BaBi_(1-x)Pb_xO_3体系的物理性质研究  

EXPLORATION ON THE PHYSICAL PROPERTIES OF THE SYSTEM BaBi_(1-x)Pb_xO_3

作　　者：黄胜利[1] 阮可青[1] 吕章明[1] 曹烈兆[1] 

机构地区：[1]中国科学技术大学结构分析开放实验室,物理系合肥230026

出　　处：《低温物理学报》2005年第A01期390-397,共8页Low Temperature Physical Letters

基　　金：国家自然科学基金(项目编号:10104013);国家重点基础研究专项经费(项目编号:G19990646)资助的课题~~

摘　　要：采用固态反应法制备了一系列BaBi1-xPbxO3（x：0～1）多晶并测定了其晶体结构和相应的物理性质．粉末法测得的X射线衍射所得的晶体结构与粉末中子衍射结果一致，晶体经历了从单斜晶系（O≤x〈0．1）、到正交晶系（0．1≤x〈0．65）、再到四方晶系（0．65≤x〈0．9）、最后到正交晶系（0．9≤x≤1．0）的转变．发现随着四价阳离子铅对铋的掺杂替代导致晶胞参数在半导体区域减小，而在超导区域振动变化，这归结于Bi^3＋和Bi^5＋被Pb^4＋的取代和呼吸模型Bi（Bb）O6的作用，从而证明了Bi两种价态的存在．电阻率的测量结果表明样品的电性与晶体结构和生长环境紧密相关，但氧缺陷不是主要因素．最佳掺杂区在x=0．75，其超导临界温度约为9K．掺杂区0≤x≤0．3的样品既可用本征半导体解释，也可用3D变程跃迁解释．在半导体区用3D变程跳跃解释时，lnρ～T^-1／4的斜率连续减小，说明掺杂改变了态密度或定域化长度．样品的金属一半导体转变可用交叠能带解释．拉曼光谱的测量结果表明改变入射激光的频率并不影响各拉曼峰的强度．随Pb的掺杂，BiO6八面体的呼吸模数逐渐减少，同时晶体的无序程度增强．超导温度与Bi（Bb）O6模的形变势的强弱无关，但受其频移的影响．Polycrystalline samples of BaBi1-xPbxO3 in the composition rangex from 0 to 1 were prepared. Crystal structure and physical properties measurements were made on these samples. The powder X-ray diffraction confirmed that the samples were pure, and their crystal structure evolved rom monoclinic for 0≤x〈0.1, through orthorhombic in 0.1≤x〈0.65 and tetragonal in 0.65≤x〈0.9, to orthorhombic in 0.9≤x≤1.0. With the doping of plumbum, the lattice constants decreased continuously in the semiconducting range, while vibrated like sine wave in the superconducting range, which was ascribed to the replacement of Bi^5＋ and Bi^3＋ by Pb^4＋ and the function of the breathing mode of Bi（Pb）O6. The temperature dependence of resistivity indicated that the electrical property of the samples, which was nearly independent of oxygen deficiency, was closely connected with the crystal structures and the growing environment. The optimum doping was x=0.75 whose Tc was 9K. For the samples with semiconducting property, the resistivity could be explained by Mott＇s VRH. The slope between lnp and T^-1/4 was decreased with increasing x, which implied the change of the states density and/or localization length. The metal-semiconductor transition could be explained by overlapping band. The result of Raman spectra indicated that the intensity of Raman spectrum was less affected by the frequency of the incident beam. When increasing x, the number of the breathing mode of Bi（Pb）O6 was reduced, and the crystal became disorder. Tc, was independent of the deformation potential of Bi（Pb）O6, but was relative to its frequency.

关 键 词：晶体结构 变程跃迁 呼吸模 

分 类 号：O511.4[理学—低温物理]