【摘要】 用第一原理的ＬＤＦＬＭＴＯＡＳＡ超元胞法，模拟由Ｘ射线吸收谱精细结构测定的ＢａＢｉＯ３中，Ｂｉ有两种价态Ｂｉ３＋和Ｂｉ５＋及与之相应的两种不同键长的Ｂｉ—Ｏ八面体，以及Ｋ掺杂对晶体结构的影响．计算了Ｂａ４Ｂｉ４Ｏ１２，（Ｂａ３Ｋ）Ｂｉ４Ｏ１２，（ＢａＫ）Ｂｉ２Ｏ６，（ＢａＫ３）Ｂｉ４Ｏ１２，Ｋ２Ｂｉ２Ｏ６（简记为（４０４），（３１４），（１１２），（１３４），（０２２））五种“样本”的电子结构．结果表明，（４０４）和（３１４）分别为Ｅｇ＝１６ｅＶ及Ｅｇ＝１５ｅＶ的半导体，其它“样本”为金属．总能的分析表明（１３４）是不稳定的，故溶解极限为ｘ＝０５．以“取样”方式按伯努利分布确定任意组分各“样本”的概率，进而计算了（Ｂａ１－ｘＫｘ）ＢｉＯ３电子结构随组分的变化．最后用逾渗模型说明了超导转变温度Ｔｃ在ｘ＝０．２５附近的突变更多还原

【Abstract】 Electronic structure for BKB has been calculated by using LMTO ASA Supercell method based on the X ray absorption fine structure (XAFS) spectroscopy measurements. Measurements show that Bi posseses two valence states Bi 3+ and Bi 5+ and their Bi O bond lengths are diffferent,the difference decreases with the increase of K concentration. Calculations are performed on five samples namely Ba 4Bi 4O 12 (404),(Ba 3K)Bi 4O 12 (314), (BaK)Bi 2O 6(112), (BaK 3)Bi 4O 12 (134)and K 2Bi 2O 6(022).Results from the calculations show that(404)and (314) are semiconductors with gaps of 1.6eV and 1.5eV,respectively. Other samples are metals. Total energy analysis shows that (314) is not stable,so that the extreme value of x is 0.5. The BKB electronic structures at x =0.1 to 0.5 are calculated by combining the probability with sample′s Bernoull′s distribution. Superconducting transition temperature T c of BKB is suddenly changed when x approximates to 0.25. The experimental data are close to the prediction values of percolation theory.更多还原