Metal-semiconductor-transition observed in Bi2Ca(Sr, Ba)2Co2O8+δ single crystals

Electrical property evolution of Bi(2)AE(2)Co(2)O(8-delta) single crystals (AE = Ca, Sr and Ba) is systematically explored. When AE changes from Ca to Ba, the electrical property of Bi2Ca2Co2O8-delta and Bi2Sr2Co2O8-delta demonstrates semiconductor-like properties. But Bi2Ba2Co2O8-delta shows the metallic behavior. Analysis of temperature-dependent resistance substantiates that from metallic Bi2Ba2Co2O8-delta to semiconductor-like Bi2Sr2Co2O8-delta can be attributed to Anderson localization. However the semiconductor behaviour of Bi2Sr2Co2O8-delta and Bi2Ca2Co2O8-delta is related to electronic correlations effect that is inferred by large negative magnetoresistance (similar to 70%). The theoretical electronic structures and valence X-ray photoemission spectroscopy substantiate that there is a relative large density of state around Fermi level in Bi2Ba2Co2O8-delta compared with other two compounds. It suggests that Bi2Ba2Co2O8-delta is more apt to be metal in this material system. (c) 2014 AIP Publishing LLC.