新铌酸盐K_6CrNb_(15)O_(42)

A NEW COMPOUND K_6CrNb_(15)O_(42)

在K_2O—Cr_2O_3—Nb_2O_5三元系统中,作者发现一种六方晶系化合物K_6CrNb_(15)O_(42)。将分析纯K_2CO_3、Cr_2O_3、Nb_2O_5按分子比6:1:15混匀(随温度制度不同,K_2CO_3可略过量),在中性保护气氛下于1350℃到1060℃间加热,保温一定时间,得到晶粒细小,但很纯净的未知晶体(可用来作X射线粉晶谱、化学分析及其它测试)。延长保温时间并在更低温度出炉,则可获得较大晶粒,个别晶粒可大于2mm,从中可选出生长良好的单晶体作X射线单晶衍射。后一方法可能出现杂质K_2Nb_(16)O_(41)。

A new compound was found in the system of K_2O-Cr_2O_3-Nb_2O_5, chemical analysis shows that the molecular formula of the compound is K_6CrNb_(1 5)O_(4 2) or K_5(CrNb_(1 5)O_(4 2). Single crystal of the synthetic compound is transparent and green color with hexagon-thin schistose shape, its index of refraction n>2.20,and density d_(obs)=4.47g/cm^3.The compound is grown in the range of 950—1185℃ and melting point is 1185℃.X-ray diffraction measurement shows that the crystal of the compound belongs to hexagonal system with space group P6_s/mcm(193) and unit cell parameters α=9.126(?), c=12.068(?), z=1.