Investigation of relaxation phenomenon in lanthanum orthoferrite extracted through complex impedance and electric modulus spectroscopy
Samiya Manzoor, Shahid Husain, Anand Somvanshi, Mehroosh Fatema
Abstract
Impedance and electric modulus spectroscopy is exploited over a broad frequency and temperature range to find the relaxation phenomenon in LaFeO3 (LFO), which otherwise was concealed by the dc conductivity in dielectric ɛ*(ω) representation. The impedance measurements and the ac resistivity determined from Z′(ω) indicate that LFO is an insulator at room temperature and divulges the negative temperature coefficient of resistance. At higher temperatures, capacitive behavior flips to inductive behavior. The ac resistivity is exploited to determine the activation energy using the Arrhenius model. The relaxation peaks appear in the imaginary parts of electric modulus [M*(ω)] and impedance [Z(ω)], which have been exploited to determine the activation energy. The single distorted semicircle in the Nyquist and complex plots of electric modulus is evidence of the contribution of grains in the conduction process. At higher temperatures, data corresponding to the grain interior transform from an arc to a line with an intercept on the Z′(ω) axis and is parallel to the imaginary axis Z″(ω). Relaxation times calculated from the imaginary parts of impedance and electric modulus fit well in accordance with the Arrhenius law. Electron hopping, hole hopping, and oxygen vacancies play an important role in the dielectric response of grains. The relaxation frequencies of Z″(ω) and M″(ω) follow the sequence of scaling of magnitude of relaxation frequencies, i.e., fz′′≤fM′′. The separation of relaxation peaks of M″(ω) and Z″(ω) are indicative of a localized conduction process. The Giuntini law is applied to determine the hopping energies of charge carriers.