Bipolaron absorption in Ba1 − xKxBiO3 and Ba0.6K0.4 − xCsxBiO3

✍ Scribed by C.H. Rüscher; A. Heinrich; W. Urland

• Publisher: Elsevier Science
• Year: 1994
• Tongue: English
• Weight: 867 KB
• Volume: 219
• Category: Article
• ISSN: 0921-4534
• DOI: 10.1016/0921-4534(94)90402-2

✦ Synopsis

We present new results on the optical absorption of the family of compounds KxBa~ _xBiO3 (KBB) and CsxKo.4_xBao.6BiO3 (CKBB) (0 < x < 0.4 ) using powder methods. All cubic compounds of the KBB system (x >/0.3, Tc ~ 30 K) possess a broad nearinfrared (NIR) absorption band, which appears to evolve on increasing the K dopant content with respect to the noncubic compounds (x< 0.3), which show no To. For the series of solid solution with Cs substitution for K (i.e. no change in the nominal charge carrier concentration), we observe a strong increase of the absorption in the visible range with increasing Cs content, simultaneous to the gradual decrease of To. The NIR absorption is analysed using the theory for small polaron absorption in disordered media. The results indicate the formation of intersite bipolarons. Characteristic differences in the absorption behaviour with the high-To family Bi2Sr2Cal _xYxCu2Os+~ (BSCC) are outlined.