Determination of Debye temperatures and Lamb–Mössbauer factors for LnFeO₃orthoferrite perovskites (Ln  =  La, Nd, Sm, Eu, Gd)

Abstract

Lanthanide orthoferrites have wide-ranging industrial uses including solar, catalytic and electronic applications. Here a series of lanthanide orthoferrite perovskites, LnFeO<sub>3</sub> (Ln = La; Nd; Sm; Eu; Gd), prepared through a standard stoichiometric wet ball milling route using oxide precursors, has been studied. Characterisation through X-ray diffraction and X-ray fluorescence confirmed the synthesis of phase-pure or near-pure LnFeO<sub>3</sub> compounds. <sup>57</sub>Fe Mössbauer spectroscopy was performed over a temperature range of 10 K to 293 K to observe hyperfine structure and to enable calculation of the recoil-free fraction and Debye temperature (θD) of each orthoferrite. Debye temperatures (Ln = La 474 K; Nd 459 K; Sm 457 K; Eu 452 K; Gd 473 K) and recoil-free fractions (Ln = La 0.827; Nd 0.817; Sm 0.816; Eu 0.812; Gd 0.826) were approximated through minimising the difference in the temperature dependent experimental Centre Shift (CS) and theoretical Isomer Shift (IS), by allowing the Debye temperature and Isomer Shift values to vary. This method of minimising the difference between theoretical and actual values yields Debye temperatures consistent with results from other studies determined through thermal analysis methods. This displays the ability of variable-temperature Mössbauer spectroscopy to approximate Debye temperatures and recoil-free fractions, whilst observing temperature induced transitions over the temperature range observed. X-ray diffraction and Rietveld refinement show an inverse relationship between FeO6 octahedral volume and approximated Debye temperatures. Raman spectroscopy show an increase in the band positions attributed to soft modes of Ag symmetry, A<sub>g</sub>(3) and A<sub>g</sub>(5) from La to GdFeO<sub>3</sub> corresponding to octahedral rotations and tilts in the [010] and [101] planes respectively.

Degree of Geometric Tilting Determines the Activity of FeO6Octahedra for Water Oxidation

“…In contrast, the values of ⟨Fe–O–Fe⟩ follow the trend AFeO 3 > β-FeOOH > ZnFe 2 O 4 , as displayed in Figure b. Notably, the average Fe–O–Fe angle of AFeO 3 increases at the same pace with the increment of A-site ionic radii, which agrees well with previous reports. , In addition, it is necessary to mention that the only value of the Fe–O–Fe angle in ZnFe 2 O 4 (94.854°) is sharply larger than the smallest one in β-FeOOH (86.619°). According to the above analysis, the main distortion in AFeO 3 , ZnFe 2 O 4 , and β-FeOOH is FeO 6 octahedral tilting.…”

Large Power Factors in Wide Band Gap Semiconducting RFeO3 Materials for High-Temperature Thermoelectric Applications

“…Additionally, q is the number of atoms, N is the Avogadro’s number, and M is the molecular weight of the solid. Furthermore, it is noteworthy to mention that our calculated θ D values were relatively close with the earlier experimental values reported in ref for RFeO 3 , with less than 10% percent difference. While it is surprising to see that our calculated values of θ D are relatively high when compared to other TE materials, these θ D values are obtained for RFeO 3 , which are meant to operate at high-temperature regions (above 900 K).…”

Spin-lattice coupling mediated giant magnetodielectricity across the spin reorientation in Ca2FeCoO5

“…A program was constructed, which Debye temperature and an IS would be simulated, resulting in theoretical SODS and CS. As given in reference [ 20,29 ], the IS values for the FeO was taken as 0.61 mm/s and the variation of CS values for different Debye temperatures were simulated. Similarly, attempts were made to estimate Debye temperature for FeT using various values of IS and Θ.…”