Structure, electrophysical and magnetic properties of (1 – x)SmFeO₃–xNaNbO₃ composites

In this work, the concentration dependencies of unit cell parameters, microstructure, dielectric, impedance spectra, and magnetic properties of (1 – x)SmFeO₃–xNaNbO₃ were studied for the first time. It was found that at a concentration x = 0.7, the unit cell parameter a, the tilt angles θ and rotation angles φ of oxygen octahedra and the bond lengths Fe-O₁ and Fe-O₃ of samarium ferrite SmFeO₃ (SFO) have a maximum, and Fe-O₂ has a minimum value. The tilt angle θ, rotation angle φ of the octahedral, and the bond lengths of sodium niobate NaNbO₃ (NNbO) change nonmonotonically. For x = 0.9, the unit cell parameters b and c, as well as all bond lengths in the NaO₉ tetradecahedra, reach their minimum values. Anomalies corresponding to the spin-reorientation transition temperatures T_SR1 and T_SR2 were detected in the dielectric spectra of SFO at temperatures of 200 and 309 °C. The jump in the real part of the dielectric constant ε′(T), starting before – 100 °C, is attributed to the response of the dipole moments to the magnetic moment jump and spin switching (T_SSW). Anomalies corresponding to transitions between different phases in this antiferroelectric were found in the temperature dependences of ε′(T) and dielectric loss tangent tgδ(T) of NNbO at temperatures of – 75, 23, 160, 278, 379, and 433 °C. From magnetic measurements, it was found that the composition with x = 0.8 has a minimum size of coherent scattering regions of D = 94 nm, representing the second critical size at which the coercive field H_c reaches its maximum value.