Crystal structure and electronic properties of BaBiOy (2.5≤y≤2.9) and Ba1-xLaxBiO3 (0≤x≤0.5)

Lattice parameters a, b, and c, the unit cell volume and the resistivity of BaBiOy (2.5 less than or equal to y less than or equal to 3.0) samples were compared with those of Ba1-xLaxBiO3 (0 less than or equal to x less than or equal to 0.5). For BaBiOy it is confirmed that the increase in the unit cell volume and the increase in resistivity with a decrease in oxygen content is not due to the oxygen vacancy but due to the decrease in the formal Bi valence. Not only BaBiOy but also Ba1-xLaxBiO3 is found to be semiconducting as in the case of BaBiO3, indicating that the charge density wave (CDW) remains with the formal Bi valence of 3.4-3.9. In order to elucidate the electronic states of BaBiOy and Ba1-xLaxBiO3, Raman spectroscopy experiments were performed. Considering that the resistivity of Ba1-xLaxBiO3, is 10(3) times larger than that of BaBiO3 and that no other Raman peaks other than those for BaBiO3 are found for Ba1-xLaxBiO3, it seems that the electronic structure of Ba1-xLaxBiO3 is similar to that of BaBiO3 except for a larger CDW gap for Ba1-xLaxBiO3 than for BaBiO3. (C) 1998 Elsevier Science B.V. All rights reserved.