3.4.1. Measurements at 300 K

In agreement with the magnetization data, the 300 K 57Fe Mössbauer spectra recorded for samples with different Fe concentrations show, on the one hand, partial (x = 0.50) or total (x = 0.25) paramagnetic behavior (see Figure 12a). On the other hand, the 300 K 57Fe Mössbauer spectra of the samples with x = 0.75 and 1.0 show six absorption lines due to the nuclear Zeeman interaction with a local magnetic hyperfine field (Bhf). The refined values of the corresponding hyperfine parameters are given in Table 3. The values of isomer shift are typical of the presence of Fe3+ ions. Another important feature that should be highlighted is that the line widths of the Mössbauer spectra are generally broader for samples with x = 0.25, 0.50, and 0.75 compared with those of the RS7 sample (x = 1.0), the latter being expected to show less atomic disorder. Therefore, the broadening effect of magnetic lines is probably caused by different iron environments, since in the orthorhombic crystal structure of these perovskites, a 3d<sup>5</sup> Fe3+ ion is usually surrounded by 2, 3, 4, 5, or 6 Cr3+ ions in octahedral sites. The result of the chemical disorder is a hyperfine magnetic field distribution, i.e., a distribution of static sextets. In particular, the fit of the 57Fe Mössbauer spectrum of the sample with x = 0.50 was done with two magnetic sextets and one quadrupolar doublet. The two sextets will represent the different local Fe environments of the orthorhombic crystal structure, while the doublet, best seen in the inset spectrum recorded in a low-velocity range, must be associated with Fe3+ ions in the paramagnetic state resulting from Cr3+-rich environments (*TN* < 300 K, e.g., for the x = 0.25, *TN* = 153 K). The features discussed above tell us that the Fe substitution is not homogeneous, leading to an assembly of clusters with different compositions, i.e., a chemical disorder in the octahedral sites (B-sites) of the orthorhombic crystal structure. Thus, the largest magnetic component can be attributed to Fe3+ ions preferentially surrounded by Fe3+ ions (*TN* > 300 K), while the quadrupolar doublet is associated with a neighborhood rich in Cr3+ ions, of course, with *TN* values lower than 300 K, as shown by our magnetization data.

**Figure 12.** (**a**) RT Mössbauer measurements of the Fe-substituted YFexCr1−xO3 compounds. Samples with x = 1.0, 0.75, and 0.5 are measured with ±12 mm/s. The inset shows the same spectra for x = 0.5 but with a maximal velocity of ±2 mm/s, as in the case of the YFe0.25Cr0.75O3 sample (last spectrum). (**b**) Same sample measured at 77 K. The subspectra used to fit these spectra are also shown. The two sextets represent the two iron configurations in octahedral sites of the orthorhombic crystal structure of the perovskite.


**Table 3.** Refined values of the hyperfine parameters at given temperatures.
