Physics of the multi-functionality of lanthanum ferrite ceramics

Abstract

In the present work, we have illustrated the physics of the multifunctional characteristics of nano-crystalline LaFeO3 powder prepared using auto-combustion synthesis. The synthesized powders were phase pure and crystallized into centro-symmetric Pnma space group. The temperature dependence of dielectric constant of pure LaFeO3 exhibits dielectric maxima similar to that observed in ferroelectric ceramics with non-centrosymmetric point group. The dielectric relaxation of LaFeO3 correlates well with small polaron conduction. The occurrence of polarization hysteresis in LaFeO3 (with centro-symmetric Pnma space group) is thought to be spin current induced type. The canting of the Fe3+ spins induce weak ferromagnetism in nano-crystalline LaFeO3. Room temperature saturation magnetization of pure LaFeO3 is reported to be 3.0 emu/g. Due to the presence of both ferromagnetic as well as polarization ordering, LaFeO3 behaves like a single phase multiferroic ceramics. The magneto-electric coupling in this system has been demonstrated through the magneto-dielectric measurements which yield about 0.8% dielectric tuning (at 10 kHz) with the application of 2 T magnetic field. As a typical application of the synthesized nano-crystalline LaFeO3 powder, we have studied its butane sensing characteristics. The efficient butane sensing characteristics have been correlated to their catalytic activity towards oxidation of butane. Through X-ray photoelectron spectroscopy analyses, we detect the surface adsorbed oxygen species on LaFeO3 surface. Surface adsorbed oxygen species play major role in their low temperature butane sensing. Finally, we have hypothesized that the desorbed H2O and O2 (originate from surface adsorbed hydroxyl and oxygen) initiate the catalytic oxidative dehydrogenation of n-butane resulting in weakening of the electrostatics of the gas molecules.

Influence of Cr substitution on structural, magnetic and electrical conductivity spectra of LaFeO3

“…Similarly, the typical composition of REFe 0.5 Cr 0.5 O 3 (RE=La, Tb, Ho, Er, Yb, Lu and Y) was prepared by Hydrothermal method [21]. Numerous literatures are available for preparing LaFeO 3 nano powder by sol gel combustion methods [22][23][24]. But, we found that the LaFe 1-x Cr x O 3 nanopowder solid solution M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 4 prepared by citrate method was hard to find in the literature.…”

Small polaron conduction in lead modified lanthanum ferrite ceramics

“…We have already reported that for unmodified LaFeO 3 , the dielectric dispersion in a wide temperature range is very well correlated to hole polaron conduction both in bulk grain and grain boundary regions [18]. Also the nature of the temperature dependence of dielectric constant is similar to conventional ferroelectric ceramics; however, for centro-symmetric point group (Pnma) dipolar polarization is not expected.…”

“…The details of the powder synthesis have been reported in our earlier publication [18]. To prepare La 1Àx Pb x FeO 3 (0 6 x 6 0.2) sol, stoichiometric precursor salts (lanthanum, lead and iron nitrate) are first dissolved in distilled water through continuous stirring.…”

“…Also the nature of the temperature dependence of dielectric constant is similar to conventional ferroelectric ceramics; however, for centro-symmetric point group (Pnma) dipolar polarization is not expected. Interestingly, for unmodified LaFeO 3 , the appearance of polarization hysteresis was found to be related with the appearance of dielectric maxima [18]. It is worth to mention that in Pb modified LFO ceramics (that exhibit CDC like characteristics) we could not measure the polarization hysteresis loops.…”

“…As a typical application of these powders recently we have reported their low temperature butane sensing characteristics [18]. The electrical properties of nanocrystalline LaFeO 3 ceramics (ABO 3 type perovskite) can be tuned by aliovalent Pb 2+ doping replacing La 3+ at A site [19,20].…”