THE 2-BAND MODEL OF THE LACOO3 SEMICONDUCTOR METAL TRANSITION - A SPECTROSCOPIC EVALUATION

Co K-edge near-edge x-ray absorption spectra are reported for RECoO3 (RE = Y, Ho, Gd, Nd) at 300 K and for LaCoO3 in the temperature range (140 less-than-or-equal-to T less-than-or-equal-to 830 K). The pre-edge structure associated with Co 1s --> 3d excitation is found to be comparable for all the cobaltates at room temperature, consistent with the proposed similarity of their electronic structure. For LaCoO3, temperature-dependent changes are observed in the pre-edge structure. These data, when compared with previously published UV photoelectron spectra and calculated density of states, are found to be consistent with a proposed model for the higher-order semiconductor-to-metal transition of LaCoO3 which involves increased sigma*-pi*-band overlap with temperature.