due to the loss of volatile matter, humidity and crystallinty’ water upon heating.
The FTIR spectra of unradiated and radiated LSCF samples are shown in Fig. 4.The entire spectra can be divided into four main regions, namely, from 4000 to 2500 cm− 1 due to the stretching mode of the hydroxyl group of bound water molecules. The second region from 2500 to 2000 cm− 1 due to due to ambient CO2. The third region from 2000 to 1000 cm− 1 due to carboxylate, nitrate groups respectively. The fourth region due to absorption peaks which appear below 800 up to 400 cm− 1 are caused by the different kinds of metal oxygen bonds present in the sample which are characteristics peaks for perovskite ; whereas, the absorption peaks appearing beyond 800 cm− 1 are due to the different kinds of organic ligands .
Morphology and microstructure analysis
The specific surface area of the samples was measured by BET technique. It was showed that, higher value of surface area and porosity for radiated LSCF sample at 20 kGy as shown in Table 1.
Figure 5. Shows FESEM microstructure of non-irradiated and irradiated LSCF powder that are calcinated at 1100 ᴼ C for 6h. It was observed that the unradiated sample, (a), has a bulky structure while the radiated samples (b, c and d) have more refined structure. Among the radiated samples, sample (b) has the more refined grains with more surface area and more total pores size. This means that the LSCF sample radiated at low dose (20 kGy-b) has higher porosity than other samples.