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

Electrical property evolution of Bi₂AE₂Co₂O_8+δ single crystals (AE = Ca, Sr and Ba) is systematically explored. When AE changes from Ca to Ba, the electrical property of Bi₂Ca₂Co₂O_8+δ and Bi₂Sr₂Co₂O_8+δ demonstrates semiconductor-like properties. But Bi₂Ba₂Co₂O_8+δ shows the metallic behavior. Analysis of temperature-dependent resistance substantiates that from metallic Bi₂Ba₂Co₂O_8+δ to semiconductor-like Bi₂Sr₂Co₂O_8+δ can be attributed to Anderson localization. However the semiconductor behaviour of Bi₂Sr₂Co₂O_8+δ and Bi₂Ca₂Co₂O_8+δ is related to electronic correlations effect that is inferred by large negative magnetoresistance (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 Bi₂Ba₂Co₂O_8+δ compared with other two compounds. It suggests that Bi₂Ba₂Co₂O_8+δ is more apt to be metal in this material system. [ABSTRACT FROM AUTHOR]