Localized-to-Itinerant Electron Transitions in Rare-Earth Cobaltates

Abstract

IVTossbauer studies show that cobalt ions in LaCo0 3 exist predominantly in the low-spin Co 111 state at low temperatures and partially transform to the high-spin Co 3+ state up to 200 K. Above 200 K, Co 11 and Co 4+ ions are formed by the transfer of d electrons from Co 3+ to Co 111 ; Co 3+ ions completely disappear at the first-order localized-to~itinerant electron transition temperature.

Experimental phase diagram determination and thermodynamic assessment of the Gd2O3–CoO system

“…Using soft-X-ray absorption spectroscopy (XAS), the latter authors conclude that LaCoO 3Àd is in the low-spin state at low temperatures, and that from 550 K to 630 K there is a gradual transition to a mixed-spin state, in agreement with previous studies [13,14]. Unlike the former groups [13,14], they found no evidence for charge disproportionation from 80 K to 630 K. Casalot et al [16] studied GdCoO 3 in the temperature range 77-1200 K using combined DTA, XRD, magnetic susceptibility, electric conductivity and thermoelectric power investigations. They stated that the properties of GdCoO 3 fit well to Goodenough's [17] localized electron model.…”

“…These authors showed that cobalt ions are in a low-spin state at low temperatures and partially transform to a high-spin state Co 3+ t 4 2g e 2 g up to 200 K. Their findings are, however, in conflict with the results from Abbate et al [15]. Using soft-X-ray absorption spectroscopy (XAS), the latter authors conclude that LaCoO 3Àd is in the low-spin state at low temperatures, and that from 550 K to 630 K there is a gradual transition to a mixed-spin state, in agreement with previous studies [13,14]. Unlike the former groups [13,14], they found no evidence for charge disproportionation from 80 K to 630 K. Casalot et al [16] studied GdCoO 3 in the temperature range 77-1200 K using combined DTA, XRD, magnetic susceptibility, electric conductivity and thermoelectric power investigations.…”

“…Non-stoichiometries, charge disproportionation of Co, and other thermophysical properties are quite similar in this group of materials, as shown by several studies [13,14]. LaCoO 3Àd perovskite serves as a wellresearched representative of rare-earth cobaltites: Raccah and Goodenough [14] proved the coexistence of low-and high-spin states in LaCoO 3 , and Bhide et al [13] performed Mö ssbauer studies of cobalt ions in LnCoO 3Àd (Ln = Gd,Co). These authors showed that cobalt ions are in a low-spin state at low temperatures and partially transform to a high-spin state Co 3+ t 4 2g e 2 g up to 200 K. Their findings are, however, in conflict with the results from Abbate et al [15].…”

Magnetic and electrical transport properties of La0.5A0.5CoO3 nanoparticles (A=Sr, Ca, and Ba)

“…The ground state of LaCoO 3 with Co 3+ (3d 6 ) ions is a charge transfer type insulator with no magnetic order. The magnetic susceptibility increases exponentially with increasing temperature to reach a maximum near 100 K. This transition was initially explained as a spin state transition from a low spin nonmagnetic state (t 6 2g , S = 0, LS) to a high spin state (t 4 2g e 2 g , S = 2, HS) [1][2][3][4] but later the existence of an intermediate spin state (t 5 2g e 1 g , S = 1, IS) was proposed. The spin state transition originates from a competition between crystal field splitting energy and interatomic Hund exchange coupling energy.…”

Characterization of NdSrCo1−xFexO4+δ (0≤x≤1.0) intergrowth oxide cathode materials for intermediate temperature solid oxide fuel cells

“…The x = 0.4 composition shows significant change at around 500 8C. The reason is assumed due to a spin transition from the smaller ionic radius of the low spin Co 3+ ion (r = 0.0545 nm) to the high spin Co 3+ ion (r = 0.061 nm) with increasing temperature [12,13], which leads to an increase in TEC [14]. The substitution of Co by Fe induced to decrease TEC values.…”