Structure and Properties of Reduced Barium Niobium Oxide Single Crystals Obtained from Borate Fluxes
Structure and Properties of Reduced Barium Niobium Oxide Single Crystals Obtained from Borate Fluxes
复制标题
由硼酸盐助熔剂获得的还原钡铌氧化物单晶的结构和性能
DOI：
--
复制
发表时间：
1991
期刊：
影响因子：
--
通讯作者：
J. Waszczak
中科院分区：
文献类型：
--
作者：
B. Hessen;S. Sunshine;T. Siegrist;A. Fiory;J. Waszczak
在高真空条件下，在BaO·3B2O3中加热NbO2，制得还原铌酸盐Ba2Nb15O32单晶。硼酸盐既作为BaO的来源，又作为结晶的助熔剂。化合物Ba2Nb15O32在空间群R3中结晶(a = 7.777 (1) a, c = 35.518 (6) a)，并含有分层排列的孤立的[Nb6O12]O6团簇。作为副产物，形成了以下相的单晶：Ba3Nb5O15(空间群P4/mbm， a = 12.598 （1) a, c = 3.9774 (5) a，具有四方钨青铜型结构）和BaNb8O14(空间群Pcab， a = 9.4222 (9) a, b = 10.3649 (9) a, c = 23.716 (3) a)，其中含有[Nb6O12]O6簇，呈三维排列，通过三种不同的氧共享模式相互连接。新化合物Ba2Nb15O32在170 K时表现出半导体到半导体的转变，同时从弱顺磁性到抗磁性的转变。在Ba3Nb5O15上的单晶电阻率测量表明其具有显著的各向异性（在300 K时ρ⊥c = 55 ρ||c）和小带隙半导体行为。
Single crystals of the reduced niobate Ba2Nb15O32 are produced by heating NbO2 in BaO·3B2O3 under high-vacuum conditions. The borate acts both as a source of BaO and as a flux for crystallization. The compound Ba2Nb15O32 crystallizes in space group R3 (a = 7.777 (1) A, c = 35.518 (6) A) and contains isolated [Nb6O12]O6 clusters arranged in layers. As side products, single crystals of the following phases are formed: Ba3Nb5O15 (space group P4/mbm, a = 12.598 (1) A, c = 3.9774 (5) A with a tetragonal tungsten bronze-type structure, and BaNb8O14 (space group Pcab, a = 9.4222 (9) A, b = 10.3649 (9) A, c = 23.716 (3) A), which contains [Nb6O12]O6 clusters in a three-dimensional arrangement, interconnected by three different modes of oxygen sharing. The new compound Ba2Nb15O32 exhibits a semiconductor-to-semiconductor transition at 170 K, coinciding with a transition from a weakly paramagnetic state to diamagnetism. Single-crystal resistivity measurements on Ba3Nb5O15 indicate a significant anisotropy (ρ⊥c = 55 ρ||c at 300 K) and small bandgap semiconducting behavior.