The Influence of Surface Terminal Layer and Surface Defects on the Electronic Structure of CMR Perovskites: La\u3csub\u3e0.65\u3c/sub\u3eA\u3csub\u3e0.35\u3c/sub\u3eMnO\u3csub\u3e3\u3c/sub\u3e (A = Ca, Sr, Ba)

The electronic structure near to the Fermi level of the colossal magnetoresistance (CMR) perovskite manganite materials, La0.65A0.35MnO3 (A = Ca, Sr, Ba), has been studied using both photoemission and inverse photoemission spectroscopy. The electronic structure for all three materials is very similar and consistent with an Mn–O terminal layer regardless of dopant. Small differences in the electronic structure among the materials are, however, observed. The observed band gap is not significant for La0.65A0.35MnO3 and La0.65A0.35MnO3 while there is a gap, about 1.5 eV, for La0.65A0.35MnO3. There is a shift to higher binding energies of the extensively hybridized Mn–O Δ5 (e) bands for the surface (the surface on the Mn–O plane with C4v symmetry) and t2g bands for the bulk in the valence band spectra with increasing atomic number or atomic radius of dopants, approximately to 5.8, 6.8, and 7.8 eV for La0.65A0.35MnO3, La0.65A0.35MnO3, and La0.65A0.35MnO3, respectively. The O–Mn–O terminal layer in these materials seems to be much more defect free than is the case for La0.65A0.35MnO3, where the Ca–O terminal layer appears to be rich in defects